Diffusion Barrier Agent

Examples of the diffusion barrier agent include a diffusion barrier component and a vehicle. The diffusion barrier component may be any element or compound that can be dissolved or dispersed into a vehicle to generate a jettable fluid and that is capable of restricting diffusion of an alloying element (that is contained in the alloying agent) from the site-specific alloyed section(s). The diffusion barrier component is selected to raise the chemical potential of the alloying element in the region(s) where the diffusion barrier component is present. The higher the concentration of an element, the higher its chemical potential, which drives the diffusion of the element from high concentration to low concentration. As such, by incorporating the diffusion barrier component in region(s) outside of the region(s) with a higher concentration of the alloying element, the chemical potential of the alloying element is raised at the boundary of the region(s) with the higher concentration of the alloying element, so that the diffusion of the alloying element out of this region(s) is suppressed.

Examples of suitable diffusion barrier elements may be selected from the group consisting of silicon, nickel, copper, chromium, vanadium, titanium, tantalum, carbon, aluminum, tantalum nitride, titanium nitride, titanium dioxide, titanium carbide, tungsten-titanium, yttria stabilized zirconia, a metal silicide, an amorphous alloy, hexagonal boron nitride, molybdenum disulfide, and ruthenium-titanium dioxide. It is to be understood that tungsten-titanium and ruthenium-titanium dioxide are alloys of the listed elements or element and compound. Examples of suitable metal silicides may have the chemical formula M₂Si, MSi, or MSi₂. Some specific examples include nickel silicides, such as Ni₂Si, NiSi, Ni₅Si₂, or Ni₃Si, cobalt silicides, such as Co₂Si, CoSi, CoSi₃, or CoSi₂, platinum silicides, such as PtSi, palladium silicides, such as Pd₂Si, titanium silicides, such as TiSi₂, molybdenum silicides, such as MoSi, tantalum silicides, such as TaSi₂, and tungsten silicides, such as WSi₂. Some specific examples of amorphous alloys include MoNi, NiW, and WZr.

In the examples disclosed herein, multiple diffusion barrier agents may be used together to form a multi-layer diffusion barrier. For example, the following diffusion barrier components may be present in separate diffusion barrier agents, which may be applied adjacent to one another to create a multi-layer diffusion barrier: Pd₂Si and chromium, CoSi₂and tungsten, PtSi and TiN, PtSi and TiC, NiSi and TaN.

The selection of the diffusion barrier element depends upon the alloying element that is to be used, which depends upon the metal-based build material that is to be used and the alloyed composition that is to be formed in the 3D object. Any metal-based build material may be used, any alloying element that can alloy with the metal-based build material may be used, and any diffusion barrier component that can at least reduce the diffusion of the alloying element may be used. Some specific combinations include: i) the metal-based build material is an iron-based steel; the alloying element is carbon; and the diffusion barrier component is selected from the group consisting of silicon, nickel, copper, and tantalum; or ii) the metal-based build material is an aluminum-based build material; the alloying element is silicon; and the diffusion barrier component is a metal silicide selected from the group consisting of M₂Si, MSi, MSi₂, Ni₂Si, NiSi, Ni₅Si₂, Ni₃Si, Co₂Si, CoSi, CoSi₂, PtSi, Pd₂Si, TiSi₂, CoSi₃, MoSi, TaSi₂, WSi₂; or iii) the metal-based build material is a copper-based build material; the alloying element is silicon; and the diffusion barrier component is selected from the group consisting of tantalum, tantalum nitride, and titanium-tungsten; or iv) the metal-based build material is an iron-chromium alloy; the alloying element is palladium; and the diffusion barrier component is yttria stabilized zirconia; or v) the metal-based build material is an aluminum-based build material; the alloying element is silicon; and the diffusion barrier component is selected from the group consisting of chromium, vanadium, titanium, tantalum nitride, titanium nitride, titanium carbide, titanium-tungsten, and an amorphous alloy; or vi) the metal-based build material is an iron-based steel; the alloying element is nickel; and the diffusion barrier component is carbon; or vii) the metal-based build material is selected from the group consisting of martensitic stainless steel, austenitic stainless steel, and carbon-manganese steel; the alloying element is copper; and the diffusion barrier component is selected from the group consisting of tantalum, tantalum nitride, titanium nitride, aluminum, hexagonal boron nitride, molybdenum disulfide, and ruthenium-titanium dioxide.

Any of the diffusion barrier components that are included as nanoparticles may have an average particle size (e.g., average diameter of the particles) ranging from about 2 nm to about 100 nm. A distribution of the diffusion barrier component nanoparticles (D10 to D90) may range from about 10 nm to about 75 nm with a median diameter (D50) of about 50 nm. In an example, the distribution values (D10, D50, D90) may be weighted by volume. The individual particle sizes can be outside of the distribution range, as D50 is defined as the median diameter at which about half of the particles are larger than the D50 value and about half of the other particles are smaller than the D50 value. Similarly, about 10% of the particles in the distribution are below the D10 value and about 90% of the particles in the distribution are below the D90 value. As noted, in an example, the distribution values may be volume-weighted mean diameters. In another example, the longest dimension of a carbon nanotube used as an alloying element (e.g., its length) may range from about 2 nm to about 100 nm.

The diffusion barrier component may be present in the diffusion barrier agent in an amount that enables good jettability from a desired inkjet printhead. When nanoparticles are included in the diffusion barrier agent, the amount may range from about 0.5 vol % to about 10 vol %, based on the total volume of the diffusion barrier agent. In one example, silicon nanoparticles may be present in the alloying agent in an amount of about 5 vol %. The amounts set forth herein may be varied if other jetting technologies are to be used. In terms of weight percent, the alloying element may be present in an amount ranging from about 0.1 wt % active to about 60 wt % active (e.g., from about 0.1 wt % active to about 10 wt % active) based on the total weight of the diffusion barrier agent, and these percentages may take into account the density of the particular diffusion barrier component. The volume and/or weight percentage of the diffusion barrier component should be selected so that the diffusion barrier agent is jettable via the desired inkjet printhead.

The diffusion barrier agent also includes a vehicle. The term “vehicle” for the diffusion barrier agent refers to the liquid(s) into which the diffusion barrier component is introduced. In an example, the diffusion barrier agent vehicle may include at least some water (e.g., deionized water). The amount of water may depend, in part, on the type of jetting architecture that is to be used. For example, if the diffusion barrier agent is to be jettable via thermal inkjet printing, water may make up 35 wt % or more of the diffusion barrier agent. In one example, water makes up from about 70 wt % to about 75 wt % of the total weight of the diffusion barrier agent. For another example, if the alloying agent is to be jettable via piezoelectric inkjet printing, water may make up from about 25 wt % to about 30 wt % of the total weight of the diffusion barrier agent, and 35 wt % or more of the total weight of the diffusion barrier agent may be an organic co-solvent, such as ethanol, isopropanol, acetone, etc. Other example vehicles include no water and include one or more of the co-solvents disclosed herein.

In addition to, or as an alternative to water, any example of the diffusion barrier vehicle may include a (co-)solvent and a surfactant. Other additives may also be included, such as antimicrobial agent(s), dispersant(s), chelating agent(s), pH adjuster(s), and/or combinations thereof. In an example, the vehicle of the diffusion barrier agent includes a co-solvent, a surfactant, and a balance of water. In another example, the vehicle of the diffusion barrier agent consists of a co-solvent, a surfactant, and a balance of water. In still another example, the vehicle of the diffusion barrier agent consists of a co-solvent, a surfactant, an additive selected from the group consisting of antimicrobial agent(s), dispersant(s), chelating agent(s), and/or combinations thereof, and a balance of water.

Any of the organic (co-)solvents, surfactant(s), antimicrobial agent(s), dispersant(s), chelating agent(s), and/or pH adjuster(s) set forth herein for the alloying agent may be used in the diffusion barrier agent. Each of these components may be included in the respective amounts set forth herein, except that the total is with respect to the diffusion barrier agent instead of the alloying agent.

Binder Agent

The binder agent is a fluid that includes water and a binder that is effective for binding layers of particulate build material when forming a 3D intermediate structure.

The binder may be polymer particles, metal nanoparticles, metal salts, or polymer coating metal nanoparticles.

In some examples, the polymer particles are latex particles. Latex particles refer to any polymer (homopolymer, co-polymer, or heteropolymer) that is capable of being dispersed in an aqueous medium.

The polymer (latex) particles may have several different morphologies. In one example, the polymer particles can include two different copolymer compositions, which may be fully separated core-shell polymers, partially occluded mixtures, or intimately comingled as a polymer solution. In another example, the polymer particles can be individual spherical particles containing polymer compositions of hydrophilic (hard) component(s) and/or hydrophobic (soft) component(s) that can be interdispersed. In one example, the interdispersion can be according to IPN (interpenetrating networks) although it is contemplated that the hydrophilic and hydrophobic components may be interdispersed in other ways. In yet another example, the polymer particles can be composed of a hydrophobic core surrounded by a continuous or discontinuous hydrophilic shell. For example, the particle morphology can resemble a raspberry, in which a hydrophobic core can be surrounded by several smaller hydrophilic particles that can be attached to the core. In yet another example, the polymer particles can include 2, 3, or 4 or more relatively large polymer particles that can be attached to one another or can surround a smaller polymer core. In a further example, the polymer particles can have a single phase morphology that can be partially occluded, can be multiple-lobed, or can include any combination of any of the morphologies disclosed herein.

In some examples, the polymer (latex) particles can be homopolymers. In other examples, the polymer (latex) particles can be heteropolymers or copolymers. In an example, a heteropolymer can include a hydrophobic component and a hydrophilic component. In this example, the heteropolymer can include a hydrophobic component that can include from about 65% to about 99.9% (by weight of the heteropolymer), and a hydrophilic component that can include from about 0.1% to about 35% (by weight of the heteropolymer). In one example, the hydrophobic component can have a lower glass transition temperature than the hydrophilic component.

Examples of monomers that may be used to form the hydrophobic component of the heteropolymer polymer (latex) particles include C4 to C8 alkyl acrylates or methacrylates, styrene, substituted methyl styrenes, polyol acrylates or methacrylates, vinyl monomers, vinyl esters, ethylene, maleate esters, fumarate esters, itaconate esters, or the like. Some specific example monomers can include, C1 to C20 linear or branched alkyl (meth)acrylate, alicyclic (meth)acrylate, alkyl acrylate, styrene, methyl styrene, polyol (meth)acrylate, hydroxyethyl (meth)acrylate, or a combination thereof. In one specific class of examples, the polymer (latex) particles can be a styrene (meth)acrylate copolymer. In still another example, the polymer (latex) particles can include a copolymer with copolymerized methyl methacrylate being present at about 50 wt % or greater, or copolymerized styrene being present at about 50 wt % or greater. Both methyl methacrylate and styrene can be present, with one or the other being present at about 50 wt % or greater.

The term “(meth)acrylate” or “(meth)acrylic acid” or the like refers to monomers, copolymerized monomers, etc., that can either be acrylate or methacrylate (or a combination of both), or acrylic acid or methacrylic acid (or a combination of both). In some examples, the terms “(meth)acrylate” and “(meth)acrylic acid” can be used interchangeably, as acrylates and methacrylates are salts and esters of acrylic acid and methacrylic acid, respectively. Furthermore, mention of one compound over another can be a function of pH. Furthermore, even if the monomer used to form the polymer was in the form of a (meth)acrylic acid during preparation, pH modifications during preparation or subsequently when added to an ejectable fluid, such as a binder agent, can impact the nature of the moiety as well (acid form vs. salt or ester form). Thus, a monomer or a moiety of a polymer described as (meth)acrylic acid or as (meth)acrylate should not be read so rigidly as to not consider relative pH levels, ester chemistry, and other general organic chemistry concepts.

In still other examples, the polymer (latex) particles in the binder agent include polymerized monomers of vinyl chloride, vinylidene chloride, vinylbenzyl chloride, vinyl ester, styrene, ethylene, maleate esters, fumarate esters, itaconate esters, α-methyl styrene, p-methyl styrene, methyl methacrylate, hexyl acrylate, hexyl methacrylate, hydroxyethyl acrylate, butyl acrylate, butyl methacrylate, ethyl acrylate, ethyl methacrylate, propyl acrylate, propyl methacrylate, 2-ethylhexyl acrylate, 2-ethylhexyl methacrylate, octadecyl acrylate, octadecyl methacrylate, stearyl methacrylate, 2-phenoxyethyl methacrylate, isobornyl acrylate, tetrahydrofurfuryl acrylate, benzyl methacrylate, benzyl acrylate, ethoxylated nonyl phenol methacrylate, isobornyl methacrylate, ethylene glycol dimethacrylate, diethylene glycol dimethacrylate, triethylene glycol dimethacrylate, cyclohexyl methacrylate, trimethyl cyclohexyl methacrylate, t-butyl methacrylate, n-octyl methacrylate, lauryl acrylate, lauryl methacrylate, tridecyl methacrylate, alkoxylated tetrahydrofurfuryl acrylate, isodecyl acrylate, dimethyl maleate, dioctyl maleate, acetoacetoxyethyl methacrylate, diacetone acrylamide, N-vinyl imidazole, N-vinylcarbazole, N-Vinyl-caprolactam, pentaerythritol tri-acrylate, pentaerythritol tetra-acrylate, pentaerythritol tri-methacrylate, pentaerythritol tetra-methacrylate, glycidol acrylate, glycidol methacrylate, tetrahydrofuryl acrylate, tetrahydrofuryl methacrylate, diacetone acrylamide, t-butyl acrylamide, divinylbenzene, 1,3-butadiene, acrylonitrile, methacrylonitrile, combinations thereof, derivatives thereof, or mixtures thereof. These monomers include low glass transition temperature (Tg) monomers that can be used to form the hydrophobic component of a heteropolymer.

In some examples, a composition of the polymer (latex) particles can include acidic monomer(s). In some examples, the acidic monomer content can range from 0.1 wt % to 5 wt %, from 0.5 wt % to 4 wt %, or from 1 wt % to 2.5 wt % of the polymer particles with the remainder of the polymer particle being composed of non-acidic monomers. Example acidic monomers can include acrylic acid, methacrylic acid, ethacrylic acid, dimethylacrylic acid, maleic anhydride, maleic acid, vinylsulfonate, cyanoacrylic acid, vinylacetic acid, allylacetic acid, crotonoic acid, fumaric acid, itaconic acid, sorbic acid, angelic acid, cinnamic acid, styrylacrylic acid, citraconic acid, glutaconic acid, aconitic acid, phenylacrylic acid, acryloxypropionic acid, aconitic acid, phenylacrylic acid, acryloxypropionic acid, vinylbenzoic acid, N-vinylsuccinamidic acid, mesaconic acid, methacroylalanine, acryloylhydroxyglycine, sulfoethyl methacrylic acid, sulfopropyl acrylic acid, styrene sulfonic acid, sulfoethylacrylic acid, 2-methacryloyloxymethane-1-sulfonic acid, 3-methacryoyloxypropane-1-sulfonic acid, 3-(vinyloxy)propane-1-sulfonic acid, ethylenesulfonic acid, vinyl sulfuric acid, 4-vinylphenyl sulfuric acid, ethylene phosphonic acid, vinyl phosphoric acid, vinyl benzoic acid, 2-acrylamido-2-methyl-1-propanesulfonic acid, combinations thereof, derivatives thereof, or mixtures thereof. These acidic monomers are hydrophilic monomers that have a higher Tg than the low Tg hydrophobic monomers described herein. These acidic monomers can be used to form the hydrophilic component of a heteropolymer. Other examples of high Tg hydrophilic monomers can include acrylamide, methacrylamide, monohydroxylated monomers, monoethoxylated monomers, polyhydroxylated monomers, or polyethoxylated monomers.

In an example, the selected monomer(s) can be polymerized with a co-polymerizable dispersing agent. The co-polymerizable dispersing agent can be a polyoxyethylene compound, such as a HITENOL® compound (Montello Inc.) e.g., polyoxyethylene alkylphenyl ether ammonium sulfate, sodium polyoxyethylene alkylether sulfuric ester, polyoxyethylene styrenated phenyl ether ammonium sulfate, or mixtures thereof.

Any suitable polymerization process can be used to form the polymer (latex) particles. In some examples, an aqueous dispersion of polymer (latex) particles can be produced by emulsion polymerization or co-polymerization of any of the above monomers.

In one example, the polymer (latex) particles can be prepared by polymerizing high Tg hydrophilic monomers to form the high Tg hydrophilic component and attaching the high Tg hydrophilic component onto the surface of the low Tg hydrophobic component. In another example, the polymer (latex) particles can be prepared by polymerizing the low Tg hydrophobic monomers and the high Tg hydrophilic monomers at a ratio of the low Tg hydrophobic monomers to the high Tg hydrophilic monomers that ranges from 5:95 to 30:70. In this example, the low Tg hydrophobic monomers can dissolve in the high Tg hydrophilic monomers. In yet another example, the polymer (latex) particles can be prepared by polymerizing the low Tg hydrophobic monomers, then adding the high Tg hydrophilic monomers. In this example, the polymerization process can cause a higher concentration of the high Tg hydrophilic monomers to polymerize at or near the surface of the low Tg hydrophobic component. In still another example, the polymer (latex) particles can be prepared by copolymerizing the low Tg hydrophobic monomers and the high Tg hydrophilic monomers, then adding additional high Tg hydrophilic monomers. In this example, the copolymerization process can cause a higher concentration of the high Tg hydrophilic monomers to copolymerize at or near the surface of the low Tg hydrophobic component.

Other suitable techniques, specifically for generating a core-shell structure, can include grafting a hydrophilic shell onto the surface of a hydrophobic core, copolymerizing hydrophobic and hydrophilic monomers using ratios that lead to a more hydrophilic shell, adding hydrophilic monomer (or excess hydrophilic monomer) toward the end of the copolymerization process so there is a higher concentration of hydrophilic monomer copolymerized at or near the surface, or any other method that can be used to generate a more hydrophilic shell relative to the core.

In one specific example, the low Tg hydrophobic monomers can be selected from the group consisting of C4 to C8 alkyl acrylate monomers, C4 to C8 alkyl methacrylate monomers, styrene monomers, substituted methyl styrene monomers, vinyl monomers, vinyl ester monomers, and combinations thereof; and the high Tg hydrophilic monomers can be selected from acidic monomers, unsubstituted amide monomers, alcoholic acrylate monomers, alcoholic methacrylate monomers, C1 to C2 alkyl acrylate monomers, C1 to C2 alkyl methacrylate monomers, and combinations thereof. The resulting polymer latex particles can exhibit a core-shell structure, a mixed or intermingled polymeric structure, or some other morphology.

In some examples, the polymer (latex) polymer can have a weight average molecular weight (Mw, g/mol) that can range from about 5,000 Mw to about 2,000,000 Mw. In yet other examples, the weight average molecular weight can range from about 100,000 Mw to about 1,000,000 Mw, from about 100,000 Mw to about 500,000 Mw, from about 150,000 Mw to about 300,000 Mw, or from about 50,000 Mw to about 250,000 Mw. Weight average molecular weight (Mw) can be measured by Gel Permeation Chromatography with polystyrene standard.

In some examples, the polymer (latex) particles can be latent and can be activated by heat (which may be applied iteratively during 3D intermediate structure formation or after 3D intermediate structure formation) and water and co-solvent evaporation. In these instances, the activation temperature can correspond to the minimum film formation temperature (MFFT) or a glass transition temperature (Tg) which can be greater than ambient temperature. As mentioned herein, “ambient temperature” may refer to room temperature (e.g., ranging about 18° C. to about 22° C.). In one example, the polymer (latex) particles can have a MFFT or Tg that can be at least about 15° C. greater than ambient temperature. In another example, the MFFT or the Tg of the bulk material (e.g., the more hydrophobic portion) of the polymer (latex) particles can range from about 25° C. to about 200° C. In another example, the polymer (latex) particles can have a MFFT or Tg ranging from about 40° C. to about 120° C. In yet another example, the polymer (latex) particles can have a MFFT or Tg ranging from about 0° C. to about 150° C. In a further example, the polymer latex particles can have a Tg that can range from about −20° C. to about 130° C., or in another example from about 60° C. to about 105° C. At a temperature above the MFFT or the Tg of a latent latex polymer particle, the polymer particles can coalesce and can bind materials, such as the metal-based build material particles.

The polymer (latex) particles can have an average particle size (e.g., average diameter of the particles) that can be jetted via thermal ejection or printing, piezoelectric ejection or printing, drop-on-demand ejection or printing, continuous ejection or printing, etc. In an example, the average particle size of the polymer (latex) particles can range from about 1 nm to about 400 nm. In yet other examples, a particle size of the polymer particles can range from about 10 nm to about 300 nm, from about 50 nm to about 250 nm, from about 100 nm to about 250 nm, or from about 25 nm to about 250 nm.

In some examples, the polymer (latex) particles have a glass transition temperature higher than 60° C. and an average particle size of 1 nm or more.

In examples of the binder agent, the polymer particles can be present, based on a total weight of the binder agent, in an amount ranging from about 1 wt % active to about 40 wt % active. In other more detailed examples, the polymer particles can be present in an amount ranging from about 5 wt % active to about 30 wt % active, from about 12 wt % active to about 22 wt % active, from about 15 wt % active to about 20 wt % active, from about 10 wt % active to about 20 wt % active, or from about 6 wt % active to about 18 wt % active, based on the total weight of the binder agent.

Metal nanoparticles can also be used as the binder. Metal nanoparticles are smaller than the build material particles and can melt at lower temperatures, and thus can form a metal binding network to generate the intermediate structure. Any example of the metal nanoparticles set forth herein for the alloying agent may be used as the binder in the binding agent, except that the binder is selected to be the same material as the metal-based build material. This is because the metal nanoparticle binder is not removed in a de-binding step (like the polymer particles), but rather, becomes part of the 3D object.

Metal salts can also be used as the binder. Metal salts decompose into metal, and thus can form a metal binding network to generate the intermediate structure. Any example of the metal salts set forth herein for the alloying agent may be used as the binder in the binding agent, with the caveat that the metal formed from the metal salt decomposition should be the same material as the metal-based build material. This is because the metal binder is not removed in a de-binding step (like the polymer particles), but rather, becomes part of the 3D object.

In addition to the binder, the binder agent includes a binder agent vehicle. In one example, the binder agent vehicle is water. In another example, the binder agent vehicle includes water and one or more additives, such as co-solvent(s), surfactant(s), antimicrobial(s), viscosity modifier(s), pH adjuster(s), chelating agent(s), anti-kogation agent(s), and the like. In one example, water can be present in an amount ranging from about 30 wt % to 100 wt % of the binder agent vehicle component—excluding the polymer particles—based on a total weight of the binder agent vehicle. Put another way, the water can be present in an amount ranging from about 60 wt % to about 99 wt %, from about 65 wt % to 90 wt %, or from about 70 wt % to about 85 wt %, based on a total weight of the binder agent.

The co-solvent can be present in the binder agent in an amount ranging from about 0.5 wt % active to about 50 wt % active, based on a total weight of the binder agent. When a single co-solvent is included, the co-solvent that is selected is a plasticizer for the polymer (latex) particles in the binder agent. When multiple co-solvents are included, at least one of the co-solvents is a plasticizer for the polymer (latex) particles in the binder agent. Some examples of suitable plasticizing co-solvents include 2-pyrrolidone, dimethyl sulfoxide (DMSO), methyl 4-hydroxybenzoate, dioctyl phthalate, N-methyl-2-pyrrolidone (i.e., N-methyl-pyrrolidone), and mixtures thereof. Other examples of suitable plasticizers include N-2-hydroxyethyl-2-pyrrolidone (i.e., 1-(2-hydroxyethyl)-2-pyrrolidone), urea, ethylene carbonate, propylene carbonate, lactones, diethylene glycol, triethylene glycol, tetraethylene glycol, decalin, gamma-butyrolactone, dimethylformamide, and phenylmethanol.

Examples of other co-solvents that can be used in combination with the plasticizing co-solvent include any of the co-solvents described for the alloying agent.

Any examples of the surfactants set forth for the alloying agent may be used in the binder agent. Some specific examples include SURFYNOL® SEF (a self-emulsifiable wetting agent based on acetylenic diol chemistry), SURFYNOL® 104 (a non-ionic wetting agent based on acetylenic diol chemistry), or SURFYNOL® 440 (an ethoxylated low-foam wetting agent) (all available from Evonik Degussa); TERGITOL® TMN-6 (a branched secondary alcohol ethoxylate, non-ionic surfactant), TERGITOL® 15-S-5 or TERGITOL® 15-S-7 (each of which is a secondary alcohol ethoxylate, non-ionic surfactant), or DOWFAX® 2A1 or DOWFAX® 8390 (each of which is an alkyldiphenyloxide disulfonate, available from The Dow Chemical Company); CAPSTONE® FS-35 (non-ionic fluorosurfactant from DuPont); or a combination thereof.

The surfactant or combinations of surfactants can be present in the binder agent in an amount ranging from about 0.1 wt % active to about 5 wt % active based on the total weight, and in some examples, can be present in an amount ranging from about 0.5 wt % active to about 2 wt % active.

With respect to antimicrobials, any compound set forth for the alloying agent can be included in the binder agent. In an example, the example binder agent may include a total amount of antimicrobials that ranges from about 0.0001 wt % active to about 1 wt % active.

Viscosity modifiers and pH adjusters (e.g., acids, bases, or buffers) may also be present, as well as other additives to modify properties of the binder agent. A desirable pH for the binder agent ranges from about 3 to about 10, and a desirable viscosity for the binder agent is any that enables it to be jetted via a thermal and/or piezoelectric inkjet print head. Some examples of the binder agent have a pH ranging from about 6 to about 10, and other examples of the binder agent have a pH ranging from about 7 to about 7.5.

Chelating agents, such as EDTA (ethylene diamine tetra acetic acid) or any other example set forth for the alloying agent may be included in the binder agent. Whether a single chelating agent is used or a combination of chelating agents is used, the total amount of chelating agent(s) in the example binder agents may range from greater than 0 wt % active to about 2 wt % active based on the total weight of the binder agent.

Examples of the binder agent that are to be dispensed from a thermal inkjet printhead may also include from about 0.1 wt % to about 1 wt % of an anti-kogation agent, based on a total weight of the binder agent. Kogation refers to the deposit of dried solids on a thermal inkjet printhead. An anti-kogation agent can be included to prevent the buildup of dried solids on the printhead. Examples of suitable anti-kogation agents include oleth-3-phosphate (commercially available as CRODAFOS™ O3A or CRODAFOS™ N-3 acid), dextran 500k, CRODAFOS™ HCE (phosphate-ester from Croda Int.), CRODAFOS® N10 (oleth-10-phosphate from Croda Int.), or DISPERSOGEN® LFH (polymeric dispersing agent with aromatic anchoring groups, acid form, anionic, from Clariant), etc.

Combined Alloying Agent and Binder Agent

The examples disclosed herein describe an alloying agent and a separate binder agent (i.e., binder agent). Separate agents allow for the patterning of the 3D object (with the binder agent) and the patterning for the site-specific alloyed section(s) of the 3D object to be separately controlled in examples of the method that utilize the binder agent. However, it is to be understood that the alloying element (of the alloying agent) and the polymer (latex) particles (of the binder agent) may be combined into a single alloying/binder agent. The combined alloying/binder agent may include the alloying element, the polymer particles, and any example of the vehicle described herein for the alloying agent and/or the binder agent. This combined alloying/binder agent may be useful so that the site-specific alloyed section(s) can be patterned with a single agent. It is to be understood that this combined alloying/binder agent may also be used with a separate binder agent that does not include the alloying element. In this example, the separate binder agent may be used to pattern portion(s) of the 3D object that are not to be alloyed, and the combined alloying/binder agent may be used to pattern portion(s) of the 3D object that are to be alloyed.

Metal-Based Build Materials

In the examples disclosed herein, the metal-based build material can include any metal-based particles. Metal-based particles include metal particles or metal alloy particles. As such, the terms “aluminum-based build material” and “aluminum-based particles” include both aluminum particles and aluminum alloy particles.

In an example, the metal-based particles are a single phase metallic material composed of one element. Examples of these metal particles include aluminum, titanium, molybdenum, tungsten, copper, iron, nickel, etc. In another example, the metal-based particles are composed of two or more elements, which may be in the form of a single phase metallic alloy or a multiple phase metallic alloy. Examples of these metal particles include ferrous alloys (e.g., iron-chromium alloys, low-to medium-carbon stainless steels,) titanium alloys, or carbon-manganese steel. In low-carbon stainless steel, the carbon level is 0.3% or less. In medium-carbon stainless steel, the carbon level ranges from about 0.31% to about 0.6%. Specific alloy examples can include stainless steel 304/304L (low-carbon), stainless steel GP1 (low-carbon), stainless steel 17-4PH (low-carbon), stainless steel 316/316L (low-carbon), stainless steel 430L (low carbon), titanium 6Al4V, titanium 6Al-4V ELI7. Inconel IN718, Inconel IN625, Maraging Steel MS1, Nickel Alloys HX, CoCr F75 and aluminum alloy 2000, 6000, 7000, and 8000 series. Metal carbides can also be suitable build materials, including tungsten carbide. While several example alloys have been provided, it is to be understood that other metal alloys may be used as the build material.

The average particle size of the metal-based particles can be similarly sized or differently sized. In one example, the average particle size of the metal-based particles can range from 0.5 μm to 200 μm. In some examples, the metal-based particles within a distribution can have a median diameter (D50) ranging from about 2 μm to about 150 μm, from about 1 μm to about 100 μm, from about 1 μm to about 50 μm, etc.

The shape of the metal-based particles can be spherical, non-spherical, random shapes, or a combination thereof.

The metal-based particles may be used in the metal-based build material composition without other additives, or may be used with other additives. Any of the metal-based build material compositions disclosed herein include from about 80 wt % to 100 wt % of the metal-based build material particles (based on the total weight of the build material composition). In other examples, the metal-based build material particles can be present in the composition in amounts ranging from about 90 wt % to 100 wt %, or from about 95 wt % to 100 wt %, or in an amount of 100 wt %. When the metal-based particles are present in the build material composition in an amount less than 100 wt %, the remainder of the build material composition may be made up of additives, such as flow aids (e.g., in amounts ranging from about 0.05 wt % to about 0.2 wt %), polymer powder material, etc.

Some examples of the metal-based build material may also include the diffusion barrier component. As one example, the metal-based build material (e.g., iron based alloy) may include some silicon particles. In these instances, a diffusion barrier agent containing the same diffusion barrier component may be used to pattern the diffusion barrier, and the concentration of the diffusion barrier component in the agent may be lower than when the agent is used with build material that does not include the diffusion barrier component.

Some examples of the metal-based build material may also include the alloying element pre-mixed therein. In these instances, the alloying agent is not used. The term “mixed build material” is used herein to refer to the pre-mixed metal-based build material and the alloying element.

Three Dimensional Printing Methods

Some examples of the printing methods disclosed herein utilize the binder agent, the alloying agent, the diffusion barrier agent, and a heat treatment to generate the 3D object having the site-specific alloyed section(s) and the diffusion barrier(s) within the 3D object.

One example of this method includes: based on a digital 3D object model of the 3D object, patterning individual layers of a metal-based build material with a binder agent to form an intermediate structure; based on the digital 3D object model, patterning a first portion of at least one of the individual layers with an alloying agent to form a pattern of the site-specific alloyed section; based on the digital 3D object model, patterning a second portion of at least one of the individual layers with a diffusion barrier agent to form a perimeter pattern at an edge of at least a portion of the pattern of the site-specific alloyed section; and exposing the intermediate structure to a heat treatment to form the 3D object. This example method will be further described in reference to FIG. 1, FIG. 2A, and FIG. 2B. In this example method, it is to be understood that the portions (e.g., first portion, second portion) that are patterned with the alloying agent or the diffusion barrier agent are also patterned with the binder agent so that these portions are bound as part of the intermediate structure.

Other examples of the printing methods disclosed herein utilize the alloying agent or the alloying element pre-mixed in with some of the metal-based build material, the diffusion barrier agent, and a localized heat source to generate the 3D object having the site-specific alloyed section(s) and the diffusion barrier(s) within the 3D object. One example of this method includes: applying a metal-based build material to form a build material layer, wherein a predetermined portion of the build material layer includes an alloying element; based on the digital 3D object model, patterning a portion of the build material layer with a diffusion barrier agent to form a perimeter pattern at an edge of at least part of the predetermined portion; and using a localized heat source to scan the build material layer based on the digital 3D object model, thereby forming a layer of the 3D object. This example method will be further described in reference to FIG. 3A through FIG. 3C and FIG. 4A and FIG. 4B.

As shown in FIG. 1, the metal-based build material 12 is deposited from a build material source 14 onto a build area platform 16 where it can be flattened or smoothed, such as by a mechanical roller or other flattening mechanism or technique, to form an individual layer L₁, L₂, L₃. . . L_x. Each layer L₁, L₂, L₃. . . L_xof the metal-based build material 12 has a substantially uniform thickness across the build area platform 16. In an example, the thickness of the build material layer L₁, L₂, L₃. . . L_xranges from about 90 μm to about 110 μm, although thinner or thicker layers may be used. For example, the thickness of each build material layer L₁, L₂, L₃. . . L_xmay range from about 50 μm to about 200 μm. In another example, the thickness of each build material layer L₁, L₂, L₃. . . L_xranges from about 30 μm to about 300 μm. The layer L₁, L₂, L₃. . . L_xthickness may be about 2× (i.e., 2 times) the average particle size of the metal-based build material 12 at a minimum for finer part definition. In some examples, the layer L₁, L₂, L₃. . . L_xthickness may be about 1.2× the average particle size of the metal-based build material 12.

In this example method, after each individual layer L₁, L₂, L₃. . . L_xis deposited, it may be patterned with the binder agent 18 or with the binder agent 18 and the alloying agent 20 or with the binder agent 18 and the diffusion barrier agent 22.

The binder agent 18 (without the alloying agent 20 or the diffusion barrier agent 22) is used to pattern any portion of the individual layer L₁, L₂, L₃. . . L_xthat is to become part of the 3D object 10 (see FIG. 2B), but is not to have the alloyed composition or include the diffusion barrier component 23. The binder agent 18 delivers the binder 19 to the individual layers L₁, L₂, L₃. . . L_xof the metal-based build material 12. The portions of the individual layer L₁, L₂, L₃. . . L_xthat are patterned with the binder agent 18 alone become the non-alloyed sections 24 of the 3D object 10 (see FIG. 2B). The composition and microstructure of the non-alloyed section 24 in the 3D object 10 are dictated by the metal-based build material 12 that is used. In some examples, the non-alloyed section 24 forms the bulk of the 3D object 10.

The combination of the binder agent 18 and alloying agent 20 is used to pattern any portion of the individual layer L₁, L₂, L₃. . . L_xthat is to become a site-specific alloyed section 26 (see FIG. 2B) of the 3D object 10. The binder agent 18 delivers the binder 19, and the alloying agent 20 delivers the alloying element 21 to portion(s) of the individual layers L₁, L₂, L₃. . . L_xof the metal-based build material 12 that is/are to become site-specific alloyed section(s) 26. The site-specific alloyed section 26 that forms at the portion patterned with the binder agent 18 and the alloying agent 20 has the alloyed composition. In some examples, the alloyed composition (and thus the site-specific alloyed section 26) has a different microstructure after sintering than the microstructure of the non-alloyed section 24 of the 3D object 10 after sintering, due, for example, to a phase transformation. The phase transformation results from the interaction or reaction between the alloying element 21 in the alloying agent 20 and the metal-based build material 12. In one example of the 3D printed object 10, the non-alloyed section 24 has a ferritic microstructure, and the site-specific alloyed section(s) 26 has a pearlite microstructure.

The combination of the binder agent 18 and diffusion barrier agent 22 is used to pattern any portion of the individual layer L₁, L₂, L₃. . . L_xthat is to become a diffusion barrier 28, 28′ (see FIG. 2B) of the 3D object 10. The binder agent 18 delivers the binder 19, and the diffusion barrier agent 22 delivers the diffusion barrier component 23 to portion(s) of the individual layers L₁, L₂, L₃. . . L_xof the metal-based build material 12 that is/are to become diffusion barrier(s) 28, 28′. The diffusion barrier agent 22 is deposited between at least some of the build material 12 patterned with the binder agent 18 alone and at least some of the build material 12 patterned with both the binder agent 18 and the alloying agent 20. As such, the diffusion barrier agent 22 is deposited at an edge of at least a portion of the pattern of the site-specific alloyed section 26. The diffusion barrier agent 22 forms a perimeter pattern at the edge(s) of the pattern of the site-specific alloyed section 26. In some instances, the diffusion barrier agent 22 is selectively applied so that the perimeter pattern is defined around the entire pattern of the site-specific alloyed section 26. In the example shown in FIG. 1, the diffusion barrier agent 22 is used to i) pattern the perimeter of the circular/spherical pattern that is generated with the binder agent 18 and the alloying agent 22, which will form the diffusion barrier 28 shown in FIG. 2B, and ii) pattern a planar section that separates some of the build material 12 patterned with the binder agent 18 from some of the build material 12 patterned with the binder agent 18 and the alloying agent 22, which will form the diffusion barrier 28′ shown in FIG. 2B.

The diffusion barrier 28, 28′ that forms at the portion patterned with the binder agent 18 and the diffusion barrier agent 22 includes the diffusion barrier component 23 intermingled with the metal-based build material composition, and may or may not include some of the alloyed composition. Whether the diffusion barrier 28, 28′ includes some of the alloyed composition depends upon the chemical potentials of the alloying element 21 and the diffusion barrier component 23, the thickness of the diffusion barrier pattern, and/or the concentration of the diffusion barrier component 23 in the diffusion barrier agent 22.

The binder agent 18 can be ejected onto the portion(s) of the metal-based build material 12 in a particular layer L₁, L₂, L₃. . . L_xfrom a fluid ejector 30 (such as a thermal inkjet printhead or a piezoelectric inkjet printhead). The fluid ejector 30 allows for (spatially) selective patterning of the metal-based build material 12 layer by layer. The deposition of the binder agent 18 in a particular layer L₁, L₂, L₃. . . L_xis based on the slice of the particular layer L₁, L₂, L₃. . . L_xfrom the digital 3D object model (e.g., a computer model).

The alloying agent 20 can be ejected onto desired portion(s) of the metal-based build material 12 in a particular layer L₁, L₂, L₃. . . L_xfrom a fluid ejector 30′ (such as a thermal inkjet printhead or a piezoelectric inkjet printhead). The fluid ejector 30′ also allows for (spatially) selective patterning of the metal-based build material 12 layer by layer. The deposition of the alloying agent 20 in a particular layer L₁, L₂, L₃. . . L_xis based on the slice of the particular layer L₁, L₂, L₃. . . L_xfrom the digital 3D object model (e.g., a computer model), when the slice includes the desired locations of the site-specific alloyed section 26.

The diffusion barrier agent 22 can be ejected onto desired portion(s) of the metal-based build material 12 in a particular layer L₁, L₂, L₃. . . L_xfrom a fluid ejector 30″ (such as a thermal inkjet printhead or a piezoelectric inkjet printhead). The fluid ejector 30″ also allows for (spatially) selective patterning of the metal-based build material 12 layer by layer. The deposition of the diffusion barrier agent 22 in a particular layer L₁, L₂, L₃. . . L_xis based on the slice of the particular layer L₁, L₂, L₃. . . L_xfrom the digital 3D object model (e.g., a computer model), when the slice includes the desired locations of the diffusion barrier 28, 28′.

The specified concentration of the alloying element 21 that is delivered to some portion(s) of the build material 12 depends upon a variety of factors including the concentration of the alloying element 21 in the alloying agent 20, the build material 12 that is used, and the deposition swath. The following equations may be used to determine the alloying element concentration per layer L1, L2, L3 . . . . Lx of build material 12:

[
w
]

×

[
l
]

×

[
m
]

×

[
C
]

=

alloying
⁢

element
⁢

weight
⁢

per
⁢

pass
⁢

(
WPP
)

[
l
]

×

[
w
]

×

[
t
]

×

[
D
]

×

[
ρ
]

=

build
⁢

material
⁢

weight
⁢

(
BMW
)

WPP

×
number
⁢

of
⁢

passes

WPP

×
number
⁢

of
⁢

passes

+

BMW

=

alloying
⁢

element
⁢

concentration
⁢

per
⁢

layer

where w and l represent the deposition swath width and length, respectively, and are multiplied by the spatial resolution (e.g., dots per inch (dpi)) in the respective direction; m is the mass of each droplet; C is the alloying element mass in the alloying agent 20; [t] is the powder layer thickness; D is the packing density of the metal-based build material 12; and ρ is the density of the metal-based build material 12. The packing density D and the density ρ are specific to the build material 12 that is used. Depending on the build material 12 characteristics, the packing density D is estimated to change from 0.3 to 0.6.

The specific concentration of the alloying element 21 that is delivered to the portion of the build material 12 that are to become the site-specific alloyed portion(s) 26 may be controlled by varying the deposition resolution width (w) and length (l) from 300-1200 dpi and 300-600 dpi, respectively, adjusting the build material layer thickness (t) (e.g., to as fine as 60 μm), and by adjusting the number of deposition passes (i.e., printing passes).

Some examples of the method include applying the alloying agent 20 over multiple printing passes. The number of printing/deposition passes influences the local alloying element concentration, which affects the alloyed composition that is formed and its properties. Thus, the number of printing/deposition passes can be controlled to tune the microstructure and the hardness of the alloyed composition in the site-specific alloyed section 26. In an example, the site-specific alloyed section 26 of the 3D object 10 exhibits a hardness correlating with a number of the multiple printing passes. Each pass may deliver a fraction of the total desired amount that is to be applied.

The multiple printing/deposition passes may be performed sequentially, or a pause between printing/deposition passes may be desirable to allow the alloying agent 20 to at least partially penetrate the layer L₁, L₂, L₃. . . L_xof build material 12.

The specified concentration of the diffusion barrier component 23 that is delivered to some portion(s) of the build material 12 depends upon a variety of factors including the concentration of the diffusion barrier component 23 in the diffusion barrier agent 22, the alloying element 21 that is used, the build material 12 that is used, the thickness of the diffusion barrier 28, 28′ that is to be formed, and the deposition swath. The equations above may be used to determine the diffusion barrier component concentration per layer L₁, L₂, L₃. . . L_xof build material 12, where C is the diffusion barrier component mass in the diffusion barrier agent 22 and the rest of the variables are as characterized herein.

Some examples of the method include applying the diffusion barrier agent 22 over multiple printing passes. The number of printing/deposition passes influences the local diffusion barrier component concentration, which can affect alloying element diffusion. Thus, the number of printing/deposition passes can be controlled to increase the diffusion barrier component concentration and decrease the alloying element diffusion. Each pass may deliver a fraction of the total desired amount that is to be applied.

The multiple printing/deposition passes may be performed sequentially, or a pause between printing/deposition passes may be desirable to allow the diffusion barrier agent 22 to at least partially penetrate the layer L₁, L₂, L₃. . . L_xof build material 12.

The diffusion barrier agent 22 can also be applied in a desirable thickness, which is measured from the edge of the pattern of the site-specific alloyed section 26. For example, when the concentration of the diffusion barrier component 23 in the diffusion barrier agent 22 is relatively low (e.g., from about from about 0.5 vol % to about 5 vol %), the thickness of the pattern of the applied diffusion barrier agent 22 may be increased to decrease diffusion of the alloying element during heating. The thickness may vary depending, at least in part, upon the size of the 3D object being formed, the concentration of the diffusion barrier component 23 in the diffusion barrier agent 22, the diffusion rate of the alloying element, etc. In some examples, the thickness of the region patterned with the diffusion barrier agent 22 may range from about 0.1 mm to about 5 mm.

While several layers L₁, L₂, L₃. . . L_xare shown deposited and patterned in FIG. 1, it is to be understood that each individual layer L₁, L₂, L₃. . . L_xis deposited and patterned with the desired agent(s) 18, 20, 22 before a subsequent layer L₂, L₃. . . L_xis deposited and patterned.

After each individual layer L₁, L₂, L₃. . . L_xis deposited and patterned with the binder agent 18 and/or the binder agent 18 and the alloying agent 20, and/or the binder agent 20 and the diffusion barrier agent 22, the build platform 16 can be dropped a distance of (x), which can correspond to at least the thickness of a patterned layer, so that another layer L₂, L₃. . . L_xof the metal-based build material 12 can be added thereon and patterned. In this example of the method, the process can be repeated on a layer-by-layer basis until all of the desired layers are patterned in accordance with the digital 3D object model.

Heat (h) can be used, such as from a heat source 32, to remove water and/or co-solvent(s) from the various layers L₁, L₂, L₃. . . L_xthroughout the patterning process. This temperature is 120° C. or less. In an example, this temperature may range from about 50° C. to about 120° C. In one example, heat can be applied from overhead, e.g., prior to application of the next layer of metal-based build material 12, or after multiple layers L₁, L₂, L₃. . . L_xare patterned, and/or can be provided by the build area platform 16 from beneath the metal-based build material 12. The build material source 14 can also be used to preheat the metal-based build material 12 prior to dispensing it on the build area platform 16 or on a previously applied and patterned layer L₁, L₂, L₃. . . L_x.

The ejector(s) 30, 30′, 30″ deposit the binder agent 18, the alloying agent 20, and the diffusion barrier agent 22 in a pattern that corresponds to the layers of the 3D object 10, and can be used to form a 3D intermediate structure in any orientation with respect to the X-Y plane of the build area platform 16, and thus with respect to the layers L₁, L₂, L₃. . . L_xof the build material 12. For example, the 3D intermediate structure can be printed from bottom to top in the Z-direction, or at an inverted orientation (e.g., from top to bottom) in the Z-direction. For another example, the 3D intermediate structure can be printed at an angle or on its side. The orientation of the build within the build material 12 can be selected in advance or even by the user at the time of printing, for example.

After all of the desired portions of the layers L₁, L₂, L₃. . . L_xof metal-based build material 12 are patterned with the binder agent 18 and/or the binder agent 18 and the alloying agent 20 (or alternatively, the combined binder/alloying agent) and/or the binder agent 18 and the diffusion barrier agent 22, low temperature heating of all of the individually patterned layers may be performed. This low temperature heating is performed at a temperature ranging from about 120° C. to about 400° C., depending upon the type of binder 19 used.

When polymer particles are used as the binder 19, at this low temperature range, heating evaporates remaining water and/or co-solvents from the agent(s) 18, 20, 22 and causes the (latex) polymer particles to coalesce and form a strong film 19′ (in this example, a polymer film) among the patterned metal-based build material particles 12, generating a bound structure.

When metal nanoparticles are used as the binder 19, at this low temperature range, heating evaporates remaining water and/or co-solvents from the agent(s) 18, 20, 22 and causes the metal nanoparticles to melt and form a strong film 19′ (in this example, a metal film) among the patterned metal-based build material particles 12, generating a bound structure.

When metal salt is used as the binder 19, at this low temperature range, heating evaporates remaining water and/or co-solvents from the agent(s) 18, 20, 22 and causes the metal salt to decompose into the same type of metal as the build material particles and form a strong film 19′ (in this example, a metal film) among the patterned metal-based build material particles 12, generating a bound structure.

The bound structure is the 3D intermediate structure 11 shown in FIG. 2A. It is to be understood that any non-patterned build material 12 surrounding the 3D intermediate structure 11 remains non-bound and can be removed.

The 3D intermediate structure 11 can then be moved to a heating device, such as a sintering oven, for exposure to the heat treatment. When polymer particles are used as the binder 19, the heat treatment involves exposure (of the 3D intermediate structure 11) to a de-binding temperature for a first predetermined time; and then exposure (of the 3D intermediate structure 11) to a sintering temperature for a second predetermined time.

It is to be understood that at the de-binding temperature, the network of the polymer particles (film 19′) can thermally degrade, thereby de-binding the 3D intermediate structure 11. The de-binding temperature range can vary, depending on the composition of the polymer network. As an example, the de-binding temperature may range from about 400° C. to about 1,000° C. The de-binding temperature may be held for a duration ranging from about 30 minutes to about 480 minutes.

When metal nanoparticles are, or a metal salt is used as the binder 19, the heat treatment involves exposure (of the 3D intermediate structure 11) to a sintering temperature for a predetermined time.

In any of the examples, the sintering temperature range can vary, depending on the metal-based build material 12. In one example, the sintering temperature can range from about 10° C. below the melting temperature of the metal-based particles to about 50° C. below the melting temperature of the metal-based particles. In another example, the sintering temperature can range from about 100° C. below the melting temperature of the metal-based particles to about 200° C. below the melting temperature of the metal-based particles. The sintering temperature can also depend upon the particle size and period of time that heating occurs, e.g., at a high temperature for a sufficient time to cause particle surfaces to become physically merged or composited together. In one example, the sintering temperature ranges from about 1,000° C. to about 2,200° C. As a specific example, the sintering temperature for stainless steel can be about 1,400° C. Temperatures outside of these ranges can be used as determined for different metal-based particles.

In some examples, during heating in the oven, the heating device can include an inert atmosphere to avoid oxidation of the metal-based particles. In one example, the inert atmosphere can be oxygen-free and can include a noble gas, an inert gas, or combination thereof. For example, the inert atmosphere can include a noble gas, or an inert gas (e.g., argon, nitrogen). In other instances, a reducing gas (e.g., hydrogen) may be used.

During the heat treatment, the alloying element 21 in the portions patterned with the alloying agent 20 interact or react with the metal-based build material 12 to form the alloyed composition. The interaction or reaction will depend upon the alloying element 21 and the metal-based build material 12. In one example, the portion of the at least one of the individual layers L₁, L₂, L₃. . . L_xpatterned with the alloying agent 20 undergoes a phase change during the heat treatment. As a specific example, a carbon alloying element in a low alloy steel build material undergoes a phase transformation from the soft ferritic microstructure to the harder pearlite microstructure, which combines ferrite and carbides arranged in a fine lamellar structure. In this particular example, the bulk portion 24 of the 3D object 10 (that had been patterned with the binder agent 18 alone) has a ferritic microstructure (from the low alloy steel build material), and the site-specific alloyed section 26 (that had been patterned with both the binder agent 18 and the alloying agent 20) has a pearlite microstructure (due to the phase transformation of the carbon alloying element).

Also during the heat treatment, the diffusion barrier component 23 in the diffusion barriers 28, 28′ suppresses (e.g., reduces or prevents) the diffusion of the alloying element 21 from the site-specific alloyed section(s) 26 to the non-alloyed section(s) 24. This can form discrete site-specific alloyed section(s) 26 and non-alloyed section(s) 24, where the intermediate diffusion barrier(s) 28, 28′ includes a minimal amount or none of the alloyed composition. Alternatively, this can form an intermediate diffusion barrier(s) 28, 28′ that includes a gradient of the alloyed composition, in which the concentration of the alloyed composition is higher closer to the site-specific alloyed section(s) 26 and the concentration of the alloyed composition is lower closer to the non-alloyed section(s) 24.

Referring now to FIG. 3A through FIG. 3C, another example of the method is depicted where the 3D object is built in a layer by layer fashion. As shown in FIG. 3A, the metal-based build material 12 is deposited from the build material source 14 onto the build area platform 16 where it can be flattened or smoothed, such as by a mechanical roller or other flattening mechanism or technique, to form the individual layer L₁. The thickness of the layer L₁(and any subsequently deposited layers) may be within the range provided herein.

When the metal-based build material 12 does not include the alloying element 21 pre-mixed therein, the alloying agent 20 is used to pattern any portion of the layer L₁that is to become a site-specific alloyed section 26 (see FIG. 3A and FIG. 4B). As such, some examples of this method include generating the predetermined portion (i.e., the portion of the build material layer L₁including the alloying element 21) by patterning a section of the build material layer L₁with an alloying agent 20 that contains the alloying element 21. The alloying agent 20 delivers the alloying element 21 to portion(s) of the layer L₁of the metal-based build material 12 that is/are to become site-specific alloyed section(s) 26. The site-specific alloyed section 26 that forms at the portion patterned with the alloying agent 20 has the alloyed composition.

In another example of this method (not depicted in the figures), some of the metal-based build material 12 is pre-mixed with the alloying element 21, and this mixed build material is used to generate the predetermined portion. In these examples, the alloying agent 20 is not used to pattern any portion of the layer L₁. Rather, the pre-mixed build material composition is applied at area(s) that are to become the site-specific alloyed section 26. As such, some examples of this method include generating the predetermined portion (i.e., the portion of the build material layer 12 including the alloying element 21) by mixing the alloying element 21 with some of the metal-based build material to generate a mixed build material; and applying the mixed build material instead of metal-based build material 12 at a predetermined location for the predetermined portion. In this example, both the metal-based build material 12 and the mixed build material are applied to form the build material layer L₁and the mixed build material is specifically applied in area(s) that are to become the site-specific alloyed section(s) 26 of the 3D object.

Whether the predetermined portion of the build material layer 12 including the alloying element 21 is generating using the alloying agent 20 or by pre-mixing the alloying element 21 with the metal-based build material 12, the diffusion barrier agent 22 is used to pattern any portion of the layer L₁that is to become a diffusion barrier 28 (see FIG. 4B). The diffusion barrier agent 22 delivers the diffusion barrier component 23 to portions of the layer L₁of the metal-based build material 12 that is/are to become diffusion barrier(s) 28. The diffusion barrier agent 22 is deposited between at least some of the build material 12 patterned with the alloying agent 20 or pre-mixed with the alloying element 21, and at least some of the build material 12 that remains non-patterned or has not be mixed with the alloying element 21 (e.g., sections 36 in FIG. 3A). As such, the diffusion barrier agent 22 is deposited at an edge of at least a portion of the pattern of the site-specific alloyed section 26 or the predetermined portion containing the alloying element 21. The diffusion barrier agent 22 forms a perimeter pattern at the edge(s) of the pattern of the site-specific alloyed section 26 or the edges(s) of the predetermined portion containing the alloying element 21. In some instances, the diffusion barrier agent 22 is selectively applied so that the perimeter pattern is defined around the entire pattern of the site-specific alloyed section 26 or the entire predetermined portion containing the alloying element 21.

The alloying agent 20 (when used) and the diffusion barrier agent 22 may be deposited using the fluid ejectors 30′, 30″ as described herein in reference to FIG. 1, FIG. 2A, and FIG. 2B.

FIG. 4A depicts a top view of the patterned build material layer L₁. In the example shown in FIG. 3A and FIG. 4A, the diffusion barrier agent 22 is used to pattern the entire perimeter of the square/cube pattern that is generated with the alloying agent 22 or the mixed build material. This will form the diffusion barrier 28 shown in FIG. 3B and FIG. 4B. The diffusion barrier 28 that forms at the portion patterned with the diffusion barrier agent 22 includes the diffusion barrier component 23 intermingled with the metal-based build material composition, and may or may not include some of the alloyed composition. Whether the diffusion barrier 28 includes some of the alloyed composition depends upon the chemical potentials of the alloying element 21 and the diffusion barrier component 23, the thickness of the diffusion barrier pattern, and/or the concentration of the diffusion barrier component 23 in the diffusion barrier agent 22.

In this example method, a localized (focused) heat source 34 (e.g., a laser, an electron beam, a radiation source and micromirror(s) that direct the beam(s), etc.) of the 3D printer is scanned over the layer L₁and is selectively activated to expose at least some of the patterned and non-patterned metal-based build material 12 in the layer L₁to heat or at least some of the metal-based build material 12 and the mixed build material in the layer L₁to heat. The selective activation of the localized heat source 34 is in accordance with the slice of the particular layer L₁from the digital 3D object model (e.g., a computer model) that is being built. The radiation exposure from the localized heat source 34 is sufficient to raise the temperature of the exposed metal-based build material 12 (whether patterned or not or pre-mixed or not) to its melting point/range. As such, the exposed metal-based build material 12 melts and coalesces to form the 3D object layer 38 (a cross-section of which is shown in FIG. 3B and a top view of which is shown in FIG. 4B).

In the example shown in FIG. 3B and FIG. 4B, the portions respectively patterned with the alloying agent 20 and the diffusion barrier agent 22 are exposed to the heat from the localized heat source 34, and form, respectively, the site-specific alloyed portion 26 and the diffusion barrier 28. In this example, some of the non-patterned metal based build material 12 adjacent to the portions patterned with the diffusion barrier agent 22 are also exposed to the laser's radiation. This exposure forms non-alloyed section(s) 24.

Alternatively, the mixed build material and the metal-based build material 12 patterned with the diffusion barrier agent 22 are exposed to the heat from the localized heat source 34, and form, respectively, the site-specific alloyed portion 26 and the diffusion barrier 28. In this example, some of the metal based build material 12 (not pre-mixed with the alloying element 21) adjacent to the portions patterned with the diffusion barrier agent 22 are also exposed to the heat. This exposure forms non-alloyed section(s) 24.

In this example method, the localized heat source 34 may be any suitable device that generates an intense beam of coherent electromagnetic radiation. The localized heat source 34 may have a narrow bandwidth.

During heat exposure, the alloying element 21, e.g., in the portions patterned with the alloying agent 20 or in the predetermined portion containing the mixed build material, interacts or reacts with the metal-based build material 12 to form the alloyed composition. The interaction or reaction will depend upon the alloying element 21 and the metal-based build material 12.

Also during the radiation exposure, the diffusion barrier component 23 in the diffusion barrier 28 suppresses (e.g., reduces or prevents) the diffusion of the alloying element 21 from the site-specific alloyed section(s) 26 to the non-alloyed section(s) 24. This can form discrete site-specific alloyed section(s) 26 and non-alloyed section(s) 24, where the intermediate diffusion barrier(s) 28 includes a minimal amount or none of the alloyed composition. Alternatively, this can form an intermediate diffusion barrier(s) 28 that includes a gradient of the alloyed composition, in which the concentration of the alloyed composition is higher closer to the site-specific alloyed section(s) 26 and the concentration of the alloyed composition is lower closer to the non-alloyed section(s) 24.

As shown in FIG. 3C, this example method then involves spreading another layer L₂of the metal-based build material 12 over the formed 3D object layer 38. Patterning with the agents 20, 22 and localized heat source scanning are repeated in accordance with the slice of the particular layer L₂from the digital 3D object model. These processes may be repeated until the entire 3D object is built.

Alternatively, this example method may then involve spreading another layer L₂of the metal-based build material 12 and the mixed build material over the formed 3D object layer 38. Patterning with the agent 22 and localized heat source scanning are repeated in accordance with the slice of the particular layer L₂from the digital 3D object model. These processes may be repeated until the entire 3D object is built.

When build layer by layer, the 3D object may be built in any orientation with respect to the X-Y plane of the build area platform 16. For example, the 3D object can be printed from bottom to top in the Z-direction, or at an inverted orientation (e.g., from top to bottom) in the Z-direction. For another example, the 3D object can be printed at an angle or on its side. The orientation of the build can be selected in advance or even by the user at the time of printing, for example.

In this example method, no additional heating step(s) are performed because the 3D object is built layer by layer.

In some examples of either of the methods disclosed herein, the diffusion barrier agent 22 includes the diffusion barrier component 23; a percentage of the metal-based build material composition includes the same type of diffusion barrier component 23 that is present in the diffusion barrier agent 22; and the method further comprises adjusting an amount of the diffusion barrier agent 22 that is applied during patterning of the second portion based on the percentage of the diffusion barrier component in the metal-based build material composition. In these examples, because the metal-based build material composition includes the diffusion barrier component 23, the amount that is applied via the diffusion barrier agent 22 may be reduced (see FIG. 8 discussed in the Examples section below).

To further illustrate the present disclosure, examples are given herein. It is to be understood that these examples are provided for illustrative purposes and are not to be construed as limiting the scope of the present disclosure.

EXAMPLES
Example 1—Simulations

Several diffusion simulations were performed using CALPHAD software from Pandat.

In the first simulation, a 3 mm wide carbon rich region (1 wt % carbon and 99 wt % iron (FCC, austenite)) was positioned adjacent to a 3 mm wide carbon lean and silicon rich region (0.02 wt % carbon, 5.78 wt % silicon, and 94.2% iron (FCC, austenite)), and the regions were exposed to 1200° C. for 1 hour. The carbon diffusion results from the simulation are shown in FIG. 5. In FIG. 5, the weight percentage of carbon is plotted against the distance (in mm) along the regions after the high temperature exposure. As depicted, about 0.12 wt % of carbon was present in the first mm of the carbon lean and silicon rich region. This simulation illustrated that silicon would be effective in substantially preventing carbon diffusion.

In the second simulation, four different adjacent regions were compared. The first was a 3 mm wide carbon rich region (1 wt % carbon and 99 wt % iron (FCC, austenite)) positioned adjacent to a 3 mm wide carbon lean region (0.02 wt % carbon, 0 wt % silicon, and 98.98% iron (FCC, austenite)). The second was a 3 mm wide carbon rich region (1 wt % carbon and 99 wt % iron (FCC, austenite)) positioned adjacent to a 3 mm wide carbon lean and silicon rich region (0.02 wt % carbon, 1 wt % silicon, and 98.98% iron (FCC, austenite)). The third was a 3 mm wide carbon rich region (1 wt % carbon and 99 wt % iron (FCC, austenite)) positioned adjacent to a 3 mm wide carbon lean and silicon rich region (0.02 wt % carbon, 3 wt % silicon, and 96.98% iron (FCC, austenite)). The fourth was a 3 mm wide carbon rich region (1 wt % carbon and 99 wt % iron (FCC, austenite)) positioned adjacent to a 3 mm wide carbon lean and silicon rich region (0.02 wt % carbon, 5.8 wt % silicon, and 94.18% iron (FCC, austenite)). Each of the simulated regions was exposed to 1200° C. for 1 hour. The carbon diffusion results from the simulation are shown in