INTERFACE LAYERS AND REMOVABLE OBJECT SUPPORTS FOR 3D PRINTING

Abstract

Materials and methods are disclosed for forming interface layers between objects being 3D printed and their underlying support structures, as well as dissolvable supports. The materials and methods facilitate separation of the objects from the supports after all processing is completed and are particularly useful when 3D printing metal objects that have to be sintered subsequent to 3D printing.

Claims

1. An interface layer formed between an object being printed by a 3D printer and an underlying support structure, said interface layer comprising a glass-based material.

2. The interface layer of claim 1 wherein said glass-based material comprises a silica glass.

3. The interface layer of claim 1 wherein the glass-based material is selected to have a glass transition temperature below a sintering temperature used to process the object after it is printed.

4. The interface layer of claim 1, wherein the glass-based material is selected from the group consisting of soda-lime glass, borosilicate glass, lead-alkali glass and fiber glass or combinations thereof.

5. The interface layer of claim 4, further including a refractory metal.

6. An interface layer formed between an object being printed by a 3D printer and an underlying support structure, said interface layer comprising a cermet.

7. The interface layer of claim 7, wherein the cermet is formed from a combination of steel and ceramic when said object being printed is steel.

8. The interface layer of claim 8, wherein the ceramic is aluminum oxide.

9. The interface layer of claim 6, wherein the cermet is selected from the group of titanium and zirconium oxide or combinations thereof, when the object being printed is titanium.

10. The interface layer of claim 7, wherein the cermet is selected from the group of titanium aluminide and zirconium dioxide when the object being printed is titanium.

11. An interface layer formed between an object being printed by a 3D printer and an underlying support structure, said interface layer comprising a ceramic macrostructure.

12. The interface layer of claim 11, wherein said interface layer comprises ceramic paper.

13. An interface layer formed between an object being printed by a 3D printer and an underlying support structure, said interface layer being formed from a polymer derived ceramic.

14. A method of 3D printing an object having a dissolvable support using binder jetting, wherein the method comprises the steps of: forming layers of said object and support by selectively depositing a binder onto a bed of powder, introducing an agent during said 3D printing to locally modify corrosion characteristics of one or more regions of said object or support or of an interface layer therebetween to facilitate dissolution of the support from the object after printing and any subsequent processing is completed.

15. The method of Clam 14, wherein the agent is introduced through an inkjet print head.

16. The method of claim 14, wherein the agent is introduced by depositing a carbon black-laden suspension.

17. The method of claim 14, wherein the agent is introduced as a polymer that may be pyrolyzed to leave a carbon-containing deposit.

18. The method of claim 14 wherein the locally modified one or more regions have a reduced corrosion characteristic.

19. The method of claim 14, wherein the locally modified one or more regions have an increased corrosion characteristic.

20. A method of 3D printing an object having a dissolvable support by using an extrusion type 3D printer, wherein the method comprises the steps of: extruding and depositing materials to form the object and the support, introducing an agent during said 3D printing to locally modify corrosion characteristics of one or more regions of said object or said support or an interface layer therebetween, to facilitate dissolution of the support from the object after printing and any subsequent processing is completed.

21. The method of claim 20, wherein the agent is introduced by depositing a carbon black-laden suspension.

22. The method of claim 20, wherein the agent is introduced by depositing a polymer that may be pyrolyzed to leave a carbon-containing deposit.

23. The method of claim 20, wherein the agent locally modifies the one or more regions to have either a reduced corrosion characteristic or increased corrosion characteristic relative to the rest of the object or support.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0034] FIG. 1 illustrates an exemplary 3D printing system that uses binder jetting, in which an interface layer is used to separate a dome-shaped object from an underlying support structure.

DETAILED DESCRIPTION

[0035] As discussed above, in the prior art interface layers designed for easy removal have been formed from ceramic powders that are resistant to sintering at the temperatures required to sinter 3D-printed metal objects. The ceramic powders form an inert sinter-resistant interface layer between support structures and the object, so that the support structures can be easily separated from the object after sintering is completed.

[0036] However, the use of ceramic powder-based interface layers is not always optimum or desirable. For example, in some instances, the use of ceramic materials as interface layers may be incompatible with the materials being sintered from a chemical perspective. In other instances, non-ceramic materials, for example as described below, may be more easily interposed between the support structures and a part due to the chemical and physical properties of these materials.

[0037] An example of how material characteristics may influence the ease of delivery of an interface-forming material to the part is illustrated by using silica-based glass powders that may be suspended in inkjet fluids to form interface layers. Advantageously, silica-based glasses have very low densities compared to other oxides previously used in the art as interface layers (e.g. crystalline aluminum oxides), and therefore may form more stable suspensions in an inkjet fluid than other, denser oxides such as ceramic oxides that have been used in the prior art.

[0038] In other cases, differences in shrinkage rates between prior interface layer formulations and the part and support structures may cause decreased tolerances or increased rates of cracking in the 3D printed object. In such circumstances, a soluble interface layer may be preferred instead of a non-bonding interface layer based on ceramic powders. Accordingly, there is a need for interface layers made from materials other than ceramic powders that will permit support structures to be easily separated and removed from a 3D-printed metal object, after all processing steps including sintering have been completed.

[0039] In another aspect, an exposed material surface may be sensitized by introducing an agent that changes the local corrosion characteristics of the material, making it possible to selectively dissolve away the local volume whose corrosion characteristics have changed so as to separate an 3D printed object from an underlying support structure, or in some cases, dissolve the support structure entirely.

[0040] The use of carbon additions to stainless steels has been explored by Hildreth et al. (see, e.g. Dissolvable Supports in Powder Bed Fusion-Printed Stainless Steel, 3D Printing And Additive Manufacturing, Vol. 4, No. 1, 2017). In this work, carbon was introduced to a 3D printed part by a carburizing treatment after the 3D printing process. The carbon was introduced to the surface of the part by solid state diffusion, allowing only the near-surface areas of the part to be dissolved away, while leaving the interior portion of the part (wherein the chemistry was not affected) substantially unaltered and corrosion resistant.

[0041] While this method may be useful for selective laser melting applications, the method has its limitations, and is not applicable to 3D metal printing that requires a post printing sintering process for several reasons. First the dissolution step intrinsically removes material everywhere on the surface of the part, which means that the resolution of the printing process is reduced and a fillet is introduced everywhere on the part. This is undesirable from the perspective of making well-toleranced geometries.

[0042] Second, in order to remove support structures, one must dissolve the entirety of the support structure, and so the amount of material dissolved is proportional to the thickness of the support structure used. Because the support structures do not need to be thick in laser melted parts (e.g. several hundred microns in their thinnest dimension in some cases), one does not need to remove a lot of material from the part overall. However, in the case of binder jetted parts, support structures often need to be substantially thicker such that the parts are properly supported during sintering (e.g. greater than 1000 microns in their thinnest dimension in many cases), and to ensure that the support structures do not fracture during handling and depowdering.

[0043] Additionally, this prior art method introduces another thermal processing step that is costly and expensive. Lastly, this method is disadvantageous because it introduces a lack of certainty about the chemical composition of the surface near the local volume whose corrosion characteristics have been changed, and may intrinsically reduce the corrosion resistance of the surface by raising its carbon level above what it otherwise would be.

[0044] The control of process parameters to facilitate dissolution of support structures has been disclosed by Hildreth et al. (e.g. in PROCESS CONTROLLED DISSOLVABLE SUPPORTS IN 3D PRINTING OF METAL OR CERAMIC COMPONENTS, U.S. Patent Publication 2019/0039137A1). This Publication discusses how changes in thermal processing parameters during what apparently is a laser-based 3D printing process, can result in local changes to the corrosion characteristics of a part by altering its microstructure. In particular, these changes are described as being produced by varying the laser power and corresponding material temperatures during 3D printing.

[0045] Such thermal parameters are not available to selectively alter metal parts made by binder jetting or extrusion-based 3D printers, since the microstructure of the metal is not altered during the 3D printing process, but rather during sintering after the 3D printing process is completed, where all of the densification and microstructural evolution takes place. Methods that rely on locally changing thermal processing during printing, as disclosed in this prior art, are therefore not applicable to metal parts made by 3D printers that use binder jetting or extrusion-based technologies.

[0046] Local alteration of the chemistry of a printed part for the purpose of changing its dissolution characteristics has also been described in the prior art for parts fabricated by directed energy deposition (see, e.g. Impact of compositional gradients on selectivity of dissolvable support structures for directed energy deposited metals, Acta Materialia Volume 153, July 2018, Pages 1-7). In this work, powders were mixed together within a layer in an attempt to create a material with a compositional gradient, and efforts are described for utilizing the compositional gradient to achieve a gradient in corrosion behavior. Although this prior art showed that one can mix various feed powders together in a directed energy deposition additive manufacturing process to achieve different compositions, the results were not clearly detailed in that the corrosion differences were introduced for very coarse layer heights and track widths (130790 microns, respectively)

[0047] Further, the compositional gradients were not well-controlled between layers or within layers, since each layer exhibiting substantial inhomogeneity within the layer, and layer-to-layer re-melting caused substantially chemical mixing between the layers. These limitations are likely inherent to the directed energy deposition process used in this prior art, which is inherently low-resolution and coarse in terms of compositional control, because the compositional control is achieved by mixing powders together. Such a highly inhomogeneous chemical compositional gradient is likely to lead to a very inhomogeneous gradient in dissolution behavior, and therefore likely to yield rough, incomplete dissolution at the interface since properties near the interface are not well-defined due to the mixing between layers.

[0048] Thus, although these efforts in the prior art have contemplated the concept of soluble supports for metals, the prior art has yet to disclose methods for producing parts with soluble support structures that can provide high resolution, high printing throughput, and that are compatible with existing machine architectures, build rates and mechanisms.

[0049] In spite of these prior art efforts, they have not taught how to achieve soluble supports for 3D printed metals in practical ways that are likely to be adopted by industrial practitioners of metal additive manufacturing. At heart, this is largely due to the intrinsic difficulties of introducing patterned gradients in the chemical and corrosion properties of 3D printed metal parts with appropriate precision and length scales.

[0050] In accordance with one aspect of this disclosure, we describe implementations of such compositional gradients that are compatible with binder jetting and material extrusion 3D printing processes that provide soluble metal support structures in additively manufactured parts. To do so, we describe novel machine architectures for these additive manufacturing processes, as well as novel printed geometries aimed at solving difficulties associated with post-processing the parts through debinding and sintering.

[0051] In order to create compositional gradients in binder jetted parts, one must re-conceive of the binder jetting processes used for metals, and how to introduce compositional gradients during printing relative to what was discussed in the prior art.

[0052] Specifically, when operating a binder jet 3D printer, it is strongly preferred to only use one powder blend during the printing process. This provides a uniform powder bed and powder bed density, uniform packing, and uniform imbibition of the binder into the powder. Prior art attempts at creating compositional gradients in metal additive manufacturing for forming soluble supports have only sought to create compositional differences by varying the composition of the input powder.

[0053] In contrast to such prior art attempts, this disclosure takes advantage of the inkjet printheads intrinsic to binder jet printing to add a compositional degree of freedom to the binder jet's binder deposition. In doing so, this approach allows the patterning of composition at a much finer length scale and in a more precise manner than achievable by the prior art.

[0054] In traditional metal binder jetting processes, only one printhead is used. Significantly, in one aspect of this disclosure a second print head may be provided in a binder jet 3D printing system, and may be used to selectively provide an agent for locally modifying the chemical composition of the support structures. This second print head is able to provide micro-patterned chemical compositions to achieve soluble metal supports for additive manufacturing with resolution, compositional control, and build rate superior to prior efforts to achieve soluble supports for metal additive manufacturing.

[0055] In one aspect of this disclosure, an agent, e.g. carbon, that changes the local corrosion characteristics may be introduced locally in select regions of a part during a 3D printing process that uses binder jetting or material extrusion. In an embodiment, the agent may be introduced by ink-jetting an ink containing the agent using the aforementioned second print head, into select regions during a binder jet fabrication process. Alternatively, this can also be achieved by using a multi-material extrusion 3D printing system to print parts, where one of the extruded materials contains the agent to be locally introduced.

[0056] In a binder jetting system, a sensitizing agent may be jetted onto a metal powder by using a supplemental pass or, in a preferred embodiment, by providing an additional print head, e.g., by incorporating deposition steps that add a material in a selected region or regions that will penetrate the exposed surface, and preferably will not diffuse away, evaporate away, or otherwise leave the selected region(s) during a subsequent thermal processing cycle.

[0057] As one example, this may include jetting down a carbon-containing agent in the form of carbon black or a polymer which imparts a carbon-containing residue. As another example, one may jet down a sulfur-containing agent, e.g., in the form of sulfates, a polymer that imparts a sulfur-containing residue, or other sulfur-containing compounds.

[0058] The change in the local corrosion characteristics introduced in the select region(s) may be utilized to thereafter dissolve away portion(s) of the structure after a sintering or infiltration process. In many cases, it will be useful to dissolve support structures and/or interface layers from a three-dimensional part.

[0059] In a case where an agent is introduced that enhances the corrosion rate of a select region relative to the corrosion rate of regions where the agent is not introduced, the agent may be introduced to the support structures to permit their dissolution without dissolving the part.

[0060] In a case where an agent is introduced that decreases the corrosion rate of the select region relative to the corrosion rate of regions where the agent is not introduced, the agent may be introduced to the three dimensional part such that the support structures may be dissolved with less effects of dissolution occurring on the three-dimensional part.

[0061] Typical dissolution steps for metal parts may occur in solutions with engineered pH and salt levels to enhance differences in corrosion rates between two materials (one that has been modified the agent and the other that has not been modified), or in order to enhance absolute corrosion rates such that the dissolution rate occurs more quickly. A voltage may also be applied between the part and a counter electrode to further enhance differences in corrosion rates. Although the effects of an additive (e.g. carbon) on the corrosion behavior of a selected region relative to a region without the additive will be dependent on many factors (e.g. alloy system, additive choice, additive level, solution chemistry), techniques may be used to identify promising conditions for good dissolution conditions. For example, one may print a specimen containing the additive at the desired level, another without the additive, and collect DC polarization curves for both of the specimens. The ratio of corrosion currents at a given voltage yields the relative corrosion rates of the two materials. Particularly good operating conditions will be ones where the corrosion rates differ by a factor of three or more between the material with the additive and the material without the additive.

[0062] Carbon introduction can have a strong effect on the corrosion behavior of some alloy systems, specifically stainless steels. Localized carbon deposition may thus usefully yield a soluble interface layer, especially when introduced into a stainless steel. This may be particularly useful in fabrication processes where the ability to change a base material is limited, e.g., powder bed fabrication techniques such as binder jetting wherein one cannot easily change the feed powder without causing potential defects in the part and contaminating powder such that it cannot be reused.

[0063] In this context, a carbon powder may be introduced to the exposed surface of the powder bed in regions where a separation interface is desired. Local carbon deposition may also be achieved during an inkjet printing process by, for example, jetting a carbon-laden ink into the powder bed in those regions where carbon is desired to be deposited.

[0064] Local carbon deposition may also be achieved during an inkjet printing process by, e.g., jetting a fluid containing a polymer that pyrolizes to leave behind a carbon-containing deposit. Many such polymers are known in the art that are soluble in typical ink-jetting solvents, including poly(acrylic acid) and methyl cellulose.

[0065] Additionally, local carbon deposition may be achieved by performing a case carburizing treatment as part of a sintering operation or a post-processing step. This may also or instead include heating the target surfaces in a carbon-rich atmosphere, e.g., where carbon is carried in a gas phase or the like.

[0066] Other related techniques may be used to change the local corrosion behavior of the part to enhance the dissolution rate of the support structures and/or interface layer. For example, non-stainless steel may be changed into a stainless-steel part by depositing suitable corrosion-controlling additives such as chromium or nickel that make the steel non-corrosive.

[0067] For a stainless steel, enhanced corrosion resistance may be achieved by jetting a chromium, nickel, or molybdenum-containing ink (e.g. including nanoparticles containing these elements, or as dissolved species in a fluid such as ammonium heptamolybdate) onto the portions which are intended to be corrosion-resistant, and jetting an ink which lacks these species onto those areas which are intended to be less corrosion-resistant. More generally, any similar technique for exposing an object to an agent that changes the corrosion behavior of the base material, or otherwise diffusing an agent that changes the corrosion behavior of the base material into a target surface may also or instead be used.

[0068] Similar results may be achieved with multi-material printing. For example, a part may be fabricated using a build material containing powdered, sinterable stainless steel, and a dissolvable interface layer may be fabricated using a stainless steel that has been enriched in, e.g., sulfur, carbon, boron, silicon, phosphorus and so forth so that the sintered interface layer can be dissolved in an acid bath or the like.

[0069] While an entire support structure may also or instead be fabricated from a dissolvable metal, this may introduce shrinkage matching issues due to the difference in chemistry between the support structure and the part. Thus, in another aspect of this disclosure, supports and the object may be fabricated from materials that have similar shrinkage rates through debinding and/or sintering, and the interface layer may be formed from a material that sinters into a sensitized material, e.g., an enriched stainless steel that can be removed through dissolution without dissolving the build material (and optionally without dissolving the support material). Building solely the interface layer out of a shrinkage-mismatched material with differing chemistry from the part and support structures may reduce the overall geometric incompatibility between the support structures and the parts during the shrinkage process, and therefore enable a higher-yield and a more geometrically accurate sintering process.

[0070] In a related aspect, corrosion-enhancing elements may be introduced as layers or regions throughout the support structure so that the support structure may be locally corroded away after sintering. This approach allows the support structure to maintain a large portion of its original physical, chemical, and shrinkage characteristics on average, while at the same time allowing the support structure to be partially disconnected/disassembled, and therefore more easily removed from the part.

[0071] In one example, a support structure may contain a tessellated pattern for the introduction of a corrosion-enhancing element such that the support structures may be removed after the dissolution step in a facile manner from underneath the part. In this manner, a support structure which is solid during sintering may be removed like Jenga blocks from underneath the part after the dissolution treatment.

[0072] Other techniques may also or instead be used to sensitize a surface to make it susceptible to corrosion or dissolvable, e.g., in an acid bath or the like. For example, galvanic corrosion may be induced by creating an electrical circuit through an object in a suitable solution and applying current to sensitize exposed surfaces. More generally, a variety of techniques may be used to apply sensitizing treatments such as those described above.

[0073] More generally, a variety of chemical pathways for sensitizing materials are known in the art, and may generally use a sensitizing agent delivered in a liquid phase, a gas phase, or as a solid. By way of example, a liquid phase coating may include a zincate coating that causes zinc to precipitate out onto part. In another aspect, electroless nickel plating or chromate conversion coatings may be used, although masking may be required to prevent sensitization of object surfaces.

[0074] For gas sensitizing, suitable paths to corresponding surfaces in the interior, or within support regions, should remain open during exposure. For gas phase sensitization, techniques such a chemical vapor deposition or physical vapor deposition may be used to maintain surface exposure to gas phase sensitizing agents. For solid phase sensitization, particle jetting, painting or dip coating of solid state particles may be used to apply sensitizing agents. Where the exposure process is not steered/steerable, e.g., where the sensitization occurs in a gas or liquid, the corresponding surfaces may be masked to limit sensitization to desired target areas.

[0075] The resulting object may then be placed in a solvent to which sensitized and unsensitized surfaces have different corrosion resistance. Alternatively, all exposed surfaces may be sensitized, but an interface between the object and the support may be fabricated to couple across minimal (e.g., proportionally small surface area) cross-sections that are engineered to dissolve/detach substantially more quickly that adjacent object surfaces in a suitable solvent.

[0076] In another aspect, mechanical embrittlement may usefully be employed to compromise the structure of a sinterable object along an interface layer. This may include plate-like filler that does not sinter, and promotes crack propagation in desired directions. More generally, any form of mechanical embrittlement may also or instead be employed. In one aspect, a material or additive may be introduced to encourage expansion, or to encourage a change in the coefficient of thermal expansion around the region of an interface layer to promote formation of mechanical defects that allow a support structure to be readily removed from the 3D printed object.

[0077] As discussed above, in accordance with one aspect of this disclosure, interface layers may be constructed from materials that form into amorphous glass-like structures during thermal processing, such as silica or other glassy materials. When used as interface layers, such glassy materials are generally brittle and may be readily fractured to permit easy separation of support structures from a 3D printed metal object, after the sintering process has been completed.

[0078] For example, materials that form amorphous glass-like structures may be selected to have glass transition or softening temperatures below the sintering temperatures reached during processing of a particular metal. During sintering, such glassy materials will melt before the maximum sintering temperature is reached without significantly infiltrating the metal build material, so as to leave a brittle glass interface layer in place upon cool down that permits easy separation of the sintered metal object from its support structures when processing has been completed.

[0079] Examples of such glassy materials suitable for use during sintering of metal objects, includes SiO.sub.2, which has a glass transition temperature in the range of 400 C. to over 1700 C. depending on the incorporated dopants. For example, pure silica glass has a softening temperature of roughly 1700 C., whereas soda lime glass has a softening temperature around 600 C. Thus, if the metal object is being fabricated from steel and requires a sintering temperature of around 1300 C., glassy materials for the interface layer may be chosen from the silicate glass family, with pure silica glass being one example. Such a glass which will begin to flow when the sintering oven reaches a temperature of around 1000 C., and form into a glass upon cool-down below 1000 C. if the cooling rate is sufficiently high.

[0080] An advantage of using such glassy materials, is that they will not significantly infiltrate the support or build materials because of their high viscosities and the timescales of most sintering processes. Rather, such glasses will form a brittle glassy interface layer that can be readily fractured for easy separation and removal of the underlying support(s).

[0081] The most common candidate glasses for such materials include soda-lime glass (SiCaNaO based), borosilicate glass (SiBAlNaO based) , and lead-alkali glass (SiPbNaKO based), and fiber glass (SiAlCaO based). The most common glasses will have between 50-80 wt. % silica, with various other additions as-needed. For use as an interface layer material, the amount of refractory additions (such as Al) may be used to control the reactivity of the glass, and the amount of other additions may be used to control its rheological properties.

[0082] Cermets are composites of metals and ceramics in which the ratio of metal to ceramic may be varied over a wide range. In another embodiment, the interface layer may be formed from a cermet that exhibits reduced bonding characteristics with the printed metal material.

[0083] For example, when the printed material is steel, a cermet formed from a combination of steel and ceramic (e.g., aluminum oxide) can be used as the material for the interface layer since the combination of steel and aluminum oxide ceramic will exhibit reduced bonding characteristics with the native steel during sintering.

[0084] Advantages that may be achieved by using cermets as the interface layer material include the ability to flexibly engineer the bonding characteristics of the interface layer and the shrinkage mismatch between parts through the selection of the chemistry of the two or more materials used to form the cermet, the particle sizes of the materials forming the cermet, and the volume fractions of the metal relative to the ceramic components of the cermet.

[0085] During sintering, the metallic portion of the cermet may weakly react along the boundary regions between the interface layer and the object and/or support. However, the ceramic particles will remain inert, causing the bond between the interface layer and object/support structures to be relatively weak and easily broken so as to allow for the object to be easily released from the support structures.

[0086] Another advantage of using cermets instead of simply ceramic powders for the interface material is that the use of cermets allows for some amount of bonding and shrinkage to be introduced across the interface layer, which may reduce instances of cracking of the parts due to a mismatch in shrinkage between the parts and support structures.

[0087] Since cermets can be made in a wide range of compositions using different metals and ceramics, they can be tailored to have similar thermal expansion characteristics to the build material to avoid undesirable stresses in the build material during thermal cycling. Yet, when used as an interface layer, they can provide a weak bond to the build material that facilitates the easy separation of the build material from any support structures due to the brittle nature of cermet materials.

[0088] As one example, when the printed material is steel, then a cermet composed of steel and aluminum oxide can be used as the interface layer since aluminum oxide and steel will not react.

[0089] As another example, when the printed material is titanium, a cermet composed of titanium and zirconium oxide may be used.

[0090] As yet another example, when the printed material is titanium, a cermet composed of titanium aluminide and zirconium dioxide may be used.

[0091] In yet another embodiment, the interface layer may be formed of a ceramic macrostructure. For example, the interface layer may be deposited as a paper or a fabric weave, or in some other form factor that maintains a cohesive structure. This layer will not reduce to a powder or dust, but will instead sinter into a structure that retains a mechanical macrostructure that resists bonding to adjacent layers of an object and/or support. Such a layer may, for example, be formed as a coating with a paper or foil backing or the like, and may be applied by hand or with a machine such as a web feeder, particularly for large, uniform planar surfaces such as single or multi-layer raft structures.

[0092] Ceramic paper (also called ceramic fiber paper) is one such feedstock that may be used to create such ceramic macrostructures. Such ceramic paper may be formed having high ceramic content suitable for resisting bonding to the object and its support structures. Suitable chemistries include alumina, silica, and aluminosilicate for the fiber materials. Ceramic paper is available from Ceramaterials (Port Jervis, N.Y.) and Morgan Thermal Ceramics, although other vendors may also provide suitable ceramic papers.

[0093] In another aspect, the interface layer may be formed using a polymer derived ceramic, or any other material that reduces into a ceramic during a thermal process such as sintering.

[0094] The polymer derived ceramic may be a low temperature polymer derived ceramic that forms a ceramic during, e.g., extrusion or some other relatively low temperature pre-sintering step. In this context, polymer derived ceramics may, for example, include any material with polymer-like properties that can cross-link for desired rheological properties and convert at elevated temperatures into a ceramic. This may include silicon nitride and silicon carbide forming materials, as well as other materials that convert to oxide-based ceramics such as alumina, zirconia, silicon oxycarbide, and the like. The viscosity of the polymeric material can be adjusted by proper selection of the ceramic precursor material's chemical structure and molecular weight, with typical molecular weights ranging from several hundred Daltons to one hundred kiloDaltons. Thus, depending on the particular materials, this interface layer former may usefully be deposited in an extrusion-based fabrication process such as fused deposition modeling, or may be sprayed as a liquid, e.g., to form an interface layer in a binder jetted structure.

[0095] In yet another aspect, a variety of surface treatments may be used to prevent or discourage adhesion at the interface between two surfaces such as an object and a support. For example, one or more of these surfaces may be passivated with an oxide, or another chemical that creates a passivated layer that will not react with or bond to the other surfaces at the interface. In another aspect, the surface treatment may create a brittle surface.

[0096] Such surface treatments may be applied as a coating or plating of a material that passivates, or encourages passivation of, the corresponding layer. For example, the surface treatment may turn a metal powder in a build material or support material into a metal oxide in situ.

[0097] More generally, any thermal or chemical process that can be applied to a surface to passivate the surface, or to embrittle an area, may be used to provide an interface layer that facilitates separation of adjacent layers after thermal processing.

[0098] Now that exemplary embodiments of the present disclosure have been shown and described in detail, various modifications and improvements thereon will become readily apparent to those of ordinary skill in the art, all of which are intended to be covered by the following claims.