Manufacturing method of sintered product and sintered product

Abstract

A method for additively manufacturing an article comprising a cemented carbide or cermet is disclosed, the article comprising at least one binder-free region. The method includes a) depositing a layer of a powder composition (102) and b) adding a binder, if present in the layer, to areas in the powder composition corresponding to a cross-section of the article, excluding the at least one binder-free region (102). The method further includes repeating steps a) and b) for each layer of the article to obtain a green article, and sintering (106) the green article to obtain the manufactured article.

Description

[Technical field]

[0001] The present disclosure relates generally to methods for making sintered articles and sintered articles. [Background technology]

[0002]

[0002] Additive manufacturing, also known as 3D printing, typically uses specialized systems to print powder one layer at a time. In particular, a layer of material is deposited onto a work surface in a build chamber and can be combined with another layer of the same or different material. Additive manufacturing can be used to produce articles from computer-aided design models using techniques such as powder bed fusion (PBF), direct metal laser sintering (DMLS), or binder jetting.

[0003]

[0003] The additive manufacturing of the cemented carbide or cermet body is preferably carried out by 3D printing techniques, first producing a green article and then sintering the green article in a separate furnace. The additive manufacturing may also include the steps of hardening the green article and de-powdering the green article before sintering it.

[0004]

[0004] In binder-based additive manufacturing techniques, such as binder jetting, a layer of powder is deposited on a working surface of a build chamber, and then a liquid binding agent, or binder, is added to the powder to adhere the powder particles together.

[0005]

[0005] However, the microstructure of products produced by binder-based additive manufacturing techniques is generally not as desirable as that of cermet or cemented carbide pressed products. In many articles, it can be beneficial for some areas to have a better microstructure, for example areas that are intended to be mating areas of the article.

[0006]

[0006] Another problem with products produced by additive manufacturing techniques using binders is porosity, which is often higher than desired.

[0007]

[0007] Thus, a need exists for improvements in methods for producing sintered articles using binder jetting. Summary of the Invention

[0008]

[0008] It is an object of the present invention to address at least some of the problems and challenges outlined above. It is an object of embodiments of the present invention to provide an improved method for additively manufacturing sintered products, in particular such that the final product has at least one of an improved microstructure and lower porosity.

[0009] According to one aspect, there is provided a method for additively manufacturing an article comprising a cemented carbide or cermet, the article comprising at least one binder-free region. The method includes a) depositing a layer of a powder composition, and b) adding a binder, if present in the layer, to areas in the powder composition corresponding to a cross-section of the article, excluding the at least one binder-free region. The method further includes repeating steps a) and b) for each layer of the article to obtain a green article, and sintering the green article to obtain the manufactured article.

[0010] According to another aspect, there is provided a sintered article produced using additive manufacturing, the article including a region to which a binder was added during additive manufacturing of the article and at least one binder-free region, the binder-free region being a region of the article to which no binder was added during additive manufacturing of the article.

[0011]

[0011] Further possible features and advantages of this solution will become apparent from the detailed description below.

[0012] BRIEF DESCRIPTION OF THE DRAWINGS

[0012] The solution will now be explained in more detail by means of an exemplary embodiment with reference to the accompanying drawings, in which: [Brief description of the drawings]

[0013] [Figure 1]1 illustrates generally the steps of a method according to one embodiment. [Figure 2A]

[0014] 1 illustrates an article including a binder-free region according to one embodiment. [Figure 2B]

[0015] 1 illustrates an article including multiple binder-free regions according to one embodiment. [Diagram 3]

[0016] 1 illustrates an article including a binder-free region according to one embodiment. [Figure 4A]

[0017] 1 illustrates the microstructure of various regions of the article. [Figure 4B] 1 illustrates the microstructure of various regions of the article. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014]

[0018] Briefly, the present disclosure provides a method for additively manufacturing a sintered article, for example using binder jetting, where the green article includes at least one binder-free area before being sintered, and the sintered article can be a finished or semi-finished part for a cutting tool or a wear part. The method includes depositing a layer of a powder composition for each layer of a plurality of layers, and then adding a binder to an area in the powder composition that corresponds to a cross-section of the article, except if at least one binder-free area is present in that layer. The method further includes repeating the steps of depositing powder and adding binder to all layers to obtain a green article, which is then sintered to obtain a sintered article. The binder-free area is used, for example, in areas that will be subject to greater stress than other parts of the finished sintered article, such as areas that will be mating areas.

[0015]

[0019] An insight relevant to this disclosure is that the microstructure of some sintered articles can be improved by removing binder in certain regions of the article during additive manufacturing processes. When a green article is sintered, it may not have a desirable microstructure due to the previous binder deposition, for example, due to the presence of regions enriched in a metal binder phase, such as cobalt, referred to herein as a cobalt or metal binder phase enriched region, in the binder-added regions compared to binder-free regions.

[0016]

[0020] "Improvement" includes herein a more uniform distribution of hard and metallic binder phases, particularly with respect to the size of the largest binder-phase-enriched regions, which are reduced in size in binder-free regions compared to binder-added regions. Such microstructural improvements can be beneficial to the local hardness distribution, which in turn affects the performance of cutting tools.

[0017]

[0021] Yet another advantage of the method of the invention is that it allows for improved means of controlling and minimizing porosity. The porosity of the binder-free regions after sintering will be lower than the regions with added binder. Furthermore, the porosity of the binder-free regions in the sintered product will be finer and have a reduced degree of surface connectivity than the binder-added regions. Preferably, the degree of sintering allows all pores in the previous binder-free regions to be separated without any surface bonding. In such a preferred case, the pressure stage of the sintering cycle transfers pressure to the regions in the binder-added regions, thereby increasing the pore connectivity to a higher degree and allowing the pores in this region to collapse and densify, at least locally. Furthermore, any surface-connected pores that may remain on the periphery of the sintered product outside the previous binder-free regions can then be removed by grinding the areas where surface performance regions are required.

[0018]

[0022] Thus, the present disclosure provides a method for improving at least one, and in most cases both, microstructure and porosity of articles produced using the methods disclosed herein, particularly in performance areas of the article, where binder-free areas can be used.

[0019]

[0023] For purposes of this disclosure, binder-free regions are defined as areas of a sintered or unsintered article where no binder was added during the additive manufacturing process. Binder-free regions should be surrounded or encapsulated by binder-added regions. Additionally, binder-free regions are often located near the surface of the article, and the thickness of the binder-free regions may depend on green strength requirements.

[0020]

[0024] Additionally, binder-added regions are defined as regions of the sintered or unsintered article to which binder has been added during the additive manufacturing process. Thus, even if no binder is present in the sintered article, the regions may still be referred to as binder-free and binder-added regions, since they are removed during the sintering process.

[0021]

[0025] Throughout this disclosure, the terms "performance area," "engagement area," and "high stress" area are used. Performance area refers to an area of ​​an article that requires or would benefit from less porosity and / or improved microstructure.

[0022]

[0026] There can be two types of performance areas: an engagement area, which is an area that includes an engagement surface, which is a part of the article that is adapted to engage with another object, such as the tip of a drill or the cutting edge of a tool.

[0023]

[0027] The other type of performance region is a high stress region, which is an area of ​​the article that also benefits from lower porosity and / or improved microstructure than other areas, but does not include the mating surface.

[0024]

[0028] The method is applicable to additive manufacturing techniques that use binders, such as binder jetting. The method may further be particularly suitable for the production of hard metal or cermet products.

[0025]

[0029] The term "cermet" is intended to refer to a material that includes hard constituents in a purely metallic bonding phase, the hard constituents including carbides or carbonitrides of one or more of Ta, Ti, Nb, Cr, Hf, V, Mo and Zr, such as TiN, TiC and / or TiCN.

[0026]

[0030] The term "hard metal" is intended to refer purely to a material that comprises hard constituents in a metallic binder phase, the hard constituents comprising at least 50% by weight of WC particles. The hard constituents may also comprise carbides or carbonitrides of one or more of Ta, Ti, Nb, Cr, Hf, V, Mo and Zr, such as TiN, TiC and / or TiCN.

[0027]

[0031] The metallic bonding phase in the cermet or cemented carbide is a metal or a metal alloy, and the metal can be selected from, for example, Cr, Mo, Fe, Co, or Ni, either alone or in any combination. The metallic bonding phase in the cermet or cemented carbide is a metal or a metal alloy, and the metal can be selected from, for example, Cr, Mo, Fe, Co, or Ni, either alone or in any combination. The average content of the metallic bonding phase in the powder is 4 to 30% by weight, preferably 6 to 17% by weight or 10 to 13% by weight.

[0028]

[0032] Referring now to FIG. 1, the steps of a method for producing a sintered article according to one embodiment will be described in more detail.

[0029]

[0033] The method includes depositing 102 a layer of a powder composition and adding 104 a binder, i.e., a liquid binder used in additive manufacturing, to areas corresponding to a cross section of the green article excluding binder-free areas, if present in the layer. As will be appreciated, there may be no binder-free areas in each layer of the powder composition, even if the article includes at least one binder-free area. The method then includes repeating depositing 102 and adding 104 for each layer required to form the green article.

[0030]

[0034] In other words, the method involves adding binder to each layer of the powder composition in areas that are not binder-free, which in most cases will represent the majority of the article, excluding the binder in the binder-free areas. The method differs from conventional binder jetting techniques in that binder is not added to the entire cross-section of the green article for each layer, as the binder is excluded from the binder-free areas. As a result, at least some layers of the powder composition in the green article after the additive manufacturing process will include one or more binder-free areas.

[0031]

[0035] After additive manufacturing steps 102 and 104 are performed and repeated for each layer, an additively manufactured article, also referred to as a green part, is obtained. The additively manufactured green part includes at least one binder-free region, i.e., a region that includes free powder with no added binder, while the remainder of the green part includes both powder and binder.

[0032]

[0036] The method further comprises sintering 106 the article, thereby producing a sintered part. In some embodiments, the sintering comprises first using vacuum sintering and then using high pressure sintering. In some embodiments, the sintering is carried out by a so-called sinter-HIP cycle, where the final stage of sintering is carried out under high pressure, e.g., 20-50 bar.

[0033]

[0037] In some embodiments, the method includes, after the additive manufacturing steps 102, 104 and prior to the sintering step 106, a step of curing the green part to harden the binder and / or a step of de-powdering the green part to remove loose powder that is not intended to form part of the sintered part.

[0034]

[0038] By using the method according to the present disclosure, a sintered article is obtained that contains at least two different types of regions, one type of region being a binder-free region that has sintering properties close to those of pressed cemented carbide or cermet articles. Preferably, the microstructure of each binder-free region of the sintered article is such that the distribution between the metallic binder phase and the hard phase is not very heterogeneous, in particular that there are no regions with large accumulations of cobalt. Yet another advantage is that these regions are less likely to contain porosity connected to the surface.

[0035]

[0039] Although it has been found that the sintering characteristics of the performance zones, i.e., binder-free zones, are superior to the surrounding zones, the reason for limiting the total volume of binder-free inclusions is that otherwise the green strength may be too low, which may have adverse effects, for example, on powder removal and handling of the green part.

[0036]

[0040] Another reason for limiting the total volume of the binder-free regions is to minimize as much as possible the effects of non-uniform shrinkage throughout the article during sintering. This effect results from the difference in shrinkage rates between the volume of the binder-added powder and the volume of the binder-free regions. Such uncontrolled effects on sintering shrinkage decrease with the decrease in the relative volume of the binder-free regions.

[0037]

[0041] In some embodiments, the binder-free areas are performance areas of the article. In some embodiments, the binder-free areas are engagement areas of the article. In some embodiments, the binder-free areas are high stress areas of the article.

[0038]

[0042] In some embodiments, the binder-free area is located at or near at least one edge or surface of the article.

[0039]

[0043] In some embodiments, the binder-free regions have an elongated shape.

[0040]

[0044] In some embodiments, the articles are manufactured using binder jetting.

[0041]

[0045] In some embodiments, the binder-free areas are located around the entire perimeter of the article, as shown in FIG. 3B.

[0042]

[0046] In some embodiments, the binder-free regions are located perpendicular to the direction in which the powder layers are deposited during the additive manufacturing process, which can further reduce porosity in the sintered article.

[0043]

[0047] 2A shows a cross-section of an embodiment of article 200, which may be either a green or sintered article, including binder-free region 210 and binder-added region 220. To connect this to the method steps discussed above, region 220 is a region where a binder has been added to the powder, and binder-free region 210 is a region where no binder has been added to the powder.

[0044]

[0048] Article 200 may further comprise one or more portions 215 outside binder-free region 210 that cover binder-free region 210. As will be appreciated, covering portion 215 is a portion that includes both powder and binder.

[0045]

[0049] 2B, which shows a cross-section or powder layer of another embodiment of article 200, which includes three binder-free regions 210 and a plurality of portions 215 covering the binder-free regions. As can be seen, the two binder-free regions 210 on the left side of article 200 are surrounded on both sides by portions 215 covering them, while the binder-free region 210 on the right side of article 200 is only covered on the surface, but is covered on one side by the covering portion 215.

[0046]

[0050] In some embodiments, after the article is sintered, these portions 215 may be removed, for example by grinding, to expose the binder-free regions 210 of the sintered article to the outside.

[0047]

[0051] In some embodiments, article 200 includes at least two binder-free regions. In some embodiments, article 200 includes multiple binder-free regions.

[0048]

[0052] In some embodiments, the finished product includes 0.1-10% binder-free regions and the remaining regions include both powder and binder, hi some embodiments, the finished product includes 0.2-1% binder-free regions and the remaining regions include both powder and binder.

[0049]

[0053] In some embodiments, the article is a machining tool, for example a component of a machining tool used for grinding or cutting.

[0050]

[0054] In some embodiments, the method further includes removing 208 portions of the sintered article that outwardly cover the binder-free regions such that the binder-free regions are located at the surface of the article.

[0051]

[0055] Turning now to Figure 3A, there is shown a cross section or powder layer of another embodiment of an article that includes one binder-free region 310 that has a different shape than the binder-free region of Figures 2A and 2B. The binder-free region 310 in Figure 3 appears to cover a corner of the article 300 and has a shape that is more like an L-shape than an elongated shape. The article 300 also includes a binder-added region 320 and a portion 315 that covers the binder-free region 310 from the outside, similar to the article of Figures 2A and 2B.

[0052]

[0056] 3B, a cross section or powder layer of another embodiment of article 350 is shown, including binder-free region 360 disposed about the entire article 350. The article further includes a portion 365 that outwardly covers binder-free region 360, and binder-added region 320. Such an embodiment may be relevant where the entire article would benefit from the possibility of applying grinding to reduce porosity within the previously binder-free regions and expose improved microstructure anywhere on the surface of the article.

[0053]

[0057] As will be appreciated, the binder-free regions of articles produced using the disclosed methods may vary depending on the article and its intended use, and there are no limitations on what shape the binder-free regions can have, except as imposed by the capabilities of the manufacturing system used.

[0054]

[0058] 4A and 4B, the microstructural differences between binder-free and binder-added regions that can be achieved using methods according to the present disclosure will now be described. As previously mentioned, it is generally preferred that there be a relatively uniform distribution between the hard and binder phases in the sintered part, so that there is not significant accumulation of the binder phase anywhere in the finished sintered part.

[0055]

[0059] Figure 4A shows the microstructure of an area of ​​the sintered part where a binder was added during the additive manufacturing process, and Figure 4B shows the microstructure of an area of ​​the sintered part without binder. The light areas in the figure represent the binder phase (cobalt in this case) and the dark areas represent a hard phase such as WC. As can be seen, there are many more large light areas in Figure 4A than in Figure 4B.

[0056]

[0060] Now, looking at Figure 4A, the area where binder was added, the distribution between the cobalt and the hard phases is not as uniform as in the area without binder. There are several areas that are mainly composed of cobalt, such as the areas indicated by 420, 430, and 440.

[0057]

[0061] Looking now at Figure 4B, which shows an area without binder, the distribution between the cobalt and the hard phase is relatively uniform. It is still possible to see that some parts of the image are brighter than others, but the overall structure is relatively uniform, and significantly more uniform than the part shown in Figure 4A.

[0058]

[0062] 4A and 4B, it can be seen that the distribution of cobalt and hard phases is more uniform in the regions where no binder was added than in the regions where binder was added, which is one of the key insights underlying this disclosure.

[0059]

[0063] Although the above description contains multiple specificities, these should not be construed as limiting the scope of the described concepts, but merely as providing illustrations of some exemplary embodiments of the described concepts. It will be understood that the scope of the concepts described herein fully encompasses other embodiments that will become apparent to those skilled in the art, and thus the scope of the presently described concepts is not limited. Reference to an element in the singular does not mean "one and only," unless expressly stated otherwise, but rather means "one or more." All structural and functional equivalents to the elements of the above-described embodiments known to those skilled in the art are expressly incorporated by reference and are intended to be included herein. Furthermore, it is not necessary for an apparatus or method to address all of the problems sought to be solved by the presently described concepts to be included herein. In the exemplary figures, dashed lines generally indicate that the features within the dashed lines are optional.

Claims

1. 1. A method for additively manufacturing an article comprising a cemented carbide or cermet, the article comprising at least one binder-free region, the method comprising: a) depositing a layer of a powder composition (102); b) adding a binder to the powder composition in an area corresponding to the cross-section of the article, except for at least one binder-free area, if any, within the layer (104); repeating steps a) and b) for each layer of the article, thereby obtaining a green article; sintering (106) the green article, thereby obtaining a product; A method comprising:

2. The method of claim 1 , wherein the binder-free areas are performance areas of the article.

3. The method of claim 1 , wherein the binder-free areas are mating areas of the article.

4. The method of claim 1 , wherein the binder-free areas are located at the edges of the article.

5. The method of claim 1 , wherein the binder-free region has an elongated shape.

6. 10. The method of claim 1, wherein the binder-free areas have fewer cobalt-enriched areas than the remainder of the article.

7. The method of claim 1 , wherein the thickness of the binder-free area is less than 2 mm.

8. The method of claim 1 comprising a cemented carbide, the cemented carbide comprising cobalt as a binder phase.

9. The method of claim 1 , wherein the article is a part of a machine tool.

10. The method of claim 1 , wherein the article is manufactured using binder jetting.

11. a region (220) to which a binder was added during additive manufacturing of the article; and at least one binder-free region (210), wherein the binder-free region is a region of the article to which no binder was added during additive manufacturing of the article.

12. 12. The sintered article (200) of claim 11, wherein the binder-free regions are performance regions of the article.

13. 12. The sintered article (200) of claim 11, wherein the binder-free region is located at an edge of the article.

14. 12. The sintered article (200) of claim 11, wherein the binder-free region has an elongated shape.

15. 12. The sintered article (200) of claim 11, manufactured using the method of any one of claims 1 to 10.

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