Material for additive manufacturing and uses thereof

Abstract

An additive manufacturing material composition, configured to be used in an additive manufacturing process or equipment, comprising: any one of a metal carbide powder and a metal nitride powder, wherein said metal is selected from the group consisting of niobium, tantalum, tungsten, hafnium, and zirconium, or combinations or mixtures of thereof.

Description

[0001]MATERIAL FOR ADDITIVE MANUFACTURING AND USES THEREOF Technical field The present disclosure relates to a material composition for additive manufacturing or 3D printing and uses thereof, in particular for high- temperature processes such as HT-CVD, PVT and other high temperature reactor applications. The present disclosure further relates to methods for additive manufacturing using the composition and objects formed from the composition. Background The semiconductor industry extensively employs high-temperature processes for the production and processing of materials. Silicon carbide ingots are for instance often produced through Physical Vapor Transport (PVT) processes such as seeded sublimation crystal growth. These processes are usually performed in gas- and vacuum-tight thermally insulated chambers which may be connected to gas supply and pressure control subsystems enabling the control of the gas environment, pressure, and temperature inside the chamber. Such systems have different types of designs and can be used for various purposes. The system components that are placed inside the chamber may be exposed to very high temperatures and chemically harsh environments. This imposes a demand for durable materials to be used inside the chamber. Such materials are required to have good thermal stability, chemical inertness, and the ability to withstand mechanical loads. Moreover, depending on the process, high or low electrical and thermal conductivities may be an important factor. In addition, semiconductor materials are extremely sensitive to contamination by impurities at extremely low concentration levels. Therefore, the internal components may need to be made of materials that do not contaminate the process above the accepted concentration levels. Graphite based materials are often used for the crucibles, heaters and other parts in the hot zone components of high temperature furnaces, i.e. in high-temperature processes, requiring temperatures higher than 1800°C or above 2400°C, even if there are other suitable materials such as tungsten. Graphite has good electrical conductivity, a low specific resistance, and structural stability up to very high temperatures (melting / sublimation point at 3600°C). However, it is quite chemically reactive and can decompose quite rapidly when exposed to chemically harsh environments at high temperatures. Therefore, graphite parts need to be replaced relatively often making the process expensive. This actually constitutes one of the major costs for the manufacturing process of SiC ingots. In some cases, the internal graphite component can be coated with a protective surface layer that allows extending their lifetime. However, due to the existence of cracks and defects in the coating, it still has a limited lifetime. In some cases, the use of protective coatings may be not economically viable. For the very high-temperature processes, requiring temperatures higher than 1800°C or even above 2400°C, the internal components at the hot zone of the chamber may instead be made from materials such as metal carbides, nitrides, or their composite materials such as cermets and cemented carbides. When good electrical and thermal conductivity is required, some metal carbides of the group 4, 5, and 6 transition metals may be very attractive candidates due to their low specific resistance, high chemical inertness, and very high melting points. For the components with more complicated geometric shapes, the carbides are usually used as coating materials, but rarely as a bulk material. The use of carbides as a bulk material for hot zone components is limited by the difficulties in producing the carbide component in complex geometries. In recent years the 3D printing technologies, also called additive manufacturing, have been used in various applications since it offers a solution for fabricating objects with complex geometries. Using a 3D printer, the objects can be produced autonomously from digital 3D models. The technology is widely developed for polymer materials and essentially pure metals. In order to make SiC based technologies more accessible, the industry needs new and improved high temperature reactors with more intrinsic hot zone designs, which requires a more versatile way of manufacturing high temperature components. Summary It is in view of the above considerations and others that the embodiments described in this disclosure have been made. It is an object of the present disclosure, to provide an improved material for additive manufacturing and a method wherein such material is used, and objects formed through the method and material. The invention is defined by the appended independent claims. Embodiments are set forth in the appended dependent claims and in the following description. According to a first aspect there is provided an additive manufacturing material composition, configured to be used in an additive manufacturing process or equipment, comprising: any one of a metal carbide powder and a metal nitride powder, wherein said metal is selected from the group consisting of niobium, tantalum, tungsten, hafnium, and zirconium, or combinations or mixtures of thereof. Replacing graphite with 3D-printed components, i.e. components made from additive manufacturing process, which are made from a more stable material could significantly reduce the costs of the process. Using metal carbides or nitrides thus allows for production of objects to be used in reactors for high temperature applications, or so called hot-zone crucibles. Metal nitrides could be advantageous for AlN and GaN applications, since they generally have a slightly lower melting point than the carbides, Further to this, carbon may lead to impurities in the GaN and AIN products as well as a risk of developing CN or HCN in the process. The main technical advantage of using additive manufacturing for manufacturing hot zone components is greatly reduced cost of manufacturing. In addition, the components can easily be manufactured with exact requested dimensions in complex geometries. Another advantage is that the material powder used for additive manufacturing does not have to be a “virgin material”, but can be powders recycled from previous additive manufacturing processes or other types of manufacturing processes. This circular utilization of material will further greatly reduce the cost of the components, and hence the cost of the manufacturing process in which they are utilized, such as for manufacturing of SiC crystals in semiconductor applications. The additive manufacturing material composition may in one example comprise a metal carbide powder. In one example, the additive manufacturing material composition may further comprise any one of a silicon powder or a silicon carbide powder, or a mixture thereof. In one example the additive manufacturing composition comprises at least 40 wt-% silicon powder or silicon carbide powder. In one example the additive manufacturing composition comprises at least 35 wt-% silicon powder or silicon carbide powder. In one example the additive manufacturing composition comprises less than 40 wt-% silicon or silicon carbide. Since the silicon will melt it will act as a binder material for the metal carbide or nitride. Moreover, as the temperature increases, the Si may form a metal silicide which generally has a substantially lower melting point than the metal carbides, or nitrides. The melting or sintering can hence continue and eventually the silicide will convert back to the carbide form. Using SiC instead of pure Si will release the Si vapors more gradually and leave a residue of carbon which is beneficial for the carbide formation. Using silicon or silicon carbide in the additive manufacturing process may enhance the formation of a silicon carbide ingot. In one example, said metal carbide powder or metal nitride powder has mean size of particles in the range of 1 to 150 µm, or in the range of 40 to 100 µm. In one example, the material comprises a mixture of powders having at least two different mean particle sizes. In one, preferred example, the composition according to the first aspect may be substantially free from cobalt. By substantially free from cobalt is meant that there is no added cobalt in the composition. Preferably, however, the composition contains no cobalt at all, or at least only very minor trace amounts of naturally occurring cobalt. In one, preferred example, the composition according to the first aspect may be substantially free from aluminum (Al). In one, preferred example, the composition according to the first aspect may be substantially free from boron (Br). This is essential, since any of these metals may compromise or contaminate the silicon carbide crystals or ingots grown in reactors for high temperature applications, or so called hot-zone crucibles where objects formed from the inventive additive manufacturing material composition. In one example, the melting point at normal conditions of said metal carbide powder is in the range of 2500 to 4000 °C. By normal condition is meant that the ambient conditions are normal, i.e. room temperature and normal pressure, since the melting point may change depending on the ambient conditions such as external pressure. According to the first aspect, the additive manufacturing equipment may be any one of an electron beam and a laser beam 3D printer. According to a first aspect there additive material composition consists of said metal carbide or said metal nitride, or a combination or mixture thereof of at least 50 wt-%. By providing an additive manufacturing material composition consisting, or comprising principally, of metal carbide or metal nitride, or a combination or mixture thereof, means that the composition mainly comprises the metal carbide or nitride, i.e. other components or additives are only minor constituents. It was a surprising finding that an additive manufacturing material composition consisting of metal carbide, or nitride, could be used in an additive manufacturing process, such as 3D-printing. Using metal carbides or nitrides thus allows for production of objects to be used in reactors for high temperature applications, or so called hot-zone crucibles. Further to this, since the additive manufacturing composition principally comprises the metal carbide or nitride, re-cycling of the material can be even further improved. According to a second aspect there is provided a method for additive manufacturing, wherein said method comprises: providing a digital model of an object to be printed; providing the additive manufacturing material composition according to the first aspect; performing an additive manufacturing operation by an additive manufacturing equipment to form said object from said additive manufacturing material composition. In one example, the additive manufacturing equipment may be any one of an electron beam and a laser beam 3D printer. According to the second aspect, the additive manufacturing operation may be performed by solidifying areas of consecutive said additive manufacturing material composition layers, where at least one electron beam successively irradiates predetermined sections of each layer, and wherein said method further comprises removing the remaining additive manufacturing material composition to form said object. The additive manufacturing method may, in another example, comprise: providing said additive manufacturing material composition in a hollow core of a plastic tube; and performing said additive manufacturing operation to form said object with said plastic tube. In one example, the additive manufacturing operation may be followed by a subsequent material treatment, and said subsequent material treatment may comprise sintering, and / or grinding and / or polishing or annealing at high temperatures. In one example, the additive manufacturing method includes pre-heating the source material, or additive manufacturing material prior to the additive manufacturing process (i.e. prior to the actual 3D printing). The pre-heating comprises pre-heating of the additive manufacturing material globally and / or locally, prior to performing said additive manufacturing operation. Preheating steps may involve heating the large area of the source material (global preheating) and preheating the source material locally. In any of the preheating steps, the temperature distribution may not be uniform and it can vary in time. Preheating can be performed using various energy sources such as electron beam, laser beam, resistive heater, etc.. By pre-heating the material, or powder, a more effective and consistent printing process may be achieved. Preheating can also increase the electrical conductivity of source material and also may result in light sintering of the powder which helps to reduce spatter or smoking. According to the method of the second aspect, said additive manufacturing material composition may further comprise re-cycled material from a previously manufactured object, and wherein said previously manufactured object was formed from an additive manufacturing material composition according to the first aspect in an additive manufacturing operation. By re-cycling material for the 3D printing material composition allows for an even cheaper material for the 3D printing process. The material may also be re-cycled from another manufacturing process such as sintering. In one example, the method may further comprise milling or grinding said previously manufactured object to a powder having a mean size of particles in the range of 1 to 150 µm. In yet another example, the method according to the second aspect may further comprise mixing said powder from said previously manufactured object with an virgin additive manufacturing material composition. According to a third aspect there is provided an object manufactured in the method according to the second aspect. According to a fourth aspect there is provided the use of an object according to the third aspect in a crucible or reactor adapted to be heated to a temperature in the range of 800°C to 1500°C, or in a range of 1500°C to 1800°C, or to at least 1800°C. In one example, the object may be any one of main body of silicon carbide growth crucible or parts of it, seed holder or parts of it, silicon carbide source container or parts of it, porous membrane, crucible lid, crystallizer / crystal guide or parts of it. Alternatively, the printed metal carbide, or nitride, parts may be utilized in applications for growing other wide bandgap materials such as AlN, GaN, or Ga2O3. Brief description of drawings Embodiments of the present solution will now be described, by way of example, with reference to the accompanying schematic drawings. Fig. 1 shows a schematic cross-sectional view of an exemplary high temperature PVT reactor. Fig.2 shows a schematic cross-sectional view of a crucible used in a PVT reactor for silicon carbide crystal growth. Fig.3 shows a schematic cross-sectional view of the disassembled crucible used in PVT reactor for silicon carbide crystal growth. Fig.4 is a graph showing energy in relation to melt depth. Fig.5 is a contour map of the melt pool depth. Description of Embodiments Physical Vapor Transport (PVT) processes such as seeded sublimation growth referred to as “modified Lely method” may be used to grow silicon carbide and aluminum nitride crystals. Usually, the process is carried out at high temperatures in an inductively heated closed graphite crucible surrounded by thermal insulation. Standard sublimation growth of silicon carbide is carried out in a quasi-closed graphite crucible in an argon environment at around 10 mbar pressure. By high temperature is meant processes that are performed at temperatures above approximately 1400°C, usually between 1800 and 3000oC in what is often called “hot zone” applications. The temperature of the process depends on the application, such as graphite furnaces, the growth temperature of SIC. A “hot zone” may comprise the components which are placed inside the gas- and vacuum-tight thermally insulated chamber, and which are heated directly or indirectly to high temperatures. In crystal growth systems, a very important part of the hot zone is a crucible which is typically placed at the center of the hot zone and is heated to the highest temperatures. The crucible may resemble a closed or open container, that contains internal voids, and it may be comprised of one or many smaller components. The crucible may or may not contain gas inlet(s) and / or outlet(s) for supplying and / or removing gases. Thermal insulation surrounding the high temperature components, such as for example the crucible, is also considered to be part of the hot zone. Thermal insulation may be produced of layered, fiber, or porous materials and consist of one or many insulating components. The present disclosure is directed to the manufacture of and use of for instance different objects, components or parts used in the so-called hot zones or crucibles adapted for high temperature applications, where the environment may also be corrosive or otherwise aggressive for the components. The hot zone is preferably heated inductively by external electromagnetic radiation, but can also be heated using resistive heating elements. Such systems may thus include physical vapor transport (PVT) systems, high temperature chemical vapor deposition (HT-CVD) crystal growth systems, and high temperature annealing furnaces where the components may now be more cost efficiently produced from metal carbide and metal nitride materials. Applications may also include other high temperature processes where inert materials are needed to form the process chamber or parts of the process chamber. In one example the additive manufacturing composition comprises at least 50 wt-% of metal carbide or metal nitride or a combination or mixture thereof. In one example, the additive manufacturing material composition comprises at least 70 wt-% of metal carbide or metal nitride. In one example, the additive manufacturing material composition comprises at least 80 wt-% of metal carbide or metal nitride. In one example, the additive manufacturing material composition comprises at least 90 wt-% of metal carbide or metal nitride. In one example, the additive manufacturing material composition comprises at least 95 wt-% of metal carbide or metal nitride. This means that the composition principally comprises or consists of the metal carbide or nitride. In one preferred example, the additive manufacturing material composition comprises at least 50 wt-% metal carbide. In one preferred example the additive manufacturing composition comprises at least 70 wt-% metal carbide. In one preferred example the additive manufacturing material comprises at least 90 wt-% metal carbide. In the embodiment of the present disclosure, some or all of the components are produced from metal carbide and metal nitride ceramics using additive manufacturing. In one example, the ceramic material may also be an alloy, i.e. comprising 50 wt-% or more of a carbide and / or nitride. In one embodiment of the present disclosure, the manufacturing of the hot zone components comprises the additive manufacturing process such as the 3D printing process. The manufacturing process may resemble the Powder Bed Fusion process, as described below. Additive manufacturing or 3D printing in which a powdered material is melted by focused energy stream layer by layer to create an object matching the precise specifications defined by a digital model, such as a CAD model. The manufacturing process may involve the following steps: (1) Spreading a thin layer of metal carbide powder on a base plate or previously processed powder. (2) Optionally pre-heating of powder layer. The pre-heating may lead to a mild sintering of the powder. (3) Heating the layer of powder by focused energy stream according to cross sectional pattern generated from the CAD model so the powder melts or / and sinters. (4) Moving the powder bed containing the printed pattern in a way that a new layer of powder can be spread on the surface. Repeating steps 1-4 until the entire component is finished resulting in a solid body suspended in the powder bed. The additive manufacturing processes may involve the energy stream in a form of the focused electron beam or the laser beam that is used to heat the material and initiate its melting and / or sintering. When the electron beam is used to melt and / or sinter the material the manufacturing process is commonly called Electron Beam Powder Bed Fusion. An electron beam contains a stream of electrons that is guided by a magnetic field, heating layer upon layer of powdered metal. Production can take a place in a vacuum chamber that guards the powder against oxidation that can compromise sensitive materials. Additive manufacturing process may alternatively use focused laser beam, wherein a laser beam is utilized to melt or / and sinter a powdered material. The bodies produced by the additive manufacturing process may require a subsequent treatment of the obtained body. That may have and advantage of reducing the porosity of the components and as a result improving its microstructure. One such example of a subsequent treatment is a sintering process. Subsequent treatment of component produced by additive manufacturing may be done by heating the components to high temperatures (above 1 / 2 of the melting temperature) with controlled gas environment and possibly subjecting the components to external pressure. Subsequent treatment of component may for example use techniques such as pressureless sintering, hot pressing (HP), hot isostatic pressing (HIP), microwave sintering, and spark plasma sintering. Subsequent treatment may also involve grinding and / or polishing the body to the specified shape and surface quality. In one embodiment the additive manufacturing material, or powder, is enclosed in a core of a plastic tube, and the plastic tube is 3D printed to a desired three-dimensional shape. Once the shape has been obtained the material may be treated by e.g. a sintering process to form the final product. In the embodiment of the present disclosure the metal carbide or nitride powders, or their alloys used in the additive manufacturing may have a mean size of particles in the range of 1 to 150 µm. According to one alternative the powder has a mean particle size of 50 to 100 µm. According to the present disclosure an additive manufacturing material composition comprising or consisting of a metal carbide powder, or metal nitride powder, or a mixture or combination thereof, is provided. That means that the additive manufacturing material composition principally consists of metl carbide or metal nitride. In the embodiment of the present disclosure, the material composition of the hot zone components comprises the metal carbide and metal nitride materials that may or may not contain porosity. By containing porosity is means that for instance the powder may have a porosity, or that the powder grains or particles may have porosity, or that the 3D printed objects may have a porosity. The metal is selected from the group consisting of; niobium (Nb), tantalum (Ta), tungsten (W) (wolfram), hafnium (Hf) and zirconium (Zr), or combinations and mixtures thereof. The metal carbide is thus selected from the group consisting of niobium carbide (NbC), tantalum carbide (TaC), tungsten carbide (or wolfram carbide, WC), hafnium carbide (HfC), and zirconium carbide (ZrC) or combinations or mixtures thereof. The metal nitride is thus selected from the group consisting of niobium nitride (NbN), tantalum nitride (TaN), tungsten nitride (or wolfram nitride, WN), hafnium nitride (HfN), and zirconium nitride (ZrN) or combinations or mixtures thereof. In one example, the material composition may comprise a mixture of metal carbide and metal nitride. In one example the metal of the carbide or nitride may be a combination or mixture of at least two different metals. The metal carbide, or nitride, chosen for a specific application might depend on for instance impurities, where the most favorable compounds are WC, TaC, and HfC where metal atoms have large atomic radii and heavy mass that makes them hard to incorporate into the other crystal materials such as SiC for example. Then there are emissivity considerations where TaC has a very low emissivity which can be advantageous in some applications. In another example the metal carbide is zirconium carbide, since it is cost effective. Preferred embodiments of the present disclosure include niobium carbide, tantalum carbide, tungsten carbide and zirconium carbide. In one example the metal carbide is niobium carbide, due to its high melting point at around 3600°C. However, HfC has a melting point at around 3900°C and TaC at around 3850°C. Further to this a mixture of different metals, such as in one example HfTaC, has the highest melting point of all known materials which is about 4000°C. In one example, the metal carbide powder or metal nitride powder may have a mean size of particles in the range of 1 to 150 µm, or in the range of 40 to 100 µm. In one alternative the composition further comprises silicon powder or a silicon carbide powder. The silicon powder or the silicon carbide powder may have a mean size of particles in the range of 1 to 150 µm. In one example, the composition further comprises a carbon additive. The carbon additive may for instance be in the form of a carbon powder, or an organic binder, such as a resin. The carbon additive may for instance have a technical effect of enhancing the density of the composition before it is pressed. Further to this, residues of carbon may assist in shifting the stoichiometry towards the carbide form rather than the silicide. The carbon additive may have a mean size of particles in the same range as the other constituents of the composition or a different mean size of particles. In one example the material composition may comprise any one of metal carbide powder, metal nitride powder and optionally silicon carbide powder having at least two different particle size distributions, i.e. a mixture of powders with different mean particle sizes. This means that a metal carbide powder may comprise particles having different ranges of particle sizes and may be mixed with a metal nitride powder comprising particles having different mean particle sizes, or that e.g. a metal carbide powder may be mixed with a metal silicon powder having a different mean particle size. The composition may also comprise other constituents for example compounds that enhance the melting properties of the metal carbide or metal nitride, or provides other advantageous characteristics through the 3D printing process or in the object formed in the process. In one alternative the additive manufacturing or 3D printing material composition is substantially free from, or completely free from cobalt. In one alternative the additive manufacturing or 3D printing material composition is substantially free from, or completely free from boron. In one alternative the additive manufacturing or 3D printing material composition is substantially free from, or completely free from aluminum. The material may also be re-cycled. In one alternative the powder bed material left from the additive manufacturing process that was not incorporated in the main printed body may be utilized again. In one alternative, the additive manufacturing material composition further comprises material which has been re-cycled from a previously 3D printed object. This means that an object may have been printed from a fresh or virgin (i.e. never-before used) additive manufacturing material composition and then used in its intended application, and after the end of its lifetime be milled or ground to be used again in a 3D printing process. The additive manufacturing material composition may alternatively comprise substantially only re-cycled material, or be a mixture between a virgin material and a re-cycled material. Re-cycling of the component back to the powder materials and re-using of the powder to produce new components and usage of them in the crystal growth process according to this disclosure brings a huge economical advantage for reducing the running costs. In one example, the recycled material is mixed with virgin material to achieve at a correct ration of C and / or N and Me (metal) for the additive manufacturing composition. In one example, the re-cycled material is essentially free from cobalt. In one example, the re-cycled material is essentially free from boron. In one example, the re-cycled material is essentially free from aluminum. By essentially or substantially free from cobalt, boron and aluminum, is meant that neither the virgin material nor the re-cycled material comprises added any added cobalt, boron and aluminum. The material may comprise very small trace amounts of cobalt, boron, and aluminum, due to the inherent characteristics of the raw material used. Figs 1 to 3 illustrates different objects or components of a high temperature reactor 1, such as for instance a PVT reactor, which can be manufactured according to the additive manufacturing process with the inventive additive manufacturing material composition. In Fig.1 an exemplary reactor 1 is illustrated in a partially cut out cross- sectional view. The reactor 1 may be adapted for inductive heating. The reactor may comprise different components, such a crucible 2, and an inductor coil 3 surrounding the crucible 2 and different parts of thermal insulation 4. Fig.2 is a schematic cross-sectional view of a crucible 2 as illustrated in Fig.1, and Fig.3 is a view of the disassembled crucible 2. Figs 2 and 3 further illustrates some of the objects or components of the crucible 2 which may be manufactured with the inventive material composition. In the exemplary Figs.2 and 3 the crucible has a lid 5 arranged at an upper part and a bottom part 10. A crystal seed 6 may be arranged at the top portion and held in place by a seed holder 7. A crystallizer or crystal guide 8 may be arranged in a section between the top and bottom parts 10. The bottom part of the crucible 2 may hold the source material 11 and may thus be a silicon carbide source container. A porous membrane 9 may be arranged between the source material 11 and the inside of crucible 2. Trials and results Electron beam powder bed fusion (EB-PBF) was used for melting niobium carbide (NbC) in a powder bed. Electron beam powder bed fusion (EB-PBF) is an additive manufacturing (AM) process that utilizes high energy electrons to melt and fuse powder particles together into a solid component. This is performed in accordance with a predetermined pattern within thin layers of powder also called powder bed. During the EB-PBF process, the powder bed normally is preheated to higher temperatures. Preheating of the powder bed to elevated temperatures contributes to lower thermal gradients between the powder and the melt pool generated by the electron beam. Lower thermal gradients can help to decrease the occurrence of cracks and thermal stresses that otherwise would occur during the printing process. Preheating can increase the electrical conductivity of the powder bed and may also induce mild sintering of the particles. This helps to reduce the spatter and smoking of powder material during the melting process. Due to the high energy input, the EB-PBF is one of the most promising additive manufacturing methods for printing refractory metals such as Tungsten, Tantalum, Molybdenum, as well as some ceramics. The purpose of this trial was to determine how well high temperature refractory ceramics such as carbides can be utilized in EB-PBF. Since NbC is a preferred embodiment, it was selected as the material of choice for the trials. The effect of electron beam scan speed and power was investigated by studying the surface quality of melted regions and melt depths. Melting NbC was proven feasible using EB-PBF. The trials were conducted using a Freemelt ONE machine where all the printing parameters such as electron beam power, scan speed, spot size, etc, could be changed. The top surfaces and cross-sections of the melted regions were evaluated visually, and using light optical (LOM, Leica DM6) and electron microscopies (SEM, Hitachi SU-70). The depths of melted regions were determined from the cross-section images. Preparation of cross-sections involved cutting the melted regions, mounting them in Polyfast mounting resin and then polishing them. The source material used in these trials was a powder made from NbC with an average grain size distribution of 0.5-1 µm. The acceleration voltage of the electron beam for the trials was kept constant (60 kV). Areas of 5x5 mm were melted using line melting in a bi- directional pattern. All squares were melted using a line offset of 100 μm, and a focused beam with a spot size of 1% (setting of Freemelt ONE system corresponding to approximately 210-280 μm spot size on the top surface of powder bed). In order to simulate / imitate the powder bed, a 4 mm thick graphite ring was placed on top of the tungsten build plate and then filled with the NbC powder. That resulted in a 4 mm thick layer of NbC powder surrounded by the graphite ring which kept the powder volume in place. The top surface of the powder was flattened manually so it resembles the surface of the powder bed used in the actual printing process. The electron beam parameters used in the trials can be seen in Table 1. Table 1. Electron beam parameters used in the EB-BPF melting trials of the NbC powder bed. The powder bed preheating procedure often comprises one, two or even more preheating steps. Global preheating, preheats and lightly sinters most of the top surface areas of the powder bed exposed to the beam where some of the areas will be used in the melting process at later steps. Global preheating is often used as a first step. The concept of global preheating is to consolidate the powder enough to eliminate the chance of smoking but at the same time to avoid over-sintering which will create a dense powder cake. Reusing such powder in another additive manufacturing process without preprocessing would be difficult. Local preheating step, usually conducted after global preheating, is meant to sinter the powder even more and further increase its electrical conductivity so a stable melting process can be performed in that area. Local preheating only sinters the powder in a small area where the melt sequence is going to take place. A preheating scheme was developed for the NbC powder in order to decrease the amount of spatter seen during melting and to avoid smoking. The aim of the study was to find out how the different process parameters, mainly electron beam power and scan speed, would affect melting of NbC powder, and to study its feasibility as a source material for EB-PBF additive manufacturing process. Characterization of the top surfaces of the melted regions reveal that too much energy input will cause swelling or / and can push the material toward the scan line direction. Low energy input results in a surface which is barely or not melted with powder particles had not fully consolidated into a squares. When melted regions have smooth surface with straight and consistent lines, the corresponding sets of electron beam parameters are considered to be in optimal range. The parameter sets with the highest line energy density (lower speed and higher power) sunk into the powder forming craters forming an uneven surface. The best surface properties could generally be seen at powers below 800 W for the studied interval. Lower scan speeds also had some contribution to better surface characteristics but could also lead to over-melting then the power was above 800 W. Higher power could potentially be used in combination with higher scan speed for a faster process as long as the linear energy density remains approximately the same. In PBF the melt depth is a very important parameter in getting a fully merged layers and as a result consolidated bodies in the actual printing process. Usually finding the optimal sets of parameters for a PBF requires some tradeoffs between surface roughness, amount of pores in the printed body and printing time. It can be seen from the optical microscopy cross-section images (images are not shown in the present disclosure) that electron beam power has a large effect on the melt depth. The melt depth was 202 μm at 400 W and 374 μm at 800 W. Pores can be observed in the images of the melted regions, which can be caused by trapped gas during the melting process as well as semi-consolidated powder particles which have not fully melted. The melted regions have more pores at the bottom of the melted areas compared to the top. As power increases, the quantity of small pores tends to decrease, whereas the impact on the quantity of larger pores is not as pronounced, as evident in the cross-section images. This potentially shows that higher power is preferred compared to lower power as less pores will appear in the melted regions. Speed was the other parameter studied in this work, where 300 mm / s and 600 mm / s were used at the constant power of 400 W. The powder bed was affected by the scanning speed, but not to the same extent as by the power. Increasing the energy density by decreasing the speed could potentially lead to pores or bubbles having enough time to migrate to the surface and out from the melted pools instead of being trapped there. Thus, adding more energy by reducing scanning speed could contribute to a better microstructure with less pores. The line energy input was calculated according to Equation 1: Increasing energy input in general will lead to deeper melts. The dependence of the melt depth on the line energy is shown in Figure 4. The results are fitted with the linear function. The melt depth has different dependence on the electron beam power and scan speed as it can be seen from the contour plot in Figure 5. There are other parameters such as spot size and height offset that also can have an effect on the results of the trials. The spot size was kept constant in terms of the settings used in Freemelt ONE system, but the size of the actual beam may vary over time due to system instabilities. Nominally, the spot size when melting the powder was around 280 μm. The difference in spot size will have an effect on the energy density impinging the powder bed surface and therefore could contribute to slightly different results among the trials. The preheating is another factor that could affect the results. Different preheating parameters were needed in order to prevent smoke event and spatter of the powder during the melting process. These tests aim to determine the feasibility of melting NbC using an electron beam and evaluate the possibility of printing this material using EB- PBF additive manufacturing process. The melt depth and surface character of the melted regions was investigated to determine if some of the parameter sets could be used in a real printing process. The test show that NbC has sufficient physical properties in terms of thermal and electrical conductivity making it suitable for 3D printing using EB- PBF. It is also suggested that tantalum carbide (TaC) could be equally feasible for printing, due to it’s similarity to NbC. Another conclusion is that the melt depth was more affected by the electron beam power than the scan speed. Modifications and other variants of the described embodiments will come to mind to ones skilled in the art having benefit of the teachings presented in the foregoing description and associated drawings. Therefore, it is to be understood that the embodiments are not limited to the specific example embodiments described in this disclosure and that modifications and other variants are intended to be included within the scope of this disclosure. Furthermore, although specific terms may be employed herein, they are used in a generic and descriptive sense only and not for purposes of limitation. Therefore, persons skilled in the art would recognize numerous variations to the described embodiments that would still fall within the scope of the appended claims. As used herein, the terms “comprise / comprises” or “include / includes” do not exclude the presence of other elements or steps. Furthermore, although individual features may be included in different claims (or embodiments), these may possibly advantageously be combined, and the inclusion of different claims (or embodiments) does not imply that a certain combination of features is not feasible and / or advantageous. In addition, singular references do not exclude a plurality. Finally, reference numerals in the claims are provided merely as a clarifying example and should not be construed as limiting the scope of the claims in any way.

Claims

CLAIMS 1. An additive manufacturing material composition, configured to be used in an additive manufacturing process or equipment, comprising: any one of a metal carbide powder and a metal nitride powder, wherein said metal is selected from the group consisting of niobium, tantalum, tungsten, hafnium, and zirconium, or combinations or mixtures of thereof.

2. The additive manufacturing material composition as claimed in claim 1, wherein said additive manufacturing material composition comprises a metal carbide powder.

3. The additive manufacturing material composition as claimed in claim 1 or 2, further comprising any one of a silicon powder or a silicon carbide powder, or a mixture thereof.

4. The additive manufacturing material composition as claimed in any one of claims 1 to 3, wherein said metal carbide powder or metal nitride powder has mean size of particles in the range of 1 to 150 µm, or in the range of 40 to 100 µm.

5. The additive manufacturing material composition as claimed in any one of the preceding claims, wherein the material comprises a mixture of powders having at least two different mean particle sizes.

6. The additive manufacturing material composition as claimed in any of claims 1 to 5, wherein said composition is substantially free from cobalt, boron and aluminum 7. The additive manufacturing material composition as claimed in any one of the preceding claims, wherein the melting point at normal conditions of said metal carbide powder is in the range of 2500 to 4000 °C.

8. The additive manufacturing material composition as claimed in any of the preceding claims, wherein said composition comprises at least 50 wt- % of said metal carbide or said metal nitride, or at least 70 wt-% of said metal carbide or said metal nitride, or at least 80 wt-% metal carbide or metal nitride, or at least 90 wt-% metal carbide or metal nitride, or at least 95 wt-% metal carbide or metal nitride.

9. An object comprising the additive manufacturing material composition as claimed in any one of claims 1 to 8, wherein said object comprises at least 50 wt-% metal carbide or metal nitride, and wherein said object is configured for a crucible (2) or reactor (1), which crucible or reactor is adapted to be heated to a temperature in the range of 800°C to 1500°C, or in a range of 1500°C to 1800°C, or to at least 1800°C.

10. Method for additive manufacturing, wherein said method comprises: providing a digital model of an object to be printed; providing the additive manufacturing material composition as claimed in any of claims 1 to 9; performing an additive manufacturing operation by an additive manufacturing equipment to form said object from said additive manufacturing material composition.

11. The method as claimed in claim 10, wherein said additive manufacturing equipment comprises any one of an electron beam and a laser beam.

12. The method as claimed in any one of claim 10 or 11, wherein said additive manufacturing operation is performed by solidifying areas of consecutive said additive manufacturing material composition layers, where at least one electron beam, or laser beam, successively irradiates predetermined sections of each layer, and wherein said method furthercomprises removing the remaining additive manufacturing material composition to form said object.

13. The method as claimed in any one of claims 10 to 12, wherein said additive manufacturing method comprises: providing said additive manufacturing material composition in a core of a plastic tube; and performing said additive manufacturing operation to form said object with said plastic tube.

14. The method as claimed in any one claims 10 to 13, wherein said additive manufacturing operation is followed by a subsequent material treatment.

15. The method as claimed in any one of claims 10 to 14, wherein said subsequent material treatment comprises sintering, and / or grinding and / or polishing.

16. The method as claimed in any one of claims 14 to 15, wherein said subsequent material treatment comprises annealing at high temperatures.

17. The method as claimed in any one of claims 10 to 16, wherein said additive manufacturing material composition further comprises re- cycled material from a previously manufactured object, and wherein said previously manufactured object was formed from an additive manufacturing material composition as claimed in any one of claims 1 to 9 in an additive manufacturing operation.

18. The method as claimed in claim 17, wherein the method further comprises milling or grinding said previously manufactured object to a powder having a mean size distribution of particles in the range of 1 to 150 µm.

19. The method as claimed in any one of claims 17 to 18 , wherein said method further comprises mixing said powder from said previously manufactured object with an virgin additive manufacturing material composition.

20. The method as claimed in any one of claims 10 to 19, wherein the method comprises pre-heating of the additive manufacturing material globally and / or locally, prior to performing said additive manufacturing operation.

21. An object manufactured in the method according to any one of claims 10 to 20.

22. The object as claimed in claim 21, wherein said object comprises at least 50 wt-% metal carbide or metal nitride, or at least 70 wt-% metal carbide or metal nitride, or at least 80 wt-% metal carbide or metal nitride, or at least 90 wt-% metal carbide or metal nitride, or at least 95 wt-% metal carbide or metal nitride.

23. Use of an object as claimed in claims 21 or 22 in a crucible (2) or reactor (1) adapted to be heated to a temperature in the range of 800°C to 1500°C, or in a range of 1500°C to 1800°C, or to at least 1800°C.

24. Use of an object as claimed in claim 21 or 22, wherein said object is any one of main body of silicon carbide growth crucible (2) or parts of it, seed holder (7) or parts of it, silicon carbide source container (10) or parts of it, porous membrane (9) or parts of it, crucible lid (5) or parts of it, crystal guide (8) or parts of it.

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