Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B22—CASTING; POWDER METALLURGY
  • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
  • B22F10/00—Additive manufacturing of workpieces or articles from metallic powder
  • B22F10/20—Direct sintering or melting
  • B22F10/28—Powder bed fusion, e.g. selective laser melting [SLM] or electron beam melting [EBM]
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B22—CASTING; POWDER METALLURGY
  • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
  • B22F10/00—Additive manufacturing of workpieces or articles from metallic powder
  • B22F10/30—Process control
  • B22F10/34—Process control of powder characteristics, e.g. density, oxidation or flowability
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
  • B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
  • B29C64/00—Additive manufacturing, i.e. manufacturing of three-dimensional [3D] objects by additive deposition, additive agglomeration or additive layering, e.g. by 3D printing, stereolithography or selective laser sintering
  • B29C64/10—Processes of additive manufacturing
  • B29C64/141—Processes of additive manufacturing using only solid materials
  • B29C64/153—Processes of additive manufacturing using only solid materials using layers of powder being selectively joined, e.g. by selective laser sintering or melting
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B33—ADDITIVE MANUFACTURING TECHNOLOGY
  • B33Y—ADDITIVE MANUFACTURING, i.e. MANUFACTURING OF THREE-DIMENSIONAL [3-D] OBJECTS BY ADDITIVE DEPOSITION, ADDITIVE AGGLOMERATION OR ADDITIVE LAYERING, e.g. BY 3-D PRINTING, STEREOLITHOGRAPHY OR SELECTIVE LASER SINTERING
  • B33Y10/00—Processes of additive manufacturing
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B33—ADDITIVE MANUFACTURING TECHNOLOGY
  • B33Y—ADDITIVE MANUFACTURING, i.e. MANUFACTURING OF THREE-DIMENSIONAL [3-D] OBJECTS BY ADDITIVE DEPOSITION, ADDITIVE AGGLOMERATION OR ADDITIVE LAYERING, e.g. BY 3-D PRINTING, STEREOLITHOGRAPHY OR SELECTIVE LASER SINTERING
  • B33Y70/00—Materials specially adapted for additive manufacturing
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B33—ADDITIVE MANUFACTURING TECHNOLOGY
  • B33Y—ADDITIVE MANUFACTURING, i.e. MANUFACTURING OF THREE-DIMENSIONAL [3-D] OBJECTS BY ADDITIVE DEPOSITION, ADDITIVE AGGLOMERATION OR ADDITIVE LAYERING, e.g. BY 3-D PRINTING, STEREOLITHOGRAPHY OR SELECTIVE LASER SINTERING
  • B33Y80/00—Products made by additive manufacturing
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C1/00—Making non-ferrous alloys
  • C22C1/04—Making non-ferrous alloys by powder metallurgy
  • C22C1/045—Alloys based on refractory metals
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C27/00—Alloys based on rhenium or a refractory metal not mentioned in groups C22C14/00 or C22C16/00
  • C22C27/04—Alloys based on tungsten or molybdenum
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C29/00—Alloys based on carbides, oxides, nitrides, borides, or silicides, e.g. cermets, or other metal compounds, e.g. oxynitrides, sulfides
  • C22C29/12—Alloys based on carbides, oxides, nitrides, borides, or silicides, e.g. cermets, or other metal compounds, e.g. oxynitrides, sulfides based on oxides
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B22—CASTING; POWDER METALLURGY
  • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
  • B22F1/00—Metallic powder; Treatment of metallic powder, e.g. to facilitate working or to improve properties
  • B22F1/06—Metallic powder characterised by the shape of the particles
  • B22F1/065—Spherical particles
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B22—CASTING; POWDER METALLURGY
  • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
  • B22F2301/00—Metallic composition of the powder or its coating
  • B22F2301/20—Refractory metals
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
  • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
  • Y02P10/00—Technologies related to metal processing
  • Y02P10/25—Process efficiency

Definitions

• the invention relates to a component with the features of the preamble of claim 1, an additive manufacturing process for producing a component with the features of the preamble of claim 16 and a use of a powder for an additive manufacturing process.
• molybdenum (Mo), tungsten (W) and their alloys are used for various high-performance applications, such as for X-ray anodes, heat sinks, high-temperature heating zones, thrusters, extrusion dies, and parts for injection molds , Hot runner nozzles, resistance welding electrodes or components for ion implantation systems.
• Mo molybdenum
• W tungsten
• these elements have a high density, which ensures good shielding behavior from electromagnetic and particle radiation. These are due to the comparatively low ductility at room temperature and the high DBTT (Ductile Brittle Transition Temperature)
• Additive manufacturing processes do not require any cutting or shaping tools, which enables low-cost production of components.
• component geometries can be realized that cannot be manufactured with conventional manufacturing processes or only with great effort.
• high resource efficiency is achieved because powder particles that have not melted or sintered together can be reused.
• a disadvantage of these processes is currently the very low build-up rate.
• WO2012055398 discloses a selective laser melting process for refractory metals, the composition of the material being changed by reaction with a reactive gas contained in the atmosphere during the construction of the component can.
• the most common additive manufacturing process is the selective laser beam melting process (SLM).
• SLM selective laser beam melting process
• a powder layer is applied to a surface using a doctor blade.
• a laser beam is then passed over this layer of powder.
• a layer of the component to be manufactured is thus created by successive local melting of powder particles and subsequent solidification.
• Another layer of powder is then applied to the already processed layer of powder and the process begins again.
• the component is thus built up with each new powder layer, the direction of construction being arranged normal to the respective levels of the powder layers. Since the additive manufacturing process forms a characteristic microstructure, it is possible for a person skilled in the art to recognize whether a component is manufactured by a conventional or an additive process.
• Molybdenum and tungsten have a high melting point, high thermal conductivity in the solid phase and high surface tension and viscosity in the liquid phase. These materials are among the most difficult to process using an additive manufacturing process.
• the balling effect also has a negative effect on the surface quality, especially on the surface roughness. Since molybdenum and tungsten have a very low fracture toughness, local defects, combined with the inherent, thermally induced stresses inherent in the process, lead to cracks.
• Components made of molybdenum and tungsten produced by selective laser or electron beam melting show a stem-crystalline structure, whereby the average grain aspect ratio (Grain Aspect Ratio - GAR value; ratio of grain length to grain width) is typically greater than 8 in the direction of assembly.
• an intercrystalline crack network is formed, which depicts the melting trace of the laser or electron beam.
• the cracks are mainly intergranular hot and cold cracks. These are partially connected to each other, which means that components often have open porosity and are not sealed against gases and liquids. If the component is subjected to stress, there is generally no plastic deformation and intercrystalline fracture behavior is predominantly observed.
• An intergranular fracture behavior is a fracture that is mainly caused by cracks along the grain boundaries. Due to this fracture behavior, components manufactured in this way have low fracture strength, low fracture toughness and low ductility.
• the object of the invention is to provide a generic component in which the problems discussed above are avoided, a generic additive manufacturing method for the reliable production of a component with the aforementioned properties and a powder which exhibits optimized behavior for use in an additive manufacturing method.
• components made of molybdenum, tungsten, molybdenum and tungsten-based alloys produced using beam-based additive manufacturing processes have an oxygen content of between 0.25 and 0.6 at%.
• oxygen content is not reduced by the additive manufacturing process, such as selective laser or electron beam melting.
• a high oxygen content also increases the balling effect.
• the oxygen is enriched in the edge area of the melting zone and reduces the surface tension there. Marangoni convection thus favors a material flow from the edge area into the center of the melting zone, which significantly increases the balling triggered by the Plateau-Rayleigh instability.
• a component according to the invention is therefore characterized in that the component has an alloy element or a plurality of alloy elements which, in the case of molybdenum and the molybdenum-based alloy, for M0O2 and / or M0O3, in the case of tungsten and the tungsten-based alloy for WO2 and / or WO3 and in the case of the molybdenum-tungsten-based alloy for at least one oxide of the group M0O2, M0O3, WO2 and WO3 have or have a reducing effect at least in the temperature range> 1500 ° C., the or at least one of the alloying element (s) being present both in at least partially non-oxidized form and in oxidized form.
• alloy element in the singular also includes several alloy elements which have a reducing effect on molybdenum and / or tungsten.
• the alloying element can be either elementary or as a component of a compound. It should be clarified that gases such as hydrogen are usually not referred to as alloying elements and also in the sense of this invention.
• gases such as hydrogen are usually not referred to as alloying elements and also in the sense of this invention.
• the invention also requires that the alloying element be present both in at least partially non-oxidized form and in oxidized form. This means that the oxidized form of the alloy element in the component is in the solid state.
• the basic idea of the invention is to reduce the formation of molybdenum or tungsten oxides, in particular at the grain boundaries, by offering oxygen in the form of the reducing, at least one alloying element, a more attractive reaction partner. It is therefore not the oxygen content of the component that is reduced, but rather the oxygen is at least partially, preferably largely, in a solid oxide form (at room temperature) formed with the alloy element (s). The oxygen bound in this way can no longer have an adverse effect on the grain boundary strength.
• Suitable alloying elements with a reducing effect can easily be found by the person skilled in the art in tables. With the help of Gibb's energy (free enthalpy) or with the help of the Richardson-Ellingham diagram, the elements that have a reducing effect on molybdenum or tungsten oxide can be found on the basis of the differences between their free standard enthalpies of formation. This makes it possible in a simple manner to find elements which are suitable as reducing agents for molybdenum or tungsten oxide.
• the alloying element preferably has a reducing effect for all molybdenum oxides (for example M0O2, M0O3) or for all tungsten oxides (for example WO2, WO3), regardless of their stoichiometry.
• the alloying element can reliably bind the oxygen in the form of an oxide, the alloying element must be at least in the temperature range> 1500 ° C for Molybdenum or tungsten oxide have a reducing effect. At temperatures ⁇ 1500 ° C the reaction kinetics are too low, so that a sufficient reduction of molybdenum or tungsten oxide no longer occurs.
• the alloying element preferably has a reducing effect for molybdenum or tungsten oxide in the temperature range from room to liquidus temperature of the molybdenum or tungsten alloy.
• the proof that the alloying element is present in the component in at least partially non-oxidized and in oxidized form can be done by conventional methods, such as XRD, micro-probe, ICP-OES, ICP-MS, RFA, REM / EDX, TEM / EDX and carrier gas hot extraction .
• the quantitative determination of the alloying element content takes place, for example, via ICP-OES or ICP-MS, the quantitative determination of the oxygen content by means of hot gas extraction or XRF.
• alloying element is present both in oxidized form and in non-oxidized form can be determined by XRD and, in the case of low contents, by spatially resolving methods, such as, for example, microsonde, REM / EDX or TEM / EDX.
• An additive manufacturing process is characterized in that the starting powder provided has at least one element which in the case of molybdenum and the molybdenum-based alloy for M0O2 and / or M0O3, in the case of tungsten and the tungsten-based alloy for WO2 and / or WO3 and in the case of the molybdenum-tungsten-based alloy for at least one oxide of the group M0O2, M0O3, WO2 and WO3, has a reducing effect at least in the temperature range> 1500 ° C. and is present in the starting powder provided in at least partially non-oxidized form and that in produced component, the or at least one of the alloy element (s) is at least partially present as an oxide.
• the at least one alloy element can be either elementary or as a component of a compound.
• the material used, from which the component is made is preferably a powder.
• All of the jet-based additive manufacturing methods known in the prior art in particular those in which a large number of individual powder particles are melted together to form a solid structure by an energy-rich jet, can be used in the invention.
• the step of providing the starting powder can include spheroidizing the particles in the melting phase. When spheroidizing in the melting phase, a high cooling rate is achieved due to the small particle volume without additional measures. This leads to a very uniform distribution of the alloy element, for example in that the alloy element is present in the Mo or W crystal lattice in a forcibly dissolved manner or is precipitated in the form of very small particles. The reducing alloying element is thus homogeneously distributed in the powder particles.
• the homogeneous distribution ensures that the alloying element is present at every point of the component and can bind the oxygen in the form of an oxide.
• spheroidized powders show very good powder loading behavior over the melting phase. It is thus possible to achieve powder layers with a uniform surface coverage.
• the step of providing the starting powder can also include granulating a raw powder to which the at least one reducing element (which is then present in the finished component as at least one alloy element) is added.
• Granulation is the aggregation and binding together of finely dispersed primary particles to form larger powder particles.
• a homogeneous granulate can be produced. Compared to a ground powder, granulated powder particles have a good flow behavior, which makes it possible to apply a uniform layer of powder.
• a high oxygen content and other impurities in the powder which can be attributed to abrasion from the grinding unit, are avoided.
• fine carbides, nitrides or borides smaller than 1 micrometer are formed during the melting process, which have a grain-refining effect and thus increase the toughness of the processed material. At the same time, they lead to an increase in strength.
• a powder for use according to the invention in an additive manufacturing method is characterized in that the powder is an element or has several elements, which in the case of molybdenum and the molybdenum-based alloy for M0O2 and / or M0O3, in the case of tungsten and the tungsten-based alloy for WO2 and / or WO3 and in the case of the molybdenum-tungsten-based alloy for at least an oxide of the group M0O2, M0O3, WO2 and WO3, has a reducing effect at least in the temperature range> 1500 ° C, and that the or at least one of the reducing element (s) (which (s) in the component as an alloy element ( e) is or are present) is at least partially unoxidized.
• the at least one reducing element can be either elementary or as a component of a compound.
• the or at least one of the reducing element (s) in the powder is partially dissolved in a phase rich in molybdenum or tungsten, preferably to more than 50 at%.
• Molybdenum-based alloy is an alloy that contains at least 50 at% molybdenum. In particular, a molybdenum-based alloy has at least 80, 90, 95 or 99 at% molybdenum. A tungsten-based alloy contains at least 50 at% tungsten. In particular, a tungsten-based alloy has at least 80, 90, 95 or 99 at% tungsten. A molybdenum-tungsten alloy is understood to mean an alloy which has at least 50 at% molybdenum and tungsten in total, in particular at least 80, 90, 95 or 99 at% molybdenum and tungsten in total. Molybdenum-tungsten alloys are a preferred embodiment in all concentration ranges.
• the individual powder particles are preferably melted using an additive manufacturing process, SLM (selective laser beam melting) or SEBM (selective electron beam melting) advantageously being used.
• SLM selective laser beam melting
• SEBM selective electron beam melting
• the component is preferably built up in layers.
• a powder layer is applied to a base plate using a doctor blade.
• the powder layer generally has a height of 10 to 150 micrometers.
• the powder particles are first sintered together with a defocused electron beam. Then by energy input (by means of Electron beam) locally melted the powder. With the SLM, the local melting of the powder can be started immediately by energy input (using a laser beam).
• the beam creates a cellular melt trace pattern with a line width of typically 30 microns to 200 microns.
• the laser or electron beam is guided over the powder layer.
• the entire powder layer or only part of the powder layer can be melted and subsequently solidified by suitable beam guidance.
• the melted and solidified areas of the powder layer are part of the finished component.
• the unmelted powder is not part of the manufactured component.
• a further layer of powder is then applied by means of a doctor blade and the laser or electron beam is again guided over this layer of powder.
• a so-called scan structure is formed in each powder layer.
• a typical layer structure also forms in the direction of construction, which is determined by the application of a new powder layer. Both the scan structure and the individual layers can be recognized on the finished component.
• the structure of powder particles melted together selectively into a solid structure by means of an additive manufacturing process by means of an energy-rich beam (preferably by means of a laser or electron beam) differs significantly from a structure produced by other processes, for example thermal spraying.
• thermal spraying individual spray particles are accelerated in a gas stream and hurled onto the surface of the component to be coated.
• the spray particles can be in the form of melted or melted (plasma spraying) or solid (cold gas spraying).
• a layer formation takes place because the individual spray particles flatten out when they hit the component surface, stick mainly through mechanical clamping and build up the spray layer in layers.
• a plate-like layer structure is formed.
• Layers produced in this way have a grain stretching perpendicular to the building direction in a plane parallel to the building direction with an average grain stretching ratio (Grain Aspect Ratio - GAR value; ratio of grain length to grain width) well over 2 and thus differ significantly from over selective Layers / components produced by laser or electron beam melting, which also have an average grain stretching ratio significantly above 2 in one plane parallel to the building direction, but with a grain stretching parallel to the building direction.
• GABA Aspect Ratio - GAR value average grain stretching ratio
• At least one of the alloy elements in the component is partially dissolved, preferably more than 50 at% dissolved, in a phase rich in molybdenum or tungsten.
• the at least one alloy element is present in every area of the component in sufficient quantity to be able to bind the oxygen in the form of an oxide. While the oxygen in the form of a molybdenum and / or tungsten oxide covers the grain boundaries over a large area and, as described, greatly reduces the grain boundary strength, the oxygen in the component according to the invention is present as an oxide which is locally bound by the at least one alloy element and does not cover the grain boundaries.
• At least one of the alloy elements is a metallic alloy element.
• This alloy element is preferably at least partially soluble in molybdenum and / or tungsten.
• At least one of the alloy elements is an element of group 2, 3 or 4 of the periodic table, preferably titanium, zirconium or hafnium. These alloying elements are characterized by a strong affinity for oxygen.
• the component contains an oxide which has a melting point> 1800 ° C., in particular> 2600 ° C.
• Preferred oxides are T1O2 (melting point: 1843 ° C), ZrÜ2 (melting point: 2715 ° C) or Hf0 2 (melting point: 2758 ° C). These oxides have a low tendency to coarsen. In addition to the grain-refining, toughness-increasing effect, there is also a strength-increasing effect in the component, particularly at high operating temperatures. Mixed oxides containing T1O2, ZrÜ2 or Hf0 2 also have the aforementioned positive effects.
• the content of the at least one alloy element in the component in non-oxidized and oxidized form is in a range from 0.05 at% to 20 at%, preferably from 0.1 at% to 10 at %, lies.
• the effect according to the invention does not occur to a sufficient extent below 0.05 at%. Above 20 at%, the strength-increasing effect of the at least one alloy element is strongly pronounced, as a result of which stresses in the building-up process are reduced to a reduced extent.
• the carbon content in the component is in a range from 0.05 at% to 20 at%.
• the carbon is preferably present in the form of Mo 2 C, in the case of tungsten preferably in the form of W 2 C.
• Mo 2 C and W 2 C have a solubility for oxygen at temperatures that occur in the component to be manufactured during the additive manufacturing process. This also makes it possible to avoid covering grain boundaries with molybdenum oxide or tungsten oxide and their resulting weakening.
• carbon in both molybdenum and tungsten and their alloys causes grain refinement through constitutional hypothermia during the solidification of the material melted by the energy beam.
• below 0.05 at% the effect is only weakly pronounced, above 20 at% there is strong consolidation, which affects the reduction of thermally induced stresses.
• the molybdenum content, the tungsten content or the total content of molybdenum and tungsten is greater than 60 at%, preferably greater than 80 at%, particularly preferably greater than 90 at% or 95 at%.
• the component has a fracture behavior with a transcrystalline fraction of more than 50%, preferably more than 80%, particularly preferably more than 90%, of the fracture surface at least in one fracture plane.
• Transcrystalline fracture behavior means that if the component breaks due to overloading, the crack does not run along the grain boundaries, but mainly through the grains.
• the transcrystalline fraction is evaluated by scanning electron microscopic examination of a fracture surface generated at room temperature. Here, the area with transcrystalline and the area with intergranular fracture behavior are measured at a representative point on the fracture surface and the transcrystalline fraction is determined from the ratio of the transcrystalline surface to the total surface examined.
• the component is manufactured in layers in one direction of construction and preferably has an average grain extension in a plane parallel to the direction of construction less than 5, preferably less than 3.
• a high grain stretch ratio parallel to the direction of the structure favors an intercrystalline fracture course along the grain boundaries, which essentially extend in the direction of the structure, when the loads are perpendicular to the direction of the structure, since the fracture path is short and thus the fracture surface generated (due to the directional course of the grain boundaries) is small.
• a small grain stretch ratio ensures that there is sufficient fracture toughness even under such loads perpendicular to the direction of construction. This ensures an isotropy of the mechanical properties that is sufficient for the customarily required performance properties.
• the component has a fine-grained structure with an average grain area of less than 10,000, in particular less than 1,000, square micrometers.
• the component has high strength and toughness combined with high ductility.
• the grain area is determined by quantitative microscopy (stereology) using planimetry.
• the component contains fine carbide, nitride or boride particles, preferably with an average size smaller than 1 micrometer. On the one hand, these particles increase the strength and, on the other hand, they can also have a grain-refining effect, which increases the fracture toughness.
• the fine particles are preferably carbides, nitrides or borides of the reducing alloying element.
• the oxidized form of the at least one alloy element in the component is in the form of fine oxide precipitates with an average size of less than 5 micrometers, preferably ⁇ 1 micrometer.
• the oxides are preferably formed by reaction of the at least one alloy element with the oxygen in the material during the additive manufacturing process. These oxides can have a nucleating effect, as a result of which the component has an advantageously fine structure with high strength and toughness.
• the sum of all reducing alloying elements in at% (based on the composition of the starting powder) in the starting powder is at least 50% higher, preferably at least 100% higher, like an oxygen content of the starting powder in at% (based on the composition of the Starting powder).
• the sum of all metallic alloy elements or reducing elements in at% is at least 50% higher, preferably at least 100% higher than an oxygen content of the component in at%.
• FIG. 1 shows a schematic representation of the SLM process
• FIG. 2 Optical microscope image of a Mo sample produced using SLM according to the prior art (sample number 1) with a ground plane perpendicular to the direction of assembly (FIG. 2a) and parallel to the direction of assembly (FIG. 2b)
• FIG. 3 scanning electron microscope image of a fracture surface according to the prior art (sample number 1)
• FIG. 4 Light microscope image of a sample according to the invention (sample number 4) produced by SLM with a ground plane perpendicular to the direction of assembly
• Spheroidized Mo powder of the sieve fraction ⁇ 40 micrometers was used for a sample not according to the invention.
• the SLM process is shown schematically in FIG. 1.
• a control system controls u. a. the laser 1, the laser mirror 2, the doctor blade 3, the powder feed 4 from a powder storage container 6 and the position of the base plate 5 in the installation space 7.
• the installation has an installation space heater.
• the Mo base plate was heated to 500 ° C.
• a powder layer was applied using the doctor blade 3.
• the laser beam guided with the help of the laser mirror 2 scanned over the powder layer and melted the particles and partially the underlying, already melted and solidified layer where there is material according to the component design (component 8).
• the base plate 5 was lowered by 30 micrometers and the doctor blade 3 applied another layer of powder and the process flow started again.
• the samples were separated from the base plate 5 by wire erosion and the sample density of the 10 mm ⁇ 10 mm ⁇ 10 mm samples was determined by the buoyancy method (hydrostatic weighing), open pores being previously closed by immersion in molten paraffin.
• the samples were examined metallographically.
• the 35 mm x 8 mm x 8 mm samples (3 parallel samples) were Point subjected to bending test.
• the fracture surface of the bending samples was examined by scanning electron microscopy and the proportion of intercrystalline or transcrystalline fracture surface was determined.
• FIG. 2 shows the structure of the Mo sample according to the prior art (sample number 1).
• the ground plane is perpendicular in FIG. 2a and parallel to the direction of construction in FIG. 2b.
• the sample has many pores and tiled intercrystalline cracks, which depict the scan structure of the process.
• the structure is formed like a stem crystal parallel to the direction of construction.
• the grain stretching ratio was determined by image analysis by determining the mean grain length and the mean grain width and subsequently dividing the mean grain length by the mean grain width. A grain stretch ratio of 8 was calculated.
• the flexural strength of the sample is shown in Table 2.
• the low value is due to the low grain boundary strength.
• the proportion of intergranular fracture is 95%.
• the scanning electron microscope examination of the fracture surface shows that the grain boundaries are covered with Mo oxide precipitates (FIG. 3).
• spheroidized powders (sample numbers 2, 3 and 4) of the sieve fraction ⁇ 40 pm were used over the melting phase.
• the chemical and physical powder properties are shown in Table 1. These powders were processed with typical parameters for the volume build-up of molybdenum at an installation temperature of 800 ° C.
• the samples for the structure characterization and the determination of the density had dimensions of 10 mm x 10 mm x 10 mm.
• the bending samples had a size of 35 mm x 8 mm x 8 mm.
• the bending strength in the samples according to the invention is about a factor of 10 higher than in the sample according to the prior art.
• the dominant fracture mechanism in all samples is a transcrystalline fracture.
• a small proportion (3%) of intercrystalline fracture surface could be detected in the samples with sample numbers 2 and 3, the grain boundaries being aligned in the plane of the transcrystalline fracture path in this area. No Mo oxide could be detected in these areas by energy-dispersive X-ray spectroscopy (EDX).
• EDX energy-dispersive X-ray spectroscopy
• the sample with sample number 4 shows only transcrystalline fracture. XRD examinations show the phases Mo and Hf0 2 for the sample with sample number 2, the phases Mo and ZrC> 2 for the sample with sample number 3 and the phases Mo and T1O2 for the sample with sample number 4.

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• 2018
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• 2019
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• 2023
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