ADDITIVELY MANUFACTURED REFRACTORY METAL COMPONENT, ADDITIVE MANUFACTURING PROCESS AND POWDER

Abstract

A component has a solid structure that is manufactured using a laser or electron beam in an additive manufacturing process. The solid structure is formed from at least one material selected from the group consisting of molybdenum, a molybdenum-based alloy, tungsten, a tungsten-based alloy, and a molybdenum-tungsten-based alloy. The component includes one or more alloying element which at least in the temperature range 1500° C. has/have a reducing effect, as follows: in the case of molybdenum and the molybdenum-based alloy, for MoO.sub.2 and/or MoO.sub.3; in the case of tungsten and the tungsten-based alloy, for WO.sub.2 and/or WO.sub.3; and, in the case of the molybdenum-tungsten-based alloy, for at least one oxide from the group of MoO.sub.2, MoO.sub.3, WO.sub.2 and WO.sub.3. The alloying element, or at least one of the alloying elements, is present both in at least partially unoxidized form and in oxidized form.

Claims

1-20. (canceled)

21. A component, comprising: a solid structure having the characteristics of having been manufactured with a laser beam or electron beam in an additive manufacturing process from at least one material selected from the group consisting of molybdenum, a molybdenum-based alloy, tungsten, a tungsten-based alloy, and a molybdenum-tungsten-based alloy; said solid structure containing one or more alloying elements which have a reducing effect, at least in a temperature range 1500° C., for the following: in the case of molybdenum and the molybdenum-based alloy, for MoO.sub.2 and/or MoO.sub.3; in the case of tungsten and the tungsten-based alloy, for WO.sub.2 and/or WO.sub.3; and in the case of the molybdenum-tungsten-based alloy, for at least one oxide selected from the group consisting of MoO.sub.2, MoO.sub.3, WO.sub.2 and WO.sub.3; and wherein at least one of said one or more alloying elements is present both in at least partially unoxidized form and in oxidized form.

22. The component according to claim 21, wherein the at least one of said one or more alloying elements is partially dissolved in a molybdenum-rich or tungsten-rich phase.

23. The component according to claim 21, wherein the at least one of said one or more alloying elements is a metallic element.

24. The component according to claim 21, wherein the at least one of said one or more alloying elements is an element of group 2, 3 or 4 of the periodic table of elements.

25. The component according to claim 24, wherein the component contains TiO.sub.2, ZrO.sub.2 or HfO.sub.2.

26. The component according to claim 21, wherein a content of the at least one alloying element in the component in unoxidized and oxidized form lies in a range from 0.05 at % to 20 at %.

27. The component according to claim 21, wherein a content of carbon in the component lies in a range from 0.05 at % to 20 at %.

28. The component according to claim 27, wherein the carbon in the component is at least partially in carbide form.

29. The component according to claim 21, wherein a molybdenum content, a tungsten content, or a total content of molybdenum and tungsten is more than 60 at %.

30. The component according to claim 21, wherein the component has at least one fracture plane exhibiting a fracture behavior with a transcrystalline proportion of more than 50% of a fracture area.

31. The component according to claim 21, wherein the component has the characteristics of having been manufactured layer-wise in a build direction, with an average grain extent in a plane parallel to the build direction of less than 5.

32. The component according to claim 21, wherein said solid structure has a fine-grained microstructure with an average grain area of less than 10,000 μm.sup.2 (micrometers squared).

33. The component according to claim 21, wherein said solid structure contains fine carbide, nitride or boride particulates.

34. The component according to claim 21, wherein the oxidized form of said at least one alloying element is in the form of fine oxide precipitations having an average size of less than 5 μm.

35. The component according to claim 21, wherein a sum of all metallic alloying elements in said solid structure, in at %, is at least 50% higher than an oxygen content of the component, in at %.

36. An additive manufacturing method for producing a component, the method comprising: providing a starting powder of particles composed of at least one material selected from the group consisting of molybdenum, a molybdenum-based alloy, tungsten, a tungsten-based alloy, and a molybdenum-tungsten-based alloy; providing the starting powder with at least one element which, in a temperature range 1500° C., has a reducing effect in the case of molybdenum and molybdenum-based alloy for MoO.sub.2 and/or MoO.sub.3, in the case of tungsten and tungsten-based alloy for WO2 and/or WO.sub.3, and in the case of molybdenum-tungsten-based alloy for at least one oxide selected from the group consisting of MoO.sub.2, MoO.sub.3, WO.sub.2, and WO.sub.3, and wherein the at least one element is present in the starting powder in at least partially unoxidized form; layer-wise fusing the particles of the starting powder using a laser or electron beam; and forming the component with the or at least one of the alloying elements at least partially in the form of an oxide.

37. The method according to claim 36, which comprises providing the starting powder with a sum of all metallic reducing elements, in at %, at least 50% higher than an oxygen content of the starting powder, in at %.

38. A powder for an additive manufacturing process, the powder comprising: powder particles formed via granulation and/or melt phase; the powder particles including at least one material selected from the group consisting of molybdenum, a molybdenum-based alloy, tungsten, a tungsten-based alloy, and a molybdenum-tungsten-based alloy; one or more reducing elements which, at least in the temperature range 1500° C., have a reducing effect in the case of molybdenum and the molybdenum-based alloy for MoO.sub.2 and/or MoO.sub.3, 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 selected from the group consisting of MoO.sub.2, MoO.sub.3, WO.sub.2, and WO.sub.3; and at least one of said one or more reducing elements being present in at least partially unoxidized form in the powder.

39. The powder according to claim 38, wherein at least one of said one or more reducing elements in the powder is at least partially dissolved in a molybdenum-rich or tungsten-rich phase.

40. The powder according to claim 38, wherein a sum of all metallic reducing elements in at % is at least 50% higher than an oxygen content of the component in at %.

Description

[0053] Exemplary embodiments of the invention are discussed with reference to the figures.

[0054] FIG. 1: Schematic representation of the SLM process

[0055] FIG. 2: Optical micrograph of a prior art Mo specimen produced by SLM (specimen number 1) having a section plane perpendicular to the build direction (FIG. 2a) and parallel to the build direction (FIG. 2b)

[0056] FIG. 3: Scanning electron micrograph of a prior art fracture surface (specimen number 1)

[0057] FIG. 4: Optical micrograph of an inventive specimen produced by SLM (specimen number 4) having a section plane perpendicular to the build direction

PRIOR ART SPECIMEN (SPECIMEN NUMBER 1)

[0058] For a noninventive specimen spheroidized Mo powder in a sieve fraction <40 micrometers was used.

[0059] The chemical and physical powder properties are reported in table 1. With typical parameters for volume construction of molybdenum this powder was processed using a commercial SLM apparatus into specimens for microstructure characterization and determination of density having dimensions of 10 mm×10 mm×10 mm and into flexural specimens having dimensions of 35 mm×8 mm×8 mm.

[0060] A schematic diagram of the SLM process is shown in FIG. 1. A control system controls inter alia the laser 1, the laser mirror 2, the coating bar 3, the powder feed 4 from a powder reservoir container 6 and the position of the base plate 5 in the build space 7. The system has a build space heating means. For the experiments the Mo base plate was heated to

[0061] 500° C. A powder layer was applied using the coating bar 3. The laser beam guided using the laser mirror 2 scanned over the powder layer and thus melted the particles, and partially the previously melted and solidified layer therebelow, where material is present according to the component design (component 8). The base plate 5 was then lowered by 30 micrometers and the coating bar 3 applied a further powder layer and the process sequence was restarted.

[0062] The specimens were separated from the base plate 5 by wire erosion and the specimen density of the 10 mm×10 mm×10 mm specimens was determined by the buoyancy method (hydrostatic weighing), wherein open pores were closed beforehand by immersion in molten paraffin. The specimens were subjected to metallographic examination. The 35 mm×8 mm×8 mm specimens (3 parallel specimens) were subjected to a 3-point flexural test. The fracture surface of the flexural specimens was investigated by scanning electron microscopy and the proportion of intercrystalline/transrystalline fracture surface was determined.

[0063] FIG. 2 shows the microstructure of the prior art Mo specimen (specimen number 1). The section plane is perpendicular to the build direction in FIG. 2a and parallel to the build direction in FIG. 2b. The specimen exhibits many pores and intercrystalline cracks arranged in a tile-like manner which reproduce the scan structure of the process. The microstructure is in the form of columnar crystals parallel to the build direction. The grain aspect ratio was determined by image analysis by determining the average grain length and the average grain width and subsequently dividing the average grain length by the average grain width. A grain aspect ratio of 8 was calculated. The flexural strength of the sample is reported in table 2. The low value is attributable to the low grain boundary strength. The proportion of intercrystalline fracture is 95%. The scanning electron microscopic examination of the fracture surface shows that the grain boundaries are areally occupied with Mo oxide precipitations (FIG. 3).

[0064] Inventive Specimens:

[0065] For the inventive specimens powders spheroidized via the melt phase (specimen numbers 2, 3 and 4) in a sieve fraction <40 micrometers were used. The chemical and physical powder properties are reported in table 1. The processing of these powders was carried out at typical parameters for volume construction of molybdenum at a build space temperature of 800° C. The specimens for microstructure characterization and determination of density had dimensions of 10 mm×10 mm×10 mm. The flexural specimens had dimensions of 35 mm×8 mm×8 mm.

[0066] The SLM process and the characterization of the specimens were performed under identical conditions as described for the prior art specimens.

[0067] Metallographic examination of the specimen having specimen number 2 (Mo—0.55 at % Hf), the specimen having specimen number 3 (Mo—1.1 at % Zr) and the specimen having specimen number 4 (Mo—0.9 at % Ti—0.09 at % Zr—0.10 at % C) shows that all inventive specimens are crack-free as documented in exemplary fashion in FIG. 4 for the specimen having specimen number 4 via an optical micrograph (section plane perpendicular to build direction). The microstructure in a plane parallel to the build direction has an average grain aspect ratio of 3.8 (specimen having specimen number 2), 3.9 (specimen having specimen number 3) and 2.9 (specimen having specimen number 4).

[0068] The results of the chemical analysis, the flexural test and the evaluation of the fracture surface are reported in table 2.

[0069] The flexural strength of the inventive specimens is about 10 times higher than that of the prior art specimen. For all specimens the dominant fracture mechanism is transcrystalline fracture. In the specimens having specimen numbers 2 and 3 a small proportion (3%) of intercrystalline fracture surface was detected, wherein in this region the grain boundaries are oriented in the plane of the transcrystalline fracture path. Energy dispersive X-ray spectroscopy (EDX) did not detect any Mo Oxide in these regions. The specimen having specimen number 4 shows only transcrystalline fracture. XRD examinations show the phases Mo and HfO.sub.2 for the specimen having specimen number 2, the phases Mo and ZrO.sub.2 for the specimen having specimen number 3 and the phases Mo and TiO.sub.2 for the specimen having specimen number 4. SEM/EDX examinations detected HfO.sub.2 particulates in the specimen having specimen number 2, ZrO.sub.2 particulates in the specimen having specimen number 3 and TiO.sub.2 particulates in the specimen having specimen number 4. However, the larger volume fraction of the respective oxides was of a fineness such that the particle size was below the limit of detection of the SEM. Initial TEM examinations of the specimen having specimen number 4 detected particulates having an average size in the range of 30 nm.

TABLE-US-00001 TABLE 1 Specimen number 1 2 3 4 Chemical O: 0.28 at % Hf: 0.55 at % Zr: 1.1 at % Ti: 0.98 at % composition of the balance Mo and O: 0.29 at % O: 0.28 at % Zr: 0.09 at % starting powder other impurities balance Mo and balance Mo and C: 0.18 at % other impurities other impurities O: 0.21 at % balance Mo and other impurities Particle size 14.5 μm 13.2 μm 12.5 μm 12.8 μm distribution 25.9 μm 24.9 μm 24.1 μm 24.5 μm (d10/d50/d90) 45.7 μm 44.1 μm 42.8 μm 43.6 μm Poured 5.5 g/cm.sup.3 5.6 g/cm.sup.3 5.2 g/cm.sup.3 5.7 g/cm.sup.3 density/tapped 6 g/cm.sup.3 6.1 g/cm 5.9 g/cm 6.2 g/cm.sup.3 density

TABLE-US-00002 TABLE 2 Specimen number 1 2 3 4 Chemical O: 0.27 at % Hf 0.55 at % Zr: 1.1 at % Ti: 0.9 at % composition balance Mo and O: 0.28 at % O: 0.29 at % Zr: 0.09 at % other impurities balance Mo and balance Mo and C: 0.10 at % other impurities other impurities O: 0.12 at % balance Mo and other impurities Specimen density 9.79 g/cm.sup.3 10.04 g/cm.sup.3 9.90 g/cm.sup.3 10.12 g/cm.sup.3 3-point flexural 88 N/mm.sup.2 880 N/mm.sup.2 850 N/mm.sup.2 907 N/mm.sup.2 fracture strength (test force parallel to the build direction) Proportion of 5 97 97 100 transcrystalline fracture (fracture surface parallel to build direction)

LIST OF REFERENCE NUMERALS

[0070] 1 Laser [0071] 2 Laser mirror [0072] 3 Coating bar [0073] 4 Powder feed [0074] 5 Base plate [0075] 6 Powder reservoir container [0076] 7 Build space [0077] 8 Component