ODS alloy powder, method for producing same by means of plasma treatment, and use thereof

Abstract

A method for producing a reinforced alloy powder containing a metal matrix in which crystalline oxide particles are dispersed, including: (i) providing a powder mixture including a parent metal powder including a master alloy for forming the metal matrix and an additional powder including an intermediate; (ii) milling the powder mixture by a mechanical synthesis process to make a precursor powder; and (iii) subjecting the precursor powder to a thermal plasma generated by a plasma torch including a plasma gas. The master alloy is iron-based, nickel-based, or aluminum-based. The intermediate is at least one of YFe.sub.3, Y.sub.2O.sub.3, Fe.sub.2O.sub.3, Fe.sub.2Ti, FeCrWTi, TiH.sub.2, TiO.sub.2, Al.sub.2O.sub.3, HfO.sub.2, SiO.sub.2, ZrO.sub.2, ThO.sub.2, and MgO. In (iii), the precursor powder is injected into the plasma torch at a flow rate of 10-30 g/min, a power of the plasma torch is 20-40 kW, and a pressure in a reaction chamber of the plasma torch is 25-100 kPa.

Claims

1. A method for producing a reinforced alloy powder comprising particles each comprising a metal matrix and crystalline oxide particles dispersed in the metal matrix, the method comprising: (i) milling a powder mixture comprising (a) a parent metal powder comprising an iron-based alloy, a nickel-based alloy, or an aluminum-based alloy, as a master alloy, and (b) an additional powder comprising YFe.sub.3, Y.sub.2O.sub.3, Fe.sub.2O.sub.3, Fe.sub.3Ti, FeCrWTi, TiH.sub.2, TiO.sub.2, Al.sub.2O.sub.3, HfO.sub.2, SiO.sub.2, ZrO.sub.2, ThO.sub.2, and/or MgO, in a gaseous milling medium by a mechanical synthesis process, thereby producing a precursor powder comprising a metal matrix in which atoms of the additional powder are incorporated; and (ii) subjecting the precursor powder to a thermal plasma generated by a plasma torch comprising a plasma gas, thereby obtaining the reinforced alloy powder, the precursor powder being injected into the plasma torch via an injector at a flow rate in a range of from 10 to 19 grams/min, a plasma torch power in a range of from 20 to 40 kW, and a reaction chamber pressure in a range of from 25 to 100 kPa, an outside surface of the injector being swept with a sheath gas comprising a principal sheath gas and an additional sheath gas, the principal sheath being fed into the plasma torch, the additional sheath as having a hither thermal conductivity than the principal sheath gas and being infected into the plasma torch at a flow rate lower than a principal sheath as feed flow rate, wherein 80 to 100 wt. % of the particles of the reinforced alloy powder have an average circularity coefficient in a range of from 0.95 to 1.

2. The method of claim 1, wherein the master alloy is an iron-based alloy, and wherein the iron-based alloy comprises chromium in a range of from 10 to 30 wt. %.

3. The method of claim 1, wherein the master alloy is an iron-based alloy, and wherein the iron-based alloy comprises aluminum in a range of from 10 to 30 wt. %.

4. The method of claim 1, wherein the master alloy is an iron-based alloy, and wherein the iron-based alloy comprises chromium in a range of from 8 to 25 wt. % of and aluminum in a range of from 3 to 8 wt. %.

5. The method of claim 1, wherein the master alloy is an iron-based alloy, and wherein the iron-based alloy is a steel.

6. The method of claim 1, wherein the master alloy is a nickel-based alloy, and wherein the nickel-based alloy comprises chromium in a range of from 10 to 40 wt. %.

7. The method of claim 6, wherein the nickel-based alloy comprises the chromium in a range of from 10 to 40 wt. %, aluminum in a range of from 0.02 to 5 wt. %, titanium in a range of from 0.3 to 5 wt. %, tungsten in a range of from 0 to 5 wt. %, molybdenum in a range of from 0 to 2 wt. %, and tantalum in a range of from 0 to 2 wt. %.

8. The method of claim 1, wherein the master alloy is a nickel-based alloy, and wherein the nickel-based alloy comprises aluminum in a range of from 10 to 30 wt. %.

9. The method of claim 1, wherein the master alloy is an iron-based alloy or a nickel-based alloy, and wherein the powder mixture comprises the additional powder in a range of from 0.1 to 2.5 wt. %.

10. The method of claim 1, wherein the master alloy is an aluminum-based alloy, and wherein the aluminum-based alloy comprises iron in a range of from 0% to 0.5 wt. %, silicon in a range of from 0% to 0.3 wt. %, and magnesium in a range of from 0 to 1 wt. %.

11. The method of claim 1, wherein the master alloy is an aluminum-based alloy, and wherein the powder mixture comprises the additional powder in a range of from 0.2 to 5 wt. %.

12. The method of claim 1, wherein the powder mixture comprises the additional powder in a range of from 0.1 to 0.3 wt. %.

13. The method of claim 1, wherein the atoms of the additional powder incorporated in the metal matrix comprise yttrium, titanium, iron, chromium, tungsten, silicon, zirconium, thorium, magnesium, aluminum, and/or hafnium.

14. The method of claim 1, wherein the plasma torch is an inductively coupled radio frequency plasma torch, a blown arc torch, or a transferred arc torch.

15. The method of claim 1, wherein the plasma gas comprises argon, helium, and/or nitrogen.

16. The method of claim 1, wherein the plasma gas is injected into the plasma torch at a flow rate in grange of from 10 to 40 liters/min.

17. The method of claim 1, wherein, in the subjecting (ii), the plasma torch power is in a range of from 25 to 40 kW, and the reaction chamber pressure of the plasma torch is in a range of from 40 to 70 kPa.

18. The method of claim 1, wherein the additional sheath gas is injected at a flow rate in a range of from 1 to 40 liters/min.

19. The method of claim 1, wherein the principal sheath gas is argon.

20. The method of claim 1, wherein the additional sheath gas is helium, nitrogen, or hydrogen.

21. The method of claim 19, wherein the additional sheath gas is helium, nitrogen, or hydrogen.

22. The method of claim 20, wherein the principal sheath gas is argon, and wherein the additional sheath gas is helium or hydrogen.

23. The method of claim 1, wherein the atoms of the additional powder incorporated in the metal matrix comprise yttrium.

24. The method of claim 1, wherein the atoms of the additional powder incorporated in the metal matrix comprise titanium.

25. The method of claim 1, wherein the atoms of the additional powder incorporated in the metal matrix comprise iron.

26. The method of claim 1, wherein the atoms of the additional powder incorporated in the metal matrix comprise chromium.

27. The method of claim 1, wherein the atoms of the additional powder incorporated in the metal matrix comprise tungsten.

28. The method of claim 1, wherein the atoms of the additional powder incorporated in the metal matrix comprise silicon.

29. The method of claim 1, wherein the atoms of the additional powder incorporated in the metal matrix comprise zirconium.

30. The method of claim 1, wherein the atoms of the additional powder incorporated in the metal matrix comprise thorium or magnesium.

31. The method of claim 1, wherein the atoms of the additional powder incorporated in the metal matrix comprise aluminum.

32. The method of claim 1, wherein the atoms of the additional powder incorporated in the metal matrix comprise hafnium.

33. The method of claim 1, wherein the additional powder comprises YFe.sub.3.

34. The method of claim 1, wherein the additional powder comprises Y.sub.2O.sub.3.

35. The method of claim 1, wherein the additional powder comprises Fe.sub.2O.sub.3.

36. The method of claim 1, wherein the additional powder comprises Fe.sub.2Ti.

37. The method of claim 1, wherein the additional powder comprises FeCrWTi.

38. The method of claim 1, wherein the additional powder comprises TiH.sub.2.

39. The method of claim 1, wherein the additional powder comprises TiO.sub.2.

40. The method of claim 1, wherein the additional powder comprises Al.sub.2O.sub.3.

41. The method of claim 1, wherein the additional powder comprises HfO.sub.2.

42. The method of claim 1, wherein the additional powder comprises SiO.sub.2.

43. The method of claim 1, wherein the additional powder comprises ZrO.sub.2.

44. The method of claim 1, wherein the additional powder comprises ThO.sub.2.

45. The method of claim 1, wherein the additional powder comprises MgO.

Description

BRIEF DESCRIPTION OF THE FIGURES

(1) FIG. 1A (general view) and 1B (sectional view) show photographs obtained by scanning electron microscopy (SEM) of a precursor powder obtained after the milling step ii) of the method of production of the invention.

(2) FIG. 2A (general view), 2B and 3A (sectional view) as well as 3B (zoom view of a section focusing on the oxide precipitates) show SEM photographs of a powder of a reinforced alloy obtained after the plasma treatment step iii) of the method of production of the invention.

(3) FIG. 3C is a table giving molar atomic percentages obtained by energy dispersive X-ray spectrometry (EDX) in the oxide precipitates identified by the numerical indices 1 to 7 in FIG. 3B.

(4) FIGS. 4A and 4B show a bright-field TEM photograph of a section of an ODS alloy obtained by the method of production of the invention.

(5) FIGS. 5A to 5D show a series of photographs for analyzing an oxide precipitate contained in the matrix of an ODS alloy powder obtained by the method of production of the invention. FIG. 5A obtained by bright-field TEM is centered on the oxide precipitate analyzed. FIGS. 5B and 5C are photographs of TEM diffraction obtained at inclination of the sample holder by an angle of 2 relative to X, respectively in the raw form and in the annotated form after analysis for locating the diffraction spots corresponding to the matrix and to the oxide precipitate. FIG. 5D is the corresponding annotated photograph obtained by inclination of the sample holder by an angle of 20 relative to X.

(6) FIG. 6 is a diagram illustrating the parameters R.sub.inscr and R.sub.circ necessary for calculating the circularity of a powder grain from a photograph taken for a given angle.

DESCRIPTION OF PARTICULAR EMBODIMENTS

(7) The particular embodiments given hereunder relate to the method of production of the invention, as well as the composition and the microstructure of the reinforced alloy obtainable thereby. 1. Implementation of the method for producing a reinforced alloy according to the invention In a ball mill, under a hydrogen atmosphere, a parent metal powder consisting of an iron-based master alloy (composition by weight: 14% Cr, 11 W, 0.3% Si, 0.3% Mn and 0.2% Ni, 1000 ppm C, and remainder Fe) is mixed with an additional powder, comprising by weight relative to the total mixture of powders, 0.3% of a titanium hydride (TiH.sub.2) powder and 0.3% of an yttrium oxide (Y.sub.2O.sub.3) powder as intermediates intended to form oxide particles.

(8) The powder mixture is milled for 176 hours in order to form, by mechanical synthesis, a precursor powder comprising a metal matrix consisting of the master alloy in which titanium, yttrium and oxygen atoms are incorporated.

(9) At this stage of the method of production of the invention, no oxide particle in the form of precipitates has yet formed.

(10) The precursor powder is then fed into an inductively coupled radio frequency plasma torch that is able to deliver up to 80 kW of power (model PL50 marketed by the company Tekna).

(11) This type of torch is described for example in the document Kim, K. S., Moradian, A., Mostaghimi, J., Soucy, G. Modeling of Induction Plasma Process for Fullerene Synthesis: Effect of Plasma Gas Composition and Operating Pressure; Plasma Chemistry and Plasma Processing 2010, 30, 91-110.

(12) The plasma torch comprises a ceramic confinement tube immersed in cooling water circulating at high speed along its external wall. Cooling of the tube is essential, to protect it from the large thermal flux generated by the plasma. Around the confinement tube and beyond the cooling channel there is the induction coil embedded in the body of the plasma torch and connected to the high-frequency generator. This coil generates the alternating magnetic field that creates the plasma medium.

(13) Inside the confinement tube, a plasma gas (also called central gas) is injected continuously.

(14) To protect the inside wall of the ceramic confinement tube, a sheath gas is introduced in a vortex along the inside wall of the confinement tube by means of a quartz intermediate tube placed inside the confinement tube.

(15) The precursor powder is injected directly in the center of the plasma discharge via a water-cooled injector positioned in the first third upstream of the reaction chamber of the plasma torch. It is then heated in flight and melted. Since the induction plasmas operate without an electrode in contact with the plasma gas, contamination-free treatment can be carried out.

(16) The precursor powder obtained beforehand is subjected to a thermal plasma according to the operating conditions shown in Table 1. The gas flow rates are as follows: plasma gas (argon)=30 L/min; principal sheath gas (argon)=from 80 to 100 L/min; additional sheath gas (helium or hydrogen)=from 0 to 30 L/min.

(17) The proportion by weight of ODS powder according to the invention (more particularly the crystalline oxide particles additionally having an average circularity coefficient that is between 0.95 and 1) relative to the total weight of powder mixture treated is shown in the last column of Table 1. It is estimated to a first approximation by an analysis of the SEM photographs of the powders obtained at the end of the method of production of the invention.

(18) TABLE-US-00001 TABLE 1 Plasma Flow rate Flow rate Flow rate Proportion of Flow rate power of the of the of the powders with of of the principal additional additional spherical grains precursor plasma Reactor sheath sheath gas sheath gas comprising powder torch pressure gas (Ar) (He) (H.sub.2) crystalline oxide (g/min) (kW) (kPa) (L/min) (L/min) (L/min) particles (wt %) Test 1 21 22 20.6 100 0 0 <5% Test 2 21 31 34.5 100 0 4 ~60% Test 3 29 25 41.4 100 10 0 ~80/90 Test 4 12 25 41.4 100 10 0 100% Test 5, 6 and 7 40 60 96.6 100 30 0 ~20 to 30% Test 8 29 60 68.9 80 30 0 ~20 to 30% Test 9 29 60 41.4 80 30 0 ~20 to 30% Test 10 29 60 96.6 80 30 0 ~20 to 30% Test 11 29 60 41.4 100 10 0 ~20 to 30% Test 12 12 25 41.4 100 10 0 100% Test 17 15 40 68.9 60 40 0 100% Test 18 15 40 68.9 80 0 20 90 to 100% Test 19 15 35 68.9 80 0 20 ~50 to 60%

(19) Table 1 shows that the proportion of oxide that has precipitated is higher for moderate plasma torch powers (typically between 10 kW and 40 kW, or even between 10 kW and 30 kW) and a moderate flow rate of injection of the precursor powder into the plasma torch (typically <30 g/min).

(20) Thus, in tests 4, 12, 17 and 18, an ODS alloy powder with spherical particles and in which 100% of the oxide nanoreinforcements have seeded is obtained with: a powder flow rate of 12 g/min (tests 4 and 12) or 15 g/min (tests 17 and 18), a power for the plasma torch of 25 kW (tests 4 and 12) or 40 kW (tests 17 and 18), a pressure of 6 psi or 41 369 Pa (tests 4 and 12) or 10 psi or 68 947 Pa (tests 17 and 18) in the reaction chamber of the plasma torch, gas flow rates of 30 liters/min of argon for the central gas, 100 liters/min of argon for the principal sheath gas and 10 liters/min of helium for the additional sheath gas (tests 4 and 12); or gas flow rates of 30 liters/min of argon for the central gas, 60 liters/min of argon for the principal sheath gas and 40 liters/min of helium for the additional sheath gas (test 17); or gas flow rates of 30 liters/min of argon for the central gas, 80 liters/min of argon for the principal sheath gas and 20 liters/min of hydrogen for the additional sheath gas (test 18).

(21) Comparison of tests 4 and 12 also shows perfect reproducibility of the method of production of the invention, and therefore control of the characteristics of the ODS alloy powder that it advantageously makes it possible to obtain.

(22) Typically, to obtain an iron-based ODS alloy powder with spherical particles (more particularly with an average circularity coefficient that is between 0.95 and 1) and comprising a defined proportion of nanoreinforcements (with average size typically between 50 nm and 500 nm, preferably between 50 nm and 200 nm) of oxide uniformly dispersed in the metal matrix of the ODS alloy, a person skilled in the art may for example use the following operating conditions for the plasma torch, the priority parameters to be acted upon separately or together being the power of the plasma torch and the flow rate of precursor powder: .Math. for 20 to 30 wt. % of crystalline oxide particles relative to the initial weight of the additional powder (i.e. 704 to 80% of the additional powder has not produced crystalline oxide particles): power of the plasma torch: between 40 kW and 80 kW (or even between 30 kW and 80 kW), flow rate of precursor powder: between 20 g/min and 45 g/min, and optionally at least one of the following operating conditions: pressure in the reaction chamber of the plasma torch: between 5 psi or 34 474 Pa and 14.5 psi (i.e. atmospheric pressure), flow rate of the principal sheath gas: between 80 L/min and 100 L/min, flow rate of the additional sheath gas: between 10 L/min and 40 L/min. .Math. for more than 80 wt. % of crystalline oxide particles relative to the initial weight of the additional powder (i.e. less than 20% of the additional powder has not produced crystalline oxide particles): power of the plasma torch: between 20 kW and 40 kW (or even between 20 kW and 30 kW), flow rate of precursor powder: between 10 g/min and 30 g/min, and optionally at least one of the following operating conditions: pressure in the reaction chamber of the plasma torch: between 4 psi and 8 psi (i.e. between 27.6 kPa and 55.1 kPa), flow rate of the principal sheath gas: between 80 L/min (or even 60 L/min) and 100 L/min, flow rate of the additional sheath gas: between 10 L/min and 40 L/min. 2. Composition and microstructure of a reinforced alloy of the invention

(23) The precursor powder and the reinforced alloy powder obtained respectively at the end of the step of mechanical synthesis and then the step of precipitation of the oxides in the plasma torch according to test No. 4 are characterized by SEM (FIGS. 1A, 1B, 2A, 2B, 3A and 3B), TEM (FIGS. 4A and 4B) and EDX (table in FIG. 3C).

(24) According to these analyses, the particles of the precursor powder are of variable shape (FIG. 1A) and have a chaotic noncrystalline microstructure not containing any oxide particle that has seeded to constitute a reinforcement of the master alloy (FIG. 1B).

(25) However, by combining the milling step ii) and the plasma treatment step iii) according to the method of production of the invention, it is possible to obtain a reinforced alloy of the ODS type for which the powder particles are essentially spherical and/or spheroidal (FIGS. 2A, 2B and 3A) and are made up of grains consisting of a crystalline metal matrix in which crystalline oxide particles are incorporated uniformly, appearing in the form of black dots on a variable shade of gray background representing the metal matrix of the grains (FIGS. 2B, 3A and 3B). The crystalline oxide particles are nanoreinforcements, their median diameter d.sub.50 being between 150 nm and 200 nm. Numerous precipitates smaller than 5 nm are also present.

(26) EDX analyses were also carried out by SEM and TEM electron microscopy. They are presented in the table in FIG. 3C, which shows that the nanoreinforcements present in zones 1 to 5 in the particles of the ODS alloy powder are rich in titanium, yttrium and oxygen. In contrast, the corresponding EDX analyses conducted in zones 6 and 7 of the metal matrix show absence of oxygen, titanium, aluminum and yttrium in the matrix (mol %<0.1% to within the margin of uncertainty, or even zero when no value is stated, such as for aluminum and yttrium). These results prove that all the atoms of the additional powder that are intended to form the dispersed oxide particles have indeed precipitated in the form of nanoreinforcements within the particles of the ODS alloy powder, as can also be seen in the close-up views in FIGS. 4A and 4B.

(27) FIGS. 5B, 5C and 5D were obtained by TEM diffraction of the zone shown in FIG. 5A that is centered on an oxide precipitate of the ODS alloy of the invention. They have superlattice diffraction peaks (i.e. one spot in two is more luminous) that are characteristic of an oxide of the pyrochlore Y.sub.2Ti.sub.2O.sub.7 type obtained conventionally in an iron-based ODS alloy.

(28) The present invention is not in any way limited to the embodiments described and presented, and a person skilled in the art will be able to combine them and supply many variants and modifications on the basis of his general knowledge.

REFERENCES CITED

(29) [1] C. Suryanarayana Mechanical alloying and milling, Progress in Materials Science, 2001, 46, 1-184. [2] D. J. Lloyd, Particle reinforced aluminium and magnesium matrix composites; International materials reviews, 1994, Vol. 39, No. 1, pages 1 to 23. [3] Fan, X., Gitzhofer, F., Boulos, M. Statistical Design of Experiments for the Spheroidization of Powdered Alumina by Induction Plasma Processing, J Therm Spray Tech 1998, 7 (2), 247-253. [4] Jiang, X.-L., Boulos, M. Induction Plasma Spheroidization of Tungsten and Molybdenum Powders, Transactions of Nonferrous Metals Society of China 2006, 16 (1), 13-17. [5] Ye, R., Ishigaki, T., Jurewicz, J., Proulx, P., Boulos, M. I. In-Flight Spheroidization of Alumina Powders in ArH2 and ArN2 Induction Plasmas, Plasma Chem Plasma Process 2004, 24 (4), 555-571. [6] P. Fauchais, Plasmas thermiques: aspects fondamentaux [Thermal plasmas: basic aspects ], Techniques de l'ingnieur, Part D2810 V1, 2005) [7] G. Mollon Mcanique des matriaux granulaires [Mechanics of granular materials], INSA de Lyon, 2015 (in particular pages 23 and 24) [reference 7] available from the following website: http://guilhem.mollon.free.fr/Telechargements/Mechanique_des_Materiaux_Granulaires.pdf [8] F. Laverne et al., Fabrication additivePrincipes gnraux [Additive manufacturingGeneral Principles], Techniques de l'ingnieur, Part BM7017 V2 (published Feb. 10, 2016); [9] H. Fayazfara et al., Critical review of powder-based additive manufacturing of ferrous alloys: Process parameters, microstructure and mechanical properties, Materials & Design, Volume 144, 2018, pages 98-128. [10] T. DebRoy et al., Additive manufacturing of metallic componentsProcess, structure and properties, Progress in Materials Science, Volume 92, 2018, pages 112-224. [11] Ministry of Economics and Finance, French Republic, Prospectivefuture of additive manufacturingfinal report, edition of January 2017, ISBN: 978-2-11-151552-9. [12] D. Moinard et al., Procds de frittage PIM [PIM sintering techniques], Techniques de l'ingnieur, Part M3320 VI (published Jun. 10, 2011) [13] A. Papyrin, Cold Spray Technology, ISBN-13:978 0-08-045155-8, 2007 edition. [14] A. Proner, Revtements par projection thermique [Hot spray coatings], Techniques de l'ingnieur, Part M1645 V2 (published Sep. 10, 1999).