ODS ALLOY POWDER, METHOD FOR PRODUCING SAME BY MEANS OF PLASMA TREATMENT, AND USE THEREOF

Abstract

A method for producing a powder of a reinforced alloy (ODS alloy) in which the grains forming the particles of the powder comprise a metal matrix, in the volume of which crystalline oxide particles are dispersed, said method comprising the following successive steps: i) providing a powder mixture to be milled comprising a master alloy intended to form the metal matrix and an additional powder comprising at least one intermediate intended to incorporate atoms intended to form the dispersed oxide particles; ii) milling the powder mixture according to a mechanical synthesis process for making a precursor powder; iii) subjecting the precursor powder to a thermal plasma generated by a plasma torch comprising a plasma gas, in order to obtain the reinforced alloy powder.

The method of the invention is particularly suitable for producing an ODS alloy that has optimized characteristics of composition and/or microstructure.

The invention also relates to the ODS alloy powder obtained by the method of production, and the use thereof.

Claims

1-50. (canceled)

51. A method for producing a powder of a reinforced alloy for which grains forming particles of the powder comprise a metal matrix, in a volume of which crystalline oxide particles are dispersed, said method comprising: i) providing a powder mixture, comprising: a parent metal powder comprising a master alloy intended to form the metal matrix, the master alloy being selected from the group consisting of an iron-based alloy, a nickel-based alloy and an aluminum-based alloy; an additional powder comprising at least one intermediate intended to incorporate, in the metal matrix, atoms intended to form dispersed oxide particles; the intermediate intended to form the dispersed oxide particles being at least one selected from the group consisting 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, ii) milling the powder mixture in a gaseous milling medium according to a mechanical synthesis process for making a precursor powder comprising a metal matrix incorporating said atoms; iii) subjecting the precursor powder to a thermal plasma generated by a plasma torch comprising a plasma gas, in order to obtain reinforced alloy powder, the precursor powder being injected into the plasma torch at a flow rate between 10 grams/min and 30 grams/min, a power of the plasma torch being between 20 kW and 40 kW, and a pressure in a reaction chamber of the plasma torch being between 25 kPa and 100 kPa.

52. The method of claim 51, wherein the master alloy is an iron-based alloy, and the iron-based alloy comprises 10 to 30 wt % of chromium.

53. The method of claim 51, wherein the master alloy is an iron-based alloy, and the iron-based alloy comprises 10 to 30 wt % of aluminum.

54. The method of claim 51, wherein the master alloy is an iron-based alloy, and the iron-based alloy comprises 8 to 25 wt % of chromium and 3 to 8 wt % of aluminum.

55. The method of claim 51, wherein the master alloy is an iron-based alloy and the iron-based alloy is a steel.

56. The method of claim 51, wherein the master alloy is a nickel-based alloy, and the nickel-based alloy comprises 10 to 40 wt % of chromium.

57. The method of claim 56, wherein the nickel-based alloy comprises 10% to 40% by weight of chromium, 0.2% to 5% of aluminum, 0.3% to 5% of titanium, 0% to 5% of tungsten, 0% to 2% of molybdenum and 0% to 2% of tantalum.

58. The method of claim 51, wherein the master alloy is a nickel-based alloy, and the nickel-based alloy comprises 10 to 30 wt % of aluminum.

59. The method of claim 51, wherein the master alloy is an iron-based alloy or a nickel-based alloy, and the powder mixture comprises 0.1 to 2.5 wt % of the additional powder.

60. The method of claim 51, wherein the master alloy is an aluminum-based alloy, and the aluminum-based alloy comprises from 0% to 0.5% by weight of iron, from 0% to 0.3% of silicon and from 0% to 1% of magnesium.

61. The method of claim 51, wherein the master alloy is an aluminum-based alloy, and the powder mixture comprises 0.2 to 5 wt % of the additional powder.

62. The method of claim 51, wherein the powder mixture comprises 0.1% to 0.3% by weight of the additional powder.

63. The method of claim 51, wherein said atoms comprise at least one metal atom selected from the group consisting of yttrium, titanium, iron, chromium, tungsten, silicon, zirconium, thorium, magnesium, aluminum and hafnium.

64. The method of claim 51, wherein the plasma torch is an inductively coupled radio frequency plasma torch, a blown arc torch or a transferred arc torch.

65. The method of claim 51, wherein the plasma gas is at least one selected from the group consisting of argon, helium, and nitrogen.

66. The method of claim 51, wherein the plasma gas is injected into the plasma torch at a flow rate between 10 liters/min and 40 liters/min.

67. A reinforced alloy powder obtained by the method of claim 51.

68. A reinforced alloy powder whose grains forming particles of the reinforced alloy powder comprise a metal matrix, the metal matrix consisting of an iron-based alloy, a nickel-based alloy or an aluminum-based alloy, in a volume of which crystalline oxide particles are dispersed having a median diameter (d.sub.50) between 1 nm and 500 nm and comprising at least one oxide selected from Y.sub.2O.sub.3, TiO.sub.2, Al.sub.2O.sub.3, HfO.sub.2, SiO.sub.2, ZrO.sub.2, ThO.sub.2, MgO Al.sub.2O.sub.3, Y.sub.2Ti.sub.2O.sub.7, and Y.sub.2TiO.sub.5, the reinforced alloy comprising a metal atom selected from the group consisting of yttrium, titanium, iron, chromium, tungsten, silicon, zirconium, thorium, magnesium, aluminum and hafnium, the crystalline oxide particles comprising 80% to 100% by weight of said metal atom contained in a whole of the reinforced alloy, the particles of the reinforced alloy powder having an average circularity coefficient measured according to standard ISO-9276-6 edition 2008 that is between 0.95 and 1.

69. The reinforced alloy powder of claim 68, wherein the metal matrix is crystalline.

70. The reinforced alloy powder of claim 68, wherein the crystalline oxide particles are distributed uniformly in the volume of the metal matrix.

71. The reinforced alloy powder of claim 68, wherein the metal matrix consists of an iron-based alloy and the iron-based alloy comprises 10 to 30 wt % of chromium.

72. The reinforced alloy powder of claim 68, wherein the metal matrix consists of an iron-based alloy and the iron-based alloy comprises 10 to 30 wt % of aluminum.

73. The reinforced alloy powder of claim 68, wherein the metal matrix consists of an iron-based alloy and the iron-based alloy comprises 8 to 25 wt % of chromium and 3 to 8 wt % of aluminum.

74. The reinforced alloy powder of claim 68, wherein the metal matrix consists of an iron-based alloy and the iron-based alloy is a steel.

75. The reinforced alloy powder of claim 68, wherein the metal matrix consists of a nickel-based alloy and the nickel-based alloy comprises 10 to 40 wt % of chromium.

76. The reinforced alloy powder of claim 75, wherein the metal matrix consists of a nickel-based alloy and the nickel-based alloy comprises 10% to 40% by weight of chromium, 0.2% to 5% of aluminum, 0.3% to 5% of titanium, 0% to 5% of tungsten, 0% to 2% of molybdenum and 0% to 2% of tantalum.

77. The reinforced alloy powder of claim 68, wherein the metal matrix consists of a nickel-based alloy and the nickel-based alloy comprises 10 to 30 wt % of aluminum.

78. The reinforced alloy powder of claim 71, wherein the metal matrix consists of an iron-based alloy or a nickel-based alloy, and the reinforced alloy comprises 0.1 to 2.5 wt % of the oxide particles.

79. The reinforced alloy powder of claim 68, wherein the metal matrix consists of an aluminum-based alloy and the aluminum-based alloy comprises from 0% to 0.5% by weight of iron, from 0% to 0.3% of silicon and from 0% to 1% of magnesium.

80. The reinforced alloy powder of claim 68, wherein the metal matrix consists of an aluminum-based alloy, and the reinforced alloy comprises 0.2 to 5 wt % of the oxide particles.

81. The reinforced alloy powder of claim 68, wherein the reinforced alloy comprises 0.1 to 0.5 wt % of the oxide particles.

82. The reinforced alloy powder of claim 68, the crystalline oxide particles have a median diameter (d.sub.50) between 1 nm and 200 nm.

83. The reinforced alloy powder of claim 68, wherein the reinforced alloy further comprises at least one of elements, by weight: from 10 to 5000 ppm of silicon; from 10 to 100 ppm of sulfur; less than 20 ppm of chlorine; from 2 to 10 ppm of phosphorus; from 0.1 to 10 ppm of boron; from 0.1 to 10 ppm of calcium; less than 0.1 ppm of each of lithium, fluorine, heavy metals, Sn, As, and Sb.

84. The reinforced alloy powder of claim 69, wherein the metal matrix comprises, in dissolved form, 0 to 20 wt % of said metal atom relative to a total weight of said metal atom contained in the whole of the reinforced alloy.

85. A method, comprising: performing densification of the reinforced alloy powder of claim 68 to produce a massive material, or to a coating process in order to coat a substrate with the reinforced alloy powder.

86. The method of claim 85, wherein the performing densification comprises an additive manufacturing process or a powder injection molding process.

87. The method of claim 86, wherein the performing densification comprises an additive manufacturing process and the additive manufacturing process is a selective laser melting process, a selective electron beam melting, a selective laser sintering, a laser spraying or a binder jetting.

88. The method of claim 87, wherein the coating process is a cold spraying process or a hot spraying process.

89. The method of claim 88, wherein the coating process comprises a hot spraying process and the hot spraying process is a flame hot spraying process, an electric arc spraying process between two wires or a blown plasma spraying process.

Description

BRIEF DESCRIPTION OF THE FIGURES

[0212] FIGS. 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.

[0213] FIGS. 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.

[0214] 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.

[0215] 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.

[0216] 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.

[0217] 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

[0218] 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

[0219] In a ball mill, under a hydrogen atmosphere, a parent metal powder consisting of an iron-based master alloy (composition by weight: 14% Cr, 1% 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.

[0220] 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.

[0221] At this stage of the method of production of the invention, no oxide particle in the form of precipitates has yet formed.

[0222] 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).

[0223] 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”.

[0224] 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.

[0225] Inside the confinement tube, a plasma gas (also called central gas) is injected continuously.

[0226] 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.

[0227] 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.

[0228] 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: [0229] plasma gas (argon)=30 L/min; [0230] principal sheath gas (argon)=from 80 to 100 L/min; [0231] additional sheath gas (helium or hydrogen)=from 0 to 30 L/min.

[0232] 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.

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% Tests 5, 6 40 60 96.6 100 30 0 ~20 to 30% and 7 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%

[0233] 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).

[0234] 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: [0235] a powder flow rate of 12 g/min (tests 4 and 12) or 15 g/min (tests 17 and 18), [0236] a power for the plasma torch of 25 kW (tests 4 and 12) or 40 kW (tests 17 and 18), [0237] a pressure of 6 psi or 41369 Pa (tests 4 and 12) or 10 psi or 68947 Pa (tests 17 and 18) in the reaction chamber of the plasma torch, [0238] 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).

[0239] 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.

[0240] 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: [0241] for 20 to 30 wt % of crystalline oxide particles relative to the initial weight of the additional powder (i.e. 70% to 80% of the additional powder has not produced crystalline oxide particles): [0242] power of the plasma torch: between 40 kW and 80 kW (or even between 30 kW and 80 kW), [0243] flow rate of precursor powder: between 20 g/min and 45 g/min, and optionally at least one of the following operating conditions: [0244] pressure in the reaction chamber of the plasma torch: between 5 psi or 34474 Pa and 14.5 psi (i.e. atmospheric pressure), [0245] flow rate of the principal sheath gas: between 80 L/min and 100 L/min, [0246] flow rate of the additional sheath gas: between 10 L/min and 40 L/min. [0247] 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): [0248] power of the plasma torch: between 20 kW and 40 kW (or even between 20 kW and 30 kW), [0249] flow rate of precursor powder: between 10 g/min and 30 g/min, and optionally at least one of the following operating conditions: [0250] 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), [0251] flow rate of the principal sheath gas: between 80 L/min (or even 60 L/min) and 100 L/min, [0252] 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

[0253] 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).

[0254] 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).

[0255] 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.

[0256] 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.

[0257] 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.

[0258] 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

[0259] [1] C. Suryanarayana “Mechanical alloying and milling”, Progress in Materials Science, 2001, 46, 1-184. [0260] [2] D. J. Lloyd, “Particle reinforced aluminium and magnesium matrix composites”; International materials reviews, 1994, Vol. 39, No. 1, pages 1 to 23. [0261] [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. [0262] [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. [0263] [5] Ye, R., Ishigaki, T., Jurewicz, J., Proulx, P., Boulos, M. I. “In-Flight Spheroidization of Alumina Powders in Ar—H2 and Ar—N2 Induction Plasmas”, Plasma Chem Plasma Process 2004, 24 (4), 555-571. [0264] [6] P. Fauchais, “Plasmas thermiques: aspects fondamentaux” [“Thermal plasmas: basic aspects”], Techniques de l'ingénieur, Part D2810 V1, 2005) [0265] [7] G. Mollon “Mécanique des matériaux 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” [0266] [8] F. Laverne et al., “Fabrication additive—Principes généraux” [Additive manufacturing—General Principles], Techniques de l'ingénieur, Part BM7017 V2 (published Feb. 10, 2016); [0267] [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. [0268] [10] T. DebRoy et al., “Additive manufacturing of metallic components—Process, structure and properties”, Progress in Materials Science, Volume 92, 2018, pages 112-224. [0269] [11] Ministry of Economics and Finance, French Republic, “Prospective—future of additive manufacturing—final report”, edition of January 2017, ISBN: 978-2-11-151552-9. [0270] [12] D. Moinard et al., “Procédés de frittage PIM” [PIM sintering techniques], Techniques de l'ingénieur, Part M3320 VI (published Jun. 10, 2011) [0271] [13] A. Papyrin, “Cold Spray Technology”, ISBN-13:978-0-08-045155-8, 2007 edition. [0272] [14] A. Proner, “Revêtements par projection thermique” [Hot spray coatings], Techniques de l'ingénieur, Part M1645 V2 (published Sep. 10, 1999).