An intermetallic compound phase-coated nano-oxide phase-reinforced iron-based alloy and its preparation method

Abstract

The present invention discloses an intermetallic compound phase-coated nano rare earth oxide phase-reinforced iron-based alloy and a preparation method thereof. A two-step mechanical alloying method can be used to form core-shell structured nanoparticles with high number density, high coherence, and high thermal stability in the iron-based alloy. The nano-coated structure has structural characteristics of a ternary or higher nano rare earth oxide phase as a core and a heat-resistant intermetallic compound phase as a shell. The intermetallic compound phase, the nano rare earth oxide phase, and the iron matrix all maintain high coherence. After the shell is formed on the surface of the nano rare earth oxide phase, the coarsening of the nano rare earth oxide can be effectively inhibited, the thermal stability of the nano rare earth oxide can be improved, and the interface bonding quality between the nano rare earth oxide and the iron matrix can be further improved. The alloy strength can be greatly improved while maintaining high plasticity / toughness, enabling the alloy to exhibit excellent comprehensive mechanical properties of high strength and high toughness at a temperature of 600°C.

Description

Technical Field

[0001] The present invention relates to the technical field of alloy materials, and in particular to an intermetallic compound phase-coated nano-oxide phase-reinforced iron-based alloy and a preparation method thereof. Background Art

[0002] Traditional ODS iron-based alloys effectively hinder dislocation and grain boundary movement by dispersing and precipitating high-density nano-oxides in the ferrite matrix, thereby achieving excellent high-temperature yield, creep resistance, and oxidation resistance, as well as outstanding radiation resistance. They have important application prospects in the fields of nuclear power, heat-resistant molds, etc. However, the dispersed and precipitated high-density nano-oxides will still coarsen under long-term high-temperature conditions, affecting the strengthening effect of the strengthening phase, resulting in the long-term high-temperature mechanical service performance of the iron-based alloy being less than expected. Some scholars have proposed introducing other types of strengthening phases such as intermetallic compounds, hoping to achieve a superimposed strengthening effect, thereby further strengthening the iron-based alloy, but the superimposed strengthening effect is not significant, especially the coarsening of nano-oxides under long-term high-temperature conditions has not been effectively suppressed.

[0003] For example, the preparation method proposed in the patent CN103233182A disclosed by the University of Science and Technology Beijing is to pre-mix matrix element powders (Fe, Cr, Mo), β' phase forming element powders (Ni, Al) and oxide forming components (Fe2O3, YH2 and Ti) uniformly, then high-energy ball milling, sintering or hot isostatic pressing densification, and obtain an iron-based ODS alloy with nano-β' phase and nano-oxide phase composite reinforcement after solution aging treatment. However, the nano-β' phase and nano-oxide phase prepared by this method only appear in the matrix together, and each independently exerts a strengthening effect, which is a simple superposition and does not play a real composite strengthening effect. Under subsequent long-term high-temperature working conditions, the nano-β' phase and nano-oxide phase each coarsen, and thermal stability is reduced, and the long-term high-temperature mechanical properties of the iron-based alloy are still not improved. At present, the problem of how to effectively suppress the coarsening of the strengthening phase under long-term high temperature has not been fundamentally solved. Summary of the Invention

[0004] In view of this, the object of the present invention is to provide an intermetallic compound phase-coated nano-oxide phase-reinforced iron-based alloy and a preparation method thereof. Through a two-step mechanical alloying method including an activation pretreatment, a ternary or higher nano-rare earth oxide phase and a heat-resistant intermetallic compound phase with high number density, high coherence, and high thermal stability are obtained in the iron-based alloy, wherein the intermetallic compound phase preferentially precipitates at the interface of the nano-rare earth oxide phase and forms an effective coating, and finally, a core-shell structured nanoparticle with a ternary or higher nano-rare earth oxide phase as the core and a heat-resistant intermetallic compound phase as the shell is obtained in the iron-based alloy. Because the intermetallic compound shell can effectively hinder element diffusion at high temperatures, it greatly improves the thermal stability of the nano-rare earth oxide phase, thereby enabling the microstructure and macroscopic properties of the heat-resistant iron alloy to maintain ultra-long-term stability under high-temperature working conditions.

[0005] The present invention adopts the following technical solutions:

[0006] Provided is a method for preparing an intermetallic compound phase-coated nano rare earth oxide phase-reinforced iron-based alloy, characterized in that it comprises the following steps:

[0007] Step S1, preparing pre-alloyed powder: preparing iron-based alloy pre-alloyed powder by vacuum melting and gas atomization method;

[0008] Step S2, the first mechanical alloying step: subjecting the raw material powder of the intermetallic compound to high-energy ball milling according to a stoichiometric ratio to prepare a mechanically alloyed intermetallic compound powder;

[0009] Step S3, ball milling and mixing: preparing rare earth element-containing powder, charging the iron-based alloy pre-alloyed powder in step S1, the intermetallic compound mechanically alloyed powder in step S2, and the rare earth element-containing powder into a high-speed oscillating ball mill, and fully mixing them under inert gas protection to obtain a mixed powder;

[0010] Step S4, second mechanical alloying: subjecting the mixed powder of step S3 to mechanical alloying ball milling under inert gas protection to obtain supersaturated solid solution mechanical alloying powder;

[0011] Step S5, thermal densification treatment: the supersaturated solid solution mechanical alloying powder described in step S4 is placed in a can, evacuated, and thermally densified by hot extrusion / hot isostatic pressing / spark plasma sintering to obtain an iron alloy block. During the thermal densification process, a large amount of dispersed nano-rare earth oxide phase begins to precipitate within the grains and grain boundaries of the iron-based alloy matrix;

[0012] Step S6, solid solution + aging heat treatment: the ferroalloy block is subjected to solid solution + aging heat treatment, and the nano rare earth oxide phase is further precipitated. The particle size of the nano rare earth oxide phase is 2 to 30 nm, and the number density is 1022 ~10 24 pcs / m 3 At the same time, the intermetallic compound phase uses the interface of the nano rare earth oxide phase as a heterogeneous nucleation point, preferentially precipitates, and gradually covers almost all of the nano rare earth oxide phase, forming a core-shell structure nanoparticle with a ternary or higher nano rare earth oxide phase as the core and the intermetallic compound phase as the shell. In addition, a small amount of single-phase intermetallic compound phase nanoparticles are also precipitated separately.

[0013] Thus, a heat-resistant iron-based alloy reinforced with an intermetallic compound phase coated with a nano rare earth oxide phase is obtained. Since almost all of the nano rare earth oxide phases are coated, the total precipitation number density of the core-shell structure nanoparticles is also 10 22 ~10 24 pcs / m 3 The core-shell structured nanoparticles can maintain high coherence and high thermal stability in the iron matrix.

[0014] Preferably, the iron-based alloy is a Cr-containing full ferrite alloy or a Cr-containing ferrite / martensite alloy.

[0015] Preferably, the intermetallic compound phase only includes the intermetallic compound in step S2, or the intermetallic compound phase includes not only the intermetallic compound in step S2 but also alloying elements in the iron-based alloy.

[0016] An ideal intermetallic compound coating layer must possess the following key characteristics: a relatively fast diffusion rate of the constituent elements in the iron matrix, preferential precipitation of the intermetallic compound at the interface of the nano-rare earth oxide, high thermal stability of the precipitated intermetallic compound phase, and the ability to simultaneously maintain a high degree of coherence with the nano-rare earth oxide and the iron matrix. Therefore, many heat-resistant intermetallic compounds, such as Ni / Ti / Fe-Al systems, Ti / Ni-Si systems, Ni-Ti systems, and heat-resistant intermetallic compounds containing other refractory metals or rare earth metal elements such as tungsten, molybdenum, tantalum, niobium, vanadium, and chromium, can be considered. Preferably, the intermetallic compound in step S2 includes one or more of the following: Ni-Al systems, Ti-Al systems, Fe-Al systems, Ti-Si systems, Ni-Si systems, Ni-Ti systems, Nb-Al systems, Ru-Al systems, Mo-Si systems, and Nb-Si systems.

[0017] Preferably, the nano rare earth oxide phase has high thermal stability.

[0018] Preferably, the nano rare earth oxide phase includes a ternary or more complex oxide phase, or the nano rare earth oxide phase includes multiple ternary or more complex oxide phases.

[0019] Preferably, the rare earth element-containing powder is an oxidized or hydrogenated powder of the rare earth element.

[0020] Preferably, the first and second steps of mechanical alloying both use an omnidirectional planetary ball mill, and the processing parameters are: disk speed of 200-400 rpm, longitudinal speed of 10-20 rpm, ball-to-material mass ratio of 5:1-10:1, ball milling time of 5-15 h; and after each ball milling for 15-30 min, the machine is stopped for 5-10 min and the forward and reverse directions are changed.

[0021] Preferably, in step S6, the solution heat treatment temperature is 800-1100° C., the time is 1-3 h, and the cooling process is water cooling; the aging heat treatment temperature is 500-650° C., the time is 1-3 h, and the cooling process is water cooling.

[0022] Therefore, the present invention also provides an intermetallic compound phase-coated nano rare earth oxide phase-reinforced iron-based alloy, which is obtained by the above-mentioned preparation method.

[0023] The reaction mechanism of the present invention is as follows: the intermetallic compound is prepared in the form of a powder through the first step of mechanical alloying and added. It has extremely high chemical activity and can be quickly dissolved back into the pre-alloyed matrix in the second step of mechanical alloying. Nano-oxides are first precipitated at the beginning of the thermal densification stage, and then the intermetallic compound is preferentially precipitated with the nano-oxide interface as the heterogeneous nucleation site during the heat treatment stage. During this process, almost all nano-oxides will be coated by the subsequently precipitated intermetallic compound phase. Different from the previous simple superposition strengthening technology, the technical key of the present invention is to realize the "activation-dissolution-preferential re-precipitation" mechanism of the intermetallic compound phase, and the re-precipitation of the intermetallic compound occurs after the precipitation of the nano-oxide. This can fundamentally achieve the full encapsulation of almost all nano-oxides of different particle sizes, and finally prepare a specific nano-precipitation structure with nano-oxide as the core and intermetallic compound as the shell, which can greatly improve the long-term thermal stability of the alloy structure and performance.

[0024] The beneficial effects of the present invention are:

[0025] 1. The novel two-step mechanical alloying method designed by the present invention, which includes an activation pretreatment of the intermetallic compound, realizes the "activation-redissolution-preferred reprecipitation" mechanism of the intermetallic compound phase, solving the technical bottleneck that the formation of a separate intermetallic compound phase and a separate nano-oxide phase in a ferrite matrix can only achieve a simple superposition strengthening effect (1+1≤2). The two-step mechanical alloying method designed by the present invention, which includes an activation pretreatment, can form a large number of core-shell structured nanoparticles in a ferrite matrix. The nanoparticles have the structural characteristics of a ternary or higher nano-oxide phase as the core and a heat-resistant intermetallic compound phase as the shell. The nanoparticles are truly "superimposed" together, greatly improving the long-term thermal stability of the nano-oxide particles and achieving the technical effect of 1+1>2.

[0026] 2. The core-shell structured nanoparticles obtained by the present invention have a heat-resistant intermetallic compound phase encapsulating the nano-oxide phase. By completely inhibiting element diffusion, the coarsening process of the nano-oxide at high temperatures can be effectively prevented, thereby greatly improving the thermal stability of the alloy structure.

[0027] 3. One or more ternary or more complex oxide phases can be formed simultaneously in the iron matrix, but they can all be coated with the same intermetallic compound, thereby obtaining high strength and heat resistance.

[0028] 4. The intermetallic compound phase is highly coherent with the ferrite matrix. Compared with the interface between the original nano-oxide and the matrix, the intermetallic compound and the matrix interface are better bonded and have stronger coordinated deformation ability. While ensuring a significant improvement in the thermal stability and room temperature / high temperature strength of the iron-based alloy, better ductility can be achieved.

[0029] 5. The core-shell structured nanoparticles obtained by the present invention have an outer shell of an intermetallic compound and an inner core of one or more ternary or higher complex oxides. Both the intermetallic compound phase and the complex oxide phase are of low nanometer scale, and are distributed in large quantities, uniformly, and dispersedly in the matrix. They are highly coherent with the matrix and can effectively hinder the movement of dislocations, subgrains, and grain boundaries at high temperatures, effectively inhibit softening behaviors such as recrystallization and creep, and enable the alloy matrix to maintain high strength and good plasticity / toughness for a long time under high-temperature service conditions. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] In order to more clearly illustrate the technical implementation effects of the present invention, the following is a brief introduction to the drawings required for use in the description of the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0031] Figure 1 TEM images, three-dimensional APT elemental analysis, HAADF-STEM images, and EDS elemental surface scans of NiAl-coated Y-Zr-O core-shell structured nanoparticles in the novel heat-resistant iron-based alloy prepared in Example 1 of the present invention;

[0032] Figure 2 HAADF-STEM images, EDS elemental surface scans, and FFT structural analysis of NiAl-coated Y-Al-O core-shell structured nanoparticles in the novel heat-resistant iron-based alloy prepared in Example 1 of the present invention;

[0033] Figure 3Room temperature and high temperature tensile curves of the novel heat-resistant iron-based alloy prepared in Example 1 of the present invention, in which NiAl is simultaneously coated with nano-oxides Y-Zr-O and Y-Al-O. DETAILED DESCRIPTION

[0034] In order to enable those skilled in the art to better understand the technical solutions in the embodiments of the present invention and to make the above-mentioned objects, features and advantages of the present invention more obvious and understandable, the specific implementation methods of the present invention are further described below.

[0035] The endpoints of the ranges and any values ​​disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoints of each range, the endpoints of each range and individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0036] The present invention provides a method for preparing an intermetallic compound phase-coated nano rare earth oxide phase-reinforced iron-based alloy, characterized in that it comprises the following steps:

[0037] Step S1, preparing pre-alloyed powder: preparing iron-based alloy pre-alloyed powder by vacuum melting and gas atomization method;

[0038] Step S2, the first mechanical alloying step: subjecting the raw material powder of the intermetallic compound to high-energy ball milling according to a stoichiometric ratio to prepare a mechanically alloyed intermetallic compound powder;

[0039] Step S3, ball milling and mixing: preparing rare earth element-containing powder, charging the iron-based alloy pre-alloyed powder in step S1, the intermetallic compound mechanically alloyed powder in step S2, and the rare earth element-containing powder into a high-speed oscillating ball mill, and fully mixing them under inert gas protection to obtain a mixed powder;

[0040] Step S4, second mechanical alloying: subjecting the mixed powder of step S3 to mechanical alloying ball milling under inert gas protection to obtain supersaturated solid solution mechanical alloying powder;

[0041] Step S5, thermal densification treatment: the supersaturated solid solution mechanical alloying powder described in step S4 is placed in a can, evacuated, and thermally densified by hot extrusion / hot isostatic pressing / spark plasma sintering to obtain an iron alloy block. During the thermal densification process, a large amount of dispersed nano-rare earth oxide phase begins to precipitate within the grains and grain boundaries of the iron-based alloy matrix;

[0042] Step S6, solid solution + aging heat treatment: the ferroalloy block is subjected to solid solution + aging heat treatment, and the nano rare earth oxide phase is further precipitated. The particle size of the nano rare earth oxide phase is 2 to 30 nm, and the number density is 10 22 ~10 24 pcs / m 3 At the same time, the intermetallic compound phase uses the interface of the nano rare earth oxide phase as a heterogeneous nucleation point, preferentially precipitates, and gradually covers almost all of the nano rare earth oxide phase, forming a core-shell structure nanoparticle with a ternary or higher nano rare earth oxide phase as the core and the intermetallic compound phase as the shell. In addition, a small amount of single-phase intermetallic compound phase nanoparticles are also precipitated separately.

[0043] Thus, a heat-resistant iron-based alloy reinforced with an intermetallic compound phase-coated nano-rare earth oxide phase is obtained. Since almost all of the nano-rare earth oxide phases are coated, the total precipitation number density of the core-shell structured nanoparticles is also 10 22 ~10 24 pcs / m 3 The core-shell structured nanoparticles can maintain high coherence and high thermal stability in the iron matrix.

[0044] Preferably, the iron-based alloy is a Cr-containing full ferrite alloy or a Cr-containing ferrite / martensite alloy.

[0045] Preferably, the intermetallic compound phase only includes the intermetallic compound in step S2, or the intermetallic compound phase includes not only the intermetallic compound in step S2 but also alloying elements in the iron-based alloy.

[0046] Preferably, the intermetallic compound in step S2 includes one or more of Ni-Al system, Ti-Al system, Fe-Al system, Ti-Si system, Ni-Si system, Ni-Ti system, Nb-Al system, Ru-Al system, Mo-Si system and Nb-Si system.

[0047] Preferably, the nano rare earth oxide phase itself has high thermal stability.

[0048] Preferably, the nano rare earth oxide phase includes a ternary or more complex oxide phase, or the nano rare earth oxide phase includes multiple ternary or more complex oxide phases.

[0049] Preferably, the rare earth element-containing powder is an oxidized or hydrogenated powder of the rare earth element.

[0050] Preferably, the first and second steps of mechanical alloying both use an omnidirectional planetary ball mill, and the processing parameters are: disk speed of 200-400 rpm, longitudinal speed of 10-20 rpm, ball-to-material mass ratio of 5:1-10:1, ball milling time of 5-15 h; and after each ball milling for 15-30 min, the machine is stopped for 5-10 min and the forward and reverse directions are changed.

[0051] Preferably, in step S6, the solution heat treatment temperature is 800-1100° C., the time is 1-3 h, and the cooling process is water cooling; the aging heat treatment temperature is 500-650° C., the time is 1-3 h, and the cooling process is water cooling.

[0052] The present invention also provides an intermetallic compound phase-coated nano rare earth oxide phase-reinforced iron-based alloy, which is obtained by the above-mentioned preparation method.

[0053] Example 1

[0054] A method for preparing a heat-resistant iron-based alloy reinforced with NiAl simultaneously coated with Y-Zr-O and Y-Al-O nanoparticles comprises the following steps:

[0055] Step S1, vacuum melting + argon atomization to obtain Fe-Cr-W-Zr pre-alloyed powder with a particle size of 5 to 30 μm;

[0056] Specifically, the following ingredients by weight percentage:

[0057] Cr 15%, W 2%, Zr 0.7%, the balance is Fe and unavoidable impurities;

[0058] Step S2, the first mechanical alloying step: high-energy ball milling of Ni and Al raw material powders according to a stoichiometric ratio to prepare a mechanically alloyed powder of an intermetallic compound NiAl;

[0059] Step S3, ball milling and mixing: the Fe-Cr-Al-W-Zr pre-alloyed powder, the intermetallic compound NiAl powder, and the Y2O3 powder in the above S1 are charged into a high-speed oscillating ball mill and thoroughly mixed under the protection of an inert gas to obtain a mixed powder; the alloying components by weight percentage are: Cr 15%, W 2%, Zr 0.7%, Ni 5.5%, Al 2.5%, and the balance is Fe and unavoidable impurities;

[0060] Step S4, second mechanical alloying: the mixed powder is subjected to a sufficient mechanical alloying treatment under the protection of an inert gas, and the [Ni] and [Al] in the intermetallic compound powder and the [Y] and [O] in the Y2O3 powder are dissolved back into the iron matrix in the form of atoms to form a supersaturated solid solution mechanical alloyed finished powder;

[0061] Step S5, thermal densification treatment: The mechanical alloying product powder is placed in a vacuum can and subjected to thermal densification treatment by hot extrusion / hot isostatic pressing / spark plasma sintering to obtain an iron alloy block. During the thermal densification process, the supersaturated [Ni], [Al], [Y], and [O] solute atoms in the iron matrix are re-precipitated to form a large amount of dispersed Y-Zr-O and Y-Al-O nano-oxide phases within the crystals and at the grain boundaries. The particle size of the Y-Zr-O and Y-Al-O nano-oxide phases is 2 to 50 nm, and the number density is 1×10 23 pcs / m 3 At the same time, a NiAl phase preferentially precipitates at the interface between the Y-Zr-O and Y-Al-O nano-oxide phases, gradually encapsulating the aforementioned Y-Zr-O and Y-Al-O nano-oxide phases to form a nano-core-shell structure with enhanced thermal stability. Furthermore, some NiAl phases also precipitate independently.

[0062] Step S6, heat treatment: subjecting the ferroalloy block to solid solution + aging heat treatment, wherein the solid solution + aging heat treatment refers to that the solid solution heat treatment temperature is 800-1100°C, the time is 1-3 hours, and the cooling process is water cooling; the aging heat treatment temperature is 500-650°C, the time is 1-3 hours, and the cooling process is water cooling.

[0063] Result analysis, Figure 1 A heat-resistant iron-based alloy with a NiAl-coated Y-Zr-O core-shell structure: (a) Transmission electron microscopy (TEM); (b) 3D atom probe (APT) characterization analysis; (c) HAADF-STEM image and EDS elemental scanning. In (a), a large number of diffusely distributed nanoparticles can be seen, with a total density of ~1×10 23 The elemental analysis of (b) and (c) confirmed that the nano-reinforced particles have a core-shell composite structure of NiAl shell + Y-Zr-O core, where the arrows mark some of the separately precipitated NiAl phases.

[0064] Figure 2 A heat-resistant iron-based alloy reinforced with a NiAl-coated Y-Al-O core-shell structure: (a) HAADF-STEM image and EDS elemental scan of the core-shell nanoparticles. (b) FFT analysis shows that the core is a Y4Al2O9 nano-oxide phase, highly coherent with the NiAl shell and ferrite matrix.

[0065] According to the data in Table 1, we can get Figure 3 Room temperature and high temperature tensile curves of the novel heat-resistant iron-based alloy prepared in Example 1 of the present invention, in which NiAl is simultaneously coated with nano-oxides Y-Zr-O and Y-Al-O.

[0066] Table 1 Room temperature and high temperature mechanical properties of the new alloy (annealed)

[0067]

[0068] Example 2

[0069] A method for preparing a heat-resistant iron-based alloy simultaneously coated with NiAl and reinforced with Y-Ti-Zr-O nanoparticles comprises the following steps:

[0070] Step S1, vacuum melting + argon atomization to obtain Fe-Cr-W-Zr-Ti pre-alloyed powder with a particle size of 5 to 30 μm;

[0071] Specifically, the following ingredients by weight percentage:

[0072] Cr 15%, W 2%, Zr 0.5%, Ti 0.5%, the balance is Fe and unavoidable impurities;

[0073] Step S2, the first mechanical alloying step: high-energy ball milling of Ni and Al raw material powders according to a stoichiometric ratio to prepare a mechanically alloyed powder of an intermetallic compound NiAl;

[0074] Step S3, ball milling and mixing: the Fe-Cr-Al-W-Zr pre-alloyed powder, the intermetallic compound NiAl powder, and the Y2O3 powder in the above S1 are charged into a high-speed oscillating ball mill and thoroughly mixed under the protection of an inert gas to obtain a mixed powder; the alloying components by weight percentage are: Cr 15%, W 2%, Zr 0.5%, Ti 0.5%, Ni 5.5%, Al 2.5%, and the balance is Fe and unavoidable impurities;

[0075] Step S4, second mechanical alloying: the mixed powder is subjected to a sufficient mechanical alloying treatment under the protection of an inert gas, and the [Ni] and [Al] in the intermetallic compound powder and the [Y] and [O] in the Y2O3 powder are dissolved back into the iron matrix in the form of atoms to form a supersaturated solid solution mechanical alloyed finished powder;

[0076] Step S5, thermal densification treatment: The mechanical alloying product powder is placed in a can, evacuated, and thermally densified by hot extrusion / hot isostatic pressing / spark plasma sintering to obtain an iron alloy block. During the thermal densification process, the supersaturated [Ni], [Al], [Y], and [O] solute atoms in the iron matrix are re-precipitated, forming a large amount of dispersed Y-Ti-Zr-O and Y-Zr-O nano-oxide phases within the crystals and at the grain boundaries. The particle size of the Y-Ti-Zr-O and Y-Zr-O nano-oxide phases is 2 to 40 nm, and the number density is 2×10 23 pcs / m 3At the same time, a NiAl phase preferentially precipitates at the interface between the Y-Ti-Zr-O and Y-Zr-O nano-oxide phases, gradually encapsulating the Y-Ti-Zr-O and Y-Zr-O nano-oxide phases to form a nano-core-shell structure with enhanced thermal stability. Furthermore, some NiAl phases also precipitate independently.

[0077] Step S6, heat treatment: subjecting the ferroalloy block to solid solution + aging heat treatment, wherein the solid solution + aging heat treatment refers to that the solid solution heat treatment temperature is 800-1100°C, the time is 1-3 hours, and the cooling process is water cooling; the aging heat treatment temperature is 500-650°C, the time is 1-3 hours, and the cooling process is water cooling.

[0078] Example 3

[0079] A method for preparing a heat-resistant iron-based alloy simultaneously coated with Ti(Al, W) and reinforced with Y-Si-Zr-O and Y-Zr-O nanoparticles comprises the following steps:

[0080] Step S1, vacuum melting + argon atomization to obtain Fe-Cr-W-Zr-Si pre-alloyed powder with a particle size of 5 to 30 μm;

[0081] Specifically, the following ingredients by weight percentage:

[0082] Cr 15%, W 2%, Zr 0.5%, Si 0.2%, the balance is Fe and unavoidable impurities;

[0083] Step S2, the first mechanical alloying step: high-energy ball milling of Ti and Al raw material powders according to a stoichiometric ratio to prepare mechanically alloyed powder of the intermetallic compound TiAl;

[0084] Step S3, ball milling and mixing: the Fe-Cr-Al-W-Zr pre-alloyed powder, the intermetallic compound NiAl powder, and the Y2O3 powder in the above S1 are charged into a high-speed oscillating ball mill and thoroughly mixed under the protection of an inert gas to obtain a mixed powder; the alloying components by weight percentage are: Cr 15%, W 2%, Zr 0.5%, Si 0.2%, Ti 3.0%, Al 2.5%, and the balance is Fe and unavoidable impurities;

[0085] Step S4, second mechanical alloying: the mixed powder is subjected to a sufficient mechanical alloying treatment under the protection of an inert gas, and the [Ni] and [Al] in the intermetallic compound powder and the [Y] and [O] in the Y2O3 powder are dissolved back into the iron matrix in the form of atoms to form a supersaturated solid solution mechanical alloyed finished powder;

[0086] Step S5, thermal densification treatment: The mechanical alloying product powder is placed in a vacuum can and subjected to thermal densification treatment by hot extrusion / hot isostatic pressing / spark plasma sintering to obtain an iron alloy block. During the thermal densification process, the supersaturated [Ni], [Al], [Y], and [O] solute atoms in the iron matrix are re-precipitated to form a large amount of dispersed Y-Si-Zr-O and Y-Zr-O nano-oxide phases within the crystals and at the grain boundaries. The particle size of the Y-Si-Zr-O and Y-Zr-O nano-oxide phases is 2 to 40 nm, and the number density is 2×10 23 pcs / m 3 At the same time, a Ti(Al, W) phase preferentially precipitates at the interface between the Y-Si-Zr-O and Y-Zr-O nano-oxide phases, gradually encapsulating the aforementioned Y-Si-Zr-O and Y-Zr-O nano-oxide phases to form a nano-core-shell structure with enhanced thermal stability. Additionally, some Ti(Al, W) phases precipitate independently.

[0087] Step S6, heat treatment: subjecting the ferroalloy block to solid solution + aging heat treatment, wherein the solid solution + aging heat treatment refers to that the solid solution heat treatment temperature is 800-1100°C, the time is 1-3 hours, and the cooling process is water cooling; the aging heat treatment temperature is 500-650°C, the time is 1-3 hours, and the cooling process is water cooling.

[0088] Example 4

[0089] A method for preparing a NiTi-coated Y-Ti-O nanoparticle-reinforced heat-resistant iron-based alloy comprises the following steps:

[0090] Step S1, vacuum melting + argon atomization to obtain Fe-Cr-W-Ti pre-alloyed powder with a particle size of 5 to 30 μm;

[0091] Specifically, the following ingredients by weight percentage:

[0092] Cr 15%, W 2%, Ti 0.5%, the balance is Fe and unavoidable impurities;

[0093] Step S2, the first mechanical alloying step: high-energy ball milling of Ni and Ti raw material powders according to a stoichiometric ratio to prepare a mechanically alloyed powder of an intermetallic compound NiTi;

[0094] Step S3, ball milling and mixing: the Fe-Cr-W-Ti pre-alloyed powder, the intermetallic compound NiTi powder, and the Y2O3 powder prepared in the above step S1 are placed in a high-speed oscillating ball mill and thoroughly mixed under the protection of an inert gas to obtain a mixed powder; the alloying components by weight percentage are: Cr 15%, W 2%, Ti 3.0%, Ni 4.5%, and the balance is Fe and unavoidable impurities;

[0095] Step S4, second mechanical alloying: the mixed powder is subjected to a sufficient mechanical alloying treatment under the protection of an inert gas, and the [Ni] and [Ti] in the intermetallic compound powder and the [Y] and [O] in the Y2O3 powder are dissolved back into the iron matrix in the form of atoms to form a supersaturated solid solution mechanical alloyed finished powder;

[0096] Step S5, thermal densification treatment: The mechanical alloying product powder is placed in a vacuum can and thermally densified by hot extrusion / hot isostatic pressing / spark plasma sintering to obtain an iron alloy block. During the thermal densification process, the supersaturated [Ni], [Ti], [Y], and [O] solute atoms in the iron matrix are re-precipitated to form a large amount of dispersed Y-Ti-O nano-oxide phase within the crystals and at the grain boundaries. The particle size of the Y-Ti-O nano-oxide phase is 2 to 40 nm, and the number density is 2×10 23 pcs / m 3 At the same time, a NiTi phase preferentially precipitates at the interface between the Y-Si-Zr-O and Y-Zr-O nano-oxide phases, gradually encapsulating the Y-Ti-O nano-oxide phase to form a nano-core-shell structure with enhanced thermal stability. Furthermore, some NiTi phases also precipitate independently.

[0097] Step S6, heat treatment: subjecting the ferroalloy block to solid solution + aging heat treatment, wherein the solid solution + aging heat treatment refers to that the solid solution heat treatment temperature is 800-1100°C, the time is 1-3 hours, and the cooling process is water cooling; the aging heat treatment temperature is 500-650°C, the time is 1-3 hours, and the cooling process is water cooling.

Claims

1. A method for preparing an intermetallic compound phase-coated nano rare earth oxide phase-reinforced iron-based alloy, characterized in that: The following steps are involved: Step S1, preparing pre-alloyed powder: preparing iron-based alloy pre-alloyed powder by vacuum melting and gas atomization method; Step S2, the first mechanical alloying step: subjecting the raw material powder of the intermetallic compound to high-energy ball milling according to a stoichiometric ratio to prepare a mechanically alloyed intermetallic compound powder; Step S3, ball milling and mixing: preparing rare earth element-containing powder, charging the iron-based alloy pre-alloyed powder in step S1, the intermetallic compound mechanically alloyed powder in step S2, and the rare earth element-containing powder into a high-speed oscillating ball mill, and fully mixing them under inert gas protection to obtain a mixed powder; Step S4, second mechanical alloying: subjecting the mixed powder of step S3 to mechanical alloying ball milling under inert gas protection to obtain supersaturated solid solution mechanical alloying powder; Step S5, thermal densification treatment: the supersaturated solid solution mechanical alloying powder described in step S4 is placed in a can, evacuated, and thermally densified by hot extrusion / hot isostatic pressing / spark plasma sintering to obtain an iron alloy block. During the thermal densification process, a large amount of dispersed nano-rare earth oxide phase begins to precipitate within the grains and grain boundaries of the iron-based alloy matrix; Step S6, solid solution + aging heat treatment: the ferroalloy block is subjected to solid solution + aging heat treatment, and the nano rare earth oxide phase is further precipitated. The particle size of the nano rare earth oxide phase is 2 to 30 nm, and the number density is 10 22 ~10 24 pcs / m 3 At the same time, the intermetallic compound phase uses the interface of the nano rare earth oxide phase as a heterogeneous nucleation point, preferentially precipitates, and gradually covers almost all of the nano rare earth oxide phase, forming a core-shell structure nanoparticle with a ternary or higher nano rare earth oxide phase as the core and the intermetallic compound phase as the shell. In addition, a small amount of single-phase intermetallic compound phase nanoparticles are also precipitated separately. Thus, a heat-resistant iron-based alloy reinforced with an intermetallic compound phase-coated nano-rare earth oxide phase is obtained. Since almost all of the nano-rare earth oxide phases are coated, the total precipitation number density of the core-shell structured nanoparticles is also 10 22 ~10 24 pcs / m 3 The core-shell structured nanoparticles can maintain high coherence and high thermal stability in the iron matrix, and the iron-based alloy is a Cr-containing full ferrite alloy.

2. The method for preparing an intermetallic compound phase-coated nano rare earth oxide phase-reinforced iron-based alloy according to claim 1, characterized in that: The intermetallic compound phase only includes the intermetallic compound in step S2.

3. The method for preparing an intermetallic compound phase-coated nano rare earth oxide phase-reinforced iron-based alloy according to claim 1, characterized in that: The intermetallic compound in step S2 includes one or more of Ni-Al system, Ti-Al system, Fe-Al system, Ti-Si system, Ni-Si system, Ni-Ti system, Nb-Al system, Ru-Al system, Mo-Si system and Nb-Si system.

4. The method for preparing an intermetallic compound phase-coated nano rare earth oxide phase-reinforced iron-based alloy according to claim 1, characterized in that: The nano rare earth oxide phase itself has high thermal stability.

5. The method for preparing an intermetallic compound phase-coated nano rare earth oxide phase-reinforced iron-based alloy according to claim 4, characterized in that: The nano rare earth oxide phase includes a ternary or more complex oxide phase, or the nano rare earth oxide phase includes multiple ternary or more complex oxide phases.

6. The method for preparing an intermetallic compound phase-coated nano rare earth oxide phase-reinforced iron-based alloy according to claim 1, characterized in that: The rare earth element-containing powder is an oxidized or hydrogenated powder of the rare earth element.

7. The method for preparing an intermetallic compound phase-coated nano rare earth oxide phase-reinforced iron-based alloy according to claim 1, characterized in that: The first and second steps of mechanical alloying both use an omnidirectional planetary ball mill, and the processing parameters are: a disk speed of 200 to 400 rpm, a longitudinal speed of 10 to 20 rpm, a ball-to-material mass ratio of 5:1 to 10:1, and a ball milling time of 5 to 15 hours; and each ball milling time is 15 to 30 minutes, and the machine is stopped for 5 to 10 minutes and the forward and reverse directions are changed.

8. The method for preparing an intermetallic compound phase-coated nano rare earth oxide phase-reinforced iron-based alloy according to claim 1, characterized in that: In step S6, the solution heat treatment temperature is 800-1100°C, the time is 1-3 hours, and the cooling process is water cooling; the aging heat treatment temperature is 500-650°C, the time is 1-3 hours, and the cooling process is water cooling.

9. An intermetallic compound phase-coated nano-rare earth oxide phase-reinforced iron-based alloy, characterized in that: The method is as described in any one of claims 1 to 8.

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