In-situ autogenous NANO oxide- and carbide-synergistically toughened fine-grained molybdenum alloy and preparation method thereof

Abstract

The present disclosure relates to an in-situ autogenous nano oxide- and carbide-synergistically toughened fine-grained molybdenum alloy and a preparation method thereof. The preparation method includes: mixing ammonium molybdate and a Ti3AlC2 powder with water and an alumina precursor solution, drying and pulverizing a resulting dried product, subjecting a resulting pulverized product to low-temperature hydrogen reduction and high-temperature hydrogen reduction, and then subjecting a resulting reduced powder to sintering, high-temperature and large-deformation thermoplastic processing, and annealing in sequence to obtain the in-situ autogenous nano oxide- and carbide-synergistically toughened fine-grained molybdenum alloy. In the present disclosure, alumina and a two-dimensional MAX ceramic material Ti3AlC2 are innovatively used to synergistically toughen a molybdenum alloy; and TiC0.67 formed by decomposition of the Ti3AlC2 shows better interface bonding with a molybdenum matrix, thereby improving a mechanical strength and a ductility of the molybdenum alloy.

Description

CROSS REFERENCE TO RELATED APPLICATION

[0001] This patent application is a national stage application of International Patent Application No. PCT / CN2023 / 088308, filed on Apr. 14, 2023, which claims the benefit and priority of Chinese Patent Application No. 202310238751.6, filed with the China National Intellectual Property Administration on Mar. 14, 2023, the disclosure of which is incorporated by reference herein in its entirety as part of the present application.TECHNICAL FIELD

[0002] The present disclosure belongs to the technical field of powder metallurgy, and particularly relates to an in-situ autogenous nano oxide- and carbide-synergistically toughened fine-grained molybdenum alloy and a preparation method thereof.BACKGROUND

[0003] With the advantages of high strength, high hardness, and desirable thermal conductivity and wear resistance, molybdenum metal is widely used in missiles, high-temperature heating elements, turbines, and fusion reactor components, as well as in electronics, aerospace, and metal processing. Therefore, the molybdenum metal is an indispensable material in high-tech fields. However, pure molybdenum metal generally shows poor ductility and toughness at room temperature. Moreover, the pure molybdenum metal has a low recrystallization temperature and is prone to brittle fracture since it is not easily deformed, thus seriously limiting the feasibility and application range of molybdenum deep processing. In view of this, it is currently a hotspot in the field of refractory metals to increase the recrystallization temperature of molybdenum metal through strengthening and toughening, thereby improving the ductility of molybdenum while increasing the material strength.

[0004] The strengthening and toughening of molybdenum alloys generally refers to continuously implanting a reinforcement material into the overall metal material matrix and achieving a dispersed distribution as much as possible. It is well known that the size, distribution, and volume fraction of reinforcement materials as well as the interface bonding between the metal matrix and reinforcement materials determine the final properties of an alloy material. Two-dimensional MAX ceramic materials are regarded as one of the most interesting in-situ metal matrix composites. Precursors for reinforcing metal matrix composites (MMCs) using ultrafine binary carbide / nitride particles decomposed from Mn+1AXn phase have also been extensively studied for more than two decades. The instability of a MAX lattice at high temperatures leads to the release of A-site atoms, and lattice transition from hexagonal to cubic occurs at the same time. A large number of research results show that sub-stoichiometric binary carbides (such as TiCx) are finer and can fully wet the metal matrix. Currently, it is an urgent problem in this field that needs to be solved to overcome the strength-ductility trade-off dilemma of molybdenum alloys to enhance their elastic modulus, specific strength and specific stiffness, wear and corrosion properties, room-temperature tensile strength, and high-temperature compressive strength without reducing the material strength.SUMMARY

[0005] An objective of the present disclosure is to provide an in-situ autogenous nano oxide- and carbide-synergistically toughened fine-grained molybdenum alloy and a preparation method thereof. In the present disclosure, alumina and a two-dimensional MAX ceramic material Ti3AlC2 are innovatively used to synergistically toughen a molybdenum alloy; and TiC0.67 formed by decomposition of the Ti3AlC2 shows better interface bonding with a matrix, thereby improving a mechanical strength and a ductility of the molybdenum alloy. The addition of alumina and subsequent thermoplastic processing further refines the grains and improves a compactness of the molybdenum alloy. Compared with a pure molybdenum metal, the high-strength and high-toughness fine-grained molybdenum alloy has a room-temperature tensile strength increased by not less than 100%, an elongation increased by not less than 100%, and a high-temperature compressive strength increased by not less than 60%.

[0006] The present disclosure is specifically achieved through the following technical solutions: an in-situ autogenous nano oxide- and carbide-synergistically toughened fine-grained molybdenum alloy and a preparation method thereof are proposed according to the present disclosure. The preparation method includes the following steps:

[0007] (1): fully dissolving a certain amount of aluminum nitrate and urea that are weighed according to a requirement of a final product in water, pouring a resulting mixed system into a polytetrafluoroethylene (PTFE) lining of a stainless steel hydrothermal reactor, and locking the stainless steel hydrothermal reactor to allow a hydrothermal reaction at 180° C. to 200° C. in a drying oven to obtain an alumina precursor solution;

[0008] (2): adding a certain amount of ammonium molybdate and a Ti3AlC2 powder that are weighed according to the requirement of the final product into an appropriate amount of distilled water, adding the alumina precursor solution obtained in step (1), stirring thoroughly, conducting suction filtration and low-temperature drying in sequence to obtain a mixture, and pulverizing the mixture to obtain a pulverized powder for later use;

[0009] (3): subjecting the pulverized powder obtained in step (2) to low-temperature reduction and high-temperature reduction in an atmosphere of reducing gas of hydrogen, where the low-temperature reduction is conducted at 400° C. to 600° C. under a hydrogen flow rate of (3-8) m3 / h for 8 h to 25 h with a powder spreading height that is less than or equal to ½ of a volume of the stainless steel hydrothermal reactor; and the high-temperature reduction is conducted at 800° C. to 1,000° C. under a hydrogen flow rate of (15-20) m3 / h for 8 h to 25 h with a powder spreading height that is less than or equal to ½ of the volume of the stainless steel hydrothermal reactor;

[0010] (4): selecting a graphite mold of an appropriate size according to a required size of the final product, loading a precursor powder obtained after the high-temperature reduction in step (3) into the graphite mold, and placing the graphite mold in a discharge plasma sintering furnace to allow low-temperature sintering to obtain a molybdenum alloy billet; where the sintering includes: heating to T1 at a speed of 50° C. / min to 100° C. / min under 20 MPa to 50 MPa, holding at the T1 for 0 min to 3 min, cooling down by 50° C. to 200° C. to T2, and holding at the T2 for 15 min to 30 min; and

[0011] the T1 is 1,300° C. to 1,900° C., T2=T1−ΔT, and the ΔT is 50° C. to 200° C.;

[0012] (5): heating the molybdenum alloy billet in step (4) to a temperature of 1,300° C. to 1,700° C. under a protective atmosphere, holding the temperature for 30 min to 60 min, and conducting high-temperature and large-deformation thermoplastic processing; and

[0013] (6): annealing a processed molybdenum alloy billet obtained in step (5) in a protective atmosphere to obtain a high-strength and high-toughness fine-grained molybdenum alloy.

[0014] The high-strength and high-toughness fine-grained molybdenum alloy prepared by the preparation method has a grain size of 0.5 μm to 5 μm, a room-temperature tensile strength of greater than 900 MPa, an elongation of greater than 52%, and a high-temperature compressive strength of greater than 390 MPa, which are improved by not less than 100%, not less than 100%, and not less than 50% compared with those of a pure molybdenum metal, respectively, achieving an increase in the plastic toughness of the molybdenum alloy without reducing its strength.

[0015] Further, the ammonium molybdate in step (1) is selected from the group consisting of ammonium tetramolybdate and ammonium dimolybdate. Based on a mass of the ammonium molybdate, a mass of the aluminum nitrate accounts for 0.5% to 3% of the mass of the ammonium molybdate, a mass of the urea accounts for 0.2% to 1.5% of the mass of the ammonium molybdate, and a mass of the Ti3AlC2 accounts for 0.2% to 2% of the mass of the ammonium molybdate.

[0016] Further, a powder obtained after the high-temperature reduction in step (3) has a particle size of 200 nm to 600 nm; the molybdenum alloy billet obtained by the sintering in step (4) includes a molybdenum grain and nano-Al2O3 and nano-TiC0.67 that are evenly distributed in the molybdenum grain; the molybdenum grain has an average width of 3 μm to 20 μm and an aspect ratio of less than or equal to 3; the nano-Al2O3 uniformly distributed in the molybdenum grain is nano-needle-shaped and has an average particle size of 10 nm to 50 nm; and the nano-TiC0.67 uniformly distributed in the molybdenum grain has an average particle size of 50 nm to 200 nm.

[0017] Preferably, the high-temperature thermoplastic processing in step (5) is one or a combination of two or more selected from the group consisting of rotary forging, rolling, extrusion, and drawing; and the high-temperature thermoplastic processing has a total number of passes of 3 to 10 times, a deformation in each pass of 25% to 35%, and a total deformation of greater than or equal to 80%. The high-temperature thermoplastic processing can be conducted to further refine the grains and improve the density and performance of the molybdenum alloy.

[0018] Preferably, the annealing in step (6) is conducted at 850° C. to 1,600° C. for 30 min to 200 min.

[0019] Further, the aluminum nitrate in step (1) is replaced with any one or more selected from the group consisting of lanthanum nitrate, chromium nitrate, zirconium nitrate, and yttrium nitrate. After replacement, the corresponding oxides in the molybdenum alloy prepared by the aforementioned process are no longer the alumina, but are the lanthanum oxide, chromium oxide, zirconium oxide, and yttrium oxide, respectively, thereby extending an application range of the preparation method in the present disclosure.

[0020] Preferably, the Ti3AlC2 in step (2) is replaced with any one or more selected from the group consisting of Zr3AlC2, Si3AlC2, Hf3AlC2, Zr2AlC, Si2AlC, Hf2AlC2, Zr4AlC3, Si4AlC3, and Hf4AlC3. In this way, the in-situ autogenous nano oxide- and carbide-synergistically toughened fine-grained molybdenum alloy can also be obtained, except that the carbide as a reinforcing phase changes.

[0021] Further, an in-situ autogenous nano oxide- and carbide-synergistically toughened fine-grained tungsten alloy is prepared by replacing the ammonium molybdate with ammonium metatungstate or ammonium paratungstate according to the preparation method; alternatively, an in-situ autogenous nano oxide- and carbide-synergistically toughened fine-grained copper alloy is prepared by replacing the ammonium molybdate with copper nitrate; alternatively, an in-situ autogenous nano oxide- and carbide-synergistically toughened fine-grained nickel alloy is prepared by replacing the ammonium molybdate with nickel nitrate, thereby extending an application range of the preparation method in the present disclosure.

[0022] Compared with the prior art, the present disclosure has obvious advantages and beneficial effects, at least the following advantages:

[0023] (1) In the present disclosure, only a small amount of secondary phase material needs to be prepared through a hydrothermal process. The hydrothermal process is simple and easy to operate, and there are no relevant parameters that require special adjustment. At the same time, problems are avoided, such as the formation of large particle agglomerates after hydrothermal treatment of ammonium molybdate as well as the inability to achieve reduction process if the powder is not refined by calcination. Omitting the calcination also prevents MoO3 from forming a mesophase Mo4O11 during the low-temperature reduction. The Mo4O11 is unstable and easily reacts with the MoO3 to form a low-melting eutectic, thereby causing the powder to harden and the particles to thicken. The preparation method of the present disclosure greatly saves production time and reduces energy consumption.

[0024] (2) The present disclosure uses two secondary phases that can synergistically enhance the performance of the matrix. It is required that the secondary phase must not only be small enough but also hard enough, and can be able to co-precipitate and decompose with the molybdenum matrix. Alumina and a two-dimensional MAX ceramic material Ti3AlC2 are innovatively used to synergistically toughen the molybdenum alloy. The two-dimensional MAX ceramic material Ti3AlC2 undergoes topological transformation during sintering, in which the A-site element is deintercalated and decomposed into an extremely-thin sub-stoichiometric two-dimensional carbide TiC0.67. The fine carbide TiC0.67 generated in situ shows better interface bonding with the matrix, restricts the growth of molybdenum grains, and triggers in-situ strengthening of the molybdenum alloy. Meanwhile, a unique lamellar structure of this carbide is evenly distributed at the intersection of grain boundaries, and increases the interlayer bonding force, deflects the growth of cracks, and inhibits the spread of cracks, thus improving the mechanical strength and ductility of the molybdenum alloy.

[0025] (3) An obtained sintered molybdenum alloy has a fine and dense structure. A microstructure of the sintered molybdenum alloy includes molybdenum grains and nano-Al2O3 and nano-TiC0.67 that are evenly distributed in the molybdenum grains. The nano-Al2O3 is nanoacoustic alumina, with a purity of not less than 99.5% and an average particle size of 10 nm to 50 nm; and the nano-TiC0.67 particles have an average particle size of 50 nm to 200 nm. The in-situ self-generated two-dimensional carbide TiC0.67 increases a toughness of the molybdenum alloy and increases a recrystallization temperature of the molybdenum alloy. Thermoplastic deformation adopts a high-temperature and large-deformation process, which not only saves time and improves production efficiency, but also further refines the grains and improves the density and performance of the molybdenum alloy.

[0026] (4) In the present disclosure, the raw materials are low-cost and easily available. The in-situ self-generated nano oxide / carbide can work synergistically to effectively enhance the high-temperature creep resistance of the molybdenum alloy. The room-temperature tensile strength has increased by not less than 100%, the elongation has increased by not less than 100%, and the high-temperature compressive strength has increased by not less than 60%. The prepared high-strength and high-toughness fine-grained molybdenum alloy has fine grains, desirable high-temperature mechanical properties, simple process, high yield, and excellent consistency. This fine-grained molybdenum alloy can be widely used as high-temperature structural parts for high-temperature heating elements, turbines, and fusion reactor components.BRIEF DESCRIPTION OF THE DRAWINGS

[0027] FIG. 1 shows a scanning electron microscopy (SEM) image of a molybdenum precursor powder obtained through two stages of hydrogen reduction in Example 1;

[0028] FIG. 2 shows a light microscopy metallographic image of the in-situ autogenous nano oxide- and carbide-synergistically toughened fine-grained molybdenum alloy prepared in Example 1;

[0029] FIG. 3 shows a light microscopy metallographic image of the in-situ autogenous nano oxide- and carbide-synergistically toughened fine-grained molybdenum alloy prepared in Example 2;

[0030] FIG. 4 shows a light microscopy metallographic image of the in-situ autogenous nano oxide- and carbide-synergistically toughened fine-grained molybdenum alloy prepared in Example 3;

[0031] FIG. 5 shows stress-strain curves of the in-situ autogenous nano oxide- and carbide-synergistically toughened fine-grained molybdenum alloys obtained in three examples;

[0032] FIG. 6 shows high-temperature stress-strain curves at 1,000° C. of the in-situ autogenous nano oxide- and carbide-synergistically toughened fine-grained molybdenum alloys obtained in three examples; and

[0033] FIG. 7 shows a SEM image of the molybdenum powder prepared in Comparative Example.DETAILED DESCRIPTION OF THE EMBODIMENTS

[0034] In order to make the objectives, technical solutions, and advantages of the embodiments of the present disclosure clearer, the technical solutions in the present disclosure are described clearly and completely below with reference to the accompanying drawings. Apparently, the described embodiments are some rather than all of the embodiments of the present disclosure. All other examples obtained by a person of ordinary skill in the art based on the examples of the present disclosure without creative efforts shall fall within the protection scope of the present disclosure.

[0035] The present disclosure provides a preparation method of an in-situ autogenous nano oxide- and carbide-synergistically toughened fine-grained molybdenum alloy, including the following steps:

[0036] (1): fully dissolving a certain amount of aluminum nitrate and urea that are weighed according to a requirement of a final product in water, pouring a resulting mixed system fully into a polytetrafluoroethylene (PTFE) lining of a stainless steel hydrothermal reactor, and locking the stainless steel hydrothermal reactor to allow a hydrothermal reaction at 180° C. to 200° C. in a drying oven to obtain an alumina precursor solution;

[0037] (2): adding a certain amount of ammonium molybdate and a Ti3AlC2 powder that are weighed according to the requirement of the final product into an appropriate amount of distilled water, adding the alumina precursor solution obtained in step (1), stirring thoroughly, conducting suction filtration and low-temperature drying in sequence to obtain a mixture, and pulverizing the mixture using a high-speed pulverizer to obtain a pulverized powder for later use; where

[0038] the ammonium molybdate is selected from the group consisting of ammonium tetramolybdate and ammonium dimolybdate, and has a content of impurity potassium of 10 ppm to 300 ppm;

[0039] (3): subjecting the pulverized powder prepared in step (2) to low-temperature reduction and high-temperature reduction in an atmosphere of reducing gas of hydrogen, where the low-temperature reduction is conducted at 400° C. to 600° C. under a hydrogen flow rate of (3-8) m3 / h for 8 h to 25 h with a powder spreading height that is less than or equal to ½ of a volume of the stainless steel hydrothermal reactor; and the high-temperature reduction is conducted at 800° C. to 1,000° C. under a hydrogen flow rate of (15-20) m3 / h for 8 h to 25 h with a powder spreading height that is less than or equal to ½ of the volume of the stainless steel hydrothermal reactor;

[0040] the ammonium molybdate is directly reduced to MoO2 in low-temperature hydrogen reduction without the formation of intermediate products, which is beneficial to the production of a high-quality ultra-fine spherical molybdenum powder with small, uniform, and nearly-spherical particles; a molybdenum precursor powder obtained by the reduction has a particle size of 200 nm to 600 nm; and

[0041] a reduced mixed powder includes a molybdenum powder, an alumina powder, and a Ti3AlC2 powder (the Ti3AlC2 does not decompose during the hydrogen reduction), where the alumina powder accounts for 0.2% to 1% of a total mass of the mixed powder, the Ti3AlC2 powder accounts for 0.2% to 2% of the total mass of the mixed powder, and the molybdenum powder serves as a balance; the Ti3AlC2 is in the form of lamellae with 1 to 5 layers, and has a purity of not less than 99% and an average particle size of 1 μm to 5 μm;

[0042] (4): selecting a graphite mold of an appropriate size according to a required size of the final product, loading a precursor powder obtained after the high-temperature reduction in step (3) into the graphite mold, and placing the graphite mold in a discharge plasma sintering furnace to allow low-temperature sintering to obtain a molybdenum alloy billet; where the sintering includes: heating to T1 at 50° C. / min to 100° C. / min under 20 MPa to 50 MPa, holding at the T1 for 0 min to 3 min, cooling down by 50° C. to 200° C. to T2, and holding at the T2 for 15 min to 30 min; and the Ti is 1,300° C. to 1,900° C., T2=T1−ΔT, and the ΔT is 50° C. to 200° C.;

[0043] the multi-stage plasma discharge rapid sintering process has a low sintering temperature and can effectively suppress grain growth (dense fine grains can be obtained only by low-temperature and long-term sintering); and the molybdenum alloy billet obtained by the sintering includes a molybdenum grain and nano-Al2O3 and nano-TiC0.67 that are evenly distributed in the molybdenum grain; the molybdenum grain has an average width of 3 μm to 20 μm and an aspect ratio of less than or equal to 3; the nano-Al2O3 uniformly distributed in the molybdenum grain is nano-needle-shaped and has an average particle size of 10 nm to 50 nm; and the nano-TiC0.67 uniformly distributed in the molybdenum grain has an average particle size of 50 nm to 200 nm;

[0044] (5): heating the molybdenum alloy billet in step (4) to a temperature of 1,300° C. to 1,600° C. under a protective atmosphere, holding the temperature for 30 min to 60 min, and conducting high-temperature and large-deformation thermoplastic processing; where the high-temperature thermoplastic processing is one or a combination of two or more selected from the group consisting of rotary forging, rolling, extrusion, and drawing; and the high-temperature thermoplastic processing has a total number of passes of 3 to 10 times, a deformation in each pass of 25% to 35%, and a total deformation of greater than or equal to 80%; and

[0045] (6): annealing a processed molybdenum alloy billet obtained in step (5) at 850° C. to 1,600° C. for 30 min to 200 min in a protective atmosphere to obtain a high-strength and high-toughness fine-grained molybdenum alloy, namely the in-situ autogenous nano oxide- and carbide-synergistically toughened fine-grained molybdenum alloy.

[0046] In the present disclosure, alumina and a two-dimensional MAX ceramic material Ti3AlC2 are innovatively used to synergistically toughen the molybdenum alloy. The two-dimensional MAX ceramic material Ti3AlC2 undergoes topological transformation during the sintering, in which the A-site element is deintercalated and decomposed into an extremely-thin sub-stoichiometric two-dimensional carbide TiC0.67. This effectively reduces the surface tension of liquid metal and the interfacial tension of solid-liquid, and is more conducive to the generation of interface products. Moreover, a wetting effect is greatly improved, and the metal matrix can be fully wetted, such that the oxide and carbide synergistically toughen the fine-grained molybdenum alloy.

[0047] In the present disclosure, the in-situ autogenous nano oxide- and carbide-synergistically toughened fine-grained molybdenum alloy prepared by the preparation method has a grain size of 0.5 μm to 5 μm. The alloy has a room-temperature tensile strength of greater than 900 MPa (improved by more than 100% compared with that of a pure molybdenum metal), an elongation of greater than 52% (improved by more than 100% compared with that of a pure molybdenum metal), and a high-temperature compressive strength of greater than 390 MPa (improved by more than 50% compared with that of a pure molybdenum metal). This achieves an increase in the plastic toughness of the molybdenum alloy without reducing its strength.

[0048] In the present disclosure, an in-situ autogenous nano oxide- and carbide-synergistically toughened fine-grained molybdenum alloy is obtained by using the above preparation method. In other examples, the two-dimensional MAX ceramic material Ti3AlC2 can be replaced with any one or more from a 312-phase MAX phase ceramic (Zr3AlC2 or Si3AlC2 or Hf3AlC2), a 211-phase MAX phase ceramic (Zr2AlC or Si2AlC or Hf2AlC2), and a 413-phase MAX phase ceramic (Zr4AlC3 or Si4AlC3 or Hf4AlC3). In this way, the in-situ autogenous nano oxide- and carbide-synergistically toughened fine-grained molybdenum alloy can also be obtained, except that the carbide as a reinforcing phase changes. For those skilled in the art, this alternative solution is easy to understand and will not be described in detail in the present disclosure.

[0049] Additionally, aluminum nitrate may be replaced with lanthanum nitrate or chromium nitrate or zirconium nitrate or yttrium nitrate in other examples. The corresponding oxides in the molybdenum alloy prepared by the aforementioned process are lanthanum oxide, chromium oxide, zirconium oxide, and yttrium oxide.

[0050] At the same time, by replacing the raw material ammonium molybdate, the above preparation method can also be used to prepare in-situ autogenous nano oxide- and carbide-synergistically toughened fine-grained tungsten alloy, in-situ autogenous nano oxide- and carbide-synergistically toughened fine-grained copper alloy, or in-situ autogenous nano oxide- and carbide-synergistically toughened fine-grained nickel alloy. For example, ammonium metatungstate and ammonium paratungstate can be used as a metal matrix material when preparing the in-situ autogenous nano oxide- and carbide-synergistically toughened fine-grained tungsten alloy; copper nitrate can be used as a metal matrix material when preparing the in-situ autogenous nano oxide- and carbide-synergistically toughened fine-grained copper alloy; and nickel nitrate can be used as a metal matrix material when preparing the in-situ autogenous nano oxide- and carbide-synergistically toughened fine-grained nickel alloy. The preparation methods of the above products are the same as the preparation method of the in-situ autogenous nano oxide- and carbide-synergistically toughened fine-grained molybdenum alloy, and will not be repeated here.

[0051] The technical solutions will be described in detail below with reference to specific examples:Example 1(1): 215 g of aluminum nitrate and 80 g of urea weighed according to a requirement of a final product were fully dissolved in water, a resulting mixed system was poured fully into a PTFE lining of a stainless steel hydrothermal reactor, and the stainless steel hydrothermal reactor was locked to allow a hydrothermal reaction at 180° C. for 20 h in a drying oven to obtain an alumina precursor solution;

[0053] (2): 10 kg of ammonium tetramolybdate and 114 g of a Ti3AlC2 powder weighed according to the requirement of the final product were added into an appropriate amount of distilled water, the alumina precursor solution obtained in step (1) was added, stirred thoroughly, suction filtration and low-temperature drying were conducted in sequence to obtain a mixture, and the mixture was pulverized using a high-speed pulverizer to obtain a pulverized powder for later use;

[0054] (3): the pulverized powder prepared in step (2) was subjected to low-temperature reduction and high-temperature reduction in an atmosphere of reducing gas of hydrogen, where the low-temperature reduction was conducted at 500° C. under a hydrogen flow rate of 8 μm3 / h for 20 h with a powder spreading height that was less than or equal to ½ of a volume of the stainless steel hydrothermal reactor; and the high-temperature reduction was conducted at 1,000° C. under a hydrogen flow rate of 20 μm3 / h for 20 h with a powder spreading height that was less than or equal to ½ of the volume of the stainless steel hydrothermal reactor; and a powder obtained by the reduction had an average particle size of 350 nm;

[0055] the reduced mixed powder included a molybdenum powder, an alumina powder, and a Ti3AlC2 powder (the Ti3AlC2 did not decompose during the hydrogen reduction), where the alumina powder accounted for 0.5% of a total mass of the mixed powder, the Ti3AlC2 powder accounted for 2% of the total mass of the mixed powder, and the molybdenum powder served as a balance;

[0056] (4): a graphite mold of an appropriate size was selected according to a required size of the final product, a precursor powder obtained after the high-temperature reduction in step (3) was loaded into the graphite mold, and the graphite mold was placed in a discharge plasma sintering furnace to allow low-temperature sintering to obtain a molybdenum alloy billet; where the sintering included: heating to 1,400° C. at a speed of 100° C. / min under 30 MPa, holding at 1,400° C. for 3 min under 30 MPa, cooling down by 100° C. to 1,300° C., and holding at 1,300° C. for 20 min; and

[0057] the molybdenum alloy billet obtained by the sintering included a molybdenum grain having an average width of 10 μm and an aspect ratio of less than or equal to 2.5; nano-Al2O3 particles uniformly distributed in the molybdenum grain had an average particle size of 15 nm; and the nano-TiC0.67 particles uniformly distributed in the molybdenum grain had an average particle size of 180 nm;

[0058] (5): the molybdenum alloy billet in step (4) was heated to a temperature of 1,400° C. under a protective atmosphere, the temperature was held for 60 min, and hot rolling was conducted; where the hot rolling was conducted using one temperature on three passes, and had a total number of passes of six times, a deformation in each pass of 25%, and a total deformation of 82.21%; and

[0059] (6): a processed molybdenum alloy billet obtained in step (5) was annealed at 1,200° C. for 60 min in a protective atmosphere to obtain a high-strength and high-toughness fine-grained molybdenum alloy with an average particle size of 1 μm, namely the in-situ autogenous nano oxide- and carbide-synergistically toughened fine-grained molybdenum alloy.

[0060] The room-temperature mechanical properties of the in-situ autogenous nano oxide- and carbide-synergistically toughened fine-grained molybdenum alloy prepared in this example were tested with the American INSTRON-5967 universal testing machine, while its high-temperature compressive strength was tested with the American Gleeble-1500D thermal simulation testing machine. The room-temperature tensile strength was 969 MPa, the elongation was 52.7%, and the high-temperature compressive strength at 1,100° C. was 420 MPa, which were increased by 106%, 110.8%, and 75% compared to those of a pure molybdenum metal, respectively, thus achieving an increase in the plastic toughness of molybdenum alloy without reducing its strength.

[0061] FIG. 1 showed a SEM image of a molybdenum precursor powder obtained through two stages of hydrogen reduction in Example 1. It indicated that the molybdenum precursor powder was a small and uniform nearly-spherical powder with a particle size of 200 nm to 600 nm.Example 2(1): 108 g of aluminum nitrate and 40 g of urea weighed according to a requirement of a final product were fully dissolved in water, a resulting mixed system was poured fully into a PTFE lining of a stainless steel hydrothermal reactor, and the stainless steel hydrothermal reactor was locked to allow a hydrothermal reaction at 180° C. for 20 h in a drying oven to obtain an alumina precursor solution;

[0063] (2): 10 kg of ammonium tetramolybdate and 86 g of a Ti3AlC2 powder weighed according to the requirement of the final product were added into an appropriate amount of distilled water, the alumina precursor solution obtained in step (1) was added, stirred thoroughly, suction filtration and low-temperature drying were conducted in sequence to obtain a mixture, and the mixture was pulverized using a high-speed pulverizer to obtain a pulverized powder for later use;

[0064] (3): the pulverized powder prepared in step (2) was subjected to low-temperature reduction and high-temperature reduction in an atmosphere of reducing gas of hydrogen, where the low-temperature reduction was conducted at 480° C. under a hydrogen flow rate of 7 μm3 / h for 18 h with a powder spreading height that was less than or equal to ⅖ of a volume of the stainless steel hydrothermal reactor; and the high-temperature reduction was conducted at 900° C. under a hydrogen flow rate of 19 μm3 / h for 18 h with a powder spreading height that was less than or equal to ⅖ of the volume of the stainless steel hydrothermal reactor; and a powder obtained by the reduction had an average particle size of 390 nm;

[0065] the reduced mixed powder included a molybdenum powder, an alumina powder, and a Ti3AlC2 powder (the Ti3AlC2 did not decompose during the hydrogen reduction), where the alumina powder accounted for 0.25% of a total mass of the mixed powder, the Ti3AlC2 powder accounted for 1.5% of the total mass of the mixed powder, and the molybdenum powder served as a balance;

[0066] (4): a graphite mold of an appropriate size was selected according to a required size of the final product, a precursor powder obtained after the high-temperature reduction in step (3) was loaded into the graphite mold, and the graphite mold was placed in a discharge plasma sintering furnace to allow low-temperature sintering to obtain a molybdenum alloy billet; where the sintering included: heating to 1,500° C. at 100° C. / min under 30 MPa, holding at 1,500° C. for 2 min, cooling down by 200° C. to 1,300° C., and holding at 1,300° C. for 20 min; and

[0067] the molybdenum alloy billet obtained by the sintering included a molybdenum grain having an average width of 10 μm and an aspect ratio of less than or equal to 1.9; nano-Al2O3 particles uniformly distributed in the molybdenum grain had an average particle size of 20 nm; and the nano-TiC0.67 particles uniformly distributed in the molybdenum grain had an average particle size of 200 nm;

[0068] (5): the molybdenum alloy billet in step (4) was heated to a temperature of 1500° C. under a protective atmosphere, the temperature was held for 40 min, and rotary forging was conducted; where the thermoplastic deformation processing was conducted at a total number of passes of 5 times, a deformation in each pass of 30%, and a total deformation of 83.2%; and

[0069] (6): a processed molybdenum alloy billet obtained in step (5) was annealed at 1,200° C. for 60 min in a protective atmosphere to obtain a high-strength and high-toughness fine-grained molybdenum alloy with an average particle size of 1.2 μm, namely the in-situ autogenous nano oxide- and carbide-synergistically toughened fine-grained molybdenum alloy.

[0070] The room-temperature mechanical properties and high-temperature compressive strength of the in-situ autogenous nano oxide- and carbide-synergistically toughened fine-grained molybdenum alloy prepared in this example were tested by the method in Example 1. The room-temperature tensile strength was 1,005 MPa, the elongation was 53.1%, and the high-temperature compressive strength at 1,100° C. was 390 MPa, which were increased by 113.8%, 112.4%, and 62.5% compared to those of a pure molybdenum metal, respectively, thus achieving an increase in the plastic toughness of molybdenum alloy without reducing its strength.Example 3(1): 65 g of aluminum nitrate and 24 g of urea weighed according to a requirement of a final product were fully dissolved in water, a resulting mixed system was poured fully into a PTFE lining of a stainless steel hydrothermal reactor, and the stainless steel hydrothermal reactor was locked to allow a hydrothermal reaction at 180° C. for 20 h in a drying oven to obtain an alumina precursor solution;

[0072] (2): 10 kg of ammonium tetramolybdate and 57 g of a Ti3AlC2 powder weighed according to the requirement of the final product were added into an appropriate amount of distilled water, the alumina precursor solution obtained in step (1) was added, stirred thoroughly, suction filtration and low-temperature drying were conducted in sequence to obtain a mixture, and the mixture was pulverized using a high-speed pulverizer to obtain a pulverized powder for later use;

[0073] (3): the pulverized powder prepared in step (2) was subjected to low-temperature reduction and high-temperature reduction in an atmosphere of reducing gas of hydrogen, where the low-temperature reduction was conducted at 550° C. under a hydrogen flow rate of 5 μm3 / h for 25 h with a powder spreading height that was less than or equal to ½ of a volume of the stainless steel hydrothermal reactor; and the high-temperature reduction was conducted at 1,000° C. under a hydrogen flow rate of 16 μm3 / h for 25 h with a powder spreading height that was less than or equal to ½ of the volume of the stainless steel hydrothermal reactor; and a powder obtained by the reduction had an average particle size of 370 nm;

[0074] the reduced mixed powder included a molybdenum powder, an alumina powder, and a Ti3AlC2 powder (the Ti3AlC2 did not decompose during the hydrogen reduction), where the alumina powder accounted for 0.15% of a total mass of the mixed powder, the Ti3AlC2 powder accounted for 1% of the total mass of the mixed powder, and the molybdenum powder served as a balance;

[0075] (4): a graphite mold of an appropriate size was selected according to a required size of the final product, a precursor powder obtained after the high-temperature reduction in step (3) was loaded into the graphite mold, and the graphite mold was placed in a discharge plasma sintering furnace to allow low-temperature sintering to obtain a molybdenum alloy billet; where the sintering included: heating to 1,300° C. at 100° C. / min under 50 MPa, holding at 1,300° C. for 2 min, cooling down by 100° C. to 1,200° C., and holding at 1,200° C. for 15 min; and

[0076] the molybdenum alloy billet obtained by the sintering included a molybdenum grain having an average width of 3 μm and an aspect ratio of less than or equal to 2.6; nano-Al2O3 particles uniformly distributed in the molybdenum grain had an average particle size of 11 nm; and the nano-TiC0.67 particles uniformly distributed in the molybdenum grain had an average particle size of 160 nm;

[0077] (5): the molybdenum alloy billet in step (4) was heated to a temperature of 1500° C. under a protective atmosphere, the temperature was held for 60 min, and extrusion was conducted; where the thermoplastic deformation processing was conducted at a total number of passes of 5 times, a deformation in each pass of 35%, and a total deformation of 88.4%; and

[0078] (6): a processed molybdenum alloy billet obtained in step (5) was annealed at 1,300° C. for 60 min in a protective atmosphere to obtain a high-strength and high-toughness fine-grained molybdenum alloy with an average particle size of 0.6 μm, namely the in-situ autogenous nano oxide- and carbide-synergistically toughened fine-grained molybdenum alloy.

[0079] The room-temperature mechanical properties and high-temperature compressive strength of the in-situ autogenous nano oxide- and carbide-synergistically toughened fine-grained molybdenum alloy prepared in this example were tested by the method in Example 1. The room-temperature tensile strength was 1,217 MPa, the elongation was 55.9%, and the high-temperature compressive strength at 1,100° C. was 450 MPa, which were increased by 158.9%, 123.6%, and 87.5% compared to those of a pure molybdenum metal, respectively, thus achieving an increase in the plastic toughness of molybdenum alloy without reducing its strength.

[0080] FIG. 2, FIG. 3, and FIG. 4 showed organizational morphology (by light microscope metallographic image) of the in-situ autogenous nano oxide- and carbide-synergistically toughened fine-grained molybdenum alloys prepared in Example 1, Example 2, and Example 3, respectively. It was seen that their average grain sizes were 1 μm, 1.2 μm, and 0.6 μm, respectively. The larger secondary phases were evenly distributed at the grain boundaries, while the fine secondary phases were evenly distributed inside the grains.

[0081] FIG. 5 showed stress-strain curves of the in-situ autogenous nano oxide- and carbide-synergistically toughened fine-grained molybdenum alloys obtained in three examples; the tensile strengths of the molybdenum alloys finally prepared by different processes were slightly different, but were overall higher than that of the pure molybdenum.

[0082] FIG. 6 showed high-of temperature stress-strain curves at 1,000° C. of the in-situ autogenous nano oxide- and carbide-synergistically toughened fine-grained molybdenum alloys obtained in three examples. The compressive strengths of the finally prepared in-situ autogenous nano oxide- and carbide-synergistically toughened fine-grained molybdenum alloys at 1,000° C. were all significantly higher than that of the pure molybdenum.Comparative Example

[0083] This comparative example followed the method of Example 3, except that no alumina or urea was added, that is, step (1) was removed, and the alumina precursor solution in step (2) was not added; while other steps were the same as those in Example 3. The SEM image of a powder finally obtained after reduction in step (3) was shown in FIG. 7. The powder had a particle size of approximately 1.6 μm, which was smaller than that of a conventional molybdenum powder at 3 m. However, the particle sizes of the powders obtained after reduction in Examples 1 to 3 were 350 nm, 390 nm, and 370 nm, respectively. This indicated that without adding the alumina, the powder showed no obvious refining effect.

[0084] The above are merely preferred examples of the present disclosure rather than limitations on the present disclosure in any form. The present disclosure can also have other forms of examples based on the above structures and functions, which will not be listed one by one. Therefore, any simple modifications, equivalent substitutions, equivalent changes, and modifications made to the above examples according to the technical essence of the present disclosure without departing from the contents of the technical solutions of the present disclosure still fall in the protection scope of the technical solutions of the present disclosure.

Claims

1. A preparation method of an in-situ autogenous nano oxide- and carbide-synergistically toughened fine-grained molybdenum alloy, comprising the following steps:(1): fully dissolving a certain amount of aluminum nitrate and urea that are weighed according to a requirement of a final product in water, pouring a resulting mixed system into a polytetrafluoroethylene (PTFE) lining of a stainless steel hydrothermal reactor, and locking the stainless steel hydrothermal reactor to allow a hydrothermal reaction at 180° C. to 200° C. in a drying oven to obtain an alumina precursor solution;(2): adding a certain amount of ammonium molybdate and a Ti3AlC2 powder that are weighed according to the requirement of the final product into an appropriate amount of distilled water, adding the alumina precursor solution obtained in step (1), stirring thoroughly, conducting suction filtration and low-temperature drying in sequence to obtain a mixture, and pulverizing the mixture to obtain a pulverized powder for later use;(3): subjecting the pulverized powder obtained in step (2) to low-temperature reduction and high-temperature reduction in an atmosphere of reducing gas of hydrogen, wherein the low-temperature reduction is conducted at 400° C. to 600° C. under a hydrogen flow rate of (3-8) m3 / h for 8 h to 25 h with a powder spreading height that is less than or equal to ½ of a volume of the stainless steel hydrothermal reactor; and the high-temperature reduction is conducted at 800° C. to 1,000° C. under a hydrogen flow rate of (15-20) m3 / h for 8 h to 25 h with a powder spreading height that is less than or equal to ½ of the volume of the stainless steel hydrothermal reactor;(4): selecting a graphite mold of an appropriate size according to a required size of the final product, loading a precursor powder obtained after the high-temperature reduction in step (3) into the graphite mold, and placing the graphite mold in a discharge plasma sintering furnace to allow low-temperature sintering to obtain a molybdenum alloy billet; wherein the sintering comprises:heating to T1 at 50° C. / min to 100° C. / min under 20 MPa to 50 MPa, holding at the T1 for 0 min to 3 min, cooling down by 50° C. to 200° C. to T2, and holding at the T2 for 15 min to 30 min; andthe T1 is 1,300° C. to 1,900° C., T2=T1−ΔT, and the ΔT is 50° C. to 200° C.;(5): heating the molybdenum alloy billet in step (4) to a temperature of 1,300° C. to 1,700° C. under a protective atmosphere, holding the temperature for 30 min to 60 min, and conducting high-temperature and large-deformation thermoplastic processing; and(6): annealing a processed molybdenum alloy billet obtained in step (5) in a protective atmosphere to obtain a high-strength and high-toughness fine-grained molybdenum alloy.

2. The preparation method of an in-situ autogenous nano oxide- and carbide-synergistically toughened fine-grained molybdenum alloy according to claim 1, wherein the ammonium molybdate is selected from the group consisting of ammonium tetramolybdate and ammonium dimolybdate.

3. The preparation method of an in-situ autogenous nano oxide- and carbide-synergistically toughened fine-grained molybdenum alloy according to claim 1, wherein a powder obtained after the high-temperature reduction in step (3) has a particle size of 200 nm to 600 nm.

4. The preparation method of an in-situ autogenous nano oxide- and carbide-synergistically toughened fine-grained molybdenum alloy according to claim 1, wherein the molybdenum alloy billet obtained by the sintering in step (4) comprises a molybdenum grain and nano-Al2O3 and nano-TiC0.67 that are evenly distributed in the molybdenum grain; the molybdenum grain has an average width of 3 μm to 20 μm and an aspect ratio of less than or equal to 3; the nano-Al2O3 uniformly distributed in the molybdenum grain is nano-needle-shaped and has an average particle size of 10 nm to 50 nm; and the nano-TiC0.67 uniformly distributed in the molybdenum grain has an average particle size of 50 nm to 200 nm.

5. The preparation method of an in-situ autogenous nano oxide- and carbide-synergistically toughened fine-grained molybdenum alloy according to claim 1, wherein the high-temperature thermoplastic processing in step (5) is one or a combination of two or more selected from the group consisting of rotary forging, rolling, extrusion, and drawing; and the high-temperature thermoplastic processing has a total number of passes of 3 to 10 times, a deformation in each pass of 25% to 35%, and a total deformation of greater than or equal to 80%.

6. The preparation method of an in-situ autogenous nano oxide- and carbide-synergistically toughened fine-grained molybdenum alloy according to claim 1, wherein the annealing in step (6) is conducted at 850° C. to 1,600° C. for 30 min to 200 min.

7. The preparation method of an in-situ autogenous nano oxide- and carbide-synergistically toughened fine-grained molybdenum alloy according to claim 1, wherein the high-strength and high-toughness fine-grained molybdenum alloy has a grain size of 0.5 μm to 5 μm, a room-temperature tensile strength of greater than 900 MPa, an elongation of greater than 52%, and a high-temperature compressive strength of greater than 390 MPa.

8. The preparation method of an in-situ autogenous nano oxide- and carbide-synergistically toughened fine-grained molybdenum alloy according to claim 1, wherein the aluminum nitrate in step (1) is replaced with any one or more selected from the group consisting of lanthanum nitrate, chromium nitrate, zirconium nitrate, and yttrium nitrate.

9. The preparation method of an in-situ autogenous nano oxide- and carbide-synergistically toughened fine-grained molybdenum alloy according to claim 1, wherein the Ti3AlC2 in step (2) is replaced with any one or more selected from the group consisting of Zr3AlC2, Si3AlC2, Hf3AlC2, Zr2AlC, Si2AlC, Hf2AlC2, Zr4AlC3, Si4AlC3, and Hf4AlC3.

10. The preparation method of an in-situ autogenous nano oxide- and carbide-synergistically toughened fine-grained molybdenum alloy according to claim 1, wherein an in-situ autogenous nano oxide- and carbide-synergistically toughened fine-grained tungsten alloy is prepared by replacing the ammonium molybdate with ammonium metatungstate or ammonium paratungstate according to the preparation method; alternatively, an in-situ autogenous nano oxide- and carbide-synergistically toughened fine-grained copper alloy is prepared by replacing the ammonium molybdate with copper nitrate; alternatively, an in-situ autogenous nano oxide- and carbide-synergistically toughened fine-grained nickel alloy is prepared by replacing the ammonium molybdate with nickel nitrate.

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