PROCESS FOR PREPARING MOLYBDENUM ALLOY BY ULTRA-HIGH-TEMPERATURE ROLLING

Description

CROSS REFERENCE TO RELATED APPLICATION

This patent application claims the benefit and priority of Chinese Patent Application No. 202410278159.3 filed with the China National Intellectual Property Administration on Mar. 12, 2024, the disclosure of which is incorporated by reference herein in its entirety as part of the present application.

TECHNICAL FIELD

The present disclosure belongs to the technical field of alloy materials, and specifically relates to a process for preparing a molybdenum alloy by ultra-high-temperature rolling.

BACKGROUND

Molybdenum alloys, due to the properties such as high melting point and high-temperature strength, low high-temperature creep rate and expansion coefficient, excellent thermal and electrical conductivity and thermal shock resistance, and strong corrosion resistance, are widely used in the fields such as chemical industry and metallurgical industry as well as metal processing industry, aerospace industry, and nuclear energy technology. The molybdenum alloys show irreplaceable advantages in high-temperature fields, for example, high-temperature components on devices such as turbine engines in the aerospace industry, missiles in the military industry and fusion reactors in the nuclear industry, as well as high-temperature nozzles on aircraft engines and molybdenum plugs in the metallurgical industry. Furthermore, the molybdenum alloy is the only ideal material for the core of a high-temperature space nuclear reactor due to suitable density and low neutron absorption cross-section. High-temperature structural components have extremely high requirements for material safety and reliability, which are reflected in high recrystallization temperatures and excellent strength and ductility at room and high temperatures.

Nano-ceramics are composites made by introducing nano-scale ceramic particles, whiskers, and fibers into a ceramic matrix to improve the performance of ceramics. The nano-ceramics improve room-temperature mechanical properties and high-temperature properties of the matrix material, and are machinable and superplastic. The properties of nano-ceramics mainly refer to mechanical properties, including hardness, fracture toughness, and low-temperature ductility of the nano-ceramics. The use of nano-ceramic particles is an effective technical means in strengthening the mechanical properties of alloy composites. Currently, further enhancement of molybdenum alloy properties generally relies on increasing a volume fraction of the nano-ceramic particles or introducing harder intermetallic compounds. However, during the high-temperature preparation of molybdenum alloys, adding nano-ceramic particles to achieve high strength of molybdenum alloys may inevitably reduce the ductility and high temperature stability.

In addition, a cogging temperature of rolling is generally selected to be close to a recrystallization temperature. Currently, a rolling temperature of pure Mo used in common technology is 1,100° C., and a rolling temperature of two-phase-doped Mo alloys such as titanium-zirconium-molybdenum (TZM), Mo—La₂O₃, and Mo—ZrC is 1,350° C. Insufficient rolling temperatures may cause a plate blank to be hard, and cracks may occur during the rolling, such that a complete plate blank cannot be obtained, resulting in product dimensions that do not meet the requirements. Excessively high rolling temperatures may cause the plate blank to fracture, making rolling impossible. In view of this, rolling temperature plays a crucial role in thermoplastic deformation.

SUMMARY

In view of the problems existing in the prior art, the present disclosure provides a process for preparing a molybdenum alloy by ultra-high-temperature rolling, which aims to achieve effective control of the size, distribution, crystal form, and interface structure of nano-ceramic particles through integrated preparation of liquid-liquid doping+co-precipitation+co-decomposition, thus greatly increasing the relative density and recrystallization temperature of sintered molybdenum alloys, and prepare an ultra-high strength and toughness molybdenum alloy with excellent mechanical properties and high-temperature stability by weakening a texture of the molybdenum alloy in <110> direction through ultra-high-temperature rolling.

The present disclosure provides a process for preparing a molybdenum alloy by ultra-high-temperature rolling, where the molybdenum alloy is an ultra-high strength and toughness molybdenum alloy, and includes 95 wt % to 99.9 wt % of molybdenum and 0.1 wt % to 5 wt % of a nano-ceramic oxide particle. The process for preparing a molybdenum alloy by ultra-high-temperature rolling includes the following steps:

• • (1) preparing an MOx—SO₃H aqueous solution: mixing benzenesulfonic acid and a nano-ceramic oxide particle with a particle size of 10 nm to 200 nm in water to be uniform to obtain a mixed system, and subjecting the mixed system to hydrothermal reaction to obtain the sulfonic acid group-modified oxide (MOx—SO₃H) aqueous solution;
  • (2) preparing a precursor composite powder: preparing a molybdenum salt aqueous solution with a concentration of 0.02 mol/L to 2.5 mol/L, adding the molybdenum salt aqueous solution into the MOx—SO₃H aqueous solution to obtain a mixed solution, adjusting the mixed solution to have a pH of 5.5 to 6.5 by adding lactic acid to obtain a solution system, and subjecting the solution system to stirring, drying, and pulverizing in sequence to obtain the precursor composite powder;
  • (3) preparing a nano-ceramic oxide-reinforced molybdenum alloy powder by reduction: subjecting the precursor composite powder to two-stage reduction (i.e. first-stage reduction and second-stage reduction) in hydrogen to obtain the nano-ceramic oxide-reinforced molybdenum alloy powder with a particle size of 0.5 μm to 5 μm; and
  • (4) preparing the ultra-high strength and toughness molybdenum alloy by pressing and sintering: pressing the nano-ceramic oxide-reinforced molybdenum alloy powder, and then conducting sintering in a hydrogen atmosphere to obtain a nano-ceramic oxide-reinforced molybdenum alloy with a of greater than 98%, and subjecting the nano-ceramic oxide-reinforced molybdenum alloy to ultra-high-temperature rolling to obtain the ultra-high strength and toughness molybdenum alloy.

In some embodiments, in step (1) the nano-ceramic oxide particle is one selected from the group consisting of zirconia, titania, alumina, hafnia, yttria, and lanthana.

In some embodiments, in step (1) the hydrothermal reaction is conducted at a temperature of 60° C. to 90° C. for 2 h to 8 h under stirring at a speed of 50 r/min to 300 r/min.

In some embodiments, in step (2) a molybdenum salt in the molybdenum salt aqueous solution is one or more selected from the group consisting of potassium molybdate, sodium molybdate, and ammonium molybdate.

In some embodiments, in step (3) the first-stage reduction is conducted at a temperature of 350° C. to 550° C. for 4 h to 9 h with a hydrogen flow rate of 15 m³/h to 18 m³/h, and the second-stage reduction is conducted at a temperature of 800° C. to 950° C. for 8 h to 12 h with a hydrogen flow rate of 18 m³/h to 25 m³/h.

In some embodiments, in step (4) the pressing is conducted in a cold isostatic press at a pressure of 150 MPa to 200 MPa for 15 min to 20 min.

In some embodiments, in step (4) the sintering is conducted in a pressureless medium-frequency furnace at a temperature of 1,700° C. to 2,000° C. for 4 h to 10 h with a hydrogen flow rate of 18 m³/h to 25 m³/h.

In some embodiments, in step (4) the ultra-high-temperature rolling is conducted at a cogging temperature of 1,500° C. to 1,700° C. by heating once in every one rolling pass with a single deformation of 30% to 50% and a total deformation of greater than 90%.

In the present disclosure, the process for preparing an ultra-high strength and toughness molybdenum alloy could also be used to prepare alloys with high specific gravity and energy content such as tungsten alloy and tungsten-nickel-iron alloy.

Compared with the prior art, the present disclosure has the following beneficial effects:

• • (1) The present disclosure provides a process for preparing a molybdenum alloy by ultra-high-temperature rolling. A mixed solution of an oxide and benzenesulfonic acid is dispersed uniformly by an ultrasonic treatment, and then subjected to hydrothermal reaction to obtain a sulfonic acid group-modified oxide (MOx—SO₃H). A soluble molybdenum salt is added therein to form (MOx—SO₃H)₂—MoO₄. The (MOx—SO₃H)₂—MoO₄ is subjected to pH adjustment with an acid and then subjected to hydrothermal reaction and hydrogen reduction to obtain a nano-ceramic oxide-reinforced molybdenum alloy powder with a particle size of 0.5 μm to 5 μm. This present disclosure allows atomic-level mixing of oxides and molybdenum, and avoids uneven powder mixing during the preparation of ceramic phase-reinforced molybdenum alloys caused by the traditional ball milling. Moreover, the process according to the present disclosure has simple steps and strong operability, and is easy to realize large-scale production.

(2) In the present disclosure, the preparation process has controllable conditions. The relative density (greater than 98%) and recrystallization temperature (above 1,500° C.) of the sintered molybdenum alloy could be improved by regulating the process conditions for pressing and sintering molybdenum alloy, thereby ensuring the smooth progress of subsequent high-temperature rolling. The sintering is adjusted to ensure that most of the nano-scale oxides are dispersed and distributed inside the grains and as little as possible segregated on the grain boundaries, thereby ensuring the toughness of the molybdenum alloy. Preparing fine grains increases the grain boundary and improves strengthening effect, such that more grain boundaries and nano-oxides hinder dislocation movement, thereby achieving a significant increase in recrystallization temperature, and ensuring that the alloy produced meets the basic requirements for ultra-high-temperature rolling. Increasing the relative density prevents the alloy from cracking during the later high-temperature-rolling.

(3) The reason for the poor toughness of molybdenum plates prepared by traditional processes: particles parallel to a <111> rolling surface have relatively high self-interstitial solubility, which makes many impurities to be biased towards the <111> rolling surface and greatly affecting the surface adhesion energy of particles parallel to the <111> rolling surface. The poor transverse plasticity of Mo alloys is closely related to a <110> structure since the <110> structure results in the production of large transverse size grains, and impurity elements tend to be biased towards the grain boundaries, resulting in a significant reduction in the interface bonding strength and poor transverse plasticity of the alloy. Based on this, in the present disclosure, by selecting an ultra-high cogging temperature of rolling, large deformation of molybdenum alloy in a single rolling pass is achieved, thereby rolling to the core at one time and thus ensuring consistent performance of all parts of the plate blank. Repeated ultra-high-temperature annealing weakens the texture of plate blank, and avoids a poor room-temperature performance caused by the formation of strong base surface texture during the rolling of molybdenum alloys. Recrystallization is an effective conditioning method to weaken the matrix structure. The ultra-high toughness of the plate blank is achieved through the fine nearly spherical grains generated after recrystallization nucleation, thus avoiding plate blank fracture during the rolling.

(4) In the present disclosure, the ultra-high strength and toughness molybdenum alloy shows superior overall performance and could take into account both desirable tensile strength and elongation. The molybdenum alloy has a tensile strength of not less than 600 MPa and an elongation of not less than 50% at room temperature, and the tensile strength is increased by not less than 35% and the elongation is increased by not less than 100% compared with those of traditional molybdenum alloys. The molybdenum alloy has a tensile strength of not less than 230 MPa and an elongation of not less than 30% at a high temperature of 1,200° C., and the tensile strength is increased by not less than 50% and the elongation is increased by not less than 80% compared with those of traditional molybdenum alloys. The finally prepared ultra-high strength and toughness molybdenum alloy could remain stable in a high-temperature environment of 1,500° C., meeting the application conditions of ultra-high-temperature environments. Therefore, this molybdenum alloy can be used as a material for high-temperature refractory structural components and is suitable for military, aerospace and other fields, showing broad application prospects.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A shows a morphology image of the ultra-high strength and toughness molybdenum alloy prepared in Example 1 of the present disclosure;

FIG. 1B shows a pole figure of the ultra-high strength and toughness molybdenum alloy prepared in Example 1 of the present disclosure;

FIG. 2A shows a morphology image of the ultra-high strength and toughness molybdenum alloy prepared in Example 2 of the present disclosure;

FIG. 2B shows a pole figure of the ultra-high strength and toughness molybdenum alloy prepared in Example 2 of the present disclosure;

FIG. 3A shows a morphology image of the ultra-high strength and toughness molybdenum alloy prepared in Example 3 of the present disclosure;

FIG. 3B shows a pole figure of the ultra-high strength and toughness molybdenum alloy prepared in Example 3 of the present disclosure;

FIG. 4A shows a morphology image of the pure molybdenum prepared in Comparative Example 1 of the present disclosure;

FIG. 4B shows a pole figure of the pure molybdenum prepared in Comparative Example 1 of the present disclosure;

FIG. 5A shows a morphology image of the ultra-high strength and toughness molybdenum alloy prepared in Comparative Example 2 of the present disclosure;

FIG. 5B shows a pole figure of the ultra-high strength and toughness molybdenum alloy prepared in Comparative Example 2 of the present disclosure; and

FIG. 6 shows engineering stress-strain curves at room temperature for the products prepared in Examples 1 to 3 and Comparative Examples 1 to 2.

DETAILED DESCRIPTION OF THE EMBODIMENTS

In order to better understand the content of the present disclosure, the present disclosure will be further explained below in conjunction with specific examples and drawings. The following examples provide detailed implementation methods and operating steps based on the technical solutions of the present disclosure, but the scope of the present disclosure is not limited to the following examples.

Example 1

(1) Benzenesulfonic acid and nano-zirconia ceramic particles with a particle size of 50 nm were mixed uniformly in water. A resulting mixture was subjected to hydrothermal reaction at 90° C. for 6 h to obtain a reactant, and the reactant was stirred to obtain an MOx—SO₃H aqueous solution.

(2) A molybdenum salt aqueous solution with a concentration of 1.0 mol/L was prepared with potassium molybdate, and then added into the MOx—SO₃H aqueous solution to obtain a mixed solution. The mixed solution was adjusted to have a pH of 6.0 by adding lactic acid, and then stirred, dried, and pulverized in sequence to obtain a precursor composite powder.

(3) The precursor composite powder was subjected to first-stage reduction at 550° C. for 8 h with a hydrogen flow rate of 17 m³/h and second-stage reduction at 925° C. for 10 h with a hydrogen flow rate of 22 m³/h, so as to obtain a nano-zirconia ceramic particle-reinforced molybdenum alloy powder with a particle size of 0.7 μm.

(4) The nano-zirconia ceramic particle-reinforced molybdenum alloy powder was pressed in a cold isostatic press at 180 MPa for 20 min, and then sintered in a pressureless medium-frequency furnace at 1,960° C. for 6 h with a hydrogen flow rate of 20 m³/h in the furnace to obtain a nano-zirconia ceramic particle-reinforced molybdenum alloy with a relative density of 98.5%.

(5) The nano-zirconia ceramic particle-reinforced molybdenum alloy was subjected to ultra-high-temperature rolling at 1,550° C. for 7 rolling passes by heating once in every one rolling pass with a single deformation of 42% and a total deformation of 97.8%.

The ultra-high strength and toughness molybdenum alloy prepared by ultra-high-temperature rolling in Example 1 consists of: 99 wt % of molybdenum and 1 wt % of nano-zirconia ceramic particles, which has a tensile strength of 737 MPa and an elongation of 53%, and is 82.9% higher in tensile strength and 89.3% higher in elongation than traditional molybdenum alloys. The ultra-high strength and toughness molybdenum alloy shows high-temperature stability and has a texture strength of 2.98, as shown in FIG. 1A and FIG. 1B.

Example 2

(1) Benzenesulfonic acid and nano-alumina ceramic particles with a particle size of 20 nm were mixed uniformly in water. A resulting mixture was subjected to hydrothermal reaction at 70° C. for 8 h to obtain a reactant, and the reactant was stirred to obtain an MOx—SO₃H aqueous solution.

(2) A molybdenum salt aqueous solution with a concentration of 1.5 mol/L was prepared with sodium molybdate, and then added into the MOx—SO₃H aqueous solution to obtain a mixed solution. The mixed solution was adjusted to have a pH of 5.5 by adding lactic acid, and then stirred, dried, and pulverized in sequence to obtain a precursor composite powder.

(3) The precursor composite powder was subjected to first-stage reduction at 500° C. for 6 h with a hydrogen flow rate of 18 m³/h and second-stage reduction at 850° C. for 12 h with a hydrogen flow rate of 25 m³/h, so as to obtain a nano-alumina ceramic particle-reinforced molybdenum alloy powder with a particle size of 0.8 μm.

(4) The nano-alumina ceramic particle-reinforced molybdenum alloy powder was pressed in a cold isostatic press at 200 MPa for 15 min, and then sintered in a pressureless medium-frequency furnace at 1,850° C. for 7 h with a hydrogen flow rate of 25 m³/h in the furnace to obtain a nano-alumina ceramic particle-reinforced molybdenum alloy with a relative density of 98.8%.

(5) The nano-alumina ceramic particle-reinforced molybdenum alloy was subjected to ultra-high-temperature rolling at 1,600° C. for 5 rolling passes by heating once in every one rolling pass with a single deformation of 47% and a total deformation of 95.82%.

The ultra-high strength and toughness molybdenum alloy prepared by ultra-high-temperature rolling in Example 2 consists of: 99.5 wt % of molybdenum and 0.5 wt % of nano-alumina ceramic particles, which has a tensile strength of 856 MPa and an elongation of 58.1%, and is 112.4% higher in tensile strength and 107.1% higher in elongation than traditional molybdenum alloys. The ultra-high strength and toughness molybdenum alloy shows high-temperature stability and has a texture strength of 2.82, as shown in FIG. 2A and FIG. 2B.

Example 3

(1) Benzenesulfonic acid and nano-titania ceramic particles with a particle size of 100 nm were mixed uniformly in water. A resulting mixture was subjected to hydrothermal reaction at 75° C. for 8 h to obtain a reactant, and the reactant was stirred to obtain an MOx—SO₃H aqueous solution.

(2) A molybdenum salt aqueous solution with a concentration of 2.5 mol/L was prepared with ammonium molybdate, and then added into the MOx—SO₃H aqueous solution to obtain a mixed solution. The mixed solution was adjusted to have a pH of 6.5 by adding lactic acid, and then stirred, dried, and pulverized in sequence to obtain a precursor composite powder.

(3) The precursor composite powder was subjected to first-stage reduction at 450° C. for 9 h with a hydrogen flow rate of 15 m³/h and second-stage reduction at 800° C. for 12 h with a hydrogen flow rate of 25 m³/h, so as to obtain a nano-titania ceramic particle-reinforced molybdenum alloy powder with a particle size of 0.5 μm.

(4) The nano-titania ceramic particle-reinforced molybdenum alloy powder was pressed in a cold isostatic press at 190 MPa for 18 min, and then sintered in a pressureless medium-frequency furnace at 1,750° C. for 10 h with a hydrogen flow rate of 23 m³/h in the furnace to obtain a nano-titania ceramic particle-reinforced molybdenum alloy with a relative density of 98.9%.

(5) The nano-titania ceramic particle-reinforced molybdenum alloy was subjected to ultra-high-temperature rolling at 1,600° C. for 9 rolling passes by heating once in every one rolling pass with a single deformation of 35% and a total deformation 97.9%.

The ultra-high strength and toughness molybdenum alloy prepared by ultra-high-temperature rolling in Example 3 consists of: 98.5 wt % of molybdenum and 1.5 wt % of nano-titania ceramic particles, which has a tensile strength of 864 MPa and an elongation of 63%, and is 114.4% higher in tensile strength and 125% higher in elongation than traditional molybdenum alloys. The ultra-high strength and toughness molybdenum alloy shows high-temperature stability and has a texture strength of 2.31, as shown in FIG. 3A and FIG. 3B.

Comparative Example 1

(1) ammonium tetramolybdate was subjected to first-stage reduction at 550° C. for 8 h with a hydrogen flow rate of 18 m3-/h and second-stage reduction at 950° C. for 10 h with a hydrogen flow rate of 25 m3-/h, so as to obtain a molybdenum powder with a particle size of 3.5 μm;

(2) the molybdenum powder was pressed in a cold isostatic press at 200 MPa for 20 min, and then sintered in a pressureless medium-frequency furnace at 1,960° C. for 10 h with a hydrogen flow rate of 20 m³/h in the furnace to obtain pure molybdenum with a relative density of 95.6%; and

(3) the pure molybdenum was subjected to ultra-high-temperature rolling at 1,100° C. for 9 rolling passes by heating once in every one rolling pass with a single deformation of 28% and a total deformation of 94.81%.

The pure molybdenum prepared in Comparative Example 1 has a tensile strength of 403 MPa, an elongation of 28%, and a texture strength of 11.79, as shown in FIG. 4A and FIG. 4B.

Comparative Example 2

(1) 100 nm nano-titania ceramic particles and ammonium tetramolybdate were mixed in a dual power mixer at a speed of 50 r/min for 6 h by solid-solid mixing to obtain a precursor composite powder;

(2) the precursor composite powder was subjected to first-stage reduction at 450° C. for 9 h with a hydrogen flow rate of 15 m³/h and second-stage reduction at 800° C. for 12 h with a hydrogen flow rate of 25 m³/h, so as to obtain a nano-titania ceramic particle-reinforced molybdenum alloy powder with a particle size of 1.5 μm;

(3) the nano-titania ceramic particle-reinforced molybdenum alloy powder was pressed in a cold isostatic press at 190 MPa for 18 min, and then sintered in a pressureless medium-frequency furnace at 1750° C. for 10 h with a hydrogen flow rate of 23 m³/h in the furnace to obtain a nano-titania ceramic particle-reinforced molybdenum alloy with a relative density of 97.7%; and

(4) the nano-titania ceramic particle-reinforced molybdenum alloy was subjected to ultra-high-temperature rolling at 1,600° C. for 9 rolling passes by heating once in every one rolling pass with a single deformation of 35% and a total deformation 97.9%.

The ultra-high strength and toughness molybdenum alloy prepared by ultra-high-temperature rolling in Comparative Example 2 includes: 98.5 wt % of molybdenum and 1.5 wt % of nano-titania ceramic particles, which has a tensile strength of 700 MPa and an elongation of 26%, and is 73.7% higher in tensile strength and 7.1% lower in elongation than traditional molybdenum alloys. The ultra-high strength and toughness molybdenum alloy has a texture strength of 6.52, as shown in FIG. 5A and FIG. 5B.

In summary, referring to FIG. 6, it can be seen that the ultra-high strength and toughness molybdenum alloy prepared according to the present disclosure has superior overall properties, and exhibits a relatively high strength and a greatly improved toughness at room temperature.

The above are only preferred embodiments of the present disclosure, and the present disclosure may have other forms of embodiments based on the above preparation methods, which will not be listed one by one. Therefore, any simple modifications, equivalent changes and variations made to the above embodiments according to the technical concept of the present disclosure without departing from the contents of the technical solutions of the present disclosure shall fall in the scope of the technical solutions of the present disclosure.