Low-temperature sintering preparation process for fine-grain molybdenum alloy

Abstract

A low-temperature sintering preparation process for a fine-grain molybdenum alloy. The process comprises: preparing a MoO3 precursor and a ZrC precursor respectively by using a hydrothermal method; in a liquid-liquid doping mode, mixing and thoroughly stirring two suspensions, which have been subjected to a hydrothermal treatment; and performing filtration and freeze-drying, so as to obtain a micron-level MoO3 precursor and a nano-level ZrC precursor. The sintering of a molybdenum alloy prepared by means of the preparation process can be implemented at a relatively low temperature, so as to obtain relatively fine grains. Spark plasma sintering involves a low temperature and takes a short time, such that the energy consumption can be reduced, thereby improving the economy and sustainability of the preparation. In addition, liquid-liquid doping enables the MoO3 precursor and the ZrC precursor to be uniformly dispersed in an aqueous solution, thereby realizing the uniform distribution of a second phase in a fine-grain molybdenum alloy, and further improving the consistency and stability of the material performance. Moreover, the prepared molybdenum alloy has a relatively small grain size, which is generally at the nano to micron level, such that the overall mechanical properties of the material can be improved.

Description

A low-temperature sintering process for preparing fine-grained molybdenum alloys Technical Field

[0001] This invention relates to the preparation of fine-grained molybdenum alloys, specifically a low-temperature sintering process for preparing fine-grained molybdenum alloys. Background Technology

[0002] Molybdenum alloys are materials with excellent mechanical properties and thermal stability, and are widely used in aerospace, engineering machinery, electronic devices and other fields. Traditional molybdenum alloy materials have problems such as coarse grains and unstable mechanical properties, which limit their application in high-temperature environments. In order to overcome these problems, researchers have proposed a preparation process for fine-grained molybdenum alloys.

[0003] However, current processes for preparing fine-grained molybdenum alloys have the following drawbacks: Firstly, the second phase cannot be uniformly dispersed in the molybdenum alloy. Secondly, the high sintering temperature and long holding time result in coarse grains, affecting the consistency and stability of the alloy's properties. Thirdly, the second phase cannot be uniformly dispersed in the matrix, easily leading to localized aggregation, which affects the uniformity and stability of the prepared molybdenum alloy. Furthermore, existing methods for adding the second phase are limited, generally requiring powder mixing, drying, and ball milling, increasing equipment and operational costs, wasting and losing raw materials, reducing material utilization, and ultimately increasing production costs. Fourthly, the high sintering temperature and long cycle of the second-phase reinforced molybdenum alloy in current processes result in coarse grains and low quality. Summary of the Invention

[0004] The purpose of this invention is to address the problems in existing molybdenum alloy preparation processes, such as the inability of the second phase to be uniformly dispersed in the molybdenum alloy, high sintering temperatures and long holding times leading to coarse grains, which in turn affect the consistency and stability of the molybdenum alloy's properties. Furthermore, existing processes for adding the second phase are limited, generally requiring powder mixing, drying, and ball milling, increasing equipment and operational costs, wasting and losing raw materials, reducing material utilization, and ultimately increasing production costs. Additionally, existing processes for preparing second-phase reinforced molybdenum alloys involve high sintering temperatures and long cycles, resulting in coarse grains and low quality. Therefore, this invention proposes a low-temperature sintering process for preparing fine-grained molybdenum alloys.

[0005] The objective of this invention can be achieved through the following technical solution: a low-temperature sintering preparation process for fine-grained molybdenum alloys, comprising preparing MoO3 and ZrC precursors separately using a hydrothermal method, mixing the two suspensions after hydrothermal treatment by liquid-liquid doping and stirring thoroughly, and then filtering and freeze-drying to obtain micron-sized MoO3 and nano-sized ZrC precursors. This low-temperature sintering preparation process includes the following steps:

[0006] Step 1: Weigh ammonium tetramolybdate according to the proportion of the second phase, i.e., the mass ratio of zirconium carbide in the finished alloy is 0.1-1.2%, add it to an aqueous solution with a pH of 1, stir magnetically for 30 minutes, and place it in a hydrothermal reactor for hydrothermal reaction to obtain solution A; weigh zirconium nitrate and starch and dissolve them in 100 ml of deionized water, wherein the amount of zirconium nitrate corresponds to the molar amount of zirconium carbide, stir magnetically for 30 minutes, and place it in a hydrothermal reactor for hydrothermal reaction to obtain solution B; mix solution A and solution B, and stir magnetically for 20 minutes to obtain solution C;

[0007] Step 2: Filter solution C, freeze the filtered material in a freezer, and then dry it in a freeze dryer under vacuum at -50°C for 24 hours. Grind and sieve the powder to obtain the precursors of zirconium carbide and molybdenum trioxide.

[0008] Step 3: Calcine the mixed powder obtained in Step 2, keep it at a certain temperature after calcination, and then cool it with the furnace to obtain a mixed powder of zirconium carbide precursor and molybdenum trioxide.

[0009] Step 4: The mixed powder obtained in Step 3 is subjected to a two-stage reduction to obtain molybdenum-doped carbide precursor powder.

[0010] Step 5: Perform spark plasma sintering on the composite powder and hold it at a certain temperature. After the spark plasma sintering is completed, the sample is cooled with the furnace to obtain a molybdenum alloy block.

[0011] A further technical improvement of the present invention is that the temperature of the hydrothermal reaction in step one, when preparing solution A, is controlled at 180-230℃ and the time is controlled at 16-24h.

[0012] A further technical improvement of the present invention is that, in step one, when preparing solution B, the temperature of the hydrothermal reaction is controlled at 180-230℃ and the time is controlled at 16-24h.

[0013] A further technical improvement of the present invention is that the molar ratio of zirconium to carbon in zirconium nitrate and starch in step one is controlled at 1:5, 1:6, 1:7, or 1:8.

[0014] A further technical improvement of the present invention is that the freezing time of the filter material in step two is controlled at 10-15 hours, and the vacuum degree of the freeze dryer vacuum environment is ≤5Pa.

[0015] A further technical improvement of the present invention is that the temperature of the mixed powder calcination in step three is controlled at 450-600℃, and the holding time is controlled at 1-2h.

[0016] A further technical improvement of the present invention is that the first-stage reduction temperature in step four is 400-550℃, and the second-stage reduction temperature is 900℃-1050℃.

[0017] A further technical improvement of the present invention is that: in step five, the sintering temperature is controlled at 1450-1650℃, the heating rate is controlled at 80-120℃ / min, and the sintering pressure is controlled at 45-55Mpa.

[0018] A further technical improvement of the present invention is that the heat preservation time in step five is controlled at 10-15 min, and the vacuum degree during heat preservation is <0.05 Pa.

[0019] Compared with the prior art, the beneficial effects of the present invention are:

[0020] (1) In this invention, the preparation process adopts the hydrothermal method. The fine-grained molybdenum alloy prepared in this way can be sintered at a lower temperature to obtain relatively fine grains. Compared with the traditional high-temperature sintering process, the discharge plasma sintering temperature is lower and the time is shorter, which can reduce energy consumption and improve the economy and sustainability of the preparation. At the same time, liquid-liquid doping can make MoO3 and ZrC precursors uniformly dispersed in the aqueous solution, which can achieve uniform distribution of fine-grained molybdenum alloy, thereby improving the consistency and stability of the material's performance. In addition, the fine-grained molybdenum alloy prepared by the hydrothermal method has a small grain size, usually in the nanometer to micrometer level, which can improve the overall mechanical properties of the material.

[0021] (2) In this invention, the preparation process adopts the liquid-liquid doping method, which adds the second phase material to the matrix material in liquid form. On the one hand, the second phase material is uniformly dispersed in the matrix. Since the liquid can flow freely in the matrix, the second phase material can be fully mixed and dispersed during the doping process, avoiding the phenomenon of local agglomeration, thereby improving the dispersion of the second phase material in the matrix, thereby enhancing the uniformity and stability of the prepared alloy. On the other hand, it is convenient to adjust the operating conditions in the liquid-liquid doping process, such as temperature and concentration, so as to achieve precise control of the amount of second phase material added. The content and distribution of the second phase material can be flexibly adjusted as needed. In addition, the liquid-liquid doping method has a lower preparation cost than other methods of adding second phase material. It does not require powder mixing, drying and ball milling, which can save some equipment and operating costs. At the same time, it can reduce the waste and loss of the second phase material, improve the material utilization rate and reduce the production cost.

[0022] (3) In this invention, the preparation process obtains a second-phase reinforced molybdenum alloy bulk by spark plasma sintering of a carbide precursor doped with molybdenum powder. By using spark plasma sintering technology, on the one hand, high-speed sealed sintering can be achieved at a lower temperature, thereby increasing the sintering speed and shortening the sintering cycle, thus improving the efficiency of the process in preparing fine-grained molybdenum alloys. On the other hand, rapid heating and cooling can be achieved, and heat can be transferred through high-temperature plasma, so that the internal temperature of the sample is uniform, and a uniform grain distribution is generated, making the grain size of the sintered molybdenum alloy smaller, so as to achieve the purpose of fine grains, thereby improving the quality of the prepared fine-grained molybdenum alloy. Detailed Implementation

[0023] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention. Example 1

[0024] A low-temperature sintering process for preparing fine-grained molybdenum alloys, comprising the following steps:

[0025] Step 1: According to the proportion of the second phase, i.e., the mass ratio of zirconium carbide in the finished alloy is 0.5%, ammonium tetramolybdate is weighed and added to an aqueous solution with a pH of 1. The solution is magnetically stirred for 30 minutes and then placed in a hydrothermal reactor for hydrothermal reaction at a temperature of 200℃ for 18 hours to obtain solution A. Zirconium nitrate and starch are weighed and dissolved in 100 ml of deionized water, wherein the amount of zirconium nitrate corresponds to the molar amount of zirconium carbide, and the molar ratio of zirconium to carbon is 1:6. The solution is magnetically stirred for 30 minutes and then placed in a hydrothermal reactor for hydrothermal reaction at a temperature of 200℃ for 18 hours to obtain solution B. Solution A and solution B are mixed and magnetically stirred for 20 minutes to obtain solution C.

[0026] Step 2: Filter solution C, freeze the filtered material in a freezer for 12 hours, then put it in a freeze dryer and dry it in a vacuum environment of -50℃ and 4Pa for 24 hours. Grind and sieve the powder to obtain the precursors of zirconium carbide and molybdenum trioxide.

[0027] Step 3: Calcine the mixed powder obtained in Step 2 at a temperature of 500℃ for 1.5 hours, and then cool it in the furnace to obtain a mixed powder of zirconium carbide precursor and molybdenum trioxide.

[0028] Step 4: The mixed powder obtained in Step 3 is subjected to two-stage reduction. The first-stage reduction temperature is 450℃, and the second-stage reduction temperature is 1000℃. After reduction, molybdenum-doped carbide precursor powder is obtained.

[0029] Step 5: The composite powder is subjected to spark plasma sintering at a temperature of 1400℃, a heating rate of 90℃ / min, a sintering pressure of 50 MPa, and a holding time of 12 min. The vacuum degree is 0.03 Pa. After spark plasma sintering, the sample is cooled with the furnace to obtain a molybdenum alloy block. Example 2

[0030] A low-temperature sintering process for preparing fine-grained molybdenum alloys, comprising the following steps:

[0031] Step 1: According to the proportion of the second phase, i.e., the mass ratio of zirconium carbide in the finished alloy is 1%, weigh ammonium tetramolybdate and add it to an aqueous solution with a pH of 1. Stir magnetically for 30 minutes, then place it in a hydrothermal reactor for hydrothermal reaction at 220℃ for 20 hours to obtain solution A. Weigh zirconium nitrate and starch and dissolve them in 100 ml of deionized water, where the amount of zirconium nitrate corresponds to the molar amount of zirconium carbide, and the molar ratio of zirconium to carbon is 1:8. Stir magnetically for 30 minutes, then place it in a hydrothermal reactor for hydrothermal reaction at 220℃ for 20 hours to obtain solution B. Mix solution A and solution B and stir magnetically for 20 minutes to obtain solution C.

[0032] Step 2: Filter solution C, freeze the filtered material in a freezer for 14 hours, then put it in a freeze dryer and dry it in a vacuum environment of -50℃ and 3.5Pa for 24 hours. Grind and sieve the powder to obtain the precursors of zirconium carbide and molybdenum trioxide.

[0033] Step 3: Calcine the mixed powder obtained in Step 2 at a temperature of 550℃ for 1.5 hours. Then, cool it in the furnace to obtain a mixed powder of zirconium carbide precursor and molybdenum trioxide.

[0034] Step 4: The mixed powder obtained in Step 3 is subjected to two-stage reduction. The first-stage reduction temperature is 500℃ and the second-stage reduction temperature is 950℃. After reduction, molybdenum-doped carbide precursor powder is obtained.

[0035] Step 5: The composite powder is subjected to spark plasma sintering at a temperature of 1500℃, a heating rate of 100℃ / min, a sintering pressure of 50 MPa, and a holding time of 14 min. The vacuum degree is 0.02 Pa. After spark plasma sintering, the sample is cooled with the furnace to obtain a molybdenum alloy block.

[0036] Working principle: This preparation process prepares MoO3 and ZrC precursors separately by hydrothermal method. The two suspensions after hydrothermal treatment are mixed by liquid-liquid doping and stirred thoroughly. After filtration and freeze drying, micron-sized MoO3 and nano-sized ZrC precursors are obtained.

[0037] The preferred embodiments of the present invention disclosed above are merely illustrative of the invention. These preferred embodiments do not exhaustively describe all details, nor do they limit the invention to any specific implementation. Clearly, many modifications and variations can be made based on the content of this specification. This specification selects and specifically describes these embodiments to better explain the principles and practical applications of the invention, thereby enabling those skilled in the art to better understand and utilize the invention. The invention is limited only by the claims and their full scope and equivalents.

Claims

1. A low-temperature sintering preparation process for fine-grained molybdenum alloys, comprising preparing MoO3 and ZrC precursors separately by hydrothermal method, mixing the two suspensions after hydrothermal treatment by liquid-liquid doping and stirring thoroughly, and obtaining micron-sized MoO3 and nano-sized ZrC precursors by filtration and freeze-drying, characterized in that: The low-temperature sintering preparation process includes the following steps: Step 1: Weigh ammonium tetramolybdate according to the proportion of the second phase, i.e., the mass ratio of zirconium carbide in the finished alloy is 0.1-1.2%, add it to an aqueous solution with a pH of 1, stir magnetically for 30 minutes, and place it in a hydrothermal reactor for hydrothermal reaction to obtain solution A; weigh zirconium nitrate and starch and dissolve them in 100 ml of deionized water, wherein the amount of zirconium nitrate corresponds to the molar amount of zirconium carbide, stir magnetically for 30 minutes, and place it in a hydrothermal reactor for hydrothermal reaction to obtain solution B; mix solution A and solution B, and stir magnetically for 20 minutes to obtain solution C; Step 2: Filter solution C, freeze the filtered material in a freezer, and then dry it in a freeze dryer under vacuum at -50°C for 24 hours. Grind and sieve the powder to obtain the precursors of zirconium carbide and molybdenum trioxide. Step 3: Calcine the mixed powder obtained in Step 2, keep it at a certain temperature after calcination, and then cool it with the furnace to obtain a mixed powder of zirconium carbide precursor and molybdenum trioxide. Step 4: The mixed powder obtained in Step 3 is subjected to a two-stage reduction to obtain molybdenum-doped carbide precursor powder. Step 5: Perform spark plasma sintering on the composite powder and hold it at a certain temperature. After the spark plasma sintering is completed, the sample is cooled with the furnace to obtain a molybdenum alloy block.

2. The low-temperature sintering preparation process of a fine-grained molybdenum alloy as described in claim 1, characterized in that: In step one, the temperature of the hydrothermal reaction during the preparation of solution A is controlled at 180-230℃, and the time is controlled at 16-24h.

3. The low-temperature sintering preparation process of a fine-grained molybdenum alloy as described in claim 1, characterized in that: In step one, when preparing solution B, the temperature of the hydrothermal reaction is controlled at 180-230℃ and the time is controlled at 16-24h.

4. The low-temperature sintering preparation process of a fine-grained molybdenum alloy as described in claim 1, characterized in that: In step one, the molar ratio of zirconium to carbon in zirconium nitrate and starch is controlled at 1:5, 1:6, 1:7, or 1:

8.

5. The low-temperature sintering preparation process of a fine-grained molybdenum alloy as described in claim 1, characterized in that: In step two, the freezing time of the filtered material is controlled at 10-15 hours, and the vacuum degree of the freeze dryer is ≤5Pa.

6. The low-temperature sintering preparation process of a fine-grained molybdenum alloy as described in claim 1, characterized in that: In step three, the temperature of the mixed powder calcination is controlled at 450-600℃, and the holding time is controlled at 1-2h.

7. The low-temperature sintering preparation process of a fine-grained molybdenum alloy as described in claim 1, characterized in that: In step four, the first stage reduction temperature is 400-550℃, and the second stage reduction temperature is 900℃-1050℃.

8. The low-temperature sintering preparation process of a fine-grained molybdenum alloy according to claim 7, characterized in that: In step five, the sintering temperature is controlled at 1450-1650℃, the heating rate is controlled at 80-120℃ / min, and the sintering pressure is controlled at 45-55 MPa.

9. The low-temperature sintering preparation process of a fine-grained molybdenum alloy according to claim 1, characterized in that: In step five, the heat preservation time should be controlled at 10-15 minutes, and the vacuum degree during heat preservation should be <0.05Pa.