Low-N high-purity aluminum-tungsten-niobium ternary intermediate alloy and preparation method thereof

Abstract

The invention provides a low-N high-purity aluminum-tungsten-niobium ternary intermediate alloy and a preparation method thereof. The alloy is composed of the following components: 25-30 wt% of Al, 30-35 wt% of W, 35-40 wt% of Nb, less than or equal to 0.002 wt% of N, less than or equal to 0.002 wt% of Si, less than or equal to 0.006 wt% of H, less than or equal to 0.03 wt% of O and the balance of other inevitable impurities. Compared with the prior art, the method has the advantages that the completeness and the yield of the reaction can be effectively improved by introducing the heat generating agent and the slag former and controlling vacuum and argon replacement pressure in the preparation process, and the obtained alloy has higher purity and lower impurity content. The alloy can be widely applied to preparation of the high-temperature titanium alloy, the heat resistance, the mechanical property and the component uniformity of the high-temperature titanium alloy are improved, and the alloy is suitable for preparation of the high-temperature titanium alloy under the long-term service environment of 550 DEG C or above.

Description

Technical Field

[0001] The invention belongs to the field of alloy preparation, and particularly relates to a low-N high-purity aluminum-tungsten-niobium ternary master alloy for high-temperature titanium alloy and a preparation method thereof. Background Art

[0002] Titanium alloys have become key materials in modern aero engines and other high-temperature structural parts due to their excellent corrosion resistance and high temperature resistance. With the continuous development of the aviation industry, higher requirements are placed on the thermal strength, forging processing performance and welding performance of titanium alloys. Traditional high-temperature titanium alloys are based on the Ti-Al-Sn-Zr-Mo-Si alloy system. By adding Nb and Ta elements, the multi-element composite solid solution strengthening effect of the alloy is further improved, and the second-generation high-temperature titanium alloys have been successfully developed. They show good thermal strength, forging processing performance and welding performance at 550°C. However, with the increasing demand for the application of titanium alloys at higher temperatures, the operating temperature of traditional high-temperature titanium alloys is gradually approaching its material limit.

[0003] In recent years, the heat resistance of solid solution strengthened high temperature titanium alloys has been further improved by introducing W elements and increasing the content of Ta elements in titanium alloys, making it possible for the long-term use temperature of titanium alloys to break through the traditional "thermal barrier" temperature of 600°C. However, since the melting point of W element is as high as 3410°C, while the melting point of titanium is only 1668°C, the melting points of the two are quite different. Directly adding tungsten to the smelting process of titanium alloys will lead to uneven distribution of components due to incomplete melting, which will in turn cause component segregation, making it difficult to ensure the uniformity and purity of the alloy.

[0004] In order to solve the above problems, the prior art usually introduces an aluminum-tungsten-niobium ternary master alloy as an additive for the tungsten element, thereby avoiding the problems of uneven melting and component segregation caused by the direct addition of tungsten. This aluminum-tungsten-niobium ternary master alloy has the characteristics of low melting point and uniform distribution of elements, which can effectively improve the distribution of tungsten elements in high-temperature titanium alloys and improve the overall performance of the alloy. In the prior art, a Chinese invention patent with publication number CN 104674034 A discloses an aluminum-tungsten-niobium ternary master alloy and a preparation method thereof. The alloy is prepared by an aluminothermic reaction method, and the specific steps include: using aluminum as a reducing agent, niobium pentoxide and tungsten trioxide as oxidants, and smelting an aluminum-tungsten-niobium ternary master alloy by aluminothermic reaction. In the prepared master alloy, the tungsten content is 25-40wt%, the niobium content is 20-35wt%, and after finishing, crushing, and selection processes, alloy particles with a particle size in the range of 0.25 to 6mm are finally prepared.

[0005] However, the above technical solution has the following shortcomings:

[0006] First, although the patent adopts the aluminothermic reaction method, it does not describe in detail the specific process parameters of the aluminothermic reaction, such as reaction temperature, time and environmental conditions, which makes it difficult to achieve industrial production in actual operation;

[0007] Secondly, the environmental pollution problems that may be caused by the thermite reaction were not analyzed and controlled, especially the impact of the smoke and waste residue produced by the reaction on the environment was not explained;

[0008] Thirdly, the technical solution does not make specific requirements on the aluminum content, which makes it difficult to control the aluminum content during the preparation process, thus affecting the purity of the alloy and its subsequent performance.

[0009] Finally, the process does not mention whether it is necessary to add exothermic agents and slag-forming agents, which play an important role in the thermite reaction and may directly affect the reaction yield and the performance of the final product. Summary of the invention

[0010] Based on the above problems, the present invention proposes a low aluminum content, high purity aluminum-tungsten-niobium ternary master alloy and a preparation method thereof.

[0011] The technical solution of the present invention is:

[0012] A low-N high-purity aluminum-tungsten-niobium ternary master alloy, the alloy consists of the following components:

[0013] 25-30wt% Al;

[0014] 30-35wt% W;

[0015] 35-40 wt% Nb;

[0016] The impurity content is controlled as follows: N≤0.002wt%, Si≤0.002wt%, H≤0.006wt%, O≤0.03wt%, and the remainder is other inevitable impurities.

[0017] The preparation method comprises the following steps:

[0018] (1) Weigh Al, WO3, Nb2O5, KClO3, CaO or CaF2 accurately according to the requirements and mix them for 60-90 minutes using a dual motion mixer;

[0019] (2) coating the inner wall of the graphite crucible with a niobium oxide layer for protection, and placing the material mixed in step (1) into the crucible;

[0020] (3) Evacuate to -0.08 MPa, replace with argon, and fill with argon until the pressure in the furnace is +0.01 MPa;

[0021] (4) Use a special ignition agent to remotely ignite electricity to trigger the aluminum thermal reduction reaction;

[0022] (5) After the reaction was completed, the reaction mixture was allowed to cool for 24 hours. During the cooling process, the pressure was evacuated to -0.08 MPa and argon protection was applied.

[0023] (6) After cooling, a low-N high-purity aluminum-tungsten-niobium ternary master alloy ingot is obtained, and alloy particles are prepared through finishing, crushing, and selection processes.

[0024] The reducing agent is aluminum powder with an average particle size of less than -100 mesh, and the purity of the reducing agent is ≥99.8%.

[0025] The oxidant is tungsten trioxide (WO3) with a purity of ≥99.95%, the exothermic agent is selected from at least one of potassium chlorate, potassium nitrate, and sodium nitrate, and the slag-forming agent is selected from at least one of calcium oxide and calcium fluoride. The purity of the exothermic agent is ≥99.5%, and the purity of the slag-forming agent is ≥98%.

[0026] The crucible is a graphite crucible, and the niobium oxide coating on the crucible and the Nb2O5 in step (1) are from the same batch of raw materials.

[0027] The ignition is carried out by electrifying a special ignition agent and adopting a remote-controlled ignition device.

[0028] During the cooling process, the argon pressure in the furnace is maintained between -0.08 and +0.01 MPa.

[0029] The total content of Al, W and Nb in the alloy prepared by the preparation method is greater than 95wt%.

[0030] The alloy has excellent thermal strength, corrosion resistance and oxidation resistance, and is suitable for the preparation of high-temperature titanium alloys above 550°C.

[0031] Compared with the prior art, the present invention has the following advantages:

[0032] The vacuum aluminothermic reaction method in the furnace is used to control the vacuum environment during the reaction process to avoid the introduction of impurity elements and improve the purity of the master alloy.

[0033] Potassium chlorate is used as a heating agent to ensure stable heat supply during the reaction process, ensuring the complete reaction and avoiding energy waste caused by excessive external heating;

[0034] Using calcium fluoride as a slag-forming agent effectively removes impurities generated during the reaction, further improving the purity and uniformity of the alloy;

[0035] The present invention optimizes the process flow to make the contents of aluminum, tungsten and niobium in the master alloy more accurately controllable, reduce component fluctuations, and improve the overall performance of the alloy.

[0036] The prepared low aluminum content, high purity aluminum tungsten niobium intermediate alloy has a melting point close to titanium, can be better integrated with the titanium matrix, reduce the component segregation during titanium alloy smelting, and effectively improve the overall performance and service life of the high temperature titanium alloy.

[0037] Therefore, the present invention provides a low aluminum content and high purity aluminum-tungsten-niobium ternary master alloy with a simple preparation process, environmental friendliness, and the ability to accurately control the tungsten content. It overcomes the defects of the prior art such as complex process, large composition fluctuations, and environmental pollution, and can be widely used in the preparation of high-temperature titanium alloys. DETAILED DESCRIPTION

[0038] The technical solution of the present invention is described in detail below in conjunction with the preferred embodiments of the present invention.

[0039] Example 1

[0040] Prepare the materials in the ratio of Al: WO3: Nb2O5: KClO3: CaO = 34.9wt%: 27wt%: 29.7wt%: 1.45wt%: 6.84wt%, add all the raw materials into a double motion mixer and mix for 60 minutes. Load the evenly mixed materials into a graphite crucible in a vacuum furnace (to avoid carbon contamination during the production process, the inner wall of the crucible is treated with niobium oxide coating before loading). Evacuate the furnace to -0.08MPa, and fill it with argon until the pressure in the furnace reaches +0.01MPa, then ignite to initiate the aluminum thermal reduction reaction. After the reaction is completed, let it stand and cool for 24 hours. After cooling, 17kg of high-purity aluminum, tungsten and niobium three-element alloy is obtained.

[0041] The alloy surface was sampled at multiple points using the cross method, and the measured component test results are shown in Table 1.

[0042] Example 2

[0043] Al, WO3, Nb2O5, KClO3, CaO, CaF2 are used as raw materials, and the ingredients are prepared according to Al: WO3: Nb2O5: KClO3: CaO: CaF2 = 34.9wt%: 27wt%: 29.7wt%: 1.45wt%: 3.93wt%: 2.91wt%, and each raw material is added to a double-motion mixer for mixing. The evenly mixed materials are loaded into a graphite crucible in a vacuum furnace (to avoid carbon pollution, niobium oxide coating protection measures are taken). The furnace is evacuated to -0.08MPa, and argon is filled in until the pressure in the furnace reaches +0.01MPa, and then ignited to initiate an aluminum thermal reduction reaction. After the reaction is completed, it is allowed to cool for 24 hours. After cooling, 20.8kg of high-purity aluminum, tungsten and niobium three-element alloy is obtained.

[0044] The alloy surface was sampled at multiple points using the cross method, and the measured component test results are shown in Table 1.

[0045] Example 3

[0046] Al, WO3, Nb2O5, KClO3, CaO, CaF2 are used as raw materials. The raw materials are weighed according to the ratio of Al: WO3: Nb2O5: KClO3: CaO: CaF2 = 34.9wt%: 27wt%: 29.7wt%: 1.45wt%: 3.93wt%: 2.91wt%, and added to a double-motion mixer for mixing for 90 minutes. The evenly mixed materials are loaded into a graphite crucible in a vacuum furnace (in order to avoid carbon pollution during the production process, the inner wall of the crucible is treated with niobium oxide coating before loading). The furnace is evacuated to -0.08MPa, and argon is filled until the pressure in the furnace reaches +0.01MPa, and then ignited to initiate the aluminum thermal reduction reaction. One hour after the reaction ends, the furnace is evacuated again to -0.08MPa and argon protection is performed. After cooling for 24 hours, it is taken out of the furnace to obtain 17.2kg of high-purity aluminum, tungsten and niobium three-element alloy.

[0047] The alloy surface was sampled at multiple points using the cross method, and the measured component test results are shown in Table 1.

[0048] Example 4

[0049] Prepare the ingredients in the ratio of Al: WO3: Nb2O5: KClO3: CaO = 34.9wt%: 27wt%: 29.7wt%: 1.45wt%: 6.84wt%. Add all the raw materials into a double-motion mixer and mix them evenly, then load them into a graphite crucible in a vacuum furnace (to avoid carbon pollution, the inner wall of the crucible is coated with a niobium oxide layer). The furnace is evacuated to -0.08MPa and replaced with argon. After filling with argon to make the pressure in the furnace reach -0.08MPa, ignite it and initiate the aluminum thermal reduction reaction. After the reaction is completed, let it stand and cool for 24 hours. After cooling, 20kg of high-purity aluminum, tungsten and niobium three-element alloy is obtained.

[0050] The alloy surface was sampled at multiple points using the cross method, and the measured component test results are shown in Table 1.

[0051] Alloy composition detection and analysis methods

[0052] The main element composition of high-purity aluminum, tungsten and niobium three-element alloy is tested using the following instruments and methods:

[0053] The C element is detected by a carbon-sulfur instrument;

[0054] O element is detected by oxygen and nitrogen analyzer;

[0055] The Al, W and Nb metal elements were detected by inductively coupled plasma atomic emission spectrometry (ICP-AES).

[0056] Table 1 Composition and properties of high purity aluminum, tungsten and niobium three-element alloys

[0057]

[0058] Result analysis:

[0059] Under different raw material ratios and furnace pressure conditions, the yield and purity of the alloy obtained in each embodiment are different. The alloy yield of Example 3 is the highest, reaching 88.4%, and the impurity C and O content are relatively low, indicating that under the furnace pressure condition of +0.01MPa, the aluminum, tungsten and niobium three-element alloy preparation process of the present invention can effectively improve the alloy yield and reduce the impurity content, thereby obtaining a higher purity alloy product.

Claims

1. A low-N high-purity aluminum-tungsten-niobium ternary master alloy, characterized in that: The alloy consists of the following components: 25-30wt% Al; 30-35wt% W; 35-40 wt% Nb; The impurity content is controlled as follows: N≤0.002wt%, Si≤0.002wt%, H≤0.006wt%, O≤0.03wt%, and the remainder is other inevitable impurities.

2. The method for preparing the low-N high-purity aluminum-tungsten-niobium ternary master alloy according to claim 1, characterized in that: The preparation method comprises the following steps: (1) Weigh Al, WO3, Nb2O5, KClO3, CaO or CaF2 accurately according to the requirements and mix them for 60-90 minutes using a dual motion mixer; (2) coating the inner wall of the graphite crucible with a niobium oxide layer for protection, and placing the material mixed in step (1) into the crucible; (3) Evacuate to -0.08 MPa, replace with argon, and fill with argon until the pressure in the furnace is +0.01 MPa; (4) Use a special ignition agent to remotely ignite electricity to trigger the aluminum thermal reduction reaction; (5) After the reaction was completed, the reaction mixture was allowed to cool for 24 hours. During the cooling process, the pressure was evacuated to -0.08 MPa and argon protection was applied. (6) After cooling, a low-N high-purity aluminum-tungsten-niobium ternary master alloy ingot is obtained, and alloy particles are prepared through finishing, crushing, and selection processes.

3. The preparation method according to claim 2, characterized in that: The reducing agent is aluminum powder with an average particle size of less than -100 mesh, and the purity of the reducing agent is ≥99.8%.

4. The preparation method according to claim 2, characterized in that: The oxidant is tungsten trioxide (WO3) with a purity of ≥99.95%, the exothermic agent is selected from at least one of potassium chlorate, potassium nitrate, and sodium nitrate, and the slag-forming agent is selected from at least one of calcium oxide and calcium fluoride. The purity of the exothermic agent is ≥99.5%, and the purity of the slag-forming agent is ≥98%.

5. The preparation method according to claim 2, characterized in that: The crucible is a graphite crucible, and the niobium oxide coating on the crucible and the Nb2O5 in step (1) are from the same batch of raw materials.

6. The preparation method according to claim 2, characterized in that: The ignition is carried out by electrifying a special ignition agent and adopting a remote-controlled ignition device.

7. The preparation method according to claim 2, characterized in that: During the cooling process, the argon pressure in the furnace is maintained between -0.08 and +0.01 MPa.

8. A low-N high-purity aluminum-tungsten-niobium ternary master alloy for high-temperature titanium alloy, characterized in that: The alloy is prepared by the preparation method described in any one of claims 1 to 7.

9. The low-N high-purity aluminum-tungsten-niobium ternary master alloy for high-temperature titanium alloy according to claim 8, characterized in that: The total content of Al, W and Nb in the alloy is greater than 95wt%.

10. The low-N high-purity aluminum-tungsten-niobium ternary master alloy according to claim 8, characterized in that: The alloy has excellent thermal strength, corrosion resistance and oxidation resistance, and is suitable for the preparation of high-temperature titanium alloys above 550°C.

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