Ti-Al-Nb-Zr-Mo series high-impact-toughness titanium alloy and preparation method thereof

Abstract

The invention belongs to the field of titanium alloys, and particularly discloses a Ti-Al-Nb-Zr-Mo series high-impact-toughness titanium alloy and a preparation method thereof.The Ti-Al-Nb-Zr-Mo series high-impact-toughness titanium alloy is prepared from, by mass, 5.5%-6.5% of Al, 2.5%-3.3% of Nb, 1.8%-2.2% of Zr, 1.2%-1.8% of Mo and the balance Ti. According to the Ti80 alloy designed by the invention, the content of a beta stable element Mo element is increased in the aspect of components, the temperature of a phase transformation point can be reduced by increasing the Mo element, meanwhile, formation of high-density dislocation is promoted, deformation twinning is promoted, and alpha-phase grains are refined, so that the impact toughness is remarkably improved while the alloy is strengthened, and the strength of the alloy is improved. And the method has the advantages of simplicity, feasibility, stable effect, great subsequent improvement potential and the like.

Description

Technical Field

[0001] The present invention belongs to the field of titanium alloys, and more specifically, relates to a Ti-Al-Nb-Zr-Mo series high impact toughness titanium alloy and a preparation method thereof. Background Art

[0002] Titanium and its alloys are known as the "metal materials of the 21st century". Due to their high strength, low density, corrosion resistance, good biocompatibility and high temperature resistance, they have been widely used in many fields such as aerospace, military industry, petrochemical industry, biomedicine, etc.

[0003] Among them, Ti80 alloy is widely used in marine engineering and other fields due to its low density, high strength, good plasticity, good corrosion resistance, and non-magnetic properties. However, during its service, it will be immersed in seawater for a long time and affected by various factors such as waves and floating bodies. Therefore, how to improve its impact toughness is the key to expanding its application field and ensuring its safe service. However, the impact toughness of Ti80 alloy in the existing technology is mostly lower than 50J / cm 2 , which cannot meet the needs of advanced marine engineering equipment. It is urgent to further explore the performance potential of the alloy and develop Ti80 alloy with high impact toughness.

[0004] At present, the improvement of the impact toughness of Ti80 alloy is mainly achieved by optimizing the preparation process and regulating the organization; for example, Patent 202411760577.2 discloses a process for improving the impact toughness of Ti80 alloy, and prepares a Ti80 alloy with a three-state organization to improve the impact toughness; Patent 202111060371.5 discloses a method for preparing a high impact toughness Ti80 alloy rod, which comprehensively regulates the phase ratio and phase morphology in the Ti80 alloy rod to make the α phase morphology and β grain size more uniform, thereby improving the impact toughness, but there is little research on improving the impact toughness of Ti80 alloy from the composition regulation level. Summary of the invention

[0005] In view of the above defects or improvement needs of the prior art, the present invention provides a Ti-Al-Nb-Zr-Mo series high impact toughness titanium alloy and a preparation method thereof, the purpose of which is to improve the impact toughness of the titanium alloy while ensuring its strength.

[0006] To achieve the above-mentioned purpose, according to one aspect of the present invention, a Ti-Al-Nb-Zr-Mo series high impact toughness titanium alloy is proposed. Calculated by mass percentage, the Ti-Al-Nb-Zr-Mo series titanium alloy comprises: 5.5% to 6.5% Al, 2.5% to 3.3% Nb, 1.8% to 2.2% Zr, 1.2% to 1.8% Mo, and the balance is Ti.

[0007] As a further preference, the Ti-Al-Nb-Zr-Mo titanium alloy comprises, by mass percentage, 5.5% to 6.5% Al, 2.5% to 3.3% Nb, 1.8% to 2.2% Zr, 1.2% Mo, and the remainder is Ti.

[0008] As a further preference, the Ti-Al-Nb-Zr-Mo titanium alloy comprises, by mass percentage, 5.5% to 6.5% Al, 2.5% to 3.3% Nb, 1.8% to 2.2% Zr, 1.5% Mo, and the remainder is Ti.

[0009] As a further preference, the Ti-Al-Nb-Zr-Mo titanium alloy comprises, by mass percentage, 5.5% to 6.5% Al, 2.5% to 3.3% Nb, 1.8% to 2.2% Zr, 1.8% Mo, and the remainder Ti.

[0010] As a further preference, the Ti-Al-Nb-Zr-Mo titanium alloy comprises, by mass percentage, 6% Al, 3% Nb, 2% Zr, 1.2-1.8% Mo, and the remainder Ti.

[0011] According to another aspect of the present invention, there is provided a method for preparing a Ti-Al-Nb-Zr-Mo series high impact toughness titanium alloy, comprising the following steps:

[0012] S1, mixing powder raw materials according to the mass percentage of the above-mentioned Ti-Al-Nb-Zr-Mo series high impact toughness titanium alloy, and cold isostatic pressing to obtain a green body;

[0013] S2, vacuum sintering the green body obtained in step S1;

[0014] S3, forging the sample obtained in step S2;

[0015] S4. Heat-treating the sample obtained in step S3 to obtain a Ti-Al-Nb-Zr-Mo titanium alloy.

[0016] As further preferred, in step S1, the pressure of cold isostatic pressing is 200-400 MPa, and the holding time is 10-60 min.

[0017] As further preferred, in step S2, the sintering temperature of the vacuum sintering is 1100-1400°C, and the holding time is 2-6 hours.

[0018] As a further preferred embodiment, in step S3, the forging temperature is 5 to 20° C. below the phase transformation point, air cooling is performed after forging, and reforging and drawing are performed so that the deformation amount is greater than 70%.

[0019] As further preferred, in step S4, the heat treatment temperature is 900-1000° C., the temperature is kept for 1-3 hours, and the Ti—Al—Nb—Zr—Mo titanium alloy is obtained by air cooling.

[0020] In general, the above technical solution conceived by the present invention has the following technical advantages compared with the prior art:

[0021] 1. The Ti-Al-Nb-Zr-Mo titanium alloy designed by the present invention has a higher content of the β-stabilizing element Mo in its composition compared to the existing Ti80 alloy. The increase of Mo can reduce the phase transition point temperature, promote the formation of high-density dislocations, promote deformation twinning, and refine the α-phase grains, thereby strengthening the alloy to ensure its strength while improving the impact toughness; and setting an upper limit for the Mo content avoids the problem of poor welding performance caused by excessive Mo content. The increase in the Mo content significantly improves the impact toughness of the Ti80 alloy, and its impact absorption energy is increased by 15 to 40% compared to the existing Ti80 alloy.

[0022] 2. The present invention further designs a preparation method of Ti-Al-Nb-Zr-Mo titanium alloy based on powder metallurgy. Based on the principle of solid phase metallurgy, it transcends the multiple melting and solidification processes in traditional melting and casting technology, greatly improving the freedom of design of titanium alloy composition, and thus effectively avoiding the Mo element segregation problem caused by excessive Mo element content (mass fraction exceeding 1%) in the melting and casting method. At the same time, powder metallurgy technology also has the advantages of low cost, fine and uniform structure, etc., which can ensure the strength of titanium alloy while better improving impact toughness.

[0023] 3. The method of improving the impact toughness of Ti80 alloy by optimizing the forging-heat treatment process in a more sophisticated and complex manner often results in a narrow forging-heat treatment process window, which is not conducive to the mass production of Ti80 alloy. The present invention has the advantages of being simple and easy to implement, having a stable effect, and having great potential for subsequent improvement.

[0024] 4. The present invention further designs the process parameters in the preparation process. Specifically: too low a cold isostatic pressing pressure will lead to too low a relative density of the green body, too many pores, thus affecting the mechanical properties; too high a pressure will place too high requirements on equipment conditions and consume too much energy. Too low a vacuum sintering temperature will lead to insufficient powder bonding and element diffusion, too many pores, and insufficient homogenization; too high a temperature will lead to too large a grain size, affecting the mechanical properties. Forging temperatures higher than the phase transition point will lead to the formation of coarse Widmanstatten structure, reducing room temperature strength and fatigue properties; too low a forging temperature will lead to excessive deformation resistance and easy cracking. Too high a heat treatment temperature will lead to abnormal grain growth and reduce mechanical properties; too low a heat treatment temperature will lead to incomplete growth of the metastable phase, and the material performance advantages cannot be fully utilized. Through the comprehensive design of the above process parameters, the mechanical properties of the titanium alloy can be further guaranteed. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 The microstructure diagram of the Ti-6Al-3Nb-2Zr-1.2Mo alloy in Example 1 of the present invention;

[0026] Figure 2 The microstructure diagram of the Ti-6Al-3Nb-2Zr-1.5Mo alloy in Example 2 of the present invention;

[0027] Figure 3 The microstructure diagram of the Ti-6Al-3Nb-2Zr-1.8Mo alloy in Example 3 of the present invention;

[0028] Figure 4 This is the microstructure diagram of the Ti-6Al-3Nb-2Zr-1Mo alloy in Comparative Example 1. DETAILED DESCRIPTION

[0029] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0030] A Ti-Al-Nb-Zr-Mo high impact toughness titanium alloy provided in an embodiment of the present invention is composed of the following raw materials in mass percentage: 5.5% to 6.5% of Al, 2.5% to 3.3% of Nb, 1.8% to 2.2% of Zr, 1.2% to 1.8% of Mo, and the remainder is Ti.

[0031] Preferably, the titanium alloy is composed of the following raw materials by mass percentage: 6% Al, 3% Nb, 2% Zr, 1.2% to 1.8% Mo, and the balance is Ti.

[0032] Specifically, the mass percentage of Mo may be 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, etc.

[0033] The embodiment of the present invention also provides a method for preparing a Ti-Al-Nb-Zr-Mo series high impact toughness titanium alloy, comprising the following steps:

[0034] S1. Mixing alloy powder raw materials according to the mass percentage of the aforementioned titanium alloy, and cold isostatic pressing to form;

[0035] S2, vacuum sintering the green body obtained in step S1;

[0036] S3, forging the sample obtained in step S2;

[0037] S4. Heat-treating the sample obtained in step S3 to obtain a Ti-Al-Nb-Zr-Mo titanium alloy.

[0038] Preferably, in step S1, the pressure of cold isostatic pressing is 200-400 MPa, and the holding time is 10-60 min to ensure compaction.

[0039] Preferably, in step S2, the sintering temperature of vacuum sintering is 1100-1400° C., the holding time is 2-6 hours, and the cooling method is furnace cooling to ensure sufficient diffusion of alloy elements.

[0040] Preferably, in step S3, the forging temperature is 5 to 20°C below the phase transformation point, and 2 to 3 reforgings and 2 to 3 stretchings are performed in sequence. After each firing, the furnace is returned to the furnace for insulation for 30 to 40 minutes. The temperature drop during the forging process does not exceed 150°C, the cooling method is air cooling, and the deformation is greater than 70%.

[0041] Preferably, in step S4, the heat treatment temperature is 900-1000° C., and the mixture is kept at this temperature for 1-3 hours and then air-cooled, so as to adjust the ratio of the α phase to the β phase, improve the structure, and optimize the mechanical properties.

[0042] The following are specific embodiments:

[0043] Embodiment 1:

[0044] A Ti-6Al-3Nb-2Zr-1.2Mo high impact toughness titanium alloy, the preparation method is as follows:

[0045] S1. The alloy powder raw materials are mixed uniformly according to the weight ratio (6% Al, 3% Nb, 2% Zr, 1.2% Mo, and the balance Ti). The powder is pressed by cold isostatic pressing technology, and the mixed titanium alloy powder is loaded into a soft rubber mold, and the titanium alloy powder is pressed and molded at 350 MPa for 30 minutes.

[0046] S2, vacuum sintering the green body obtained in step S1. First, vacuumize to 5×10 -3 Pa, to avoid contamination by oxygen, nitrogen, hydrogen and other elements during the sintering process; then slowly increase the temperature to ensure uniform thermal field and reduce sintering thermal stress; the sintering temperature is 1200℃, the holding time is 4h, and the furnace is cooled after sintering. When the pressure difference between the inside and outside of the sintering furnace is 0, open the sintering furnace and take out the sintered sample.

[0047] S3, forging the sample obtained in step S2. The forging temperature is 15°C below the phase transformation point, and 2-3 times of reforging and 2-3 times of drawing are carried out in sequence. After each firing, the sample is returned to the furnace for 35 minutes of heat preservation. The temperature drop during the forging process does not exceed 150°C. The cooling method is air cooling, and the deformation is greater than 70%.

[0048] S4, heat-treating the sample obtained in step S3 to obtain a Ti-6Al-3Nb-2Zr-1.2Mo high impact toughness titanium alloy. The heat treatment temperature is 960°C, and the heat treatment is maintained for 2 hours and then air-cooled.

[0049] Embodiment 2:

[0050] A Ti-6Al-3Nb-2Zr-1.5Mo titanium alloy was prepared, wherein the raw materials were 6% Al, 3% Nb, 2% Zr, 1.5% Mo, and the balance was Ti; the other steps were the same as those in Example 1.

[0051] Embodiment 3:

[0052] A Ti-6Al-3Nb-2Zr-1.8Mo titanium alloy is prepared, wherein the raw materials are 6% Al, 3% Nb, 2% Zr, 1.8% Mo, and the balance is Ti; the other steps are the same as those in Example 1.

[0053] Comparative Example 1:

[0054] A Ti-6Al-3Nb-2Zr-1Mo titanium alloy is prepared, wherein the raw materials are 6% Al, 3% Nb, 2% Zr, 1% Mo, and the balance is Ti; the other steps are the same as those in Example 1.

[0055] The impact toughness of the titanium alloys obtained in Examples 1 to 3 and Comparative Example 1 was analyzed, and the experimental results are shown in Table 1.

[0056] Table 1 Impact absorption energy of four alloy compositions at room temperature

[0057]

[0058] It can be seen from Table 1 that, compared with the Ti80 alloy of Comparative Example 1, the impact absorption work of the titanium alloy obtained by adjusting the Mo element content in the present invention is significantly improved by 15-40%, and the impact toughness is significantly improved.

[0059] The microstructure images of the titanium alloys obtained in Examples 1 to 3 and Comparative Example 1 are obtained, including optical microscopy images and scanning electron microscopy images, such as Figures 1 to 4 As shown in the figure, it can be seen that when the Mo content is gradually increased on the basis of the Ti80 alloy composition, when it is added to 1.2%, the heat-treated microstructure has no obvious change and is a Widmanstatten structure; when the Mo content is added to 1.5%, the heat-treated microstructure changes from the Widmanstatten structure to a mixed structure of a dual-state structure and a basket structure; when the Mo content is added to 1.8%, the heat-treated microstructure changes from the Widmanstatten structure to a structure with short rod-like α phases uniformly and closely distributed similar to the basket structure. It can be seen that with the increase of Mo content, its heat-treated microstructure has a tendency to change from the Widmanstatten structure to a shorter and more uniform structure, which is also one of the reasons for the improvement of the impact toughness of the alloy.

[0060] The tensile properties of the Ti-6Al-3Nb-2Zr-1.8Mo alloy with the best impact toughness were analyzed, and the experimental results are shown in Table 2. It can be seen that compared with the tensile properties of the Ti80 alloy in GB / T 35364-2017 (tensile strength 880MPa, yield strength 785MPa, elongation after fracture 12%), the Ti-Al-Nb-Zr-Mo titanium alloy designed in the present invention increases the Mo element content to improve the impact toughness while also ensuring good strength and plasticity, which can meet its service conditions.

[0061] Table 2 Tensile properties of Ti-6Al-3Nb-2Zr-1.8Mo alloy

[0062]

[0063] It will be easily understood by those skilled in the art that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A Ti-Al-Nb-Zr-Mo series high impact toughness titanium alloy, characterized in that: Calculated by mass percentage, the Ti-Al-Nb-Zr-Mo titanium alloy comprises: 5.5% to 6.5% Al, 2.5% to 3.3% Nb, 1.8% to 2.2% Zr, 1.2% to 1.8% Mo, and the balance is Ti.

2. The Ti-Al-Nb-Zr-Mo series high impact toughness titanium alloy according to claim 1, characterized in that: Calculated by mass percentage, the Ti-Al-Nb-Zr-Mo titanium alloy comprises: 5.5% to 6.5% Al, 2.5% to 3.3% Nb, 1.8% to 2.2% Zr, 1.2% Mo, and the balance is Ti.

3. The Ti-Al-Nb-Zr-Mo series high impact toughness titanium alloy according to claim 1, characterized in that: Calculated by mass percentage, the Ti-Al-Nb-Zr-Mo titanium alloy comprises: 5.5% to 6.5% Al, 2.5% to 3.3% Nb, 1.8% to 2.2% Zr, 1.5% Mo, and the balance is Ti.

4. The Ti-Al-Nb-Zr-Mo series high impact toughness titanium alloy according to claim 1, characterized in that: Calculated by mass percentage, the Ti-Al-Nb-Zr-Mo titanium alloy comprises: 5.5% to 6.5% Al, 2.5% to 3.3% Nb, 1.8% to 2.2% Zr, 1.8% Mo, and the balance is Ti.

5. The Ti-Al-Nb-Zr-Mo series high impact toughness titanium alloy according to claim 1, characterized in that: Calculated by mass percentage, the Ti-Al-Nb-Zr-Mo titanium alloy comprises: 6% Al, 3% Nb, 2% Zr, 1.2-1.8% Mo, and the balance Ti.

6. A method for preparing a Ti-Al-Nb-Zr-Mo series high impact toughness titanium alloy, characterized in that: The steps include: S1. Mixing powder raw materials according to the mass percentage of the Ti-Al-Nb-Zr-Mo series high impact toughness titanium alloy according to any one of claims 1 to 5, and cold isostatic pressing to obtain a green body; S2, vacuum sintering the green body obtained in step S1; S3, forging the sample obtained in step S2; S4. Heat-treating the sample obtained in step S3 to obtain a Ti-Al-Nb-Zr-Mo titanium alloy.

7. The method for preparing the Ti-Al-Nb-Zr-Mo series high impact toughness titanium alloy according to claim 6, characterized in that: Step S1, the pressure of cold isostatic pressing is 200-400 MPa, and the holding time is 10-60 min.

8. The method for preparing the Ti-Al-Nb-Zr-Mo series high impact toughness titanium alloy according to claim 6, characterized in that: Step S2, the sintering temperature of vacuum sintering is 1100-1400°C, and the holding time is 2-6 hours.

9. The method for preparing the Ti-Al-Nb-Zr-Mo series high impact toughness titanium alloy according to claim 6, characterized in that: Step S3, the forging temperature is 5 to 20°C below the phase transformation point, air cooling is performed after forging, and reforging and stretching are performed to make the deformation amount greater than 70%.

10. The method for preparing the Ti-Al-Nb-Zr-Mo series high impact toughness titanium alloy according to any one of claims 6 to 9, characterized in that: Step S4, heat treatment temperature is 900-1000°C, heat preservation is 1-3 hours, and air cooling is performed to obtain Ti-Al-Nb-Zr-Mo titanium alloy.

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