A forging method for improving the uniformity of the microstructure of large-sized TiZrNb high-entropy alloys

Abstract

The present invention relates to a forging method for improving the uniformity of the structure of a large-size TiZrNb-based high-entropy alloy, and belongs to the technical field of alloys. First, the TiZrNb-based high-entropy alloy ingot is heated, and then the first fire forging is performed, and the forging temperature, deformation amount and pressing rate are controlled throughout; then, the second and third fire forgings are performed again, and finally recrystallization annealing is performed. The TiZrNb-based alloy forged by the method has increased uniformity of the structure, obtained refined grains, and improved shrinkage and shrinkage cavities generated by casting, which can avoid the generation of defects such as cracks, and achieve the matching of alloy strength and plasticity.

Description

Technical Field

[0001] The invention relates to a forging method for improving the uniformity of the structure of a large-size TiZrNb-based high-entropy alloy, and belongs to the technical field of alloys. Background Art

[0002] TiZrNb-based high-entropy alloys composed of highly active and refractory elements have both good mechanical properties and high energy release characteristics. They can exhibit characteristics of chemical energy release similar to those of active materials under impact loads, and are expected to solve the problem of insufficient energy release effect of traditional inert metals.

[0003] Hot forging is to heat metal materials to a certain temperature, which can improve the plasticity of the metal, make it not easy to crack after large deformation, and reduce the deformation resistance of the metal, so that the force required for forging is greatly reduced. At the same time, the forgings undergo large forging deformation in the appropriate temperature range, resulting in recrystallization, so that the forgings have uniform and fine grains and good organizational structure, thereby improving the mechanical properties. However, the existing technology often causes problems such as high oxidation degree, surface cracking, and coarse grains in the forging process of large-sized ingots. Summary of the invention

[0004] In view of this, the object of the present invention is to provide a forging method for improving the uniformity of the structure of a large-sized TiZrNb-based high entropy alloy. The TiZrNb-based alloy forged by the method has increased uniformity of the structure, obtained refined grains, and improved shrinkage and shrinkage cavities produced by casting, which can avoid the generation of defects such as cracks and achieve the matching of strength and plasticity of the alloy.

[0005] To achieve the above objectives, the technical solution of the present invention is as follows.

[0006] A forging method for improving the uniformity of the structure of a large-sized TiZrNb-based high-entropy alloy, the method comprising the following steps:

[0007] (1) In an inert gas atmosphere, a TiZrNb high entropy alloy ingot is heated to a temperature T1 and kept at this temperature for 0.45d0 to 0.6d0 minutes; after the end of the heat preservation, the first fire forging is immediately carried out, and after 1 to 2 times of roughening and drawing, the final forging temperature is 750 to 850°C, the deformation is 50% to 70%, and after the forging is completed, air cooling is carried out to obtain the first fire forging piece;

[0008] (2) In an inert gas atmosphere, heat the first forging piece to T2 temperature and keep it warm for 0.15d0 to 0.2d0 minutes. After the end of the heat preservation, the second forging is immediately carried out. After 1 to 2 times of roughening and drawing, the final forging temperature is 750 to 850 ° C, the deformation is 35% to 45%, and after the forging is completed, air cooling is performed;

[0009] (3) Repeat step (2) to perform a third forging to obtain a high entropy alloy forging;

[0010] (4) in an inert gas atmosphere, heating the high entropy alloy forging to 850-900° C. and then keeping the temperature for 0.2d0-0.4d0 minutes, and cooling after the end of the temperature keeping to obtain a TiZrNb-based high entropy alloy;

[0011] Wherein, the diameter d0 of the TiZrNb high entropy alloy ingot is 200-600 mm, and the aspect ratio is ≥5;

[0012] T1 is 900-1000℃, T2 is 20-50℃ lower than T1;

[0013] During each forging, the strain rate is 0.006~0.05s -1 , the forging ratio is greater than or equal to 4:1, and the forging hammer pressing rate is is the strain rate, h0 is the ingot length, and E is the deformation amount.

[0014] Preferably, the chemical formula of the TiZrNb high entropy alloy is Ti a Zr b Nb c M x , M is one or more of Hf, W, Ni, Al, Cr, Mo, Fe and V, 10≤a≤30, 45≤b≤60, 15≤c≤30, 0≤x≤10, a+b+c+x=100.

[0015] Preferably, the aspect ratio of the TiZrNb-based high entropy alloy ingot is 5-10.

[0016] Preferably, the forging ratio is 4 to 6:1.

[0017] Preferably, the deformation amount of the first forging is 50% to 55%, and the deformation amount of the second and third forging is 40% to 42%.

[0018] Preferably, during heating, the heating rate is 300 to 600° C. / h, more preferably, the heating rate is 500 to 600° C. / h.

[0019] Preferably, in step (1) and step (4), an anti-oxidation coating is evenly applied to the surface of the forging before heating.

[0020] Preferably, after each air cooling, the forging surface is ground.

[0021] A large-size TiZrNb-based high-entropy alloy is prepared by the above method.

[0022] Beneficial Effects

[0023] The present invention provides a forging method for improving the uniformity of the structure of a large-sized TiZrNb-based high-entropy alloy. The initial forging temperature is 900-1000°C. If it is too high, it is easy to cause severe oxidation of the alloy and high loss. The holding time is (0.45-0.6)d0 minutes. If the time is too long, the grains will be too coarse. If the time is too short, the forging may be heated unevenly, and the temperature difference between the core and the outside of the forging may be too large. The final forging temperature needs to be controlled at 750-850°C. When the temperature is too low, the refined grains cannot be obtained, and the possibility of cracking of the workpiece is greatly increased. In the method described in the present invention, the downward pressure rate during forging needs to be strictly controlled. If it is too fast, the surface of the forging may crack. If it is too slow, the exposure time of the forging in the air will increase, and oxidation will be aggravated. In the post-forging heat treatment, the temperature is controlled at 850-900℃, (0.2-0.4)d0 minutes to transform the deformed grains into uniform equiaxed grains, and to prevent the grains from growing excessively, eliminate work hardening and residual stress, and make the strength and plasticity of the workpiece better. The temperature should not be too high and the time should not be too long. In all heating processes, inert gas must be introduced into the heating furnace to slow down the oxidation of the alloy and reduce forging losses.

[0024] The method of the present invention can increase the uniformity of the structure of TiZrNb alloys, refine the grains, improve the processing performance of workpieces, effectively avoid defects such as cracking, and improve the performance quality of the alloy. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 (a) is the microstructure of the sample of Example 1; (b) is the quasi-static tensile curve.

[0026] Figure 2 (a) is the microstructure of the sample of Example 2; (b) is the quasi-static tensile curve.

[0027] Figure 3 (a) is the microstructure of the sample of Example 3; (b) is the quasi-static tensile curve.

[0028] Figure 4 (a), (b), and (c) are the microstructures of the alloy samples of Comparative Examples 1, 2, and 3, respectively.

[0029] Figure 5 The quasi-static tensile curve comparison diagram of the samples obtained in Example 1 and Comparative Examples 1, 2, and 3. DETAILED DESCRIPTION

[0030] The present invention will be further described in detail below in conjunction with specific embodiments.

[0031] Example 1: φ200×1000mmTi 25 Zr 50 Nb 25 Alloy Forging

[0032] (1) Forging process:

[0033] Ti with anti-oxidation coating on the surface 25 Zr 50 Nb 25 The alloy ingot is placed in a heating furnace, and in an argon atmosphere, the temperature is raised to 1000℃ at a heating rate of 600℃ / min, and the temperature is kept for 120min; then the first fire forging is carried out, the initial forging temperature is 900-1000℃, the final forging temperature is 750-850℃, the forging ratio is 4.5:1, and the forging hammer pressing rate is 25mm / s. The deformation of the first fire forging is 50%. After two times of roughening and drawing, the surface oxide scale is polished after cooling in the air. The forging is returned to the heating furnace and heated to 950℃ at a heating rate of 600℃ / min, and kept for 40min; after taking it out, the second fire forging is carried out immediately, the final forging temperature is 750-850℃, the deformation is 40%, the forging hammer pressing rate is 25mm / s, after one time of roughening and drawing, the surface oxide scale is polished after cooling in the air, and then the third fire forging is carried out, and the conditions are the same as the second fire to obtain the forging.

[0034] (2) Heat treatment after forging

[0035] The forgings obtained in the above steps are subjected to recrystallization annealing, and after being evenly coated with an anti-oxidation coating, the forgings are placed in a heating furnace, argon gas is introduced into the furnace, and the temperature is increased to 850°C at a heating rate of 600°C / h, maintained for 60 minutes, and then air-cooled to obtain a TiZrNb-based high entropy alloy.

[0036] Samples were cut from the obtained forgings and polished. Under a scanning electron microscope, it was observed that there were uniform equiaxed grains and no obvious defects such as cracks. Figure 1 (a) As shown. The stress-strain curve can be obtained through quasi-static tensile test, such as Figure 1 As shown in (b), the strength of the alloy after forging is increased from 660MPa to 720MPa, and the elongation is increased from 13% to 20%. The method of this embodiment achieves the purpose of closing defects, refining grains, and enhancing plasticity.

[0037] Example 2: φ250×1400mmTi 23 Zr 48 Nb 20 Al9 alloy forging

[0038] (1) Forging process:

[0039] Ti with anti-oxidation coating on the surface 23 Zr 48 Nb 20The Al9 alloy ingot is placed in a heating furnace, and in an argon atmosphere, the temperature is raised to 1000℃ at a heating rate of 600℃ / min, and the temperature is kept for 120min; then the first forging is carried out, the initial forging temperature is 900-1000℃, the final forging temperature is 750-850℃, the forging ratio is 5:1, and the forging hammer pressing rate is 40mm / s. The deformation of the first forging is 50%. After two times of roughening and drawing, the surface oxide scale is polished after cooling in the air. The forging is returned to the heating furnace and heated to 950℃ at a heating rate of 600℃ / min, and kept for 50min; after taking it out, the second forging is carried out, the final forging temperature is 750-850℃, the deformation is 40%, the forging hammer pressing rate is 40mm / s, after one roughening and drawing, the surface oxide scale is polished after cooling in the air. Then the third forging is carried out, the conditions are the same as the second forging, and the forging is finally obtained.

[0040] (2) Heat treatment after forging

[0041] The forgings obtained in the above steps are subjected to recrystallization annealing, and are placed in a heating furnace. Anti-oxidation coating is evenly applied before placement, and argon gas is introduced into the furnace. The temperature is increased to 850°C at a heating rate of 600°C / h, and then kept at this temperature for 75 minutes and then cooled with the furnace to obtain a TiZrNb-based high entropy alloy.

[0042] Samples were cut from the obtained forgings and polished. Under a scanning electron microscope, it was observed that there were uniform equiaxed grains and no obvious defects such as cracks. Figure 2 (a) As shown. The stress-strain curve of the alloy can be obtained through quasi-static tensile test, as shown in Figure 2 As shown in (b), the strength of the alloy after forging is increased from 550MPa before forging to 900MPa, and the elongation is increased from 30% to 45%. The method of this embodiment improves the uniformity of the material structure, and improves the strength and plasticity.

[0043] Example 3: φ300×2000mmTi 24 Zr 47 Nb 23 Hf6 alloy forging

[0044] (1) Forging process:

[0045] Ti with anti-oxidation coating on the surface 24 Zr 47 Nb 23The Hf6 alloy ingot is placed in a heating furnace, and in an argon atmosphere, the temperature is raised to 1000℃ at a heating rate of 600℃ / min, and the temperature is kept for 120min; then the first forging is carried out, the initial forging temperature is 900-1000℃, the final forging temperature is 750-850℃, the forging ratio is 4.7:1, and the forging hammer pressing rate is 55mm / s. The deformation of the first forging is 50%. After two times of roughening and drawing, the surface oxide scale is polished after cooling in the air. The forging is returned to the heating furnace and heated to 980℃ at a heating rate of 600℃ / min, and kept for 60min; after taking it out, the second forging is carried out, the final forging temperature is 750-850℃, the deformation is 40%, and after two times of roughening and drawing, the surface oxide scale is polished after cooling in the air. Then the third forging is carried out, and the conditions are the same as the second forging, and finally the forging is obtained.

[0046] (2) Heat treatment after forging

[0047] The forgings obtained in the above steps are subjected to recrystallization annealing, and are placed in a heating furnace. Anti-oxidation coating is evenly applied before placement, and argon gas is introduced into the furnace. The temperature is increased to 900°C at a heating rate of 600°C / h, and then kept at this temperature for 90 minutes and then cooled with the furnace to obtain a TiZrNb-based high entropy alloy.

[0048] Samples were cut from the obtained forgings and polished. Under a scanning electron microscope, it was observed that there were uniform equiaxed grains and no obvious defects such as cracks. Figure 3 (a) As shown. The stress-strain curve of the alloy can be obtained through quasi-static tensile test, as shown in Figure 3 As shown in (b), the strength of the alloy after forging is increased from 550MPa before forging to 680MPa, and the elongation is increased from 12% to 18%. The method of this embodiment achieves the purpose of closing defects, refining grains, and improving strength-plasticity matching.

[0049] Comparative Example 1: φ200×1000mmTi 25 Zr 50 Nb 25 Alloy Forging

[0050] The difference from Example 1 is that the initial forging temperature is controlled to be 850-900°C, and the other conditions remain unchanged. Samples were cut from the obtained forgings to characterize the microstructure and mechanical properties. Under a scanning electron microscope, it was found that many defects were not completely closed, such as Figure 4 (a) As shown. The stress-strain curve is obtained by quasi-static tensile test, as shown in Figure 5 As shown, the strength of the alloy forged by this method is only 550 MPa and the elongation is 13%, which is worse than that of Example 1.

[0051] Comparative Example 2: φ200×1000mmTi 25 Zr50 Nb 25 Alloy Forging

[0052] Different from Example 1, the forging hammer downward speed was controlled to be 50 mm / s, and the other conditions remained unchanged. Samples were cut from the forged piece to characterize the microstructure and mechanical properties. Under a scanning electron microscope, it was found that the dynamic recrystallization of the alloy was not yet completed, most of the grains were still large in size, and many fine grains appeared around the large grains, such as Figure 4 (b) As shown. The stress-strain curve is obtained by quasi-static tensile test, as shown in Figure 5 As shown, the strength of the alloy forged by this method is 650 MPa and the elongation is 12%, both of which are weaker than the alloy in Example 1.

[0053] Comparative Example 3: φ200×1000mm Ti 25 Zr 50 Nb 25 Alloy Forging

[0054] The difference from Example 1 is that the holding time of the heat treatment after forging is 180 minutes, and the other conditions remain unchanged. Samples are cut from the forging to characterize the microstructure and mechanical properties. Under a scanning electron microscope, it is found that the second phase precipitates at the grain boundaries and in the grains of the alloy. Figure 4 (c) As shown. The stress-strain curve of the forged alloy under this method was obtained by quasi-static tensile test, as shown in Figure 5 As shown, due to the presence of precipitation phase at the grain boundary, although the strength of the sample reaches 950MPa, the elongation is only 12%, and it breaks in the uniform deformation stage, with poor plasticity.

[0055] In summary, the invention includes but is not limited to the above embodiments. Any equivalent substitution or partial improvement made under the spirit and principle of the invention shall be deemed to be within the protection scope of the invention.

Claims

1. A forging method for improving the uniformity of the structure of a large-sized TiZrNb-based high-entropy alloy, characterized in that: The method steps include: (1) In an inert gas atmosphere, the TiZrNb high entropy alloy ingot is heated to T1 temperature and kept warm for 0.45d0~0.6d0 minutes; after the end of the heat preservation, the first fire forging is carried out immediately. After 1~2 times of roughening and drawing, the final forging temperature is 750~850℃, the deformation is 50%~70%, and after the forging is completed, air cooling is carried out to obtain the first fire forging part; (2) In an inert gas atmosphere, heat the first forging to T2 temperature and keep it warm for 0.15d0~0.2d0 minutes. After the end of the heat preservation, the second forging is carried out immediately. After 1~2 times of roughening and drawing, the final forging temperature is 750~850℃, the deformation is 35%~45%, and after forging, air cooling is performed; (3) Repeat step (2) to perform a third forging to obtain a high entropy alloy forging; (4) In an inert gas atmosphere, the high entropy alloy forging is heated to 850-900° C., then kept at this temperature for 0.2 d0-0.4 d0 minutes, and then cooled after the end of the holding period to obtain a TiZrNb-based high entropy alloy; Among them, the diameter d0 of the TiZrNb high entropy alloy ingot is 200~600mm, and the aspect ratio is ≥5; T1 is greater than 900℃ and less than or equal to 1000℃, and T2 is 20~50℃ lower than T1; During each forging, the strain rate is 0.006~0.05s -1 , the forging ratio is greater than or equal to 4:1, and the forging hammer pressing rate is mm / s, is the strain rate, is the ingot length and E is the deformation.

2. A forging method for improving the uniformity of the structure of a large-sized TiZrNb-based high-entropy alloy as claimed in claim 1, characterized in that: The chemical formula of the TiZrNb series high entropy alloy is Ti a Zr b Nb c M x , M is one or more of Hf, W, Ni, Al, Cr, Mo, Fe and V, 10≤a≤30, 45≤b≤60, 15≤c≤30, 0≤x≤10, a+b+c+x=100.

3. A forging method for improving the uniformity of the structure of a large-sized TiZrNb-based high-entropy alloy as claimed in claim 1, characterized in that: The aspect ratio of TiZrNb high entropy alloy ingots is 5~10.

4. A forging method for improving the uniformity of the structure of a large-sized TiZrNb-based high-entropy alloy as claimed in claim 1, characterized in that: The forging ratio is 4~6:

1.

5. A forging method for improving the uniformity of the structure of a large-sized TiZrNb-based high-entropy alloy as claimed in claim 1, characterized in that: The deformation of the first forging is 50%~55%, and the deformation of the second and third forging is 40%~42%.

6. A forging method for improving the uniformity of the microstructure of a large-sized TiZrNb-based high-entropy alloy as claimed in claim 1, characterized in that: When heating, the heating rate is 300~600℃ / h.

7. A forging method for improving the uniformity of the microstructure of a large-sized TiZrNb-based high-entropy alloy as claimed in claim 6, characterized in that: The heating rate is 500~600℃ / h.

8. A forging method for improving the uniformity of the structure of a large-sized TiZrNb-based high entropy alloy as claimed in claim 1, characterized in that: In step (4), before heating, an anti-oxidation coating is evenly applied on the surface of the forging.

9. A forging method for improving the uniformity of the structure of a large-sized TiZrNb-based high-entropy alloy as claimed in claim 1, characterized in that: After each air cooling, grind the forging surface.

10. A large-size TiZrNb high-entropy alloy, characterized in that: It is prepared by the method according to any one of claims 1 to 9.

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