NiTiNb alloy and preparation process thereof

Abstract

The NiTiNb alloy comprises the following components in percentage by weight: 5.4%-7.1% of Al, 9.4%-13.5% of Cr, 0.1%-0.5% of Ni, 0.1%-0.5% of Ti, 0.1%-0.5% of Ti, and the balance of Ni. 5.6 to 8.4 percent of Mo; 3.5% to 5.5% of Nb; mn accounts for 3.0%-4.5%, Ta accounts for 1.5%-3.3%; 4.0% to 6.0% of Ni; pt, 0.05% to 0.10%; 0 < = 0.05%; c is less than or equal to 0.02%; h is less than or equal to 0.01%; s is less than or equal to 0.01%; the process comprises the steps of S1, smelting, S2, casting forming, S3, stepped forging, S4, stress relief annealing, S5, solution treatment and S6, aging treatment.The process has the advantages that a more stable beta-phase solid solution is formed, a secondary alpha phase is separated out in cooperation with a beta phase, the hindering effect on dislocation is achieved, slippage deformation is restrained, and the mechanical property of the alloy is improved; and the balance of strength and toughness in mechanical properties of the alloy is realized.

Description

Technical Field

[0001] The present invention relates to the field of alloys, and particularly to a NiTiNb alloy and its preparation process. Background Art

[0002] With the continuous development of science and technology, the technology of aerospace and nautical vehicles has also been updated and the equipment iterated.

[0003] At present, most of the main components used in aerospace and nautical vehicles are made of austenitic stainless steel. Generally, the tensile strength of 316 austenitic stainless steel is about 515 Mpa, and it has good toughness. However, in a working environment of high temperature, high pressure and high corrosion, the tensile strength of the material will further decrease with the increase of temperature, and the brittleness of the material increases, resulting in a decrease in service life. In addition, the stainless steel itself has a large density and a low specific strength, which cannot meet the current requirements of lightweight and high strength.

[0004] It should be noted that the information disclosed in the above background art section is only used to enhance the understanding of the background of the present disclosure, and thus may include information that does not constitute the prior art known to those of ordinary skill in the art. Summary of the Invention

[0005] In view of the deficiencies of the prior art, the present invention discloses a NiTiNb alloy and its preparation process.

[0006] The technical solution adopted by the present invention is as follows:

[0007] A NiTiNb alloy, comprising components by weight percentage: Al, 5.4 - 7.1%; Cr, 9.4 - 13.5%; Mo, 5.6 - 8.4%; Nb, 3.5 - 5.5%; Mn, 3.0 - 4.5%; Ta, 1.5 - 3.3%; Ni, 4.0 - 6.0%; Pt, 0.05 - 0.10%; O ≤ 0.05%; C ≤ 0.02%; H ≤ 0.01%; S ≤ 0.01%; the balance is Ti.

[0008] Further, it includes a β phase, and the β phase equivalent βeq = Mo + 0.19Cr + 0.28Nb + 0.17Mn + 0.58Ta + 0.21Ni + 0.02Ti - 0.20Al.

[0009] Further, the range of the β phase equivalent βeq is controlled within 9.4 - 16.8%.

[0010] A preparation process of NiTiNb alloy, characterized by comprising the following steps: Step S1, melting: Put raw materials into an electric arc furnace for melting according to the designed proportion, and conduct 2-3 times of repeated melting. Except for the last melting, clean the surface of the material after each melting; Step S2, casting and forming to obtain a blank; Step S3, stepped forging: In the first stage of forging, heat the blank to 520-620 °C for forging, and cool it to room temperature after forging; In the second stage of forging, heat the blank to 650-720 °C for forging to obtain a forging; Step S4, stress relief annealing: Heat the forging to 400-430 °C for heat preservation; Step S5, solution treatment: First, preheat the forging to 200-250 °C for heat preservation, then heat the forging to 860-920 °C for heat preservation, then heat the forging to 1120-1270 °C for heat preservation, and finally cool the forging to room temperature with oil cooling; Step S6, aging treatment: Heat the forging to 620-675 °C for heat preservation, and finally cool the forging to room temperature with water cooling.

[0011] Further, in Step S1, the electric arc furnace is filled with argon, and the air pressure in the electric arc furnace is controlled at 0.2-0.25 Mpa.

[0012] Further, in Step S2, the casting temperature is controlled at 1400-1550 °C, and the casting process is carried out in an argon environment.

[0013] Further, in Step S3, the forging force F = σ avg ×A×k, where σavg is the deformation resistance. In the first forging stage, the value of σavg is 450 Mpa. In the second forging stage, the value of σavg is 350 Mpa. A is the cross-sectional area of the blank, and k is the strain coefficient, and the value of k is 4.0.

[0014] Further, in Step S4, the heat preservation time ranges from 3 to 8 h, and then it is cooled to room temperature.

[0015] Further, in Step S5, in the stage of 860-920 °C, the heat preservation time ranges from 5 to 12 h, and the heating rate is controlled at 5-10 °C / min. In the stage of 1120-1270 °C, the heat preservation time ranges from 10 to 18 h, and the heating rate is controlled at 15-20 °C / min.

[0016] Further, in Step S6, the heat preservation time is controlled at 4-8 h.

[0017] The beneficial effects of the present invention are as follows:

[0018] 1. Cr, Mo, Ta, Mn, and Nb are the main eutectic elements that form the β phase. Because there is space in the electron layer of Ti atoms, it undergoes substitutional solid solution with atoms of elements with similar atomic radii, thereby forming a more stable β-phase solid solution. There are also interactions such as metallic bonds between Ti and other metal elements, further enhancing the stability of the β phase. By strictly controlling the contents of the elements Cr, Mo, Ta, Mn, and Nb, it promotes nucleation of metal elements in all orientations, increases the content of the β-phase solid solution, and hinders dislocation slip, thus improving the tensile strength and toughness of the alloy.

[0019] 2. Conduct multiple solvent extractions to adjust the content of the input elements, ensuring that the actual element content approaches the designed value and reducing errors. The melting process is carried out in an argon environment to reduce the chance of contact between the material and air, avoiding excessive oxidation of the material. After each melting, clean the oxide scale on the surface to prevent oxides from entering the material during subsequent melting.

[0020] 3. Adopt a two-stage forging method to gradually achieve dynamic softening of the alloy, break up the coarse grains in the structure, control the forging temperature window, promote the occurrence of dynamic recrystallization during the deformation process, which is conducive to the formation of a fine-grained structure, and control the deformation force to avoid dynamic instability caused by excessive deformation and prevent fracture during the forging deformation process.

[0021] 4. After forging, relieve the internal stress accumulated in the forgings through stress relief annealing. During the annealing process, the atoms of the material obtain sufficient energy when heated, and this energy is sufficient to overcome the resistance to dislocation movement, promoting dislocation. The annealing temperature window is lower than the recrystallization temperature window to avoid lattice distortion in the structure and the precipitation of harmful phases.

[0022] 5. In the solution treatment, first perform preheating so that the heat has enough time to transfer to the core of the forging, reducing the internal and external temperature gradient in the forging. Then heat it to 860 - 920 °C, close to the β-phase transformation temperature. The metal elements in the alloy start to accelerate diffusion and crystallization. During the heating process, α and β phases appear in the alloy. As the temperature approaches the phase transformation point, the proportion of the β phase increases. Give sufficient holding time to allow the alloy elements to fully diffuse and gradually form a uniform β-phase solid solution. Finally, raise the temperature to the β-phase region, and metal elements such as Nb and Ta fully dissolve in the β phase to form a uniform supersaturated solid solution.

[0023] 6. In the aging treatment, the β phase precipitates and secondary α phase precipitates. During this process, dislocations appear at the interface between the α and β phases, forming a fine lamellar structure, which hinders the dislocations and inhibits slip deformation. Macroscopically, the alloy improves its strength without losing too much toughness, achieving a balance between strength and toughness in the mechanical properties of the alloy. Description of the Drawings

[0024] Figure 1 It is a schematic diagram of the steps of the preparation process of NiTiNb alloy.

[0025] Figure 2 It is the metallographic diagram of the specimen in Example 1.

[0026] Figure 3 It is the metallographic diagram of the specimen in Example 2.

[0027] Figure 4 It is the metallographic diagram of the specimen in Example 3.

[0028] Figure 5 It is the metallographic diagram of the specimen in Example 4.

[0029] Figure 6 It is the metallographic diagram of the specimen in Example 5. Specific embodiments

[0030] The following combines with the attached drawings to illustrate the specific embodiments of the present invention.

[0031] Example 1:

[0032] A NiTiNb alloy includes components by weight percentage: Al, 5.8%; Cr, 10.4%; Mo, 5.6%; Nb, 3.5%; Mn, 3.0%; Ta, 2.0%; Ni, 4.0%; Pt, 0.05%; O≤0.05%; C≤0.02%; H≤0.01%; S≤0.01%; the balance is Ti≈65.6%.

[0033] Its β equivalent βeq = Mo + 0.19Cr + 0.28Nb + 0.17Mn + 0.58Ta + 0.21Ni + 0.02Ti - 0.20Al = 11.2%. The βeq of this Example 1 meets the range requirements of 9.4 - 16.8%.

[0034] Its preparation process, as Figure 1 shown, includes the following steps:

[0035] Step S1, melting: Put the raw materials into the electric arc furnace for melting according to the designed ratio. The electric arc furnace is filled with argon, and the air pressure in the electric arc furnace is controlled at 0.2 - 0.25 Mpa. Conduct 2 times of repeated melting to reduce the element content error. Except for the last melting, clean the surface of the material after each melting, clean the oxide layer on the surface of the material, and the melting is carried out in an argon environment to avoid generating too many oxides.

[0036] Step S2, casting and forming: Control the casting temperature at 1400°C, and the casting process is carried out in an argon environment to obtain a blank. Also avoid the material from contacting too much air to avoid material oxidation.

[0037] Step S3: Stepwise forging. In the first stage of forging, the blank is heated to 550 °C for forging, and after forging is completed, it is cooled to room temperature, and the cooling method is water cooling. In the second stage of forging, the blank is heated to 650 °C for forging, and then air-cooled to room temperature to obtain a forging.

[0038] Among them, the forging force F = σ avg ×A×k, where σavg is the deformation resistance. In the first forging stage, the value of σavg is 450 Mpa, and in the second forging stage, the value of σavg is 350 Mpa. A is the cross-sectional area of the blank, and k is the strain coefficient, and the value of k is 4.0. Ensure that the material has sufficient deformation force to fully break the coarse grain structure, but avoid the deformation force exceeding the limit that the material can bear, and reduce forging defects such as collapse or cracks in the material.

[0039] Step S4: Stress relief annealing. The forging is heated to 400 °C for heat preservation, the heat preservation time is controlled at 3 h, and then it is cooled to room temperature.

[0040] Step S5: Solution treatment. First, the forging is preheated to 200 °C for heat preservation. Since it takes time for heat to transfer from the outside to the inside of the forging, preheating in advance can ensure that the core of the forging is heated and reduce the temperature gradient between the inside and outside of the forging.

[0041] After preheating is completed, the forging is heated to 860 °C for heat preservation, the heating rate is controlled at 5 °C / min, and after reaching the target temperature, it is heat-preserved for 5 h. Then the forging is heated to 1130 °C for heat preservation, the heating rate is controlled at 15 °C / min, and after reaching the target temperature, it is heat-preserved for 10 h. Finally, it is oil-cooled to room temperature.

[0042] Step S6: Aging treatment. The forging is heated to 620 °C for heat preservation, the heat preservation time is controlled at 5 h, and finally the forging is water-cooled to room temperature.

[0043] Example 2:

[0044] A NiTiNb alloy, comprising components by weight percentage: Al, 6.6%; Cr, 11.3%; Mo, 7.1%; Nb, 4.2%; Mn, 3.5%; Ta, 2.6%; Ni, 5.3%; Pt, 0.05%; O ≤ 0.05%; C ≤ 0.02%; H ≤ 0.01%; S ≤ 0.01%; the balance is Ti ≈ 59.3%.

[0045] Its β equivalent βeq = Mo + 0.19Cr + 0.28Nb + 0.17Mn + 0.58Ta + 0.21Ni + 0.02Ti - 0.20Al = 12.4%. The βeq of this Example 2 meets the range requirements of 9.4 - 16.8%.

[0046] Example 1 and Example 2 use the same title, preparation process, and process parameters.

[0047] Example 3:

[0048] A NiTiNb alloy, including components by weight percentage: Al, 7.0%; Cr, 13.2%; Mo, 8.0%; Nb, 5.0%; Mn, 4.5%; Ta, 3.0%; Ni, 6.0%; Pt, 0.10%; O ≤ 0.05%; C ≤ 0.02%; H ≤ 0.01%; S ≤ 0.01%; the balance is Ti ≈ 53.2%.

[0049] Its β equivalent βeq = Mo + 0.19Cr + 0.28Nb + 0.17Mn + 0.58Ta + 0.21Ni + 0.02Ti - 0.20Al = 15.3%. The βeq of this Example 2 meets the range requirements of 9.4 - 16.8%.

[0050] Example 4:

[0051] The difference from Example 1 is:

[0052] A preparation process of NiTiNb alloy, including the following steps:

[0053] Step S1, melting: Put the raw materials into the electric arc furnace for melting according to the designed ratio. The electric arc furnace is filled with argon, and the air pressure in the electric arc furnace is controlled at 0.2 - 0.25 Mpa. Conduct 2 repeated meltings to reduce the element content error. Except for the last melting, clean the material surface after each melting to remove the oxide layer on the material surface, and the melting is carried out in an argon environment to avoid generating too many oxides.

[0054] Step S2, casting and forming: Control the casting temperature at 1500 °C, and the casting process is carried out in an argon environment to obtain a blank. Also avoid the material contacting too much air to prevent the material from oxidizing.

[0055] Step S3, stepped forging: In the first stage of forging, heat the blank to 580 °C for forging, and cool it to room temperature after forging. The cooling method is water cooling. In the second stage of forging, heat the blank to 700 °C for forging, and then air-cool it to room temperature to obtain a forging.

[0056] Where the forging force F = σ avg×A×k, where σavg is the deformation resistance. In the first forging stage, the value of σavg is 450 Mpa, and in the second forging stage, the value of σavg is 350 Mpa. A is the cross-sectional area of the blank, and k is the strain coefficient with a value of 4.0. Ensure that the material has sufficient deformation force to fully break the coarse grain structure, but avoid the deformation force exceeding the limit that the material can withstand, and reduce forging defects such as collapse or cracks in the material.

[0057] Step S4, stress relief annealing. The forging is heated to 410 °C and held for 3 h, and then cooled to room temperature.

[0058] Step S5, solution treatment. First, the forging is preheated to 220 °C and held. Since it takes time for heat to transfer from the outside to the inside of the forging, preheating in advance ensures that the core of the forging is heated and reduces the temperature gradient between the inside and outside of the forging.

[0059] After preheating, the forging is heated to 890 °C and held, with the heating rate controlled at 7 °C / min. After reaching the target temperature, it is held for 8 h. Then the forging is heated to 1220 °C and held, with the heating rate controlled at 20 °C / min. After reaching the target temperature, it is held for 15 h, and finally oil-cooled to room temperature.

[0060] Step S6, aging treatment. The forging is heated to 650 °C and held for 7 h, and finally the forging is water-cooled to room temperature.

[0061] Example 4:

[0062] The difference from Example 1 is:

[0063] A preparation process of NiTiNb alloy, including the following steps:

[0064] Step S1, melting. The raw materials are put into an electric arc furnace for melting according to the designed ratio. The electric arc furnace is filled with argon, and the air pressure in the electric arc furnace is controlled at 0.2 - 0.25 Mpa. Two repeated meltings are carried out to reduce the element content error. Except for the last melting, the surface of the material is cleaned after each melting to clean the oxide layer on the material surface, and the melting is carried out in an argon environment to avoid generating too many oxides.

[0065] Step S2, casting and forming. The casting temperature is controlled at 1500 °C, and the casting process is carried out in an argon environment to obtain a blank. Similarly, avoid the material contacting too much air to prevent the material from oxidizing.

[0066] Step S3, stepped forging. In the first stage of forging, the blank is heated to 600 °C for forging, and after forging, it is cooled to room temperature, and the cooling method is water-cooling. In the second stage of forging, the blank is heated to 720 °C for forging, and then air-cooled to room temperature to obtain a forging.

[0067] Among them, the forging force F = σ avg × A × k, where σavg is the deformation resistance. In the first forging stage, the value of σavg is 450 Mpa, and in the second forging stage, the value of σavg is 350 Mpa. A is the cross-sectional area of the blank, and k is the strain coefficient, with k taking a value of 4.0. Ensure that the material has sufficient deformation force to fully break the coarse grain structure, but avoid the deformation force exceeding the limit that the material can withstand, and reduce forging defects such as collapse or cracks in the material.

[0068] Step S4, stress relief annealing: Heat the forging to 425 °C and hold for a heat preservation time controlled at 6 h, and then cool it to room temperature.

[0069] Step S5, solution treatment: First, preheat the forging to 250 °C and hold. Since it takes time for heat to transfer from the outside to the inside of the forging, preheat in advance to ensure that the core of the forging is heated and reduce the temperature gradient between the inside and outside of the forging.

[0070] After the preheating is completed, heat the forging to 900 °C and hold, with the heating rate controlled at 10 °C / min. After reaching the target temperature, hold for 10 h. Then heat the forging to 1250 °C and hold, with the heating rate controlled at 20 °C / min. After reaching the target temperature, hold for 15 h, and finally cool it to room temperature in oil.

[0071] Step S6, aging treatment: Heat the forging to 670 °C and hold, with the heat preservation time controlled at 8 h, and finally cool the forging to room temperature in water.

[0072] Product performance testing:

[0073] Samples: Randomly select experimental samples from the products prepared in Examples 1 to 5.

[0074] Test results, see Table 1 for details.

[0075]

[0076] Conclusion:

[0077] Tensile strength: Under room temperature conditions, it is increased by about 20% compared with the standard; under high temperature conditions, it is increased by about 28% compared with the standard.

[0078] Yield strength: Under room temperature conditions, it is increased by about 10% compared with the standard; under high temperature conditions, it is increased by about 15% compared with the standard.

[0079] Elongation: Under room temperature conditions, it is increased by about 80% compared with the standard; under high temperature conditions, it is increased by about 90% compared with the standard.

[0080] In summary, the alloy has good tensile strength and yield strength at room temperature, and also has good toughness. At high temperatures, the alloy still retains good tensile strength, yield strength and toughness, which proves from the side that the alloy has a fine β-phase solid solution and the precipitated α-phase forms a dense microstructure.

[0081] Product microstructure detection:

[0082] Samples: Products produced in Examples 1 to 5.

[0083] Magnification: 100μm.

[0084] Detection standard: GB / T6394.

[0085] Metallographic detection results:

[0086] Example 1: As Figure 2 shown, in the alloy microstructure, the α-phase transformed by heat treatment is evenly and staggeredly distributed in the β-phase, and a uniform and interlaced network structure can be seen. Grain size is grade 6.

[0087] Example 2: As Figure 3 shown, in the alloy microstructure, the α-phase transformed by heat treatment is evenly and staggeredly distributed in the β-phase, and a uniform and interlaced network structure can be seen. Grain size is grade 6.

[0088] Example 3: As Figure 4 shown, in the alloy microstructure, the α-phase transformed by heat treatment is evenly and staggeredly distributed in the β-phase, and a uniform and interlaced network structure can be seen. Grain size is grade 6.

[0089] Example 4: As Figure 5 shown, in the alloy microstructure, the α-phase transformed by heat treatment is evenly and staggeredly distributed in the β-phase, and a uniform and interlaced network structure can be seen. Grain size is grade 6.

[0090] Example 5: As Figure 6 shown, in the alloy microstructure, the α-phase transformed by heat treatment is evenly and staggeredly distributed in the β-phase, and a uniform and interlaced network structure can be seen. Grain size is grade 6.

[0091] The technical features of the above-described embodiments can be combined arbitrarily. For the sake of brevity of description, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, it should be considered as the scope described in this specification.

[0092] The above-described embodiments merely represent several implementation manners of the present invention. The description is relatively specific and detailed, but it should not be construed as a limitation on the scope of the invention patent. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present invention, several modifications and improvements can still be made, and these all fall within the protection scope of the present invention. Therefore, the protection scope of the present invention patent shall be subject to the appended claims.

Claims

1. A NiTiNb alloy, characterized in that, Comprising components by weight percentage: Al, 5.4 - 7.1%; Cr, 9.4 - 13.5%; Mo, 5.6 - 8.4%; Nb, 3.5 - 5.5%; Mn, 3.0 - 4.5%; Ta, 1.5 - 3.3%; Ni, 4.0 - 6.0%; Pt, 0.05 - 0.10%; O ≤ 0.05%; C ≤ 0.02%; H ≤ 0.01%; S ≤ 0.01%; the balance is Ti.

2. The NiTiNb alloy according to claim 1, wherein: Comprising a β phase, and the β phase equivalent βeq = Mo + 0.19Cr + 0.28Nb + 0.17Mn + 0.58Ta + 0.21Ni + 0.02Ti - 0.20Al.

3. The NiTiNb alloy according to claim 2, wherein: The range of the β phase equivalent βeq is controlled within 9.4 - 16.8%.

4. A preparation process of the NiTiNb alloy according to any one of claims 1 to 3, characterized in that, Comprising the following steps: Step S1, melting: Put the raw materials into an electric arc furnace for melting according to the designed ratio, and conduct 2 - 3 repeated meltings. Except for the last melting, clean the surface of the material after each melting. Step S2, casting and forming to obtain a blank. Step S3, stepped forging: In the first - stage forging, heat the blank to 520 - 620 °C for forging, and cool it to room temperature after forging; in the second - stage forging, heat the blank to 650 - 720 °C for forging to obtain a forging. Step S4, stress - relieving annealing: Heat the forging to 400 - 430 °C for heat preservation. Step S5, solution treatment: First, pre - heat the forging to 200 - 250 °C for heat preservation, then heat the forging to 860 - 920 °C for heat preservation, then heat the forging to 1120 - 1270 °C for heat preservation, and finally cool the forging in oil to room temperature. Step S6, aging treatment: Heat the forging to 620 - 675 °C for heat preservation, and finally cool the forging in water to room temperature.

5. The preparation process of the NiTiNb alloy according to claim 4, characterized in that: In step S1, the electric arc furnace is filled with argon, and the air pressure in the electric arc furnace is controlled at 0.2 - 0.25 Mpa.

6. The preparation process of the NiTiNb alloy according to claim 4, characterized in that: In step S2, the casting temperature is controlled at 1400 - 1550 °C, and the casting process is carried out in an argon environment.

7. The preparation process of the NiTiNb alloy according to claim 4, characterized in that: In step S3, the forging force F = σ avg avg × A × k, where σavg is the deformation resistance. In the first forging stage, the value of σavg is 450 Mpa, and in the second forging stage, the value of σavg is 350 Mpa. A is the cross-sectional area of the blank, and k is the strain coefficient, with k taking a value of 4.

0.

8. The preparation process of the NiTiNb alloy according to claim 4, characterized in that: In step S4, the heat - preservation time range is 3 - 8 h, and then it is cooled to room temperature.

9. The preparation process of the NiTiNb alloy according to claim 4, characterized in that: In step S5, in the 860 - 920 °C stage, the heat - preservation time range is 5 - 12 h, and the heating rate is controlled at 5 - 10 °C / min; in the 1120 - 1270 °C stage, the heat - preservation time range is 10 - 18 h, and the heating rate is controlled at 15 - 20 °C / min.

10. The preparation process of the NiTiNb alloy according to claim 4, characterized in that: In step S6, the heat - preservation time is controlled at 4 - 8 h.

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