Nb-si alloy grain refinement and strengthening method based on multi-step forming

Abstract

The application relates to a Nb-Si alloy grain refining and strengthening method based on multi-step forming, and aims to fill the gap of the current Nb-Si alloy hot deformation process, solve the problem of insufficient hot forming capacity of the Nb-Si alloy, and propose a multi-step-refining forming method, so that the Nbss grain size is significantly refined through the multi-step-refining hot deformation process, and the room temperature strength and toughness of the alloy are simultaneously improved. The Nbss grain is significantly refined through hot deformation, the strength and toughness of the Nb-Si alloy are simultaneously improved, the stress is released through the refining heat preservation process by combining the variable temperature and variable pressing amount technology, the cracking caused by stress concentration during deformation is relieved, and the hot forming of the Nb-Si alloy is facilitated. The application is applied to the alloy heat treatment field.

Description

Technical Field

[0001] This invention relates to a method for refining and strengthening the grains of Nb-Si alloys based on multi-step forming. Background Technology

[0002] With the development of the aviation industry, the demand for high-temperature resistance of engine hot-end components is constantly increasing. Ni-based alloys can no longer meet the needs of next-generation aero-engines, and there is an urgent need to develop new high-temperature resistant structural materials. Nb-Si alloys can withstand service temperatures above 1200℃ and are considered one of the alternative materials to aerospace Ni-based alloys. The microstructure of this alloy is mainly composed of two phases: ductile niobium-based solid solution (Nbss) and hard silicides (Nb5Si3 or Nb3Si). The matching state of the two phases cannot fully compensate for their inherent defects, resulting in a mismatch between strength and toughness. In recent years, a lot of efforts have been made to improve the room temperature toughness of Nb-Si based alloys, but there is still a gap between the requirements of industrial applications and the actual performance. The high silicide content in Nb-Si alloys makes them prone to cracking even with low deformation under high-temperature deformation conditions, which restricts the hot deformation process of Nb-Si alloys. Summary of the Invention

[0003] The purpose of this invention is to fill the gap in the current hot deformation process of Nb-Si based alloys, solve the problem of insufficient hot forming capability of Nb-Si alloys, and provide a method for grain refinement and toughening of Nb-Si alloys based on multi-step forming.

[0004] The present invention discloses a method for refining and strengthening the grains of Nb-Si alloys based on multi-step forming, which is carried out according to the following steps:

[0005] I. Preparation of Nb-Si-Ti-Fe alloy ingots;

[0006] 2. Place the Nb-Si-Ti-Fe alloy ingot in a muffle furnace and hold it at a temperature of 1300℃-1500℃ for 30min-60min to obtain the workpiece after holding.

[0007] Third, after heat preservation, the workpiece is transferred to the worktable for the first step of compression deformation, with the pressure head pressing down at a speed of 0.01 mm / s. -1 Downward pressure 15%-25%;

[0008] 4. Transfer the compressed workpiece back to the muffle furnace and hold it for 30 to 60 minutes, then press down at a speed of 0.01 mm / s. -1 Under these conditions, the second step of compression forming is performed;

[0009] 5. Repeat step four 0-5 times to perform multi-step compression deformation on the compressed workpiece;

[0010] 6. Transfer the compressed workpiece after multi-step deformation to an environment of 1000℃-1200℃ for stabilization annealing for 1-4 hours, and then air cool to room temperature to complete the process.

[0011] The reduction in Nbss grain size, accompanied by an increase in the number of grain boundaries, can effectively improve the room-temperature toughness of Nb-Si based alloys. Hot deformation is an effective and convenient technique for grain refinement. After hot deformation, the Nbss grains are significantly refined, and the size and morphology of silicides are also adjusted, which can significantly improve the overall mechanical properties of the material.

[0012] The present invention has the following beneficial effects:

[0013] I. This invention significantly refines Nbss grains through hot deformation, synergistically improving the strength and toughness of Nb-Si based alloys, and providing a new means for optimizing the microstructure and properties of Nb-Si based alloys.

[0014] II. This invention utilizes a multi-step, reheating method to release stress during the reheating and holding process, thus mitigating cracking caused by stress concentration during deformation. Temperature and strain are key process parameters for material deformation. Increasing the temperature promotes dynamic softening during deformation, while controlling the strain affects the deformation texture and mechanical properties. Therefore, the combination of multi-step deformation with variable temperature-variable strain technology is beneficial for the hot forming of Nb-Si based alloys. By matching different process parameters (temperature, strain) between each step, such as multi-step pressure increase-temperature increase deformation, pressure decrease-temperature decrease deformation, pressure decrease-temperature increase deformation, and pressure increase-temperature decrease deformation, the microstructure and properties of the deformed alloy can be controlled.

[0015] Third, the multi-step hot deformation method proposed in this invention can be applied to the hot forming of various high-temperature alloys. Attached Figure Description

[0016] Figure 1 The as-cast microstructure of the 56Nb-16Si-24Ti-4Fe alloy;

[0017] Figure 2 Multi-step deformation microstructures of 56Nb-16Si-24Ti-4Fe alloys in Examples 1 to 3; where a is Example 1, b is Example 2, and c is Example 3;

[0018] Figure 3 Grain size analysis diagrams of the as-cast 56Nb-16Si-24Ti-4Fe alloy and the 56Nb-16Si-24Ti-4Fe alloy treated in Example 2; where a is the as-cast alloy and b is the 56Nb-16Si-24Ti-4Fe alloy treated in Example 2;

[0019] Figure 4Nanoindentation test results of 56Nb-16Si-24Ti-4Fe as-cast alloy and 56Nb-16Si-24Ti-4Fe alloys treated in Examples 1 to 3; where a represents the as-cast state, b represents Example 1, c represents Example 2, and d represents Example 3;

[0020] Figure 5 Vickers hardness and room temperature fracture toughness of 56Nb-16Si-24Ti-4Fe as-cast alloy and 56Nb-16Si-24Ti-4Fe alloys treated in Examples 1 to 3; where a represents the as-cast state, b represents Example 1, c represents Example 2, and d represents Example 3. Detailed Implementation

[0021] The technical solution of the present invention is not limited to the specific embodiments listed below, but also includes any combination of the specific embodiments.

[0022] Specific Implementation Method 1: This implementation method for refining and strengthening the grains of Nb-Si alloys based on multi-step forming is carried out according to the following steps:

[0023] I. Preparation of Nb-Si-Ti-Fe alloy ingots;

[0024] 2. Place the Nb-Si-Ti-Fe alloy ingot in a muffle furnace and hold it at a temperature of 1300℃-1500℃ for 30min-60min to obtain the workpiece after holding.

[0025] Third, after heat preservation, the workpiece is transferred to the worktable for the first step of compression deformation, with the pressure head pressing down at a speed of 0.01 mm / s. -1 Downward pressure 15%-25%;

[0026] 4. Transfer the compressed workpiece back to the muffle furnace and hold it for 30 to 60 minutes, then press down at a speed of 0.01 mm / s. -1 Under these conditions, the second step of compression forming is performed;

[0027] 5. Repeat step four 0-5 times to perform multi-step compression deformation on the compressed workpiece;

[0028] 6. Transfer the compressed workpiece after multi-step deformation to an environment of 1000℃-1200℃ for stabilization annealing for 1-4 hours, and then air cool to room temperature to complete the process.

[0029] Specific Implementation Method Two: This implementation method differs from Specific Implementation Method One in that the chemical formula of the Nb-Si-Ti-Fe alloy is Nb-(12~20)Si-(10~24)Ti-(2~6)Fe. Everything else is the same as in Specific Implementation Method One.

[0030] Specific Implementation Method Three: This implementation method differs from Specific Implementation Method One or Two in that the Nb-Si-Ti-Fe alloy is composed of 56% Nb, 24% Ti, 16% Si, and 4% Fe by atomic percentage, with the chemical formula 56Nb-16Si-24Ti-4Fe. Everything else is the same as in Specific Implementation Method One or Two.

[0031] Specific Implementation Method Four: This implementation method differs from Specific Implementation Methods One to Three in that: Step One uses vacuum non-consumable arc melting to prepare Nb-Si-Ti-Fe alloy ingots. Everything else is the same as in Specific Implementation Methods One to Three.

[0032] Specific Implementation Method Five: This implementation method differs from Specific Implementation Methods One to Four in that the ambient temperature is 1000℃ during each compression deformation. Everything else is the same as in Specific Implementation Methods One to Four.

[0033] Specific Implementation Method Six: This implementation method differs from Specific Implementation Methods One to Five in that the compression deformation in steps Three, Four, and Five adopts isothermal compression deformation. When isothermal compression deformation is adopted, the amount of compression deformation remains unchanged in each compression deformation. Everything else is the same as in Specific Implementation Methods One to Five.

[0034] Specific Implementation Method Seven: This implementation method differs from Specific Implementation Methods One to Six in that: the compression deformation in steps three, four, and five adopts heated compression deformation. When heated compression deformation is adopted, the amount of compression is increased or decreased each time; wherein the heated compression deformation refers to increasing the muffle furnace holding temperature by 50°C each time after each compression deformation and when returning to the furnace. Everything else is the same as in Specific Implementation Methods One to Six.

[0035] Specific Implementation Method Eight: This implementation method differs from Specific Implementation Methods One to Seven in that: in steps three, four, and five, the compression deformation adopts cooling compression deformation. When cooling compression deformation is adopted, the amount of compression is increased or decreased each time; wherein the cooling compression deformation refers to reducing the muffle furnace holding temperature by 50°C each time after each compression deformation and when returning to the furnace. The rest is the same as in Specific Implementation Methods One to Seven.

[0036] Specific Implementation Method Nine: This implementation method differs from Specific Implementation Methods One to Eight in that: the increase in downward pressure is achieved by gradually increasing the downward pressure by 5% each time during compression deformation; the decrease in downward pressure is achieved by gradually decreasing the downward pressure by 5% each time during compression deformation. Everything else is the same as in Specific Implementation Methods One to Eight.

[0037] Specific Implementation Method Ten: This implementation method differs from Specific Implementation Methods One to Nine in that step four is repeated once to perform the third step of compression deformation on the compressed workpiece. Everything else is the same as in Specific Implementation Methods One to Nine.

[0038] The beneficial effects of the present invention are verified using the following embodiments:

[0039] Example 1: This example describes a method for refining and strengthening the grains of Nb-Si alloys based on multi-step forming, which is carried out according to the following steps:

[0040] I. Weigh the raw materials according to the atomic percentage content: 56% Nb; 16% Si; 24% Ti; 4% Fe, and then prepare 56Nb-16Si-24Ti-4Fe alloy ingots by vacuum non-consumable arc melting. The as-cast microstructure of 56Nb-16Si-24Ti-4Fe alloy consists of Nbss, Nb5Si3 and Nb4FeSi.

[0041] 2. Place the 56Nb-16Si-24Ti-4Fe ingot in a muffle furnace and hold it at 1350℃ for 60 minutes.

[0042] 3. After heat preservation, the ingot is subjected to compression deformation, with the pressure head pressing down at a speed of 0.01 mm / s. -1 Downward pressure 20%;

[0043] IV. Immediately after the first step of deformation is completed, transfer the compressed part to a muffle furnace and hold it at 1400℃ for 30 minutes. Then proceed to the second step of compression forming, with the press head pressing down at a speed of 0.01 mm / s. -1 Downward pressure 25%;

[0044] 5. Transfer the compressed part after deformation in the two steps to a 1000℃ environment for stabilization annealing for 2 hours, and then air cool to room temperature.

[0045] Example 2: This example describes a method for refining and strengthening the grains of Nb-Si alloys based on multi-step forming, which is carried out according to the following steps:

[0046] I. Weigh the raw materials according to the atomic percentage content: 56% Nb; 16% Si; 24% Ti; 4% Fe, and then prepare 56Nb-16Si-24Ti-4Fe alloy ingots by vacuum non-consumable arc melting. The as-cast microstructure of 56Nb-16Si-24Ti-4Fe alloy consists of Nbss, Nb5Si3 and Nb4FeSi.

[0047] 2. Place the 56Nb-16Si-24Ti-4Fe ingot in a muffle furnace and hold it at 1350℃ for 60 minutes.

[0048] 3. After heat preservation, the ingot is subjected to compression deformation, with the pressure head pressing down at a speed of 0.01 mm / s. -1 Downward pressure 20%;

[0049] IV. Immediately after the first step of deformation is completed, transfer the compressed part to a muffle furnace and hold it at 1350℃ for 30 minutes. Then proceed to the second step of compression forming, with the press head pressing down at a speed of 0.01 mm / s. -1 Downward pressure 20%;

[0050] 5. Repeat step four once, that is, transfer the compressed part to the muffle furnace and keep it at 1350℃ for 30 minutes. After keeping it at 1350℃, perform the third step of compression deformation.

[0051] 6. Transfer the compressed part after the three-step deformation to a 1000℃ environment for stabilization annealing for 2 hours, and then air cool to room temperature.

[0052] Example 3: This example describes a method for refining and strengthening the grains of Nb-Si alloys based on multi-step forming, which is carried out according to the following steps:

[0053] I. Weigh the raw materials according to the atomic percentage content: 56% Nb; 16% Si; 24% Ti; 4% Fe, and then prepare 56Nb-16Si-24Ti-4Fe alloy ingots by vacuum non-consumable arc melting. The as-cast microstructure of 56Nb-16Si-24Ti-4Fe alloy consists of Nbss, Nb5Si3 and Nb4FeSi.

[0054] 2. Place the 56Nb-16Si-24Ti-4Fe ingot in a muffle furnace and hold it at 1400℃ for 60 minutes.

[0055] 3. After heat preservation, the ingot is subjected to compression deformation, with the pressure head pressing down at a speed of 0.01 mm / s. -1 Downward pressure 25%;

[0056] IV. Immediately after the first step of deformation is completed, transfer the compressed part to a muffle furnace and hold it at 1350℃ for 30 minutes. Then proceed to the second step of compression forming, with the press head pressing down at a speed of 0.01 mm / s. -1 Downward pressure 20%;

[0057] 5. Repeat step four once, that is, immediately after the deformation in step four, transfer the compressed part to a muffle furnace and hold it at 1300℃ for 30 minutes. Then proceed to the third step of compression forming, with the press head pressing down at a speed of 0.01 mm / s. -1 Downward pressure 15%;

[0058] 6. Transfer the compressed part after the three-step deformation to a 1000℃ environment for stabilization annealing for 2 hours, and then air cool to room temperature.

[0059] In the above embodiment, the ambient temperature during compression is 1000°C to slow down the natural cooling of the workpiece during compression. The compressed workpiece is separated from the upper and lower pressure heads by asbestos to prevent heat conduction during contact.

[0060] The as-cast microstructure of the 56Nb-16Si-24Ti-4Fe alloy is as follows: Figure 1 As shown, the as-cast microstructure consists of an Nbss / Nb5Si3 eutectic and an Nb4FeSi phase. Light gray, gray, and dark colors correspond to Nbss, Nb5Si3, and Nb4FeSi, respectively.

[0061] The deformed microstructures of the 56Nb-16Si-24Ti-4Fe alloys prepared in Examples 1 and 2 are as follows: Figure 2 As shown. For the alloy of Example 1, after two-step deformation ( Figure 2 (a) In this study, deformation streamlines appeared perpendicular to the compression direction, the Nbss / Nb5Si3 eutectic structure was disrupted, the Nbss matrix exhibited continuity, while Nb5Si3 bulk particles were dispersed within the Nbss matrix. After multi-step deformation (Example 2), Figure 2 (b) The deformation streamlines are significantly enhanced, and no micropores or microcracks appear in the Nb5Si3 bulk after deformation. (Comparison) Figure 2 (a) and Figure 2 (b) It was found that with the increase of machining steps, the amount of workpiece deformation increased, which helped to refine the silicide mass while enhancing the deformation texture. In Example 3, the alloy showed significant refinement of deformation streamlines and microstructure under cooling-reducing pressure conditions, such as... Figure 2 (c). However, the grain boundaries of Nbss grains cannot be distinguished under the contrast of SEM-BSE, and the grain refinement features after multi-step deformation cannot be observed. It is necessary to characterize them by EBSD technology.

[0062] like Figure 3 As shown, the phase diagram and grain boundary diagram of EBSD were superimposed to analyze the grain size after multi-step deformation. Red represents the Nbss phase, sky blue the Nb5Si3 phase, and yellow the Nb4FeSi phase. Comparison with the as-cast microstructure ( Figure 3 (a) and the organization of Example 2 ( Figure 3(b) Grain size. Clearly, after hot deformation, the average grain size of Nbss was significantly refined, decreasing from 13 μm in the as-cast state to 4.8 μm in Example 2. The average grain sizes of Nbss in Examples 1 and 3 were 6.5 μm and 4.3 μm, respectively. As the main toughening phase in Nb-Si alloys, the refinement of the Nbss phase grains can improve the room-temperature toughness of the alloy. Furthermore, compared to the as-cast structure, the Nb5Si3 bulk structure was also significantly refined after multi-step deformation. During mechanical testing, the hard Nb5Si3 bulk structure easily causes local stress concentration, which is detrimental to the strength and toughness of the alloy. With the refinement of the Nb5Si3 bulk structure, it can act as a continuous dislocation source under external force, improving the deformation capacity of the material under high stress. Combined with the grain refinement strengthening effect, a strengthening-toughening effect can be achieved.

[0063] The nanoindentation test results of the as-cast 56Nb-16Si-24Ti-4Fe alloy and the 56Nb-16Si-24Ti-4Fe alloy treated in Examples 1 to 3 are as follows: Figure 4 As shown in the figure. Nanoindentation results show that the hardness of Nbss in the as-cast state is 5.86 GPa, and the hardness of Nb5Si3 is 12.57 GPa. After multi-step deformation, the hardness of both phases was significantly improved. In the alloy microstructure of Example 3, the hardness of Nbss reached 8.56 GPa, and the hardness of Nb5Si3 reached 17.24 GPa, which were increased by 46.1% and 37.2% respectively compared with the as-cast alloy. The Vickers hardness and room temperature fracture toughness test results are as follows. Figure 5 As shown. The Vickers hardness of the alloys in Examples 1, 2, and 3 are 724 HV, 761 HV, and 814 HV, respectively, which are significantly improved compared to the 587 HV of the as-cast alloy. Furthermore, the room temperature toughness of the alloys after multi-step deformation is also simultaneously improved. Compared to the 6.85 MPa·m of the as-cast alloy... 1 / 2 The alloys in Examples 2 and 3 achieved a toughness of 9.62 MPa·m, respectively. 1 / 2 and 10.12 MPa·m 1 / 2 The improvements were 40.4% and 47.7%. Compared to the multi-step isothermal deformation of Example 2, Example 3 adopted a multi-step cooling-reducing deformation process. By reducing the amount of reduction, the hot deformation stability of the alloy was ensured, while the deformation temperature was reduced, which significantly improved the work hardening and grain refinement of the alloy.

Claims

1. A method of grain refinement and strengthening of Nb-Si alloys based on multi-step forming, characterized in that The method is performed according to the following steps: I. preparing a Nb-Si-Ti-Fe alloy ingot; the Nb-Si-Ti-Fe alloy is composed of 56% Nb, 24% Ti, 16% Si and 4% Fe in atomic percentage, and the chemical formula is 56Nb-16Si-24Ti-4Fe; II. placing the Nb-Si-Ti-Fe alloy ingot in a muffle furnace for heat preservation, the heat preservation temperature is 1300-1500 ℃, and the heat preservation time is 30-60 min, to obtain a heat preserved workpiece; III. The workpiece after heat preservation is transferred to the workbench to perform the first step compression deformation, the pressing head down speed is 0.01 mm·s -1 , and the down amount is 15%-25%. Four, the compression workpiece is re-transferred to the muffle furnace for heat preservation for 30 min ~ 60 min, and then the pressure head is pressed at a speed of 0.01 mm·s -1 The second step compression forming is carried out under the condition that V. repeating step IV for 0-5 times to perform multi-step compression deformation on the compressed workpiece; VI. transferring the multi-step deformed compressed workpiece to an environment at 1000-1200 ℃ for stabilization annealing, the annealing time is 1-4 h, and then air cooling to room temperature, thereby completing the process.

2. A method of grain refinement and strengthening of Nb-Si alloys based on multi-step forming according to claim 1, characterized in that, Step I uses vacuum non-consumable arc melting to prepare the Nb-Si-Ti-Fe alloy ingot.

3. A method of grain refinement and strengthening of Nb-Si alloys based on multiple-step forming according to claim 1, characterized in that, The temperature of the ambient atmosphere during each compression deformation is 1000 ℃.

4. A method of grain refinement and strengthening of Nb-Si alloys based on multiple-step forming according to claim 1, characterized in that, In steps III, IV and V, the compression deformation uses isothermal compression deformation, and when the isothermal compression deformation is used, the amount of each compression deformation is constant.

5. A method of grain refinement and strengthening of Nb-Si alloys based on multiple-step forming according to claim 1, characterized in that, In steps III, IV and V, the compression deformation uses temperature increasing compression deformation, and when the temperature increasing compression deformation is used, the amount of each compression deformation increases or decreases; wherein the temperature increasing compression deformation is to increase the muffle furnace heat preservation temperature when the workpiece is returned after each compression deformation, and each time the temperature is increased by 50 ℃.

6. A method of grain refinement and strengthening of Nb-Si alloys based on multiple-step forming according to claim 1, characterized in that, In steps III, IV and V, the compression deformation uses temperature decreasing compression deformation, and when the temperature decreasing compression deformation is used, the amount of each compression deformation increases or decreases; wherein the temperature decreasing compression deformation is to decrease the muffle furnace heat preservation temperature when the workpiece is returned after each compression deformation, and each time the temperature is decreased by 50 ℃.

7. A method of grain refinement and strengthening of Nb-Si alloys based on multi-step forming according to claim 5 or 6, characterized in that, The amount of each compression deformation is gradually increased by 5% each time when the amount of each compression deformation is increased, and the amount of each compression deformation is gradually decreased by 5% each time when the amount of each compression deformation is decreased.

8. A method of grain refinement and strengthening of Nb-Si alloys based on multiple-step forming according to claim 1, characterized in that, Step IV is repeated once to perform third step compression deformation on the compressed workpiece.

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