Heat treatment process for strengthening and toughening TC18 titanium alloy

Abstract

The invention discloses a heat treatment process for strengthening and toughening a TC18 titanium alloy. The process comprises the following steps: step 1, heating the TC18 titanium alloy to 450-550 DEG C for preheating; secondly, the preheated TC18 titanium alloy is heated to 980 DEG C to 1020 DEG C for solution treatment; thirdly, the TC18 titanium alloy subjected to solution treatment is subjected to water quenching; and fourthly, the TC18 titanium alloy subjected to water quenching is subjected to tempering treatment, and the toughened TC18 titanium alloy is obtained. According to the process, the beta phase of the TC18 titanium alloy is subjected to water quenching after being subjected to solid solution treatment, so that the beta phase is converted into a martensite structure, the strength and toughness of the TC18 titanium alloy are improved, then the residual stress of the TC18 titanium alloy is reduced through tempering treatment, the toughness of the TC18 titanium alloy is further improved, and the process is suitable for the technical field of titanium alloy heat treatment and machining and manufacturing.

Description

Technical Field

[0001] The invention belongs to the technical field of heat treatment and processing and manufacturing of titanium alloys, and in particular relates to a heat treatment process for strengthening and toughening a TC18 titanium alloy. Background Art

[0002] TC18 titanium alloy has a nominal composition of Ti-5Al-5Mo-5V-1Cr-1Fe. It is a high-strength near-β-type titanium alloy developed in the 1970s. TC18 titanium alloy is widely used in aviation, aerospace and marine engineering due to its high strength, corrosion resistance and good weldability. However, its mechanical properties in its original state often cannot meet the requirements of extreme environments and need to be improved through appropriate heat treatment.

[0003] After processing and heat treatment, the mechanical properties of TC18 titanium alloy can be significantly changed by controlling the changes in microstructure. The traditional heat treatment process of TC18 titanium alloy is solid solution-single-stage aging. The general process is single phase (β phase transformation temperature T β above) or two-phase solid solution (β phase transformation temperature T β The following) is combined with a single-stage aging treatment (400℃~600℃ for 2h~24h). Among them, the microstructure of TC18 titanium alloy after single-phase solid solution-aging treatment will contain a large number of dispersed fine α phases, and the plasticity and fracture toughness are poor. The microstructure of TC18 titanium alloy after dual-phase solid solution-single-stage aging treatment will contain coarse equiaxed α phase and strip α phase at the same time, and the strength is relatively low; the above two methods cannot make TC18 titanium alloy achieve both strength and toughness.

[0004] Therefore, it is urgent to develop a heat treatment process that can make TC18 titanium alloy have both strength and toughness. Summary of the invention

[0005] The purpose of the present invention is to overcome the deficiencies in the above-mentioned prior art and provide a heat treatment process for strengthening and toughening TC18 titanium alloy. The process transforms the β phase of TC18 titanium alloy into a martensitic structure by solid solution and then water quenching to improve the strength and toughness of TC18 titanium alloy, and then reduces the residual stress of TC18 titanium alloy by tempering to further increase toughness, thereby solving the problem that TC18 titanium alloy is difficult to balance strength and toughness.

[0006] To achieve the above object, the technical solution adopted by the present invention is: a heat treatment process for strengthening and toughening TC18 titanium alloy, characterized in that the process comprises the following steps:

[0007] Step 1: Preheating: Preheat the TC18 titanium alloy to 450°C to 550°C;

[0008] Step 2: Solution treatment: heating the TC18 titanium alloy preheated in step 1 to 980°C to 1020°C for solution treatment;

[0009] Step 3, rapid cooling: water quenching the TC18 titanium alloy after the solution treatment in step 2;

[0010] Step 4: Tempering: The TC18 titanium alloy quenched by water in step 3 is tempered to obtain a strengthened TC18 titanium alloy.

[0011] The present invention controls the preheating temperature to 450°C to 550°C. Within this temperature range, the TC18 titanium alloy is in a relatively stable state and will not undergo phase change, which helps to maintain microstructural stability during the preheating process and avoid unnecessary organizational changes caused by phase change. The thermal expansion coefficient, thermal conductivity and other physical properties of the TC18 titanium alloy show good controllability within this temperature range, thereby making the heat treatment have good process stability. At the same time, this temperature range can effectively release the residual stress inside the TC18 titanium alloy, because the movement and rearrangement of dislocations inside the TC18 titanium alloy can be activated within this temperature range, thereby promoting stress relaxation. The temperature can also avoid overheating of the alloy and grain growth, thereby maintaining the strength and toughness of the TC18 titanium alloy.

[0012] The above-mentioned heat treatment process for strengthening and toughening TC18 titanium alloy is characterized in that the preheating time in step 1 is 20 minutes to 30 minutes.

[0013] The present invention can ensure the elimination of stress concentration of TC18 titanium alloy by controlling the preheating time, and combined with controlling the preheating temperature, can eliminate residual stress to the maximum extent without changing the alloy phase structure, while providing ideal initial conditions for subsequent processing steps.

[0014] The above-mentioned heat treatment process for strengthening and toughening TC18 titanium alloy is characterized in that the duration of the solid solution treatment in step 2 is 60 minutes to 120 minutes.

[0015] The present invention controls the solution treatment time to 60 minutes to 120 minutes and combines the solution treatment temperature to 980°C to 1020°C, so that the β phase of the TC18 titanium alloy can be fully dissolved, avoiding coarse grains caused by overheating and too long treatment time, achieving microstructure refinement, and effectively improving the strength and toughness of the TC18 titanium alloy.

[0016] The above-mentioned heat treatment process for strengthening and toughening TC18 titanium alloy is characterized in that the TC18 titanium alloy after solution treatment in step three is water quenched within 5 seconds, and the cooling rate of the water quenching is not less than 40°C / s.

[0017] The present invention controls the water quenching of the TC18 titanium alloy after the solid solution treatment within 5 seconds, and ensures that the cooling rate of the water quenching is not less than 40°C / s, thereby ensuring that the β phase is transformed into a martensitic structure.

[0018] The above-mentioned heat treatment process for strengthening and toughening TC18 titanium alloy is characterized in that the temperature of the tempering treatment in step 4 is 600°C to 700°C, and the duration of the tempering treatment is more than 1 hour.

[0019] The present invention controls the tempering temperature to be 600° C. to 700° C., within which temperature range the atomic diffusion rate inside the TC18 titanium alloy can be increased, which is conducive to stress relaxation and residual stress release; and the tempering treatment within this temperature range can optimize the phase structure of the material's microstructure, improve fracture toughness and enhance comprehensive mechanical properties; at the same time, within this temperature range the grain growth and performance degradation caused by overheating are avoided.

[0020] The above-mentioned heat treatment process for strengthening and toughening TC18 titanium alloy is characterized in that the tensile strength of the strengthened and toughened TC18 titanium alloy in step 4 is not less than 1000 MPa, and the elongation is greater than 10%.

[0021] Compared with the prior art, the present invention has the following advantages:

[0022] 1. The present invention preheats the TC18 titanium alloy to eliminate stress concentration inside the TC18 titanium alloy, raises the temperature to 980°C to 1020°C to promote full solid solution of the β phase of the TC18 titanium alloy, and then rapidly cools the TC18 titanium alloy to ensure that the β phase is transformed into a martensitic structure, thereby effectively increasing the strength and toughness of the TC18 titanium alloy. Finally, the residual stress in the TC18 titanium alloy is reduced by tempering treatment, thereby further improving the toughness of the TC18 titanium alloy and achieving strengthening and toughening of the TC18 titanium alloy.

[0023] 2. The heat treatment process of the present invention has simple steps and a short cycle, and does not require the use of laser and other equipment for cladding, which effectively reduces the cost of performance optimization and is suitable for large-scale industrial promotion.

[0024] 3. The present invention can quickly lock the martensitic structure by precisely controlling the cooling rate of the water quenching process, effectively preventing the titanium alloy from changing to other structures, retaining the strengthening effect brought by the high temperature treatment, and reducing brittleness.

[0025] 4. The present invention controls the temperature and duration of the tempering treatment, and emphasizes the importance of toughness recovery more than the traditional process, so that the material can greatly improve the plasticity and impact resistance while ensuring the strength, thereby achieving balanced optimization of high performance indicators.

[0026] The technical solution of the present invention is further described in detail below through embodiments. DETAILED DESCRIPTION

[0027] Example 1

[0028] The process of this embodiment includes the following steps:

[0029] Step 1: Preheating: Preheat the TC18 titanium alloy in a furnace at 500°C for 30 minutes;

[0030] Step 2: Solution treatment: The TC18 titanium alloy preheated in step 1 is heated to 1000°C for solution treatment for 90 minutes;

[0031] Step 3: Rapid cooling: The TC18 titanium alloy after the solution treatment in step 2 is taken out from the furnace and water quenched within 3 seconds; the cooling rate of the water quenching is 45°C / s;

[0032] Step 4: Tempering: The TC18 titanium alloy quenched in step 3 is heated to 650°C and tempered for 1 hour to obtain a strengthened TC18 titanium alloy.

[0033] After testing, the tensile strength of the toughened TC18 titanium alloy in this embodiment is 1127 MPa, the yield strength is 986 MPa, the elongation after fracture is 11.8%, and the shrinkage after fracture is 22.1%.

[0034] Example 2

[0035] The process of this embodiment includes the following steps:

[0036] Step 1: Preheating: Preheat TC18 titanium alloy at 450°C for 25 minutes;

[0037] Step 2: Solution treatment: Heat the TC18 titanium alloy preheated in step 1 to 980°C for solution treatment for 120 minutes;

[0038] Step 3: Rapid cooling: The TC18 titanium alloy that has been solution treated in step 2 is taken out of the furnace and water quenched within 3 seconds; the cooling rate of the water quenching is 50°C / s;

[0039] Step 4: Tempering: The TC18 titanium alloy quenched in step 3 is heated to 650°C and tempered for 1.5 hours to obtain a strengthened TC18 titanium alloy.

[0040] After testing, the toughened TC18 titanium alloy in this embodiment has a tensile strength of 1085 MPa, a yield strength of 945 MPa, an elongation at break of 13.2%, and a shrinkage at break of 25.6%.

[0041] Example 3

[0042] The process of this embodiment includes the following steps:

[0043] Step 1: Preheating: Preheat TC18 titanium alloy at 550°C for 20 minutes;

[0044] Step 2: Solution treatment: Heat the TC18 titanium alloy preheated in step 1 to 1020°C for solution treatment for 60 minutes;

[0045] Step 3: Rapid cooling: The TC18 titanium alloy that has been solution treated in step 2 is taken out of the furnace and water quenched within 3 seconds; the cooling rate of the water quenching is 60°C / s;

[0046] Step 4: Tempering: The TC18 titanium alloy quenched in step 3 is heated to 650°C and tempered for 2 hours to obtain a strengthened TC18 titanium alloy.

[0047] After testing, the toughened TC18 titanium alloy in this embodiment has a tensile strength of 1256 MPa, a yield strength of 1107 MPa, an elongation at break of 13.9%, and a shrinkage at break of 28.0%.

[0048] The above description is only a preferred embodiment of the present invention and does not limit the present invention in any way. Any simple modification, change and equivalent structural transformation made to the above embodiment based on the technical essence of the present invention still falls within the protection scope of the technical solution of the present invention.

Claims

1. A heat treatment process for strengthening and toughening TC18 titanium alloy, characterized in that: The process includes the following steps: Step 1: Preheating: Preheat the TC18 titanium alloy to 450°C to 550°C; Step 2: Solution treatment: heating the TC18 titanium alloy preheated in step 1 to 980°C to 1020°C for solution treatment; Step 3, rapid cooling: water quenching the TC18 titanium alloy after the solution treatment in step 2; Step 4: Tempering: The TC18 titanium alloy quenched by water in step 3 is tempered to obtain a strengthened TC18 titanium alloy.

2. The heat treatment process for strengthening and toughening TC18 titanium alloy according to claim 1 is characterized in that: The preheating time in step 1 is 20 minutes to 30 minutes.

3. The heat treatment process for strengthening and toughening TC18 titanium alloy according to claim 1 is characterized in that: The duration of the solution treatment in step 2 is 60 min to 120 min.

4. The heat treatment process for strengthening and toughening TC18 titanium alloy according to claim 1, characterized in that: In step 3, the TC18 titanium alloy after the solution treatment is water quenched within 5 seconds, and the cooling rate of the water quenching is not less than 40°C / s.

5. The heat treatment process for strengthening and toughening TC18 titanium alloy according to claim 1, characterized in that: The temperature of the tempering treatment in step 4 is 600° C. to 700° C., and the duration of the tempering treatment is more than 1 hour.

6. The heat treatment process for strengthening and toughening TC18 titanium alloy according to claim 1, characterized in that: The tensile strength of the toughened TC18 titanium alloy in step 4 is not less than 1000 MPa, and the elongation is greater than 10%.