A heat treatment method to improve the strength of Ti-5321 titanium alloy formed by laser cladding

Abstract

The invention discloses a heat treatment method for improving the strength of laser cladding formed Ti‑5321 titanium alloy, which performs multiple heat treatment processes on the laser cladding formed Ti‑5321 titanium alloy, so that the rough sheet layer α formed by laser cladding is transformed into ultrafine needle-shaped α, thereby improving the strength of the laser cladding formed Ti‑5321 titanium alloy. The invention performs multiple heat treatment processes on the laser cladding formed Ti‑5321 titanium alloy, so that the rough sheet layer α formed by laser cladding is transformed into ultrafine needle-shaped α, and the strength of the laser cladding formed Ti‑5321 titanium alloy is greatly improved to more than 1400MPa by regulating the size and morphological organization type of the α phase, meeting the demand for high-strength Ti‑5321 titanium alloy in practical applications; the process flow of the invention is simple, easy to implement, suitable for industrial production, and has good promotion prospects.

Description

Technical Field

[0001] The invention belongs to the technical field of titanium alloy materials, and in particular relates to a heat treatment method for improving the strength of Ti-5321 titanium alloy formed by laser cladding. Background Art

[0002] Laser cladding forming technology is an efficient and fast near-net-shape additive manufacturing technology that breaks through traditional subtractive manufacturing methods and integrates computer technology, laser technology and material processing technology. This technology can greatly shorten the design time, quickly form complex structures, greatly shorten the development cycle and reduce costs. It has broad application prospects in aerospace, national defense and military equipment. Compared with traditional forming and processing technologies such as casting, forging and welding, this technology has incomparable advantages, especially in forming and repairing parts with complex shapes.

[0003] In order to meet the demand for high-performance titanium alloys in my country's aerospace industry, from the perspective of material composition innovation, a new titanium alloy Ti-5321 titanium alloy (Ti-5Al-3Mo-3V-2Zr-2Cr-1Nb-1Fe) with both high strength and high plasticity and toughness was designed and developed by comprehensively considering high-strength titanium alloys Ti-1300 and TC21. This alloy is a metastable β titanium alloy with a Mo equivalent of 11.5 and has a large space for organizational regulation. The tensile strength of the Ti-5321 titanium alloy prepared by laser cladding forming technology is only at the 1100MPa level, which cannot meet the demand for ultra-high-strength titanium alloys in the aviation field. Summary of the invention

[0004] The technical problem to be solved by the present invention is to provide a heat treatment method for improving the strength of laser cladding Ti-5321 titanium alloy in view of the shortcomings of the above-mentioned prior art. The method transforms the coarse lamellar layer α formed by laser cladding into ultrafine needle-shaped α by performing multiple heat treatment processes on the laser cladding Ti-5321 titanium alloy, thereby regulating the size and morphological structure type of the α phase, greatly improving the strength of the laser cladding Ti-5321 titanium alloy, and solving the problem of low strength of laser cladding Ti-5321 titanium alloy components.

[0005] In order to solve the above technical problems, the technical solution adopted by the present invention is: a heat treatment method for improving the strength of Ti-5321 titanium alloy formed by laser cladding, characterized in that the method performs multiple heat treatment processes on the Ti-5321 titanium alloy formed by laser cladding, so that the coarse sheet layer α formed by laser cladding is transformed into ultrafine needle-shaped α, thereby improving the strength of the Ti-5321 titanium alloy formed by laser cladding.

[0006] The heat treatment system in the prior art cannot effectively eliminate the internal residual stress of the laser cladding Ti-5321 titanium alloy, nor can it make the organization have good uniformity and obtain an organization with ultra-high strength. The present invention performs multiple heat treatment processes on the laser cladding Ti-5321 titanium alloy, which not only effectively eliminates the forming residual stress, but also effectively regulates the original organization of the laser cladding Ti-5321 titanium alloy, so that the coarse lamellar layer α formed by laser cladding is transformed into ultrafine needle-shaped α, and the size and morphology of the α phase are improved. The ultrafine needle-shaped α is smaller in size, has no brittle grain boundary α, and is staggered and woven into a basket shape, which has extremely high strength. The ultrafine needle-shaped α fractures through the grain, and has higher fracture resistance than the coarse lamellar layer α, thereby greatly improving the strength of the laser cladding Ti-5321 titanium alloy. Usually, its tensile strength is increased to more than 1400MPa, which meets the demand for high-strength Ti-5321 titanium alloy in practical applications.

[0007] The above-mentioned heat treatment method for improving the strength of laser cladding formed Ti-5321 titanium alloy is characterized in that the multiple heat treatment process includes the following steps:

[0008] Step 1: Heat the laser cladding formed Ti-5321 titanium alloy to 530°C to 540°C and keep it at this temperature for 6h to 8h, and then air cool it to room temperature;

[0009] Step 2: heating the laser cladding formed Ti-5321 titanium alloy air-cooled to room temperature in step 1 to 870° C. to 890° C. and keeping the temperature for 1 h to 2 h, and then air-cooling to room temperature;

[0010] Step 3: Heat the laser cladding formed Ti-5321 titanium alloy air-cooled to room temperature in step 2 to 570° C. to 580° C. and keep it at this temperature for 6 h to 8 h, and then air-cool it to room temperature.

[0011] In the multiple heat treatment process of the present invention, the laser cladding formed Ti-5321 titanium alloy is first heated to 530°C-540°C and kept warm for 6h-8h, and air-cooled to room temperature to eliminate the internal residual stress of the laser cladding formed Ti-5321 titanium alloy and improve the uniformity of the structure, and then continued to heat to 570°C-580°C and keep warm for 6h-8h, and air-cooled to room temperature, so that the coarse sheet layer α is completely dissolved to prepare for subsequent heat treatment, and then heated to 570°C-580°C and kept warm for 6h-8h, and air-cooled to room temperature, so that the ultrafine needle-shaped α is completely precipitated, thereby improving the strength of the Ti-5321 titanium alloy.

[0012] The above-mentioned heat treatment method for improving the strength of laser cladding formed Ti-5321 titanium alloy is characterized in that the tensile strength of the laser cladding formed Ti-5321 titanium alloy after multiple heat treatment processes exceeds 1400 MPa.

[0013] Compared with the prior art, the present invention has the following advantages:

[0014] 1. The present invention transforms the coarse lamellar layer α formed by laser cladding into ultrafine needle-shaped α by performing multiple heat treatment processes on the laser cladding Ti-5321 titanium alloy. By regulating the size and morphology of the α phase, the strength of the laser cladding Ti-5321 titanium alloy is greatly improved, solving the problem of low strength of laser cladding Ti-5321 titanium alloy components.

[0015] 2. The present invention performs multiple heat treatment processes on the laser cladding formed Ti-5321 titanium alloy, effectively eliminating the laser cladding stress, improving its organizational size and morphology, and improving the quality of the laser cladding formed Ti-5321 titanium alloy.

[0016] 3. The tensile strength of the laser cladding formed Ti-5321 titanium alloy after multiple heat treatment processes of the present invention exceeds 1400 MPa, which meets the demand for high-strength Ti-5321 titanium alloy in practical applications.

[0017] 4. The process flow of the present invention is simple, easy to implement, suitable for industrial production, and has good promotion prospects.

[0018] The technical solution of the present invention is further described in detail below through the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 The microstructure diagram of the Ti-5321 titanium alloy formed by laser cladding in Examples 1 to 4 of the present invention and Comparative Example 1 is shown.

[0020] Figure 2 This is a low-magnification microstructure image of the laser cladding formed Ti-5321 titanium alloy after multiple heat treatment processes in Example 1 of the present invention.

[0021] Figure 3 This is a high-magnification microstructure image of the laser cladding formed Ti-5321 titanium alloy after multiple heat treatment processes in Example 1 of the present invention. DETAILED DESCRIPTION

[0022] Figure 1 The microstructure diagram of the Ti-5321 titanium alloy formed by laser cladding in Examples 1 to 4 of the present invention and Comparative Example 1 is shown in FIG. Figure 1 It can be seen that the microstructure of the laser cladding formed Ti-5321 titanium alloy has a coarse lamellar layer α.

[0023] Example 1

[0024] In this embodiment, a laser cladding-formed Ti-5321 titanium alloy is subjected to a multiple heat treatment process, so that the coarse sheet layer α formed by laser cladding is transformed into an ultrafine needle-shaped α; the multiple heat treatment process includes the following steps:

[0025] Step 1: Place the laser cladding formed Ti-5321 titanium alloy into a box-type resistance furnace and heat it to 530°C and keep it for 6 hours, then air cool it to room temperature;

[0026] Step 2: Place the laser cladding formed Ti-5321 titanium alloy air-cooled to room temperature in step 1 into a box-type resistance furnace, heat it to 870° C. and keep it warm for 2 hours, and then air-cool it to room temperature;

[0027] Step 3: Place the laser cladding formed Ti-5321 titanium alloy air-cooled to room temperature in step 2 into a box-type resistance furnace, heat it to 580° C. and keep it warm for 8 hours, and then air-cool it to room temperature.

[0028] According to the test, the tensile strength of the laser cladding formed Ti-5321 titanium alloy after multiple heat treatment processes in this embodiment is 1419 MPa.

[0029] Figure 2 This is a low-magnification microstructure image of the laser cladding formed Ti-5321 titanium alloy after multiple heat treatment processes in this embodiment. Figure 3 This is a high-magnification microstructure diagram of the laser cladding Ti-5321 titanium alloy after multiple heat treatment processes in this embodiment. Figure 2 and Figure 3 It can be seen that the microstructure of the laser cladding Ti-5321 titanium alloy after multiple heat treatment processes contains ultrafine needle-shaped α Figure 3 The ultrafine needle-shaped α with extremely high strength is interwoven into a basket shape, so that the microstructures after various heat treatments obtain good strength.

[0030] Will Figure 1 and Figures 2-3 By comparison, it can be seen that the present invention transforms the coarse sheet layer α formed by laser cladding into ultrafine needle-shaped α by performing multiple heat treatment processes on the laser cladding formed Ti-5321 titanium alloy, thereby greatly improving the strength of the laser cladding formed Ti-5321 titanium alloy.

[0031] Example 2

[0032] In this embodiment, a laser cladding-formed Ti-5321 titanium alloy is subjected to a multiple heat treatment process, so that the coarse sheet layer α formed by laser cladding is transformed into an ultrafine needle-shaped α; the multiple heat treatment process includes the following steps:

[0033] Step 1: Place the laser cladding formed Ti-5321 titanium alloy into a box-type resistance furnace and heat it to 540°C and keep it warm for 8 hours, then air cool it to room temperature;

[0034] Step 2: Place the laser cladding formed Ti-5321 titanium alloy air-cooled to room temperature in step 1 into a box-type resistance furnace, heat it to 890° C. and keep it warm for 1 hour, and then air-cool it to room temperature;

[0035] Step 3: Place the laser cladding formed Ti-5321 titanium alloy air-cooled to room temperature in step 2 into a box-type resistance furnace, heat it to 580° C. and keep it warm for 6 hours, and then air-cool it to room temperature.

[0036] According to the test, the microstructure of the laser cladding formed Ti-5321 titanium alloy after multiple heat treatment processes in this embodiment contains ultrafine needle-shaped α, and the tensile strength is 1406 MPa.

[0037] Example 3

[0038] In this embodiment, a laser cladding-formed Ti-5321 titanium alloy is subjected to a multiple heat treatment process, so that the coarse sheet layer α formed by laser cladding is transformed into an ultrafine needle-shaped α; the multiple heat treatment process includes the following steps:

[0039] Step 1: Place the laser cladding formed Ti-5321 titanium alloy into a box-type resistance furnace and heat it to 535°C and keep it warm for 7 hours, then air cool it to room temperature;

[0040] Step 2: Place the laser cladding formed Ti-5321 titanium alloy air-cooled to room temperature in step 1 into a box-type resistance furnace, heat it to 880° C. and keep it warm for 1.5 hours, and then air-cool it to room temperature;

[0041] Step 3: Place the laser cladding formed Ti-5321 titanium alloy air-cooled to room temperature in step 2 into a box-type resistance furnace, heat it to 575° C. and keep it warm for 7 hours, and then air-cool it to room temperature.

[0042] According to the test, the microstructure of the laser cladding formed Ti-5321 titanium alloy after multiple heat treatment processes in this embodiment contains ultrafine needle-shaped α, and the tensile strength is 1412 MPa.

[0043] Example 4

[0044] In this embodiment, a laser cladding-formed Ti-5321 titanium alloy is subjected to a multiple heat treatment process, so that the coarse sheet layer α formed by laser cladding is transformed into an ultrafine needle-shaped α; the multiple heat treatment process includes the following steps:

[0045] Step 1: Place the laser cladding formed Ti-5321 titanium alloy into a box-type resistance furnace and heat it to 530°C and keep it for 6 hours, then air cool it to room temperature;

[0046] Step 2: Place the laser cladding formed Ti-5321 titanium alloy air-cooled to room temperature in step 1 into a box-type resistance furnace, heat it to 880° C. and keep it warm for 1.5 hours, and then air-cool it to room temperature;

[0047] Step 3: Place the laser cladding formed Ti-5321 titanium alloy air-cooled to room temperature in step 2 into a box-type resistance furnace, heat it to 570° C. and keep it warm for 8 hours, and then air-cool it to room temperature.

[0048] According to the test, the microstructure of the Ti-5321 titanium alloy formed by laser cladding after multiple heat treatment processes in this embodiment contains ultrafine needle-shaped α, and the tensile strength is 1404 MPa.

[0049] Comparative Example 1

[0050] In this comparative example, conventional heat treatment is performed on the laser cladding formed Ti-5321 titanium alloy. The specific process is: the laser cladding formed Ti-5321 titanium alloy is placed in a box-type resistance furnace and heated to 880°C and kept warm for 1 hour, and then air-cooled to room temperature.

[0051] After testing, the microstructure of the laser cladding formed Ti-5321 titanium alloy after conventional heat treatment process in this comparative example is irregular shape α, the α phase precipitation is uneven, and does not contain ultrafine needle-shaped α, and the tensile strength is only 1120 MPa.

[0052] By comparing Examples 1 to 4 of the present invention with Comparative Example 1, it can be seen that compared with the laser cladding formed Ti-5321 titanium alloy subjected to conventional heat treatment in Comparative Example 1, the laser cladding formed Ti-5321 titanium alloy subjected to multiple heat treatment processes in Examples 1 to 4 contains fine needle-shaped α with good uniformity in its structure, thereby greatly improving the tensile strength.

[0053] In summary, the above are only preferred embodiments of the present invention and do not limit the present invention in any way. Any simple modification, change and equivalent changes made to the above embodiments according to the technical essence of the invention still fall within the protection scope of the technical solution of the present invention.

Claims

1. A heat treatment method for improving the strength of laser cladding formed Ti-5321 titanium alloy, characterized in that: The method performs multiple heat treatment processes on a laser cladding formed Ti-5321 titanium alloy, so that a coarse sheet layer α formed by laser cladding is transformed into an ultrafine needle-shaped α, thereby improving the strength of the laser cladding formed Ti-5321 titanium alloy; the multiple heat treatment process comprises the following steps: Step 1: Heat the laser cladding formed Ti-5321 titanium alloy to 530°C to 540°C and keep it at this temperature for 6h to 8h, and then air cool it to room temperature; Step 2: heating the laser cladding formed Ti-5321 titanium alloy air-cooled to room temperature in step 1 to 870° C. to 890° C. and keeping the temperature for 1 h to 2 h, and then air-cooling to room temperature; Step 3: heat the laser cladding formed Ti-5321 titanium alloy air-cooled to room temperature in step 2 to 570°C to 580°C and keep it warm for 6h to 8h, and then air-cool it to room temperature; the tensile strength of the laser cladding formed Ti-5321 titanium alloy after multiple heat treatment processes exceeds 1400MPa.

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