A heat treatment method for improving fatigue stability of high-strength titanium alloy

Abstract

This invention discloses a heat treatment method for improving the fatigue stability of high-strength titanium alloys. The method involves heating the titanium alloy to 30°C~50°C below its phase transformation point, maintaining this temperature for a first holding period, and then removing it from the furnace. The titanium alloy after the first holding period is then heated to 10°C~20°C above its phase transformation point and held for a second time before cooling. The cooled titanium alloy is then subjected to a first aging treatment and a second aging treatment sequentially. The temperature of the first aging treatment is lower than the temperature of the second aging treatment. This invention utilizes the initial aging process during the first holding period to generate... α Phase, can be suppressed during the second heat preservation. β Excessive grain growth; simultaneously, the formation of fine, dispersed grains through the first aging treatment. ω When the phase is treated as a second aging process α s The nucleation point of the phase, making α s The phase distribution is more uniform, thereby improving the fatigue stability of titanium alloys.

Description

Technical Field

[0001] This invention belongs to the field of titanium alloy heat treatment technology, and particularly relates to a heat treatment method for improving the fatigue stability of high-strength titanium alloys. Background Technology

[0002] High-strength titanium alloys, due to their excellent specific strength, corrosion resistance, and good high-temperature performance, have significant application value in the aerospace field and are widely used in critical load-bearing structures such as aircraft fuselages and landing gear components. However, under the coupled effects of complex alternating loads and extreme environments, high-strength titanium alloy structural components often exhibit poor fatigue stability, specifically manifested in problems such as dispersed fatigue life and difficulty in predicting fatigue life. Especially in the context of the long service life and high reliability requirements of modern aerospace equipment, the insufficient fatigue stability of high-strength titanium alloy structural components has become a key bottleneck restricting their engineering applications.

[0003] Currently, the main heat treatment process for high-strength titanium alloys is the traditional solution aging treatment, which typically involves heating the alloy to... β A single-stage solution treatment is performed above the phase transformation point, followed by single-stage aging in a moderate temperature range. However, the alloy obtained by this method has a large number of non-precipitate regions within the grains, resulting in a large dispersion in fatigue life, which makes it difficult to meet the stringent reliability requirements of modern aerospace equipment for critical components. Summary of the Invention

[0004] The purpose of this invention is to provide a heat treatment method to improve the fatigue stability of high-strength titanium alloys, thereby enhancing the fatigue stability of titanium alloys.

[0005] This invention adopts the following technical solution: a heat treatment method for improving the fatigue stability of high-strength titanium alloys, comprising the following steps: The titanium alloy is heated to 30°C to 50°C below the phase transformation point, and the temperature is kept constant for the first heat preservation. After the heat preservation, the alloy is not removed from the furnace. The titanium alloy after the first heat preservation is heated to 10°C~20°C above the phase transformation point, then heat-preserved a second time and cooled. The cooled titanium alloy was subjected to a first aging treatment and a second aging treatment in sequence; the temperature of the first aging treatment was lower than that of the second aging treatment.

[0006] Furthermore, the temperature for the first aging treatment is 250℃~350℃.

[0007] Furthermore, the temperature for the second aging treatment is 470~520℃.

[0008] Furthermore, the initial heat preservation time is 1 to 2 hours.

[0009] Furthermore, the second insulation time is 0.5 to 1 hour.

[0010] The beneficial effects of this invention are: this invention generates primary heat during the first heat preservation process. α Phase, can be suppressed during the second heat preservation. β Excessive grain growth; simultaneously, the formation of fine, dispersed grains through the first aging treatment. ω When the phase is treated as a second aging process α s The nucleation point of the phase, making α s The phase distribution is more uniform, thereby improving the fatigue stability of titanium alloys. Attached Figure Description

[0011] Figure 1 This is a schematic diagram of the heat treatment process in Comparative Example 1 of the present invention; Figure 2 This is a schematic diagram of the heat treatment process of the method of the present invention; Figure 3 This is a microstructure diagram of the titanium alloy obtained in Comparative Example 1 of the present invention; Figure 4 This is a microstructure diagram of the titanium alloy obtained in Example 1 of the present invention; Figure 5 The titanium alloy obtained in Example 1 of this invention ω Schematic diagram of phase diffraction spots and dark field image. Detailed Implementation

[0012] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments.

[0013] Traditional heat treatment methods for high-strength titanium alloys are simple to operate, but single-stage aging is difficult to control precisely. α The size and distribution of the strengthening phase result in an unsatisfactory effect in hindering dislocation movement, leading to a large number of non-precipitated regions within the crystal and resulting in a large dispersion in fatigue life.

[0014] To address the aforementioned problems, there is an urgent need to develop a novel heat treatment method to achieve the following objectives: effectively control... β Grain size and grain boundary morphology, optimization α The size distribution of the strengthening phase synergistically improves the fatigue limit and fatigue stability of the alloy, providing important support for the manufacture of high-strength titanium alloy components in the aerospace field.

[0015] This invention discloses a heat treatment method for improving the fatigue stability of high-strength titanium alloys, such as... Figure 2As shown, the process includes the following steps: heating the titanium alloy to 30°C to 50°C below the phase transformation point, maintaining the temperature for the first heat preservation, and removing it from the furnace after the heat preservation; the heat preservation time is 1 to 2 hours; heating the titanium alloy after the first heat preservation to 10°C to 20°C above the phase transformation point and heat preservation for the second time, followed by cooling, the heat preservation time is 0.5 to 1 hour, and the cooling method is water cooling.

[0016] The cooled titanium alloy was subjected to a first aging treatment and a second aging treatment in sequence; the temperature of the first aging treatment was lower than that of the second aging treatment. Specifically, the temperature of the first aging treatment was 250℃~350℃, and the holding time was 24 hours; the temperature of the second aging treatment was 470~520℃, and the holding time was 3~5 hours.

[0017] This invention generates the initial heat during the first heat preservation. α Phase, can be suppressed during the second heat preservation. β Excessive grain growth; simultaneously, the formation of fine, dispersed grains through the first aging treatment. ω When the phase is treated as a second aging process α s The nucleation point of the phase, making α s The phase distribution is more uniform, and the microstructure of the titanium alloy is precisely controlled, thereby improving the fatigue stability of the titanium alloy and providing important support for the manufacturing of high-strength titanium alloy components in the aerospace field.

[0018] It should be noted that the high-strength titanium alloy in this invention refers to a titanium alloy with a tensile strength higher than 1100 MPa.

[0019] More specifically, this invention relates to a heat treatment process developed to improve the fatigue stability of high-strength titanium alloys. Performing a primary solution treatment at 30°C to 50°C below the phase transformation point can induce the formation of primary phases in the microstructure. α Xiang, newly born α The existence of phases can β Obstacles during phase region heat treatment β Further grain growth occurs. The titanium alloy after primary solution treatment is heated to 10°C~20°C above the phase transformation point for secondary solution treatment, held at that temperature for 0.5~1 hour, which ensures the formation of... β The grains are fine and uniform, which can avoid β The grains grew excessively, and then the grains were immediately quenched in water.

[0020] Then, the water-quenched titanium alloy undergoes a double aging treatment. First, it is aged at a low temperature of 250–350°C for 24 hours. This temperature range can eliminate processing stress and form fine, dispersed... ω Mutually, ω In the subsequent time limit processα s The precipitation of the phase provides nucleation sites, making α s The phase distribution is more uniform, and the number and area of ​​non-precipitated regions are reduced, thereby significantly improving the fatigue stability of the alloy.

[0021] Comparative Example 1: like Figure 1 As shown, a Ti-1300 titanium alloy sample was taken, heated to 850℃, and held for 1 hour; then aging treatment was performed, and the sample was held at 510℃ for 4 hours.

[0022] like Figure 3 The image shows the microstructure of Comparative Example 1. It can be seen from the image that a large number of non-precipitated regions exist in this titanium alloy sample, which inevitably affects the fatigue performance of the titanium alloy sample. The titanium alloy sample treated with this process was tested, and under a stress ratio of 0.6, the fatigue limit measured by the rise-fall method was 870.7 MPa, and the standard deviation of fatigue life was 1.1. Example 1:

[0023] Take a Ti-1300 titanium alloy sample (its phase transformation point is 830℃), heat it to 780℃ and hold it for 1.5 hours; then rapidly heat it to 845℃ for a two-stage solution treatment, hold it for 1 hour and then quench it in water; finally, perform a double aging treatment, first holding it at 300℃ for 24 hours and then holding it at 490℃ for 4 hours.

[0024] like Figure 4 The image shown is a microstructure diagram of Example 1. It can be seen from the image that there are essentially no non-precipitated regions in this titanium alloy sample. Figure 5 As shown, after aging at 350℃ for 24 hours, a large number of [unclear] particles were observed within the grains and at the grain boundaries. ω These ω The phase precipitates at 490℃ α s The phase is finer and more uniform. Testing showed that the fatigue limit of the titanium alloy sample treated with this process reached 950 MPa, and the standard deviation of fatigue life was 0.2. Therefore, it is evident that the fatigue limit of the titanium alloy sample in this embodiment is much greater than that of Comparative Example 1, and the standard deviation of fatigue life is significantly smaller than that of Comparative Example 1. Example 2:

[0025] Take a TB18 titanium alloy sample (its phase transformation point is 800℃), heat it to 770℃ and hold it for 2 hours; then rapidly heat it to 810℃ for a two-stage solution treatment, hold it for 0.5 hours and then quench it in water; finally, perform a double aging treatment, first holding it at 250℃ for 24 hours and then holding it at 520℃ for 3 hours.

[0026] Tests showed that the fatigue limit of the samples treated with this process reached 935.6 MPa, and the standard deviation of fatigue life was 0.17. Example 3:

[0027] Take a Ti-1300 titanium alloy sample, heat it to 790℃ and hold it for 1 hour; then rapidly heat it to 850℃ for a two-stage solution treatment, hold it for 1 hour and then quench it in water; finally, perform a double aging treatment, first holding it at 350℃ for 24 hours and then holding it at 470℃ for 5 hours.

[0028] Tests showed that the fatigue limit of the samples treated with this process reached 896.1 MPa, and the standard deviation of fatigue life was 0.23. Example 4:

[0029] Take a Ti-1300 titanium alloy sample, heat it to 800℃ and hold it for 1.5 hours; then rapidly heat it to 840℃ for a two-stage solution treatment, hold it for 0.5 hours and then quench it in water; finally, perform a double aging treatment, first holding it at 325℃ for 24 hours and then holding it at 485℃ for 4 hours.

[0030] Tests showed that the fatigue limit of the samples treated with this process reached 933.0 MPa, and the standard deviation of fatigue life was 0.14.

[0031] As can be seen from the above embodiments, the heat treatment process of the present invention can improve the fatigue performance of high-strength titanium alloys and significantly enhance their fatigue stability.

Claims

1. A heat treatment method for improving the fatigue stability of high-strength titanium alloys, characterized in that, For application in Ti-1300 titanium alloy and TB18 titanium alloy, the following steps are included: First-stage solution treatment: The titanium alloy is heated to 30°C to 50°C below the phase transformation point, and the temperature is kept constant for the first heat treatment. The alloy is then removed from the furnace after the first heat treatment. The first heat treatment lasts for 1 to 2 hours. Secondary solution treatment: The titanium alloy after the first heat treatment is heated to 10°C~20°C above the phase transformation point and then heat-treated a second time and water-cooled; the second heat treatment time is 0.5~1 hour; The cooled titanium alloy was subjected to a first aging treatment and a second aging treatment in sequence; wherein the temperature of the first aging treatment was lower than the temperature of the second aging treatment. The temperature for the first aging treatment is 250℃~350℃, and the holding time is 24 hours; the temperature for the second aging treatment is 470~520℃, and the holding time is 3~5 hours.

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