Heat treatment method for regulating and controlling alpha variant selection behavior at beta grain boundary of TC18 titanium alloy

Abstract

The invention relates to the technical field of titanium alloy heat treatment, in particular to a heat treatment method for regulating and controlling an alpha variant selection behavior at a TC18 titanium alloy beta grain boundary. According to the specific technical scheme, the method comprises the following steps that (1) solution treatment is conducted, specifically, the TC18 titanium alloy is heated to the temperature below the phase transformation point at the speed of 10 DEG C / min, heat preservation is conducted for 1-1.5 h, and then air cooling is conducted; and (2) aging treatment is conducted, specifically, the TC18 titanium alloy is heated to 550-650 DEG C at the speed of 10 DEG C / min, heat preservation is conducted for 0.5-1 h, and then air cooling is conducted. The method solves the problem that the alpha variant selection behavior of the existing TC18 titanium alloy at the beta grain boundary is difficult to regulate and control.

Description

Technical Field

[0001] The present invention relates to the technical field of titanium alloy heat treatment, and particularly relates to a heat treatment method for regulating the α-variant selection behavior at the β grain boundaries of TC18 titanium alloy Background Art

[0002] Titanium alloys generally have advantages such as low density, light weight, good fracture toughness, high heat resistance, high specific strength, good corrosion resistance, good fatigue strength and crack propagation resistance, and are widely used in the fields of aviation, aerospace, military, weapons, shipbuilding, vehicle engineering, biomedicine, etc. The microstructure of titanium alloys is closely related to their properties, and the regulation of the microstructure is generally achieved by using the phase transformation between α and β. During the phase transformation between α and β, the two phases generally follow the Burgers orientation relationship, that is: {0001} α ∥{110} β and ∥<111> β According to the crystallographic symmetry relationship, 12 different orientations of α will randomly appear during the β→α phase transformation. However, due to certain special reasons, some α with specific orientations will be preferentially precipitated, especially at the β grain boundaries, which will lead to the appearance of strong texture (macro region) in the micro region. Past studies have shown that various properties of titanium alloys are not only related to the spatial and macroscopic crystallographic distributions of α, but the formation of the "macro region" will also have an important impact on the properties of the alloy, and this impact is generally negative. Therefore, regulating the α-variant selection behavior will be one of the potential methods to further improve the properties of titanium alloys

[0003] In summary, the α-variant selection behavior mainly has an adverse effect on the properties of the alloy by forming a strong texture in the micro region. To address this problem, recent studies have found that grain boundary engineering can be used to allow the β grains to undergo sufficient dynamic recrystallization during the deformation process, thereby refining the grains while reducing the β texture strength and enabling as many α-variants with different crystal orientations to be precipitated as possible to reduce the harm of the "macro region" to the properties of titanium alloys, or a heat treatment process of low-temperature aging can be adopted. However, these two methods are obviously only applicable to some intermediate products that can be deformed again during production and titanium alloy parts that can meet the performance requirements through low-temperature aging. Therefore, at present, how to regulate or further eliminate the adverse effects of the α-variant selection behavior on titanium alloys through simple and practical medium- and high-temperature aging treatments will still be a key research direction for titanium alloys in the future Summary of the Invention

[0004] In view of the deficiencies of the prior art, the present invention provides a heat treatment method for regulating the α-variant selection behavior at the β grain boundaries of TC18 titanium alloy. This method involves solution treatment of TC18 titanium alloy within a certain temperature range and then aging treatment within a relatively high temperature range. By introducing more primary α, the variant selection behavior of secondary α at the β grain boundaries is effectively regulated, reducing the negative impact of "macro regions" on the mechanical properties of TC18 titanium alloy, coordinating the deformation between the constituent phases, suppressing the occurrence of intergranular brittle fracture, improving the plasticity and fracture toughness of TC18 titanium alloy, and effectively solving the problem that it is difficult to regulate the α-variant selection behavior at the β grain boundaries of existing TC18 titanium alloy.

[0005] To achieve the above objectives, the present invention is realized through the following technical solutions:

[0006] The present invention discloses a heat treatment method for regulating the α-variant selection behavior at the β grain boundaries of TC18 titanium alloy, comprising the following steps:

[0007] (1) Solution treatment: Heat the TC18 titanium alloy at a rate of 10 °C / min to below the phase transformation point, hold for 1 h to 1.5 h, and then air cool.

[0008] (2) Aging treatment: Heat the TC18 titanium alloy at a rate of 10 °C / min to 550 °C to 650 °C, hold for 0.5 h to 1 h, and then air cool.

[0009] Preferably, the composition of the TC18 titanium alloy is Ti-5Al-5Mo-5V-1Cr-1Fe.

[0010] Preferably, the phase transformation temperature point of the TC18 titanium alloy is 870 ± 5 °C.

[0011] Preferably, in step (1), the TC18 titanium alloy is heated to 800 °C to 830 °C.

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

[0013] 1. The heat treatment method of the present invention has a simple process and low requirements for heat treatment equipment. By means of simple two-step heat treatment, the α-variant selection behavior at the β grain boundaries of TC18 titanium alloy can be effectively regulated, with high economic value and being easy to be applied and popularized in actual production.

[0014] 2. In the present invention, by retaining a certain volume fraction of primary α during the solution treatment stage, during the aging stage, competitive behavior occurs between the β grain boundaries and the α / β phase boundaries during the precipitation process of secondary α, thereby making the crystal orientation of secondary α more randomly distributed, effectively reducing the texture strength of α near the β grain boundaries of TC18 titanium alloy, greatly avoiding strain localization during the deformation process and service of the alloy, and improving the plasticity and toughness of TC18 titanium alloy and the service life of its components.

[0015] 3. Since the variant selection behavior of α at the β grain boundaries is a common phenomenon in titanium alloys, therefore, the present invention can also be extended and applied to other types of titanium alloys, with universality. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 It is a schematic diagram of the heat treatment process for regulating the variant selection behavior of α at the β grain boundaries of the present invention;

[0017] Figure 2 It is a distribution diagram of the α volume fraction after solution treatment at 800 °C in Example 1;

[0018] Figure 3 It is an inverse pole figure (a) and an orientation difference angle distribution diagram (b) of secondary α after aging treatment in Example 1;

[0019] Figure 4 It is a distribution diagram of the α volume fraction after solution treatment at 830 °C in Example 2;

[0020] Figure 5 It is an inverse pole figure (a) and an orientation difference angle distribution diagram (b) of secondary α after aging treatment in Example 2;

[0021] Figure 6 It is a distribution diagram of the α volume fraction after solution treatment at 890 °C in Comparative Example 1;

[0022] Figure 7 It is an inverse pole figure (a) and an orientation difference angle distribution diagram (b) of secondary α after aging treatment in Comparative Example 1. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0023] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0024] Unless otherwise specified, the technical means used in the implementation examples are conventional means well-known to those skilled in the art.

[0025] As Figure 1 shown, the present invention discloses a heat treatment method for regulating the α-variant selection behavior at the β grain boundaries of TC18 titanium alloy, comprising the following steps:

[0026] (1) Solution treatment: Heat the TC18 titanium alloy at 10 °C / min to a temperature below the phase transformation point (T β ), i.e., heat it to 800 °C to 830 °C, hold for 1 h to 1.5 h, and then air cool.

[0027] Among them, the phase transformation temperature point (T β ) of the TC18 titanium alloy is 870 ± 5 °C. The chemical composition of the TC18 titanium alloy is Ti-5Al-5Mo-5V-1Cr-1Fe.

[0028] (2) Aging treatment: Heat the TC18 titanium alloy at 10 °C / min to 550 °C to 650 °C, hold for 0.5 h to 1 h, and then air cool. After heat treatment, more secondary α with randomly distributed crystal orientations appears at the β grain boundaries of the TC18 titanium alloy.

[0029] The present invention will be further elaborated below with specific embodiments.

[0030] Example 1

[0031] A heat treatment method for regulating the α-variant selection behavior at the β grain boundaries of TC18 titanium alloy, comprising the following steps:

[0032] (1) Heat the TC18 titanium alloy at 10 °C / min to 800 °C, hold for 1 h, and then air cool to room temperature to retain the microstructure morphology after solution treatment.

[0033] (2) Then heat the solution-treated TC18 titanium alloy in step (1) at 10 °C / min to 650 °C, hold for 0.5 h, and then air cool to room temperature to retain the microstructure morphology after aging treatment.

[0034] The microstructure of the TC18 titanium alloy after solution treatment is as Figure 2 shown. It can be seen from the figure that the primary α is equiaxed and its volume fraction is approximately 12.8%. Figure 3 The EBSD characterization result of the TC18 titanium alloy after aging treatment is shown. It can be seen that there are secondary α variants with various crystal orientations, and no obvious "macro region" is formed near the β grain boundaries.

[0035] Example 2

[0036] A heat treatment method for regulating the α-variant selection behavior at the β grain boundaries of TC18 titanium alloy, comprising the following steps:

[0037] (1) Heat the TC18 titanium alloy to 830 °C at a rate of 10 °C / min, hold for 1 h, and then air cool to room temperature to retain the microstructure morphology after solution treatment.

[0038] (2) Then heat the solution-treated TC18 titanium alloy in step (1) to 650 °C at a rate of 10 °C / min, hold for 0.5 h, and then air cool to room temperature to retain the microstructure morphology after aging treatment.

[0039] The microstructure of the TC18 titanium alloy after solution treatment is as Figure 4 shown. It can be seen from the figure that the primary α is also equiaxed, and its volume fraction slightly decreases, about 8.77%. Figure 5 The EBSD characterization results of the TC18 titanium alloy after aging treatment are shown. It can be seen that there are also secondary α variants with multiple crystal orientations, and there is no obvious "macro zone" formed near the β grain boundary.

[0040] Comparative Example 1

[0041] The heat treatment process of the TC18 titanium alloy is as follows:

[0042] (1) Heat the TC18 titanium alloy to 890 °C at a rate of 10 °C / min, hold for 1 h, and then air cool to room temperature to retain the microstructure morphology after solution treatment.

[0043] (2) Then heat the solution-treated TC18 titanium alloy in step (1) to 650 °C at a rate of 10 °C / min, hold for 0.5 h, and then air cool to room temperature to retain the microstructure morphology after aging treatment.

[0044] The microstructure of the TC18 titanium alloy after solution treatment is as Figure 6 shown. It can be seen from the figure that the primary α has completely disappeared. Figure 7 The EBSD characterization results of the TC18 titanium alloy after aging treatment are shown. It can be seen that there are basically only α variants with two crystal orientations, and obvious microzone strong texture appears near the β grain boundary, and the α orientation difference angle distribution is also more concentrated than at 800 °C and 830 °C. This indicates that retaining a certain amount of primary α during the heat treatment process can effectively regulate the variant selection behavior of secondary α near the β grain boundary and prevent the emergence of "macro zones" that are not conducive to the plasticity and fracture toughness of the titanium alloy.

[0045] The above-described embodiments are only descriptions of the preferred embodiments of the present invention and do not limit the scope of the present invention. Without departing from the design spirit of the present invention, various deformations and improvements made by those of ordinary skill in the art to the technical solutions of the present invention should fall within the protection scope determined by the claims of the present invention.

Claims

1. A heat treatment method for regulating the α variant selection behavior at the β grain boundary of TC18 titanium alloy, characterized in that: The following steps are involved: (1) Solution treatment: Heat the TC18 titanium alloy at 10 °C / min to below the phase transition point, keep it at this temperature for 1 h to 1.5 h, and then air cool it; (2) Aging treatment: Heat the TC18 titanium alloy to 550°C~650°C at 10°C / min, keep it at that temperature for 0.5h~1h, and then air cool it.

2. A heat treatment method for regulating the α variant selection behavior at the β grain boundary of TC18 titanium alloy according to claim 1, characterized in that: The composition of the TC18 titanium alloy is Ti-5Al-5Mo-5V-1Cr-1Fe.

3. A heat treatment method for regulating the α variant selection behavior at the β grain boundary of TC18 titanium alloy according to claim 1, characterized in that: The phase transition temperature of the TC18 titanium alloy is 870±5°C.

4. A heat treatment method for regulating the α variant selection behavior at the β grain boundary of TC18 titanium alloy according to claim 1 or 3, characterized in that: In step (1), TC18 titanium alloy is heated to 800°C to 830°C.

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