Method for obtaining microstructure of high-strength and high-toughness titanium alloy

Abstract

The application provides a method for obtaining high-strength and high-toughness titanium alloy microstructure and belongs to the technical field of titanium alloy organization regulation. The titanium alloy is slowly cooled to 70-150 DEG C below the beta phase point after being solid-solved in the beta phase zone and quenched to obtain coarse alpha lamellar organization and residual beta phase matrix, then is aged in the alpha+beta two-phase zone to decompose and precipitate fine secondary alpha phase lamella from the residual beta phase, and finally the coarse alpha phase+fine beta transformation microstructure is obtained. The microstructure has higher strength and toughness. Therefore, the application can improve the strength and toughness of the titanium alloy.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of titanium alloy microstructure control, and particularly relates to a method for obtaining high-strength and high-toughness titanium alloy microstructure. BACKGROUND

[0002] High-strength and high-toughness titanium alloys have very important applications in the field of aerospace, and are mainly used for airplane landing gears, key structural parts of airplane bodies, fasteners and the like. However, the strength and toughness of metal materials are mutually contradictory, and the toughness is lost when high strength is obtained. In order to obtain a match of strength and toughness, multiple grades of titanium alloys have been developed at home and abroad through composition design, such as BT22 (Russia, corresponding domestic grade TC18), Ti-1023 (USA, corresponding domestic grade TB6), Ti-5553 (USA), Ti-55531 (USA), Ti-1300 (China) and the like. At present, it is more and more difficult to develop high-strength and high-toughness titanium alloys through composition design, and attention is paid to further optimizing the match of strength and toughness of existing high-strength and high-toughness titanium alloys through fine microstructure control.

[0003] At present, high-strength and high-toughness titanium alloys need to be deformed in the alpha and beta two-phase region to refine beta grains and break lamellar primary alpha, and then are subjected to aging after alpha and beta two-phase region solid solution treatment, so that the microstructure is mainly large equiaxed or short rod-shaped primary alpha phase + fine beta transformed structure (fine secondary alpha phase lamella is distributed in the beta phase matrix). The large equiaxed or short rod-shaped primary alpha phase makes the alloy obtain high toughness, and the fine beta transformed structure makes the alloy obtain high strength. However, the toughness of this microstructure is still low. SUMMARY

[0004] The purpose of the present application is to provide a method for obtaining high-strength and high-toughness titanium alloy microstructure, which can obtain a more optimal high-strength and high-toughness match.

[0005] In order to achieve the above-mentioned purpose of the application, the present application provides the following technical scheme:

[0006] The present application provides a method for obtaining high-strength and high-toughness titanium alloy microstructure, comprising the following steps:

[0007] The titanium alloy is subjected to solid solution treatment in the beta phase region to obtain a beta phase titanium alloy;

[0008] The beta phase titanium alloy is cooled to 70-150 DEG C below the beta phase transition point at a rate of 1-20 DEG C / min, and is subjected to heat preservation for 0.5-2 h and then is air-cooled or water-quenched to obtain an intermediate titanium alloy; the intermediate titanium alloy is coarse alpha lamellar structure and residual beta phase matrix;

[0009] The intermediate titanium alloy is subjected to aging treatment; the temperature of the aging treatment is 500-650 DEG C.

[0010] Preferably, the temperature of the solution treatment is 20-100℃ above the β transus point.

[0011] Preferably, the holding time of the solution treatment is 1-4h.

[0012] Preferably, the holding time of the aging treatment is 4-8h.

[0013] Preferably, the cooling mode of the aging treatment is air cooling.

[0014] Preferably, the titanium alloy comprises TC18, Ti-1023, Ti-5553, Ti-55531 or Ti-1300.

[0015] The present application provides a method for obtaining a high-strength and high-toughness titanium alloy microstructure, comprising the following steps: solution treating a titanium alloy in the β phase region to obtain a β phase titanium alloy; cooling the β phase titanium alloy to 70-150℃ below the β transus point at a rate of 1-20℃ / min, holding for 0.5-2h, and then air cooling or water quenching to obtain an intermediate titanium alloy; the intermediate titanium alloy is coarse α lamellar structure and residual β phase matrix; aging treating the intermediate titanium alloy; the temperature of the aging treatment is 500-650℃.

[0016] The present application slowly cools the titanium alloy to 70-150℃ below the β transus point (α+β two-phase region) after solution treating in the β phase region, obtains coarse α lamellar structure and residual β phase matrix, and then ages in the α+β two-phase region to decompose the residual β phase and precipitate fine secondary α phase lamellae, finally obtains lamellar coarse α phase+fine β transformed structure, which has higher strength and toughness. Therefore, the present application can improve the strength and toughness of the titanium alloy. BRIEF DESCRIPTION OF DRAWINGS

[0017] Figure 1 is another microstructure diagram of the titanium alloy of Example 2 after heat treatment;

[0018] Figure 2 is another microstructure diagram of the titanium alloy of Example 2 after heat treatment;

[0019] Figure 3 is a microstructure diagram of Comparative Example 2;

[0020] Figure 4 is a microstructure diagram of Comparative Example 3. DETAILED DESCRIPTION

[0021] The present application provides a method for obtaining a high-strength and high-toughness titanium alloy microstructure, comprising the following steps:

[0022] solution treating a titanium alloy in the β phase region to obtain a β phase titanium alloy;

[0023] cooling the beta phase titanium alloy at a rate of 1-20℃ / min to 70-150℃ below the beta transus point, holding for 0.5-2h and then air cooling or water quenching to obtain an intermediate titanium alloy; the intermediate titanium alloy is coarse alpha lamellar structure and residual beta phase matrix;

[0024] aging the intermediate titanium alloy; the aging temperature is 500-650℃.

[0025] The present application carries out solid solution treatment on the titanium alloy in the beta phase region to obtain a beta phase titanium alloy.

[0026] The present application has no special requirements for the titanium alloy, and any titanium alloy known in the art can be used, such as the existing high-strength and high-toughness titanium alloys TC18, Ti-1023, Ti-5553, Ti-55531 or Ti-1300. The present application has no special requirements for the microstructure of the titanium alloy, and any microstructure can be used.

[0027] In the present application, the solid solution treatment temperature is preferably 20-100℃ above the beta transus point, more preferably 40-80℃ above the beta transus point, and further preferably 50-60℃ above the beta transus point. In the present application, the holding time for the solid solution treatment is preferably 1-4h, and more preferably 2-3h. The present application uses solid solution treatment to eliminate the initial microstructure of the titanium alloy and obtain a complete beta phase.

[0028] After obtaining the beta phase titanium alloy, the present application cools the beta phase titanium alloy at a rate of 1-20℃ / min to 70-150℃ below the beta transus point, holds for 0.5-2h and then air cools or water quenches to obtain an intermediate titanium alloy.

[0029] In the present application, when the cooling rate is greater than 20℃ / min, coarse alpha lamellar structure cannot be obtained. In the present application, it is preferred to cool to 80-140℃ below the beta transus point, and further preferred to 100-120℃ below the beta transus point. In the present application, the holding time after cooling to 70-150℃ below the beta transus point is preferably 1-1.5h. The present application slowly cools the beta phase titanium alloy to 70-150℃ below the beta transus point to quench, which can obtain a certain content of coarse alpha lamellar structure, and the obtained intermediate titanium alloy is coarse alpha lamellar structure and residual beta phase matrix.

[0030] After obtaining the intermediate titanium alloy, the present application ages the intermediate titanium alloy.

[0031] In the present application, the aging temperature is 500-650℃, preferably 540-620℃, and further preferably 560-600℃. In the present application, the holding time for the aging is preferably 4-8h, and more preferably 5-7h. In the present application, the cooling mode for the aging is preferably air cooling.

[0032] The present application utilizes aging treatment to decompose residual beta phase and precipitate fine secondary alpha phase lamella, to obtain fine beta transformed structure, and finally to obtain lamellar coarse alpha phase + fine beta transformed structure, which has higher strength and toughness.

[0033] The method for obtaining high-strength and high-toughness titanium alloy microstructure provided by the present application is described in detail below in combination with examples, but they should not be understood as limiting the scope of protection of the present application.

[0034] Example 1

[0035] TC18 titanium alloy was selected, and the beta phase transition temperature of the alloy was 870℃; the alloy was solid-solved at 900℃ for 1.5h, then cooled to 750℃ at a cooling rate of 10℃ / min, and then kept at 750℃ for 1.5h and air-cooled; then aging treatment was performed, specifically, kept at 500℃ for 5h and air-cooled.

[0036] Example 2

[0037] The difference from Example 1 is only that the aging treatment temperature is 550℃.

[0038] Example 3

[0039] The difference from Example 1 is only that the aging treatment temperature is 600℃.

[0040] Comparative Example 1

[0041] The difference from Example 1 is only that no aging treatment is performed.

[0042] Comparative Example 2

[0043] TC18 titanium alloy was selected, and the beta phase transition temperature of the alloy was 870℃; the alloy was solid-solved at 900℃ for 1.5h, then cooled to 810℃ at a cooling rate of 10℃ / min, and then kept at 810℃ for 1.5h and air-cooled, and the microstructure after cooling is shown in Figure 3 Coarse alpha lamella was not formed.

[0044] Comparative Example 3

[0045] TC18 titanium alloy was selected, and the beta phase transition temperature of the alloy was 870℃; the alloy was solid-solved at 900℃ for 1.5h, then cooled to 750℃ at a cooling rate of 50℃ / min, and then kept at 750℃ for 1.5h and air-cooled, and the microstructure after cooling is shown in Figure 4 Coarse alpha lamella was not formed.

[0046] Microstructure and performance characterization:

[0047] The titanium alloy after Example 2 treatment was observed for microstructure, and the results are shown in Figures 1-2 and Figure 1 andFigure 2 It can be seen that the microstructure of the titanium alloy is lamellar coarse alpha phase + fine beta transformed structure. The macrostructure morphology of Example 1 is consistent with that of Comparative Example 1. Figure 1 and Figure 2 The mechanical properties of Examples 1-3 are shown in Table 1.

[0048] Table 1 Mechanical properties of TC18 titanium alloy of Examples and Comparative Examples

[0049] Aging temperature °C Yield strength MPa Tensile strength MPa Elongation % Area reduction % Fracture toughness MPa-m 1 / 2 ]] Hardness Hv Comparative Example 1 Not aged 918 948 21.5 57.3 98 291 Comparative Example 2 Not aged 920 952 20.4 55.2 97 288 Comparative Example 3 Not aged 932 971 18.3 50.1 92 296 Example 1 500 1185 1330 8.0 15.0 68 380 Example 2 550 1135 1230 9.0 16.5 76 365 Example 3 600 1080 1155 13.0 29.5 88 343

[0050] As shown in Table 1, the solid solution alloy has very good fracture toughness and better tensile properties; after aging treatment, the strength of the alloy increases, and although the toughness decreases, it still has a better strength-toughness match compared with existing high-strength high-toughness titanium alloys.

[0051] In addition, as shown in the results of Comparative Example 2, when the temperature after cooling is too high, lamellar coarse alpha phase cannot be obtained. As shown in the results of Comparative Example 3, when the cooling rate is too high, lamellar coarse alpha phase cannot be obtained.

[0052] The above only describes the preferred embodiments of the present application, and it should be noted that those skilled in the art can make several improvements and refinements without departing from the principles of the present application, and these improvements and refinements should also be considered within the protection scope of the present application.

Claims

1. A method for obtaining a high-strength, high-toughness titanium alloy microstructure, characterized in that, Includes the following steps: Titanium alloys are solution treated in the β phase region to obtain β phase titanium alloys; The β-phase titanium alloy is cooled at a rate of 10~20℃ / min to 100~120℃ below the β-phase transformation point, held at that temperature for 0.5~2h, and then air-cooled or water-quenched to obtain an intermediate titanium alloy; the intermediate titanium alloy has a coarse α-lamellar structure and a residual β-phase matrix; The intermediate titanium alloy is subjected to aging treatment at a temperature of 500~650℃.

2. The method according to claim 1, characterized in that, The solution treatment temperature is 20~100℃ above the β phase transition point.

3. The method according to claim 1 or 2, characterized in that, The heat preservation time for the solution treatment is 1 to 4 hours.

4. The method according to claim 1, characterized in that, The heat preservation time for the aging treatment is 4~8 hours.

5. The method according to claim 1 or 4, characterized in that, The cooling method for the aging process is air cooling.

6. The method according to claim 1, characterized in that, The titanium alloys include TC18, Ti-1023, Ti-5553, Ti-55531, or Ti-1300.

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