Ti-55531 titanium alloy with high ductility and method of making

Abstract

The application discloses a Ti-55531 titanium alloy with high toughness and plasticity and a preparation method thereof. The preparation method specifically comprises the following steps: (1) placing the Ti-55531 titanium alloy into a muffle furnace or a resistance box-type heating furnace, and heating the Ti-55531 titanium alloy to 880 DEG C to 910 DEG C with the furnace, and keeping the temperature for 1 h to 2 h; (2) transferring the Ti-55531 titanium alloy treated in the step (1) into a heating furnace with a furnace temperature of 660 DEG C to 680 DEG C, keeping the temperature for 10 h to 15 h, and then air cooling the Ti-55531 titanium alloy to room temperature, so that the Ti-55531 titanium alloy with high toughness and plasticity is obtained. The lamellar structure of the obtained Ti-55531 titanium alloy has a multi-level structure, the multi-level structure comprises original beta grains, alpha beam sets, lamellar alpha, nanometer twinning structures and discontinuous grain boundary alpha, so that the Ti-55531 titanium alloy has high toughness and high plasticity.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of materials, and relates to light alloy processing, in particular to a Ti-55531 titanium alloy with high toughness and plasticity and a preparation method thereof. BACKGROUND

[0002] The development of high-speed and large-scale aerospace vehicles and the structural complexity of the vehicles also makes the material selection criterion of the vehicles gradually change from the past "safety-life" design concept to a "damage-durability" design concept. High-strength and high-toughness titanium alloys are widely used in key structural materials in the fields of aerospace and the like due to high specific strength, excellent corrosion resistance and fatigue damage resistance, such as Ti-55531 (Ti-5Al-5Mo-5V-3Cr-1Zr) titanium alloy.

[0003] However, the key to whether the alloy can exhibit damage tolerance lies in whether it has excellent fracture toughness. Generally, the plasticity of the equiaxed structure or the bimodal structure in the titanium alloy is good, but the fracture toughness is low. The damage tolerance performance of the lamellar structure is better than that of other structures, but the fatal weakness is that the plasticity is extremely poor, which seriously restricts its application in the field of aerospace. The existing method is to use a hot working process to control the grain morphology, distribution, size and orientation of the alpha phase, and thus to optimize the plasticity to a certain extent. However, the spheroidization of the lamellar alpha grain is usually accompanied by a decrease in fracture toughness. Therefore, the mechanical properties obtained by the general hot working process have the problems of improved plasticity but reduced toughness, or reduced plasticity but improved toughness. SUMMARY

[0004] In view of the above problems in the prior art, the purpose of the present application is to provide a Ti-55531 titanium alloy with high toughness and plasticity and a preparation method thereof. The Ti-55531 titanium alloy obtained by the preparation method has high toughness and high plasticity.

[0005] The technical scheme of the present application is as follows:

[0006] A Ti-55531 titanium alloy with high toughness and plasticity, the lamellar structure of the titanium alloy has a multi-level structure, the multi-level structure includes original beta grains, alpha beam sets, lamellar alpha, nanotwin structures and discontinuous grain boundary alpha.

[0007] Further, the alpha beam set is contained in the original beta grain, the lamellar alpha is contained in the alpha beam set, the nanotwin structure is contained in the lamellar alpha, and the discontinuous grain boundary alpha is distributed on the beta grain boundary.

[0008] Further, the grain size of the original beta grain is 180-310 mu m; the size of the alpha bundle set is 15-40 mu m; the thickness of the lamellar alpha is 200-580 nm; and the thickness of the nano-twin structure is 15-30 nm.

[0009] The preparation method of the Ti-55531 titanium alloy with high toughness and plasticity comprises the following steps:

[0010] (1) placing the Ti-55531 titanium alloy into a muffle furnace or a resistance box-type heating furnace, and heating the Ti-55531 titanium alloy to 880-910 DEG C at the same speed as the furnace, and keeping the temperature for 1-2 hours;

[0011] (2) transferring the Ti-55531 titanium alloy treated in the step (1) to a heating furnace with a furnace temperature of 660-680 DEG C, keeping the temperature for 10-15 hours, and then air-cooling the Ti-55531 titanium alloy to room temperature, so that the Ti-55531 titanium alloy with high toughness and plasticity is obtained.

[0012] Compared with the prior art, the present application has the following beneficial effects:

[0013] 1. The present application can obtain a multi-level structure of the Ti-55531 titanium alloy composed of original beta grains, alpha bundle sets, lamellar alpha, nano-twin structures and discontinuous grain boundary alpha by sequentially performing beta phase zone and alpha+beta phase zone heat treatment on the Ti-55531 titanium alloy, which is beneficial to improving the average free distance of dislocation slip, thereby improving the plasticity of the titanium alloy; the introduction of the discontinuous grain boundary alpha can effectively reduce the intergranular fracture of the titanium alloy and improve the plasticity of the titanium alloy; and the introduction of the nano-twin structure can further improve the plasticity of the titanium alloy.

[0014] In addition, the large size of the alpha bundle set is beneficial to prolonging the crack propagation path and improving the energy consumption required for crack propagation, thereby improving the toughness; meanwhile, the large size of the alpha bundle set can reduce the micropore nucleation points, so that the cutting of a large number of lamellar alpha in the crack propagation process can also improve the toughness; when the crack propagates along the grain boundary, the formation of the discontinuous grain boundary alpha can cause the deflection of the crack, thereby improving the toughness; and the introduction of the nano-twin structure can relieve the stress concentration at the alpha / beta interface, thereby delaying the nucleation of micropores and improving the toughness. Therefore, the alpha bundle set, the lamellar alpha, the nano-twin structure and the discontinuous grain boundary alpha are beneficial to improving the toughness of the titanium alloy.

[0015] Therefore, the titanium alloy with the multi-level structure composed of the original beta grain, the alpha bundle set, the lamellar alpha, the nano-twin structure and the discontinuous grain boundary alpha has good high toughness and high plasticity.

[0016] 2. The titanium alloy with the lamellar structure prepared by the present application has a tensile strength of 1150 MPa or more, an elongation of 14% or more, and a fracture toughness (KⅠC) of 70 MPa·m1 / 2 The above describes the heat treatment process of this invention, which is simple, easier to operate and control, and suitable for industrial production. Attached Figure Description

[0017] Figure 1 - Process flow diagram of the present invention.

[0018] Figure 2 - Microstructure of Ti-55531 titanium alloy with original dual-state structure.

[0019] Figure 3 - Microstructure of the high-toughness and plasticity Ti-55531 titanium alloy obtained in Example 1.

[0020] Figure 4 - Microstructure of Ti-55531 titanium alloy obtained in Comparative Example 1.

[0021] Figure 5 - Transmission electron microscopy image of Ti-55531 titanium alloy obtained in Comparative Example 2.

[0022] Figure 6 -Statistical results of the mechanical properties of Ti-55531 titanium alloys obtained in Example 1, Comparative Example 1 and Comparative Example 2.

[0023] Figure 7 - Scanning electron microscope images of tensile fracture specimens of Ti-55531 titanium alloy obtained in Example 1 and Comparative Example 1. Detailed Implementation

[0024] A method for preparing a Ti-55531 titanium alloy with high toughness and plasticity, the process flow diagram of which is shown below. Figure 1 As shown, the specific steps include:

[0025] (1) Heat treatment of the β phase region: The original biphase structure of Ti-55531 titanium alloy is placed in a muffle furnace or resistance box furnace and heated to 880℃~910℃ with the furnace and held for 1h~2h.

[0026] (2) Heat treatment of α+β phase region: The Ti-55531 titanium alloy treated in step (1) is quickly transferred to a heating furnace with a furnace temperature of 660℃~680℃ and held for 10h~15h. Then it is air-cooled to room temperature to obtain the Ti-55531 titanium alloy with high toughness and plasticity.

[0027] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments.

[0028] Example 1

[0029] (1) The original biphase-structured Ti-55531 titanium alloy was put into a muffle furnace or a resistance box furnace and heated to 900℃ at a furnace temperature, and held for 1 h;

[0030] (2) The Ti-55531 titanium alloy treated in step (1) was quickly transferred to a heating furnace with a furnace temperature of 670℃, and held for 15 h, and then air-cooled to room temperature, to obtain a Ti-55531 titanium alloy with high toughness and plasticity.

[0031] Example 2

[0032] (1) The original biphase-structured Ti-55531 titanium alloy was put into a muffle furnace or a resistance box furnace and heated to 880℃ at a furnace temperature, and held for 1 h;

[0033] (2) The Ti-55531 titanium alloy treated in step (1) was quickly transferred to a heating furnace with a furnace temperature of 660℃, and held for 10 h, and then air-cooled to room temperature, to obtain a Ti-55531 titanium alloy with high toughness and plasticity.

[0034] Example 3

[0035] (1) The original biphase-structured Ti-55531 titanium alloy was put into a muffle furnace or a resistance box furnace and heated to 890℃ at a furnace temperature, and held for 1 h;

[0036] (2) The Ti-55531 titanium alloy treated in step (1) was quickly transferred to a heating furnace with a furnace temperature of 680℃, and held for 12 h, and then air-cooled to room temperature, to obtain a Ti-55531 titanium alloy with high toughness and plasticity.

[0037] Comparative Example 1

[0038] (1) The original biphase-structured Ti-55531 titanium alloy was put into a muffle furnace or a resistance box furnace and heated to 900℃ at a furnace temperature, and held for 1 h;

[0039] (2) The Ti-55531 titanium alloy treated in step (1) was quickly transferred to a heating furnace with a furnace temperature of 590℃, and held for 15 h, and then air-cooled to room temperature, to obtain a Ti-55531 titanium alloy after heat treatment.

[0040] Comparative Example 2

[0041] (1) The original biphase-structured Ti-55531 titanium alloy was put into a muffle furnace or a resistance box furnace and heated to 900℃ at a furnace temperature, and held for 1 h;

[0042] (2) The Ti-55531 titanium alloy treated in step (1) was quenched to room temperature, and then held in a heating furnace with a furnace temperature of 670℃ for 15 h, and then air-cooled to room temperature, to obtain a Ti-55531 titanium alloy after heat treatment.

[0043] 1、The microstructure morphology diagram of the original duplex structure Ti-55531 titanium alloy adopted by the present application is shown in Figure 2 As can be seen from the diagram, the original duplex structure Ti-55531 titanium alloy is composed of equiaxed α phase and β transformed matrix, and a large number of equiaxed α phases are uniformly distributed in the β transformed matrix, and part of the grain boundary α phase is clearly visible.

[0044] 2、The titanium alloy organizations obtained after the titanium alloys of Example 1 and Comparative Example 1 are heat treated in the β phase region and the α+β phase region are mechanically ground, electrolytically polished and ion thinned, and then observed under an electron microscope to obtain microstructure morphology diagrams as shown in Figure 3 and Figure 4 .

[0045] As can be seen from Figure 3 (a), the titanium alloy obtained in Example 1 has a multi-level structure in the lamellar structure, which is composed of original β grains, α bundle sets, lamellar α, nanotwin structures and discontinuous grain boundary α. As can be seen from the diagram, the average diameter of the α bundle set is 23 μm, and the average length is 47 μm, and the average thickness of the lamellar α is 430 nm. As can be seen from Figure 3 (b), the nanotwin structure has a low dislocation density, and the thickness of the nanotwin structure is about 20 nm.

[0046] As can be seen from Figure 4 (a), the α bundle set in the titanium alloy organization obtained in Comparative Example 1 tends to disappear, and is replaced by lamellar α with uniform distribution. At the same time, the lamellar α is obviously refined, with an average length of 45 μm and an average thickness of 95 nm, and the grain boundary α presents a continuous straight morphology. As can be seen from Figure 4 (b), no nanotwin structure is found in the lamellar α of Comparative Example 1.

[0047] 3、The titanium alloy organization obtained after Comparative Example 2 is heat treated in the β phase region and the α+β phase region is observed under a transmission electron microscope to obtain a transmission electron microscope diagram as shown in Figure 5 As can be seen from the diagram, the α phase in Comparative Example 2 presents a short rod-like morphology, and no nanotwin structure appears in the α phase.

[0048] 4、The Ti-55531 titanium alloys obtained in Example 1-3 and Comparative Examples 1-2 are subjected to mechanical property testing, and the mechanical property parameters are shown in Table 1, wherein the statistical results of the mechanical properties of the Ti-55531 titanium alloys obtained in Example 1, Comparative Example 1 and Comparative Example 2 are shown in Figure 6 As can be seen from Figure 6 (a1), the plasticity of the titanium alloy of Example 1 after heat treatment is 17.2%, and the tensile strength is maintained at about 1150 MPa, while the plasticity of the titanium alloy of Comparative Example 1 is only 2.5%, and as can be seen from Figure 6(a2) It can be seen that the plasticity of the titanium alloy of Comparative Example 2 after heat treatment is only 2.3%. Figure 6 (b1) and Figure 6 (b2) It can be seen that the fracture toughness (KIC) of the titanium alloy of Example 1, Comparative Example 1 and Comparative Example 2 after heat treatment is 72.5 MPa·m 1 / 2 , 47.6 MPa·m 1 / 2 , 41.2 MPa·m 1 / 2 .

[0049] Table 1. Mechanical property parameters of Example 1-3 and Comparative Examples 1-2

[0050] Example Tensile strength (MPa) Elongation (%) [ KIC (MPa-m½) 1 / 2 )]]> Example 1 1180 17.2 72.5 Example 2 1166 14.7 71.2 Example 3 1172 15.4 72.2 Comparative Example 1 1360 2.5 47.6 Comparative Example 2 1245 2.3 41.2

[0051] It can be seen from Table 1 that the titanium alloy after heat treatment of the present application has good plasticity, high fracture toughness and tensile strength maintained above 1150 MPa. Compared with the titanium alloy materials prepared in Comparative Example 1 and Comparative Example 2, the comprehensive mechanical properties are obviously improved. This may be due to the (1) fast transfer of the titanium alloy in the present application and (2) high heat treatment temperature in the second step, which inhibits the formation of continuous flat grain boundary α phase and promotes the growth of α bundle and lamellar α, while the formation of nanotwin phase helps to relieve local stress concentration, thereby inhibiting the proportion of intergranular fracture and increasing the average free path of dislocation; while in Comparative Example 1, the lower heat treatment temperature in the second step promotes the formation of continuous flat grain boundary α phase and inhibits the growth of α bundle and lamellar α, thereby promoting the proportion of intergranular fracture and reducing the average free path of dislocation, resulting in deterioration of plasticity and reduction of toughness; and in Comparative Example 2, quenching is carried out in the second step (2), so that the α phase of the obtained titanium alloy material presents short rod shape, and the nanotwin structure in the α phase is missing, so that the stress concentration at the α / β interface cannot be relieved, causing the premature nucleation of micro pores and reducing the plasticity of the material. It can be seen that the plasticity and fracture toughness of the titanium alloy after heat treatment of the present application are both improved on the basis of ensuring strength.

[0052] 5. Scanning electron microscope observation was carried out on the tensile fracture specimen of the Ti-55531 titanium alloy obtained in Example 1 and Comparative Example 1, and the obtained scanning electron microscope image is shown in Figure 7 It can be seen from the figure that there is a great difference in the deformation degree of the structure near the crack, the deformation structure region involved near the crack in Example 1 is larger, about 35 μm or so, while the deformation structure region involved near the crack in Comparative Example 1 is very small, about 5 μm or so, and a small amount of holes were also found at the intersection of different morphology lamellar α, with a diameter of about 2 μm or so. This indicates that the macroscopic deformation coordination ability and the ability to resist crack initiation and propagation of the structure of Example 1 under external load are stronger, further indicating that the titanium alloy after heat treatment of the present application has good plasticity and toughness.

[0053] Finally, it should be noted that the above-described embodiments of the present application are merely given as an example of the application but are not a limitation of the present application. It will be obvious to a person skilled in the art that, based on the above description of the embodiments, other changes in the form and details can be made to the application. Here, it is not possible to describe all of the embodiments of the application. Any changes or modifications of the present application that are obvious to a person skilled in the art are still within the scope of the present application.

Claims

1. A method of producing a Ti-55531 titanium alloy having high ductility, characterized in that, Specifically comprising the following steps: (1) placing Ti-55531 titanium alloy into a muffle furnace or a resistance box furnace, and heating to 880-910 DEG C with the furnace, and holding for 1-2 h; (2) quickly transferring the Ti-55531 titanium alloy treated in step (1) into a heating furnace with a furnace temperature of 660-680 DEG C, holding for 10-15 h, and then air cooling to room temperature, to obtain the Ti-55531 titanium alloy with high toughness and plasticity.

2. A Ti-55531 titanium alloy having high ductility, characterized in that, The titanium alloy is prepared by the method of claim 1, and the titanium alloy has a multi-level structure in the lamellar structure, wherein the multi-level structure comprises original β grains, α bundle sets, lamellar α, nanometer twin structures and discontinuous grain boundary α.

3. The Ti-55531 titanium alloy with high ductility of claim 2, wherein, The α bundle sets are contained in the original β grains, the lamellar α is contained in the α bundle sets, the nanometer twin structures are contained in the lamellar α, and the discontinuous grain boundary α is distributed on the β grain boundaries.

4. The Ti-55531 titanium alloy with high ductility of claim 3, wherein, The grain size of the original β grains is 180-310 μm, the size of the α bundle sets is 15-40 μm, the thickness of the lamellar α is 200-580 nm, and the thickness of the nanometer twin structures is 15-30 nm.

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