Biequiaxed titanium alloy and preparation method thereof

Abstract

The invention discloses a biequiaxed titanium alloy and a preparation method thereof, relates to the technical field of titanium alloy preparation, and aims to solve the technical problem of poor fatigue resistance of existing titanium alloys manufactured by additive manufacturing. The preparation method of the biequiaxed titanium alloy comprises the following steps that a first titanium alloy workpiece prepared through a laser directional deposition process is obtained; and after hot isostatic pressing treatment is conducted on the first titanium alloy workpiece, the first titanium alloy workpiece is cooled to 500 DEG C or below, heat treatment is conducted at the temperature of 580-1050 DEG C, and a second titanium alloy workpiece is obtained.

Description

Technical Field

[0001] The present application relates to the technical field of titanium alloy preparation, and particularly relates to a double equiaxed titanium alloy and a preparation method thereof. Background Art

[0002] The microstructure of laser additive manufactured titanium alloy has the characteristic of epitaxial growth, and it is easy to form columnar grains that penetrate multiple deposition layers, showing the characteristics of directional solidification. The initial β grains grow into slender columnar grains along the vertical direction, and a large amount of basket weave structure or coarse Widmanstätten structure often forms inside the columnar grains. A continuous grain boundary α phase is formed at the columnar grain boundary, and even lamellar α phases with consistent orientations are formed on the grain boundary α phase.

[0003] And these microstructure characteristics are extremely likely to cause the reduction of the fatigue resistance of the manufactured titanium alloy, thus limiting its application. Therefore, researching a heat treatment method for equiaxing the lamellar α phase in additive manufactured titanium alloy and titanium matrix composites is an urgent problem to be solved at present. Summary of the Invention

[0004] The main purpose of the present application is to provide a method for regulating equiaxed crystal heat treatment of titanium alloy, aiming to solve the technical problem of poor fatigue resistance of existing additive manufactured titanium alloy.

[0005] To solve the above technical problem, the present application proposes: A preparation method of a double equiaxed titanium alloy, comprising the following steps:

[0006] Obtain a first titanium alloy workpiece prepared by a laser directed energy deposition process;

[0007] After hot isostatic pressing treatment on the first titanium alloy workpiece, cool it to below 500 °C, and perform heat treatment at 580 °C to 1050 °C to obtain a second titanium alloy workpiece.

[0008] As some optional embodiments of the present application, the heat treatment includes the following steps:

[0009] After hot isostatic pressing treatment on the first titanium alloy workpiece, cool it to below 500 °C, and perform a first heat preservation treatment at a first preset temperature T 1 ; After the first heat preservation treatment is completed, cool the second titanium alloy workpiece to room temperature, and perform a second heat preservation treatment at a second preset temperature T 2 ; After the second heat preservation treatment is completed, cool the second titanium alloy workpiece to room temperature, and perform a third heat preservation treatment at a third preset temperature T 3 , and cool it to room temperature to obtain a third titanium alloy workpiece.

[0010] As some optional embodiments of the present application, the first preset temperature T 1is 980°C to 1050°C, and the first heat preservation treatment time is 0.5h to 2h.

[0011] As some alternative embodiments of the present application, the second preset temperature T 1 is 920°C to 980°C, and the second heat preservation treatment time is 1h to 4h.

[0012] As some alternative embodiments of the present application, the third preset temperature T 1 is 580°C to 750°C, and the third heat preservation treatment time is 2h to 6h.

[0013] As some alternative embodiments of the present application, the treatment temperature of the hot isostatic pressing treatment is 900°C to 980°C, the treatment pressure is 120MPa to 160MPa, the treatment atmosphere is argon, and the treatment time is 2 to 4 hours.

[0014] As some alternative embodiments of the present application, the average particle size of the powder used in the laser direct deposition process is 53μm to 150μm.

[0015] As some alternative embodiments of the present application, the cooling treatment method is: adopting at least one of furnace cooling and air cooling.

[0016] As some alternative embodiments of the present application, the cooling treatment method is: cooling to below 600°C by furnace cooling, and then cooling to room temperature by air cooling.

[0017] To solve the above technical problems, the embodiments of the present application also provide: a double equiaxed titanium alloy, obtained by the method described above; the microstructure of the titanium alloy is double equiaxed, that is, the original β grains are equiaxed and the α phases inside the β grains are equiaxed.

[0018] The microstructure of the titanium alloy prepared by laser additive manufacturing has the characteristic of epitaxial growth, and it is easy to form columnar grains that penetrate multiple deposition layers, showing the characteristics of directional solidification. The initial β grains grow into slender columnar grains along the vertical direction, and a large amount of basket-weave structure or coarse Widmanstätten structure often forms inside the columnar grains. A continuous grain boundary α phase is formed at the columnar grain boundaries, and even lamellar α phases with consistent orientations are formed on the grain boundary α phase. These microstructure characteristics result in the fatigue performance of the manufactured titanium alloy workpieces being often lower than that of the workpieces, bringing great challenges to the large-scale application of titanium alloy workpieces in critical fatigue parts. In the prior art, both the titanium matrix composite material and TC18 titanium alloy prepared by cyclic heat treatment have achieved the equiaxed transformation of β columnar grains, but the α phase inside the network still presents a lamellar shape. The resistance of these lamellar α phases with consistent orientations to hinder the propagation of fatigue cracks is relatively low, which is harmful to the fatigue strength. Therefore, in the preparation method of the double equiaxed titanium alloy described in this application, the first titanium alloy workpiece prepared by the laser direct deposition process is subjected to hot isostatic pressing treatment to eliminate defects such as microcracks and pores inside the first titanium alloy workpiece. After the hot isostatic pressing treatment of the first titanium alloy workpiece, it is cooled to below 500 °C and heat-treated at 580 °C to 1050 °C to obtain the second titanium alloy workpiece. The microstructure of the second titanium alloy workpiece prepared by the method described in this application is double equiaxed, that is, the original β grains are equiaxed and the α phase inside the β grains is equiaxed, thereby improving the tensile strength and fatigue resistance of the titanium alloy workpiece. Description of the Drawings

[0019] Figure 1 is the microstructure diagram of the double equiaxed titanium alloy workpiece described in the embodiment of this application;

[0020] Figure 2 is the microstructure diagram of the titanium alloy workpiece described in the comparative example of this application. Detailed Embodiments

[0021] It should be understood that the specific embodiments described herein are only used to explain this application and are not used to limit this application.

[0022] The microstructure of the titanium alloy prepared by laser additive manufacturing has the characteristic of epitaxial growth, and it is easy to form columnar grains that penetrate multiple deposition layers, showing the characteristics of directional solidification. The initial β grains grow into slender columnar grains along the vertical direction, and a large amount of basket weave structure or coarse Widmanstätten structure often forms inside the columnar grains. A continuous grain boundary α phase is formed at the columnar grain boundary, and even lamellar α phases with consistent orientations are formed on the grain boundary α phase. These microstructure characteristics lead to the fatigue performance of the manufactured titanium alloy workpieces being often lower than that of the workpieces, which brings great challenges to the large-scale application of titanium alloy workpieces in critical fatigue parts. The titanium matrix composites and TC18 titanium alloys prepared by cyclic heat treatment in the prior art have achieved the equiaxed transformation of β columnar grains, but the α phase inside the network still presents a lamellar shape. The resistance of these lamellar α phases with consistent orientations to hinder the propagation of fatigue cracks is relatively low, which is harmful to the fatigue strength. Therefore, in the preparation method of the double equiaxed titanium alloy described in this application, the first titanium alloy workpiece prepared by the laser direct deposition process is subjected to hot isostatic pressing treatment under the conditions of 900°C to 980°C and 120 MPa to 160 MPa, aiming to eliminate defects such as microcracks and pores inside the first titanium alloy workpiece. The first titanium alloy workpiece after hot isostatic pressing treatment is cooled to below 500°C and then subjected to heat treatment to obtain a second titanium alloy workpiece. The microstructure of the second titanium alloy workpiece prepared by the method described in this application is double equiaxed, that is, the original β grains are equiaxed and the α phase inside the β grains is equiaxed, thereby improving the tensile strength and fatigue strength of the titanium alloy workpiece.

[0023] Based on this, an embodiment of this application provides a double equiaxed titanium alloy and a preparation method thereof. Among them, the preparation method of the double equiaxed titanium alloy includes the following steps:

[0024] Step S10, obtain a first titanium alloy workpiece prepared by the laser direct deposition process.

[0025] In specific applications, the laser directed energy deposition process and its process selection are all prior arts, so no specific elaboration will be made here in this application. In actual applications, the powder used in the laser directed energy deposition process of this application is obtained by mixing an additive with a titanium alloy powder or by methods such as gas atomization, and the average particle size is 53 μm to 150 μm. After the laser directed energy deposition process is completed, the first titanium alloy workpiece is removed from the substrate by wire cutting for subsequent steps. Moreover, the titanium alloy microstructure manufactured by laser directed energy deposition has the characteristic of epitaxial growth, and it is easy to form columnar grains that penetrate multiple deposition layers, showing the characteristics of directional solidification. The initial β grains grow into slender columnar grains along the vertical direction, and a large amount of basket weave structure or coarse Widmanstätten structure often forms inside the columnar grains. A continuous grain boundary α phase is formed at the columnar grain boundaries, and even a lamellar α phase with consistent orientation is formed on the grain boundary α phase. These microstructure characteristics result in the fatigue performance of the manufactured titanium alloy workpiece being often lower than that of the workpiece, bringing great challenges to the large-scale application of titanium alloy workpieces in critical fatigue parts. Therefore, after the first titanium alloy workpiece is prepared by the existing laser directed energy deposition technology, the embodiment of this application conducts equiaxed crystal heat treatment regulation on it, that is, step S20.

[0026] Step S20: After hot isostatic pressing the first titanium alloy workpiece, cool it below 500 °C and conduct heat treatment at 580 °C to 1050 °C to obtain a second titanium alloy workpiece.

[0027] In specific applications, the treatment temperature of the hot isostatic pressing is 900 °C to 980 °C, the treatment pressure is 120 MPa to 160 MPa, the treatment atmosphere is argon, and the treatment time is 2 to 4 hours. The hot isostatic pressing aims to eliminate the defects inside the titanium matrix composites of additive manufacturing matrices such as TC11, TA15, and Ti60. Because the formability of these matrices is poor, and due to the introduction of difficult-to-deform ceramic particles, microcracks and pores are prone to appear inside during the laser direct deposition of titanium matrix composites. Thereby improving the anti-fatigue performance of the titanium alloy workpiece.

[0028] Among them, the heat treatment includes the following steps:

[0029] After hot isostatic pressing the first titanium alloy workpiece, cool it below 500 °C and conduct the first heat preservation treatment at the first preset temperature T 1 ; after the first heat preservation treatment is completed, cool the second titanium alloy workpiece to room temperature and conduct the second heat preservation treatment at the second preset temperature T 2 ; after the second heat preservation treatment is completed, cool the second titanium alloy workpiece to room temperature and conduct the third heat preservation treatment at the third preset temperature T 3 ; cool it to room temperature to obtain a third titanium alloy workpiece.

[0030] In specific applications, the first preset temperature T 1 is 980°C to 1050°C, and the first heat preservation treatment time is 0.5 h to 2 h. In actual applications, the above-mentioned first heat preservation treatment is carried out in a high-temperature air resistance furnace. Since the heat treatment temperature of the titanium matrix composite material is relatively high and the microstructure includes a reinforcement-rich region and a reinforcement-poor region, in order to prevent the rapid cooling in the reinforcement-poor region from forming a martensite phase during the heat treatment cooling process, it should be avoided to cool by water cooling or oil cooling, but air cooling or furnace cooling should be selected as much as possible. And there will be a period of time when the temperature in the furnace is unstable after the first titanium alloy workpiece is put into the high-temperature air resistance furnace. Therefore, the calculation of the first heat preservation treatment time should start after the temperature in the furnace is stable. If elements B and C are introduced into the titanium alloy powder used during laser direct deposition, ceramic phases such as TiB and TiC will be in-situ generated. Therefore, the phase transformation point of the titanium alloy workpiece material will increase by 20°C to 50°C, that is, the first preset temperature will be increased by 20°C to 50°C on the basis of the above temperature range value.

[0031] In specific applications, the second preset temperature T 1 is 920°C to 980°C, and the second heat preservation treatment time is 1 h to 4 h. In actual applications, the above-mentioned first heat preservation treatment is carried out in a high-temperature air resistance furnace. Since the heat treatment temperature of the titanium matrix composite material is relatively high and the microstructure includes a reinforcement-rich region and a reinforcement-poor region, in order to prevent the rapid cooling in the reinforcement-poor region from forming a martensite phase during the heat treatment cooling process, it should be avoided to cool by water cooling or oil cooling, but air cooling or furnace cooling should be selected as much as possible. And there will be a period of time when the temperature in the furnace is unstable after the first titanium alloy workpiece is put into the high-temperature air resistance furnace. Therefore, the calculation of the first heat preservation treatment time should start after the temperature in the furnace is stable.

[0032] In specific applications, the third preset temperature T 1 is 580°C to 750°C, and the third heat preservation treatment time is 2 h to 6 h. In actual applications, the above-mentioned first heat preservation treatment is carried out in a high-temperature air resistance furnace. Since the heat treatment temperature of the titanium matrix composite material is relatively high and the microstructure includes a reinforcement-rich region and a reinforcement-poor region, in order to prevent the rapid cooling in the reinforcement-poor region from forming a martensite phase during the heat treatment cooling process, it should be avoided to cool by water cooling or oil cooling, but air cooling or furnace cooling should be selected as much as possible. And there will be a period of time when the temperature in the furnace is unstable after the first titanium alloy workpiece is put into the high-temperature air resistance furnace. Therefore, the calculation of the first heat preservation treatment time should start after the temperature in the furnace is stable.

[0033] In a specific application, the cooling treatment method is as follows: furnace cooling to below 600 °C and then air cooling to room temperature.

[0034] Meanwhile, the embodiment of the present application also provides a double equiaxed titanium alloy, which is prepared by the method described above; the microstructure of the titanium alloy is double equiaxed, that is, the original β grains are equiaxed and the α phases inside the β grains are equiaxed.

[0035] The following combines specific embodiments to detail the double equiaxed titanium alloy and its preparation method of the present application:

[0036] Example 1

[0037] The titanium alloy workpiece in this example is a (TiB + TiC) / TC11 composite material. The preparation method includes the following steps:

[0038] Prepare a titanium alloy block by laser direct deposition and remove the titanium alloy block from the substrate by wire cutting.

[0039] Put the titanium alloy block into a hot isostatic pressing furnace for hot isostatic pressing treatment, where the treatment temperature of the hot isostatic pressing treatment is 920 °C, the treatment pressure is 150 MPa, and the treatment time is 2 hours, and then take it out after furnace cooling to 500 °C to eliminate internal microcracks and pores and other defects.

[0040] After raising the temperature in the high-temperature air resistance furnace to 1000 °C, put the titanium alloy workpiece into the furnace for the first heat preservation treatment; start timing after the temperature in the high-temperature air resistance furnace rises back to 1000 °C, stop heat preservation after 2 hours, cool to room temperature, and reserve for use.

[0041] After raising the temperature in the high-temperature air resistance furnace to 920 °C, put the titanium alloy workpiece into the furnace for the second heat preservation treatment; start timing after the temperature in the high-temperature air resistance furnace rises back to 920 °C, stop heat preservation after 1 hour, cool to room temperature, and reserve for use.

[0042] After raising the temperature in the high-temperature air resistance furnace to 600 °C, put the titanium alloy workpiece into the furnace for the third heat preservation treatment; start timing after the temperature in the high-temperature air resistance furnace rises back to 600 °C, stop heat preservation after 4 hours, cool to room temperature, and obtain a titanium alloy workpiece with a double equiaxed microstructure.

[0043] Comparative Example 1

[0044] The titanium alloy workpiece in this comparative example is a (TiB + TiC) / TC11 composite material. The preparation method includes the following steps:

[0045] Prepare a titanium alloy block by laser direct deposition and remove the titanium alloy block from the substrate by wire cutting.

[0046] Put the titanium alloy block into a hot isostatic pressing furnace for hot isostatic pressing treatment, where the treatment temperature of the hot isostatic pressing treatment is 950 °C, the treatment pressure is 150 MPa, and the treatment time is 4 hours. Then, take it out after cooling in the furnace to 500 °C to obtain a titanium alloy workpiece.

[0047] Experimental Example 1

[0048] Perform microstructure observation and mechanical property testing on the titanium alloy workpiece obtained in the above Example 1 and the titanium alloy workpiece obtained in Comparative Example 1. Among them, the microtopography of the titanium alloy workpiece obtained in Example 1 is as Figure 1 shown, and the microtopography of the titanium alloy workpiece obtained in Comparative Example 1 is as Figure 2 shown. The comparison table of the mechanical properties and room temperature tensile properties (the test standard is GB / T 228.1 Metallic materials - Tensile testing - Part 1: Method of test at room temperature) of the titanium alloy workpiece obtained in Example 1 and the titanium alloy workpiece obtained in Comparative Example 1 is shown in Table 1:

[0049] Table 1:

[0050] Comparative Example 1 Example 1 Yield strength (MPa) 1321 1250 Tensile strength (MPa) 1367 1335

[0051] It can be seen that in the microstructure of the titanium alloy workpiece prepared in Comparative Example 1, although the coarse columnar β grains have been equiaxed, the internal α phase still presents a long lamellar morphology; while in the microstructure of the titanium alloy workpiece prepared in the present application, the α phase inside the β grains presents an equiaxed shape with a relatively small aspect ratio, that is, the original β grains are equiaxed and the α phase inside the β grains is equiaxed. Moreover, compared with Comparative Example 1, the yield strength and tensile strength of the titanium alloy workpiece prepared in the present application have been significantly improved.

[0052] The above are only the preferred embodiments of the present application, and do not limit the patent scope of the present application. Any equivalent structure or equivalent process transformation made by using the content of the specification and drawings of the present application, or directly or indirectly applied in other related technical fields, shall be included in the patent protection scope of the present application by the same token.

Claims

1. A method for preparing a bi-equiaxed titanium alloy, characterized in that: The following steps are involved: Obtaining a first titanium alloy workpiece prepared by a laser directional deposition process; After the first titanium alloy workpiece is subjected to hot isostatic pressing, it is cooled to below 500° C. and heat treated at 580° C. to 1050° C. to obtain a second titanium alloy workpiece.

2. The method for preparing a dual equiaxed titanium alloy according to claim 1, characterized in that: The heat treatment comprises the following steps: After the first titanium alloy workpiece is subjected to hot isostatic pressing treatment, it is cooled to below 500°C and then subjected to a first insulation treatment at a first preset temperature T1; after the first insulation treatment is completed, the second titanium alloy workpiece is cooled to room temperature, and then subjected to a second insulation treatment at a second preset temperature T2; after the second insulation treatment is completed, the second titanium alloy workpiece is cooled to room temperature, and then subjected to a third insulation treatment at a third preset temperature T3, and then cooled to room temperature to obtain a third titanium alloy workpiece.

3. The method for preparing a bi-equiaxed titanium alloy according to claim 2, characterized in that: The first preset temperature T1 is 980° C. to 1050° C., and the first heat preservation treatment time is 0.5 h to 2 h.

4. The method for preparing a dual equiaxed titanium alloy according to claim 2, characterized in that: The second preset temperature T1 is 920° C. to 980° C., and the second heat preservation treatment time is 1 hour to 4 hours.

5. The method for preparing a bi-equiaxed titanium alloy according to claim 2, characterized in that: The third preset temperature T1 is 580° C. to 750° C., and the third heat preservation treatment time is 2 h to 6 h.

6. The method for preparing a dual equiaxed titanium alloy according to claim 1, characterized in that: The processing temperature of the hot isostatic pressing treatment is 900° C. to 980° C., the processing pressure is 120 MPa to 160 MPa, the processing atmosphere is argon gas, and the processing time is 2 to 4 hours.

7. The method for preparing a bi-equiaxed titanium alloy according to claim 1, characterized in that: The average particle size of the powder used in the laser directional deposition process is 53 μm to 150 μm.

8. The method for preparing a bi-equiaxed titanium alloy according to claim 3, characterized in that: The cooling treatment method is: at least one of furnace cooling and air cooling.

9. The method for preparing a bi-equiaxed titanium alloy according to claim 8, characterized in that: The cooling treatment method is: cooling to below 600° C. by furnace, and then cooling to room temperature by air.

10. A dual equiaxed titanium alloy, characterized in that: The titanium alloy is prepared by the method according to any one of claims 1 to 9; the microstructure of the titanium alloy is bi-equiaxed, that is, the original β grains are equiaxed and the α phase inside the β grains are equiaxed.

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