A method for obtaining a large number of equiaxed crystals in a 3D printed titanium alloy by multistage cycle heat treatment and application thereof

Abstract

The application provides a method for obtaining a large number of equiaxed crystals of a 3D printed titanium alloy through multistage cycle heat treatment, which adopts a step cycle heat treatment method in three temperature intervals, and the multiple step temperature rising and falling is more conducive to the spheroidization of alpha grains, so that a higher proportion of equiaxed grains is obtained. In the method, the parameters can be adjusted in a wide range, not only a large number of equiaxed crystal structures are obtained, but also the required mechanical properties can be obtained by arbitrarily changing the heat treatment temperature of each stage and the final cooling starting temperature. The titanium alloy material obtained by the method provided by the application has an equiaxed crystal proportion greater than 20%, and more preferably 27.6% to 36.8%, and can significantly improve the comprehensive mechanical properties of the titanium alloy material, and the prepared titanium alloy material has the advantages of high tensile strength, high yield strength, good ductility and the like. The application has the advantages of reasonable design, simple method steps, easy operation, continuous production and wide application prospect.

Description

Technical Field

[0001] This invention belongs to the field of titanium alloy additive manufacturing technology, specifically relating to a method for obtaining a large number of equiaxed crystals in a 3D-printed titanium alloy through multi-stage cyclic heat treatment, and also relating to the application of a method for obtaining a large number of equiaxed crystals in a 3D-printed titanium alloy through multi-stage cyclic heat treatment. Background Technology

[0002] Selective laser melting (SLM) is an additive manufacturing technology that uses a high-energy laser beam to selectively melt metal powder layer by layer based on three-dimensional model data, directly obtaining parts with arbitrary shapes. This technology boasts advantages such as high precision, fast forming speed, and a wide range of printable materials, and can be customized to meet different user needs. After printing, the unmelted metal powder can be reused, significantly reducing production costs. Titanium alloys are widely used in aerospace, biomedicine, shipbuilding, and defense fields due to their high specific strength, good biocompatibility, strong corrosion resistance, low elastic modulus, and excellent fatigue performance. However, traditional methods for producing titanium alloys suffer from numerous limitations, including processing difficulties, low material utilization, long production cycles, and high production costs. Therefore, the use of SLM, a "near-net-shape" process, has gained increasing attention in recent years. Because the SLM process has an extremely fast cooling rate (10⁻⁶),... 4 -10 6 In the formed sample (K / s), columnar crystals growing along the deposition direction and acicular martensite inside them usually appear, resulting in high strength and low elongation of the material, which cannot meet the requirements of industrial applications.

[0003] Numerous experiments have shown that obtaining a certain proportion of equiaxed grains in the microstructure can significantly improve the overall mechanical properties of materials. Plastic deformation combined with annealing is the most common method for spheroidizing the microstructure, but this is not suitable for near-net-shape forming (SLM) technology. Therefore, heat treatment becomes the only effective post-processing method. Currently, the most common heat treatment method for SLM-formed titanium alloys is single annealing, which involves holding the sample at a certain temperature for a period of time, followed by air cooling or furnace cooling to room temperature. Although this method can obtain a certain proportion of equiaxed grains in the sample, the quantity is relatively small and cannot significantly improve the elongation of the material.

[0004] Generally, only when the upper limit of equiaxed grains obtained by the heat treatment process exceeds the required proportion of equiaxed grains can any proportion of equiaxed grains below that upper limit be obtained. Correspondingly, a higher proportion of equiaxed grains indicates a wider range of control over mechanical properties, and thus a wider range of applicable application environments. Based on this, when higher strength is required for titanium alloy materials, the proportion of equiaxed grains can be appropriately reduced; conversely, when higher plasticity is required, the proportion of equiaxed grains can be increased, thereby achieving flexible control over the mechanical properties of titanium alloy materials.

[0005] Based on this, a heat treatment method for 3D printed titanium alloys that can obtain a large number of equiaxed crystals is provided, which is of great significance for improving the mechanical properties of alloy materials and is also a technical problem that urgently needs to be solved. Summary of the Invention

[0006] One of the objectives of this invention is to provide a method for obtaining a large number of equiaxed crystals through multi-stage cyclic heat treatment of 3D printed titanium alloys.

[0007] The second objective of this invention is to provide a 3D-printed titanium alloy with a large number of equiaxed crystals and excellent mechanical properties.

[0008] One of the technical solutions adopted by this invention to achieve its objective is to provide a method for obtaining a large number of equiaxed crystals through multi-stage cyclic heat treatment of 3D printed titanium alloys, comprising the following steps:

[0009] S1. The titanium alloy prepared by 3D printing is placed in an inert atmosphere and subjected to a first heat treatment at temperature T1 for a certain period of time to obtain the first sample;

[0010] S2. The first sample is first heated to temperature T2 for a certain period of time, and then heated to temperature T3 for a certain period of time to obtain the second sample.

[0011] S3. Cool the second sample in the furnace to temperature T2 and perform a fourth heat treatment for a certain period of time, then cool it in the furnace to temperature T1.

[0012] S4. Repeat steps S1-S3 multiple times until a third sample with the required proportion of equiaxed crystals is obtained.

[0013] The T1 temperature is higher than the martensitic decomposition temperature of the titanium alloy, and the T3 temperature is lower than the β-phase transformation point temperature of the titanium alloy, and T1 <T2<T3。

[0014] The overall concept of the multi-stage cyclic heat treatment method provided by this invention is as follows:

[0015] Due to the extremely high cooling rate during the Selective Laser Melting (SLM) process, the sample forms extremely fine acicular martensite and contains a large number of dislocations, twins, and substructures. At the initial stage of multi-stage cyclic heat treatment, the acicular martensite will decompose and transform into α and β phases; due to the existence of the above crystallographic defects, grain boundary splitting will occur in some α laths. As the number of cycles increases, the grain boundary splitting gradually deepens until the laths are completely fractured. These fractured laths gradually coarsen during the heat treatment and finally form equiaxed grains. Preferably, in step S4, the number of repetitions of steps S1-S3 is 2 to 15 times, and more preferably, the number of repetitions of steps S1-S3 is 4 to 9 times.

[0016] Compared with the conventional single annealing treatment method (i.e., keeping the sample at a certain temperature for a period of time and then air-cooling or furnace-cooling to room temperature), the present invention adopts a stepped cyclic heat treatment method in three temperature ranges. The multi-step heating and cooling are more conducive to the spheroidization of α grains and the number of cycles can be adjusted according to needs, so as to obtain a higher proportion of equiaxed grains. In the selection of the three temperature ranges, the present invention defines that the T1 temperature is higher than the martensite decomposition temperature of the titanium alloy, the T3 temperature is lower than the β phase transformation point temperature of the titanium alloy, and T1 < T2 < T3. Among them, the setting of the T1 temperature is to ensure that the martensite decomposes and transforms into the α phase, which is conducive to the subsequent occurrence of spheroidization; the setting of the T3 temperature is considered that when the temperature exceeds the β phase transformation point, the microstructure will significantly coarsen, thus significantly reducing the comprehensive mechanical properties of the material; T2 is between T1 and T3, which can play a transitional role, making the splitting of the lath α phase more sufficient, and thus being conducive to the formation of more equiaxed grains; at the same time, the setting of the intermediate temperature T2 can also effectively reduce the treatment time at the T3 temperature. If the T2 temperature is not set, the sample needs to be kept at the T3 temperature for a longer time to ensure the formation of equiaxed grains, and the long-term high-temperature treatment is likely to cause grain growth, resulting in a reduction in the strength of the material.

[0017] In the above method, various different proportions of microstructures can be obtained by adjusting the annealing temperature of each section and the final cooling starting temperature, and thus workpieces with controllable mechanical properties can be obtained.

[0018] Furthermore, the 3D printing is a selective laser melting process; the titanium alloy is a near-α type titanium alloy or an α + β type titanium alloy. In the present invention, the titanium alloys used are all prepared by the selective laser melting process, and there is no grain boundary α phase in the sample. Therefore, no subsequent treatment is required to eliminate the grain boundary α phase, and the treatment process is simplified and the treatment efficiency is improved.

[0019] Preferably, the temperature T1 is 700–800℃, the temperature T2 is 800–900℃, and the temperature T3 is 900–1000℃. More preferably, 80℃≤T2-T1≤120℃ and 80℃≤T3-T2≤120℃.

[0020] Preferably, the heating rate is 8–12 °C / min. The duration of the first, second, and third heat treatments is 1–3 hours, and the three heat treatment times can be the same or different. Specifically, it can be adjusted according to the actual required comprehensive mechanical properties.

[0021] Preferably, the furnace cooling rate is 2–8 °C / min.

[0022] Furthermore, the method for obtaining a large number of equiaxed crystals in a 3D-printed titanium alloy through multi-stage cyclic heat treatment provided by the present invention further includes the following step: S5, cooling the third sample to room temperature.

[0023] In this invention, after step S4, the heat treatment temperature is T1, which is a relatively low temperature. The third sample mainly consists of equiaxed α phases and short rod-shaped α phases. If the third sample is directly air-cooled to room temperature, the microstructure will not change significantly compared to T1. Extensive research has found that, based on obtaining the desired proportion of equiaxed crystals, selecting different cooling methods for the third sample can not only help control the proportion of equiaxed crystals but also further control the mechanical properties of the titanium alloy material. In step S5 of this invention, by heating the third sample to different temperatures (containing different proportions of β phase) and then cooling it, different proportions of microstructure can be obtained, thereby controlling the final mechanical properties of the sample.

[0024] Preferably, step S5 includes: first subjecting the third sample to a first heat treatment at temperature T1 for a certain period of time, then raising the temperature to T2 for a second heat treatment for a certain period of time, then raising the temperature to T3 for a third heat treatment for a certain period of time, and finally air-cooling to room temperature. Studies have found that when air-cooled to room temperature at temperature T3, the sample contains a higher proportion of β phase, which transforms into lath-like α phase, resulting in a material with higher mechanical strength.

[0025] Preferably, step S5 includes: first heat-treating the third sample at temperature T1 for a certain period of time, then heating it to temperature T2 for a certain period of time, then heating it to temperature T3 for a certain period of time, then cooling it in the furnace to temperature T2 for a certain period of time, and finally taking it out and air-cooling it to room temperature.

[0026] Preferably, step S5 includes: first heat-treating the third sample at temperature T1 for a certain period of time, then heating it to temperature T2 for a certain period of time, then heating it to temperature T3 for a certain period of time, then cooling it in the furnace to temperature T2 for a certain period of time, then cooling it in the furnace to temperature T1, and finally taking it out and air-cooling it to room temperature.

[0027] Preferably, the fourth heat treatment lasts for 1 to 3 hours.

[0028] In the above operation, the sample after the S4 cycle is gradually heated to temperature T3, and then different cooling methods are used to control the proportion of isometric crystals and secondary α laths in the final sample to obtain the desired mechanical properties. In the multi-stage cyclic heat treatment method provided by this invention, the heating stage of heat treatment is a process of α phase dissolving and transforming into β phase, while the cooling stage is a process of β phase transforming into α phase. Different cooling methods and cooling rates in step S5 will result in different morphologies of the α phase transformed from β phase, and consequently, different mechanical properties. Unlike the cooling method of the cyclic heat treatment in step S4, the air cooling step in step S5 has a higher cooling rate, and the β phase will directly transform into lamellar α phase. The isometric α phase provides good plasticity, while the lamellar α phase provides higher strength. In this invention, by adjusting the air cooling at different temperatures, the ratio of isometric α phase to lamellar α phase is controlled, thereby obtaining the final sample with the expected mechanical strength.

[0029] The second objective of this invention is to provide a 3D-printed titanium alloy prepared by the method described in one of its objectives. In this invention, by adjusting various parameters in the multi-stage cyclic heat treatment method, arbitrary proportions of equiaxed crystals can be controlled, thereby optimizing the comprehensive mechanical properties of the titanium alloy material.

[0030] In some preferred embodiments, the equiaxed crystal ratio of the 3D printed titanium alloy after treatment by the method provided by the present invention reaches 21.4% to 36.8%, and it also has excellent comprehensive mechanical properties, with a tensile strength of 880 to 939 MPa, a yield strength of 731 to 850 MPa, and an elongation of 14.4% to 17.2%.

[0031] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0032] (1) The present invention provides a method for obtaining a large number of equiaxed crystals in 3D printed titanium alloys through multi-stage cyclic heat treatment. By using multi-stage cyclic heat treatment, a large number of equiaxed crystal structures are obtained in the titanium alloys prepared by SLM, and the comprehensive mechanical properties of the material are significantly improved.

[0033] (2) The parameters in this invention have a wide range of adjustment. The required mechanical properties can be obtained by arbitrarily changing the heat treatment temperature at each stage and the final cooling start temperature.

[0034] (3) The present invention is reasonably designed, the method is simple and easy to operate, and can realize continuous production, and has broad prospects for promotion and application. Attached Figure Description

[0035] Figure 1 A schematic diagram of a method for obtaining a large number of equiaxed crystals in a 3D-printed titanium alloy through multi-stage cyclic heat treatment according to the present invention;

[0036] Figure 2 The image shows the microstructure of the SLM TA15 alloy after four cycles of multi-stage cyclic heat treatment in Example 1 of this invention.

[0037] Figure 3 The image shows the microstructure of the SLM TA15 alloy after nine cycles of multi-stage cyclic heat treatment in Example 2 of this invention.

[0038] Figure 4 The image shows the microstructure of the SLM TC4 alloy after four cycles of multi-stage cyclic heat treatment in Example 3 of this invention.

[0039] Figure 5 The image shows the microstructure of the SLM TC4 alloy after nine cycles of multi-stage cyclic heat treatment in Example 4 of this invention.

[0040] Figure 6 The image shows the microstructure of the SLM TA15 alloy after four cycles of multi-stage cyclic heat treatment in Example 5 of this invention. Detailed Implementation

[0041] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0042] It should be noted that, unless otherwise specified, the embodiments and features described in the present invention can be combined with each other.

[0043] The present invention will be further described below with reference to specific embodiments, but these are not intended to limit the scope of the invention.

[0044] The main parameters involved in Examples 1-9 are shown in Table 1 below:

[0045] Table 1

[0046]

[0047]

[0048] Example 1

[0049] A multi-stage cyclic heat treatment method for obtaining a large number of equiaxed grains and significantly improving the plasticity of 3D printed titanium alloys includes the following steps:

[0050] Step 1: Heat the heat treatment furnace filled with high-purity argon gas to 750°C, and then place the TA15 alloy sample prepared by SLM into the furnace to begin heat treatment.

[0051] Step 2: Hold the sample after Step 1 at 750℃ for 1 hour, then raise the temperature to 850℃ in the furnace at a rate of 10℃ / min and hold for 1 hour, then raise the temperature to 950℃ in the furnace at a rate of 10℃ / min and hold for 1 hour.

[0052] Step 3: The sample after step 2 is cooled to 850°C in the furnace at a cooling rate of 6°C / min and held at that temperature for 1 hour, and then cooled to 750°C in the furnace at a cooling rate of 6°C / min.

[0053] Step 4: Repeat steps 2 and 3 a total of 4 times;

[0054] Step 5: Perform the heat treatment described in Step 2 on the sample after Step 4 again, then cool it in the furnace to 850°C and keep it at that temperature for 1 hour, then cool it in the furnace to 750°C, and then take it out and air cool it to room temperature to obtain the final product.

[0055] Example 2

[0056] A multi-stage cyclic heat treatment method for obtaining a large number of equiaxed grains and significantly improving the plasticity of 3D printed titanium alloys includes the following steps:

[0057] Step 1: Heat the heat treatment furnace filled with high-purity argon gas to 750°C, and then place the TA15 alloy sample prepared by SLM into the furnace to begin heat treatment.

[0058] Step 2: Hold the sample after Step 1 at 750℃ for 1 hour, then raise the temperature to 850℃ in the furnace at a rate of 10℃ / min and hold for 1 hour, then raise the temperature to 950℃ in the furnace at a rate of 10℃ / min and hold for 1 hour.

[0059] Step 3: The sample after step 2 is cooled to 850°C in the furnace at a cooling rate of 6°C / min and held at that temperature for 1 hour, and then cooled to 750°C in the furnace at a cooling rate of 6°C / min.

[0060] Step 4: Repeat steps 2 and 3 a total of 9 times;

[0061] Step 5: Perform the heat treatment described in Step 2 on the sample after Step 4 again, then cool it in the furnace to 850°C and keep it at that temperature for 1 hour, then cool it in the furnace to 750°C, and then take it out and air cool it to room temperature to obtain the final product.

[0062] Example 3

[0063] A multi-stage cyclic heat treatment method for obtaining a large number of equiaxed grains and significantly improving the plasticity of 3D printed titanium alloys includes the following steps:

[0064] Step 1: Heat the heat treatment furnace filled with high-purity argon gas to 750°C, and then place the TC4 alloy sample prepared by SLM into the furnace to begin heat treatment;

[0065] Step 2: Hold the sample after Step 1 at 750℃ for 1 hour, then raise the temperature to 850℃ in the furnace at a rate of 10℃ / min and hold for 1 hour, then raise the temperature to 950℃ in the furnace at a rate of 8℃ / min and hold for 1 hour.

[0066] Step 3: The sample after step 2 is cooled to 850°C in the furnace at a cooling rate of 4°C / min and held at that temperature for 1 hour, and then cooled to 750°C in the furnace at a cooling rate of 4°C / min.

[0067] Step 4: Repeat steps 2 and 3 a total of 4 times;

[0068] Step 5: Perform the heat treatment described in Step 2 on the sample after Step 4 again, then cool it in the furnace to 850°C and keep it at that temperature for 1 hour, then cool it in the furnace to 750°C, and then take it out and air cool it to room temperature to obtain the final product.

[0069] Example 4

[0070] A multi-stage cyclic heat treatment method for obtaining a large number of equiaxed grains and significantly improving the plasticity of 3D printed titanium alloys includes the following steps:

[0071] Step 1: Heat the heat treatment furnace filled with high-purity argon gas to 750°C, and then place the TC4 alloy sample prepared by SLM into the furnace to begin heat treatment;

[0072] Step 2: Hold the sample after Step 1 at 750℃ for 1 hour, then raise the temperature to 850℃ in the furnace at a rate of 10℃ / min and hold for 1 hour, then raise the temperature to 950℃ in the furnace at a rate of 8℃ / min and hold for 1 hour.

[0073] Step 3: The sample after step 2 is cooled to 850°C in the furnace at a cooling rate of 2°C / min and held at that temperature for 1 hour, and then cooled to 750°C in the furnace at a cooling rate of 2°C / min.

[0074] Step 4: Repeat steps 2 and 3 a total of 9 times;

[0075] Step 5: Perform the heat treatment described in Step 2 on the sample after Step 4 again, then cool it in the furnace to 850°C and keep it at that temperature for 1 hour, then cool it in the furnace to 750°C, and then take it out and air cool it to room temperature to obtain the final product.

[0076] Example 5

[0077] A multi-stage cyclic heat treatment method for obtaining a large number of equiaxed grains and significantly improving the plasticity of 3D printed titanium alloys includes the following steps:

[0078] Step 1: Heat the heat treatment furnace filled with high-purity argon gas to 750°C, and then place the TA15 alloy sample prepared by SLM into the furnace to begin heat treatment.

[0079] Step 2: Hold the sample after Step 1 at 750℃ for 1 hour, then raise the temperature to 850℃ in the furnace at a rate of 10℃ / min and hold for 1 hour, then raise the temperature to 950℃ in the furnace at a rate of 12℃ / min and hold for 1 hour.

[0080] Step 3: The sample after step 2 is cooled to 850°C in the furnace at a cooling rate of 5°C / min and held at that temperature for 1 hour, and then cooled to 750°C in the furnace at a cooling rate of 5°C / min.

[0081] Step 4: Repeat steps 2 and 3 a total of 4 times;

[0082] Step 5: Perform the heat treatment described in Step 2 on the sample after Step 4, then remove it and air-cool it to room temperature to obtain the final product.

[0083] Example 6

[0084] A multi-stage cyclic heat treatment method for obtaining a large number of equiaxed grains and significantly improving the plasticity of 3D printed titanium alloys includes the following steps:

[0085] Step 1: Heat the heat treatment furnace filled with high-purity argon gas to 750°C, and then place the TA15 alloy sample prepared by SLM into the furnace to begin heat treatment.

[0086] Step 2: Hold the sample after Step 1 at 750℃ for 2 hours, then raise the temperature to 850℃ in the furnace at a rate of 10℃ / min and hold for 2 hours, then raise the temperature to 950℃ in the furnace at a rate of 10℃ / min and hold for 2 hours.

[0087] Step 3: The sample after step 2 is cooled to 850°C in the furnace at a cooling rate of 8°C / min and held at that temperature for 2 hours, and then cooled to 750°C in the furnace at a cooling rate of 8°C / min.

[0088] Step 4: Repeat steps 2 and 3 a total of 6 times;

[0089] Step 5: Perform the heat treatment described in Step 2 on the sample after Step 4 again, then cool it in the furnace to 850°C and keep it at that temperature for 2 hours. Then take it out and air cool it to room temperature to obtain the final product.

[0090] Example 7

[0091] A multi-stage cyclic heat treatment method for obtaining a large number of equiaxed grains and significantly improving the plasticity of 3D printed titanium alloys includes the following steps:

[0092] Step 1: Heat the heat treatment furnace filled with high-purity argon gas to 700°C, and then place the TA15 alloy sample prepared by SLM into the furnace to begin heat treatment.

[0093] Step 2: Hold the sample after Step 1 at 700℃ for 1 hour, then raise the temperature to 800℃ in the furnace at a rate of 10℃ / min and hold for 1 hour, then raise the temperature to 900℃ in the furnace at a rate of 10℃ / min and hold for 1 hour.

[0094] Step 3: The sample after step 2 is cooled to 800°C in the furnace at a cooling rate of 8°C / min and held at that temperature for 1 hour, and then cooled to 750°C in the furnace at a cooling rate of 8°C / min.

[0095] Step 4: Repeat steps 2 and 3 a total of 4 times;

[0096] Step 5: Perform the heat treatment described in Step 2 on the sample after Step 4 again, then cool it in the furnace to 800°C and keep it at that temperature for 1 hour, then cool it in the furnace to 700°C, and then take it out and air cool it to room temperature to obtain the final product.

[0097] Example 8

[0098] A multi-stage cyclic heat treatment method for obtaining a large number of equiaxed grains and significantly improving the plasticity of 3D printed titanium alloys includes the following steps:

[0099] Step 1: Heat the heat treatment furnace filled with high-purity argon gas to 800°C, and then place the TA15 alloy sample prepared by SLM into the furnace to begin heat treatment.

[0100] Step 2: Hold the sample after Step 1 at 800℃ for 1 hour, then raise the temperature to 900℃ in the furnace at a rate of 10℃ / min and hold for 1 hour, then raise the temperature to 970℃ in the furnace at a rate of 10℃ / min and hold for 1 hour.

[0101] Step 3: The sample after step 2 is cooled to 900°C in the furnace at a cooling rate of 8°C / min and held at that temperature for 1 hour, and then cooled to 800°C in the furnace at a cooling rate of 8°C / min.

[0102] Step 4: Repeat steps 2 and 3 a total of 4 times;

[0103] Step 5: Perform the heat treatment described in Step 2 on the sample after Step 4 again, then cool it in the furnace to 900°C and keep it at that temperature for 1 hour, then cool it in the furnace to 800°C, and then take it out and air cool it to room temperature to obtain the final product.

[0104] Example 9

[0105] A multi-stage cyclic heat treatment method for obtaining a large number of equiaxed grains and significantly improving the plasticity of 3D printed titanium alloys includes the following steps:

[0106] Step 1: Heat the heat treatment furnace filled with high-purity argon gas to 730°C, and then place the TC4 alloy sample prepared by SLM into the furnace to begin heat treatment;

[0107] Step 2: Hold the sample after Step 1 at 730℃ for 3 hours, then raise the temperature to 830℃ in the furnace at a rate of 10℃ / min and hold for 3 hours, then raise the temperature to 930℃ in the furnace at a rate of 10℃ / min and hold for 3 hours.

[0108] Step 3: The sample after step 2 is cooled to 830°C in the furnace at a cooling rate of 6°C / min and held at that temperature for 3 hours, and then cooled to 730°C in the furnace at a cooling rate of 6°C / min.

[0109] Step 4: Repeat steps 2 and 3 a total of 9 times;

[0110] Step 5: Perform the heat treatment described in Step 2 on the sample after Step 4 again, then cool it in the furnace to 830°C and keep it at that temperature for 3 hours, then cool it in the furnace to 730°C, and then take it out and air cool it to room temperature to obtain the final product.

[0111] Performance testing and characterization

[0112] (I) Microstructure and Equiaxed Crystal Ratio

[0113] Figure 2-6 Microstructure images of the titanium alloy samples from Examples 1-5 of this invention after undergoing different numbers of cyclic treatments are shown. Figure 2-6 It can be seen that the microstructure of the titanium alloy materials treated in Examples 1-5 consists of equiaxed α grains, rod-shaped α grains, lath-shaped α grains, and a small amount of residual β phase. It can also be seen that the α grains of different morphologies are all relatively small in size, and this small grain size is beneficial to improving the material strength.

[0114] Furthermore, the isoaxial grain ratio of the titanium alloy materials in each embodiment was calculated, as shown in Table 2 below:

[0115] Table 2

[0116]

[0117] As shown in the table above, the isometric crystal ratio in the microstructure of the samples treated in Examples 1-9 is all higher than 20%, with the isometric crystal ratio in Examples 2, 3, 4, 6 and 9 reaching more than 30%.

[0118] (II) Mechanical property testing

[0119] The titanium alloy materials treated in Examples 1-5 were subjected to comprehensive mechanical property tests, including tensile strength, yield strength, and elongation. The test results are shown in Table 3 below.

[0120] Table 3

[0121]

[0122]

[0123] As can be seen from the above table,

[0124] The titanium alloy material treated using the method provided in this invention exhibits excellent comprehensive mechanical properties in addition to a high proportion of equiaxed grains. Its tensile strength is 880–939 MPa, yield strength is 750–850 MPa, and elongation is 13.7%–17.2%. This demonstrates that the multi-stage cyclic heat treatment scheme provided in this invention can effectively spheroidize the microstructure, offering a novel method for optimizing the microstructure and properties of 3D-printed titanium alloys.

[0125] The above are merely preferred embodiments of the present invention and are not intended to limit the implementation methods and protection scope of the present invention. Those skilled in the art should recognize that any equivalent substitutions and obvious changes made based on the content of this specification should be included within the protection scope of the present invention.

Claims

1. A method for obtaining a large number of equiaxed crystals in a 3D-printed titanium alloy through multi-stage cyclic heat treatment, characterized in that, Includes the following steps: S1. The titanium alloy prepared by 3D printing is placed in an inert atmosphere and subjected to a first heat treatment at temperature T1 for a certain period of time to obtain the first sample; S2. The first sample is first heated to temperature T2 for a certain period of time, and then heated to temperature T3 for a certain period of time to obtain the second sample. S3. Cool the second sample in the furnace to temperature T2 and perform a fourth heat treatment for a certain period of time, then cool it in the furnace to temperature T1. S4. Repeat steps S1-S3 multiple times until a third sample with the required proportion of equiaxed crystals is obtained. The T1 temperature is higher than the martensitic decomposition temperature of the titanium alloy, the T3 temperature is lower than the β phase transformation point temperature of the titanium alloy, and T1 < T2 < T3. In the 3D printed titanium alloy, the proportion of equiaxed crystals is higher than 20%.

2. The method according to claim 1, characterized in that, The 3D printing process is selective laser melting; the titanium alloy is a near-α type titanium alloy or an α+β type titanium alloy.

3. The method according to claim 1, characterized in that, The T1 temperature is 700~800℃, the T2 temperature is 800~900℃, and the T3 temperature is 900~1000℃.

4. The method according to claim 1, characterized in that, The heating rate is 8~12℃ / min.

5. The method according to claim 1, characterized in that, The furnace cooling rate is 2~8℃ / min.

6. The method according to claim 1, characterized in that, The method further includes the following steps: S5. Cool the third sample to room temperature.

7. The method according to claim 6, characterized in that, Step S5 includes: first heat-treating the third sample at temperature T1 for a certain period of time, then raising the temperature to T2 for a second heat treatment for a certain period of time, then raising the temperature to T3 for a third heat treatment for a certain period of time, and then air-cooling it to room temperature.

8. The method according to claim 6, characterized in that, Step S5 includes: first, heat the third sample at temperature T1 for a certain period of time, then heat it to temperature T2 for a certain period of time, then heat it to temperature T3 for a certain period of time, then cool it in the furnace to temperature T2 for a certain period of time, and finally take it out and air cool it to room temperature.

9. The method according to claim 6, characterized in that, Step S5 includes: first, heat the third sample at temperature T1 for a certain period of time, then heat it to temperature T2 for a certain period of time, then heat it to temperature T3 for a certain period of time, then cool it in the furnace to temperature T2 for a certain period of time, then cool it in the furnace to temperature T1, and finally take it out and air cool it to room temperature.

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