Post-treatment method for laser additive manufacturing of titanium alloy

Abstract

The invention provides a post-treatment method for laser additive manufacturing of titanium alloy. The post-treatment method comprises the steps that a titanium alloy workpiece is sequentially subjected to first annealing treatment, beta heat treatment, hot isostatic pressing treatment and second annealing treatment. Through the specific process combining beta heat treatment and hot isostatic pressing treatment, comprehensive regulation and control over the stress, defects and tissue of the titanium alloy workpiece are achieved, the internal stress of the laser additive manufacturing titanium alloy workpiece is eliminated, and meanwhile the microstructure of the laser additive manufacturing titanium alloy workpiece can be regulated and controlled while most metallurgical defects are eliminated; the strength, toughness and damage tolerance performance of the titanium alloy are synergistically improved, and the service scene of the titanium alloy can meet the static strength and fatigue damage tolerance requirements at the same time.

Description

TECHNICAL FIELD

[0001] The application belongs to the post-processing method of alloy parts, and relates to a post-processing method of laser additive manufacturing of titanium alloy. BACKGROUND

[0002] Titanium alloy has good room temperature and high temperature mechanical properties, low density, high specific strength, high corrosion resistance and many other performance advantages, and is widely used in aerospace and other high-end fields. Among them, the α-β type titanium alloy has good weldability and heat treatable strengthening, and is very suitable for additive manufacturing technology. With the increasing requirements of advanced aerospace equipment for weight reduction and performance, more and more complex integral structural parts are used in the current design. These complex components cannot be manufactured by traditional casting and forging methods. Additive manufacturing technology provides a feasible technical approach to solve the processing and manufacturing problems of α-β type titanium alloy complex parts in the aerospace field.

[0003] As a manufacturing technology different from traditional processes, the principle of laser additive manufacturing technology is that laser and powder bed interact to realize structure forming and manufacturing by high-temperature heat source melting and solidification of metal. Due to the residual gas and unmelted powder particles in the forming process, metallurgical defects exist inside the parts. Under the action of cyclic load, such defects can benefit the initiation and propagation of cracks, causing fatigue failure. Fatigue fracture is one of the most common failure forms of structural parts in engineering applications. According to statistics, about 80% to 90% of component failures are caused by fatigue.

[0004] For civil aircraft, different performance requirements are put forward for parts according to different application conditions. For static strength parts, a small amount of defects and lower load can ensure that the structure has sufficient safety margin to meet the application requirements. The corresponding yield strength and tensile strength requirements are the main indicators. However, for main structural parts, the design idea is based on the damage tolerance design principle. The comprehensive regulation of stress, defects and microstructure of the parts can effectively improve the crack propagation resistance of the parts, and then improve the service life of the parts. In order to meet the requirements of static strength and damage tolerance performance, under the premise of meeting the requirements of defect and crack propagation control of damage tolerance, it is also necessary to ensure that the parts have high static strength indicators, and realize the comprehensive improvement of strength and toughness and damage tolerance performance.

[0005] In summary, how to obtain a titanium alloy with static strength, strength and toughness and damage tolerance performance is a technical problem that needs to be solved in the field. SUMMARY

[0006] The application aims to provide a post-processing method for laser additive manufacturing of titanium alloy, which realizes comprehensive regulation of stress, defects and microstructure of the titanium alloy part, eliminates internal stress of the laser additive manufacturing titanium alloy part, and regulates microstructure of the laser additive manufacturing titanium alloy part while eliminating most metallurgical defects, so as to realize synergistic improvement of strength and toughness of the titanium alloy and damage tolerance performance, and make the service scene of the titanium alloy satisfy the requirements of static strength and fatigue damage tolerance at the same time.

[0007] To achieve the above object, the application adopts the following technical scheme:

[0008] The application provides a post-processing method for laser additive manufacturing of titanium alloy, which comprises sequentially performing first annealing treatment, beta heat treatment, hot isostatic pressing treatment and second annealing treatment on the titanium alloy part.

[0009] The post-processing method provided by the application realizes comprehensive regulation of stress, defects and microstructure of the titanium alloy part, eliminates internal stress of the laser additive manufacturing titanium alloy part, and regulates microstructure of the laser additive manufacturing titanium alloy part while eliminating most metallurgical defects, so as to realize synergistic improvement of strength and toughness of the titanium alloy and damage tolerance performance, and make the service scene of the titanium alloy satisfy the requirements of static strength and fatigue damage tolerance at the same time.

[0010] As a preferred technical scheme of the application, the titanium alloy comprises TC4 titanium alloy.

[0011] Preferably, the titanium alloy part is prepared by a laser selective melting method.

[0012] As a preferred technical scheme of the application, the heating rate of the first annealing treatment is 7-12 ℃ / min, for example, can be 7.5 ℃ / min, 8 ℃ / min, 8.5 ℃ / min, 9 ℃ / min, 9.5 ℃ / min, 10 ℃ / min, 10.5 ℃ / min, 11 ℃ / min or 11.5 ℃ / min, but is not limited to the listed values, and other values in the value range are also applicable.

[0013] In the application, the first annealing treatment is performed under vacuum condition.

[0014] Preferably, the heating end point of the first annealing treatment is (T β -250) to (T β -150) ℃, for example, can be (T β -240) ℃, (T β -230) ℃, (T β -220) ℃, (T β-210) °C, (T β -200) °C, (T β -190) °C, (T β -180) °C, (T β -170) °C or (T β -160) °C, etc., but are not limited to the listed values, and other values within the range of values are equally applicable.

[0015] wherein T β is the beta phase transition temperature of the titanium alloy part.

[0016] Preferably, the holding time of the first annealing treatment is 1-3 h, for example, it can be 1.2 h, 1.5 h, 1.8 h, 2 h, 2.2 h, 2.5 h or 2.7 h, etc., but is not limited to the listed values, and other values within the range of values are equally applicable.

[0017] Preferably, after the first annealing treatment, the furnace cooling to room temperature is further carried out before the beta heat treatment.

[0018] In the present application, by carrying out the first annealing treatment on the laser additive manufacturing titanium alloy part, the residual internal stress of the titanium alloy part after forming is eliminated, and the deformation of the part caused by the release of internal stress during part processing is prevented.

[0019] As a preferred technical solution of the present application, the heating rate of the beta heat treatment is 7-12 °C / min, for example, it can be 7.5 °C / min, 8 °C / min, 8.5 °C / min, 9 °C / min, 9.5 °C / min, 10 °C / min, 10.5 °C / min, 11 °C / min or 11.5 °C / min, etc., but is not limited to the listed values, and other values within the range of values are equally applicable.

[0020] In the present application, the beta heat treatment is carried out under vacuum conditions.

[0021] Preferably, the heating end point of the beta heat treatment is (T β +15) to (T β +25) °C, for example, it can be (T β +16) °C, (T β +17) °C, (T β +18) °C, (T β +19) °C, (T β +20) °C, (T β +21) °C, (T β +22) °C, (T β +23) °C or (T β +24) °C, etc., but is not limited to the listed values, and other values within the range of values are equally applicable.

[0022] Preferably, the holding time of the beta heat treatment is 30-90 min, for example, it can be 40 min, 50 min, 60 min, 70 min, 80 min or 85 min, etc., but is not limited to the listed values, and other values within the value range are also applicable.

[0023] It is worth noting that by controlling the temperature and time of the beta heat treatment, the original microstructure of the laser additive manufacturing titanium alloy part is comprehensively controlled, and the strong columnar orientation microstructure caused by rapid cooling during the laser additive manufacturing process is adjusted.

[0024] Preferably, after the beta heat treatment, the hot isostatic pressing treatment is further subjected to furnace cooling to room temperature.

[0025] As a preferred technical solution of the present application, the hot isostatic pressing treatment is carried out under inert gas.

[0026] In the present application, the inert gas includes argon.

[0027] Preferably, the pressure of the hot isostatic pressing treatment is 100-150 MPa, for example, it can be 105 MPa, 110 MPa, 115 MPa, 120 MPa, 125 MPa, 130 MPa, 135 MPa, 140 MPa or 145 MPa, etc., but is not limited to the listed values, and other values within the value range are also applicable.

[0028] As a preferred technical solution of the present application, the heating rate of the hot isostatic pressing treatment is 7-12 ℃ / min, for example, it can be 7.5 ℃ / min, 8 ℃ / min, 8.5 ℃ / min, 9 ℃ / min, 9.5 ℃ / min, 10 ℃ / min, 10.5 ℃ / min, 11 ℃ / min or 11.5 ℃ / min, etc., but is not limited to the listed values, and other values within the value range are also applicable.

[0029] Preferably, the heating end point of the hot isostatic pressing treatment is (T β -50) to (T β -40) ℃, for example, it can be (T β -49) ℃, (T β -48) ℃, (T β -47) ℃, (T β -46) ℃, (T β -45) ℃, (T β -44) ℃, (T β -43) ℃, (T β -42) ℃ or (T β -41) ℃, etc., but is not limited to the listed values, and other values within the value range are also applicable.

[0030] Preferably, the holding time of the hot isostatic pressing treatment is 2-4h, for example, it can be 2.2h, 2.5h, 2.8h, 3h, 3.2h, 3.5h or 3.7h, etc., but is not limited to the listed values, other values within the value range are also applicable.

[0031] As a preferred technical solution of the present application, after the hot isostatic pressing treatment, the second annealing treatment is further carried out by continuously passing inert gas to cool to room temperature.

[0032] It is worth noting that by controlling the hot isostatic pressing temperature, time and cooling method, the morphology of primary alpha phase can be retained and more metastable beta phase can be obtained, most of the internal metallurgical defects of the titanium alloy part can be eliminated, the macroscopic crack initiation behavior can be effectively controlled, and the comprehensive performance of the part can be improved.

[0033] As a preferred technical solution of the present application, the heating rate of the second annealing treatment is 7-12℃ / min, for example, it can be 7.5℃ / min, 8℃ / min, 8.5℃ / min, 9℃ / min, 9.5℃ / min, 10℃ / min, 10.5℃ / min, 11℃ / min or 11.5℃ / min, etc., but is not limited to the listed values, other values within the value range are also applicable.

[0034] In the present application, the second annealing treatment is carried out under inert gas.

[0035] Preferably, the end point of the second annealing treatment is (T β -350)~(T β -250)℃, for example, it can be (T β -340)℃, (T β -330)℃, (T β -320)℃, (T β -310)℃, (T β -300)℃, (T β -290)℃, (T β -280)℃, (T β -270)℃ or (T β -260)℃, etc., but is not limited to the listed values, other values within the value range are also applicable.

[0036] Preferably, the holding time of the second annealing treatment is 1-3h, for example, it can be 1.2h, 1.5h, 1.8h, 2h, 2.2h, 2.5h or 2.7h, etc., but is not limited to the listed values, other values within the value range are also applicable.

[0037] Preferably, the second annealing treatment is followed by air cooling to room temperature.

[0038] In the present application, by performing the second annealing treatment, the titanium alloy part is heated to the two-phase region and then air-cooled, decomposing the metastable beta phase formed by rapid cooling during the hot isostatic pressing process to form a lamellar secondary alpha phase cluster.

[0039] As a preferred technical solution of the present application, after the second annealing treatment, the internal microstructure of the titanium alloy part is a dual-state structure of columnar beta phase matrix and lamellar secondary alpha phase cluster.

[0040] In the present application, the volume fraction of the lamellar secondary alpha phase cluster in the dual-state structure is 30-50%, for example, it can be 32%, 35%, 38%, 40%, 42%, 45% or 48%, etc., but is not limited to the listed values, other values within the numerical range are also applicable.

[0041] It is worth noting that by reconstructing the beta microstructure, the alpha cluster is combined with the reconstructed beta structure to form a dual-state structure, which comprehensively adjusts the proportion and size of the typical structure, avoids a significant reduction in material tensile strength, and based on the characteristics of beta grain boundaries, hinders the expansion behavior of micro-cracks, combined with the lamellar structure orientation characteristics of the beta cluster structure, prolongs the micro-crack propagation path, while creating a rough crack propagation front structure feature, hindering macro-crack propagation, and achieving comprehensive improvement of strength and toughness and damage tolerance performance.

[0042] As a preferred technical solution of the present application, the post-processing method comprises the following steps:

[0043] The titanium alloy part prepared by the laser selective melting method is heated to (T β -250)~(T β -150)℃ for first annealing treatment and holding for 1-3h, then furnace cooling to room temperature, then heated to (T β +15)~(T β +25)℃ for beta heat treatment and holding for 30-90min, then furnace cooling to room temperature, then heated to (T β -50)~(T β -40)℃ for hot isostatic pressing treatment and holding for 2-4h, then continuously cooling to room temperature by inert gas, and finally heated to (T β -350)~(T β-250) ℃, and then air-cooled to room temperature after 1-3 h of holding, to obtain a titanium alloy part with a columnar beta phase matrix and a lamellar secondary alpha phase cluster.

[0044] Compared with the prior art, the present application has the following beneficial effects:

[0045] The post-processing method provided by the present application restructures the beta structure by combining the first annealing treatment, beta heat treatment, hot isostatic pressing treatment and second annealing treatment, and adopts the specific beta heat treatment coupled with the hot isostatic pressing treatment process, combined with the regulation of corresponding parameters, to form a dual-state structure combined with alpha clusters and the reconstructed beta structure, to realize stress relief, defect adjustment and structure control of the laser additive manufacturing titanium alloy part, reduce metallurgical defects, effectively improve the density of the laser additive manufacturing titanium alloy part and obtain a dual-state structure with excellent crack resistance, realize the synergistic improvement of strength and toughness and damage tolerance performance, solve the competitive problem of mismatched strength and toughness, and make the service scene meet the static strength and fatigue damage tolerance requirements at the same time. BRIEF DESCRIPTION OF DRAWINGS

[0046] Figure 1 A defect CT image of the TC4 titanium alloy obtained in Example 1 is shown in Figure 1.

[0047] Figure 2 A metallographic structure image of the TC4 titanium alloy obtained in Example 1 is shown in Figure 2.

[0048] Figure 3 A defect CT image of the TC4 titanium alloy obtained in Comparative Example 1 is shown in Figure 3.

[0049] Figure 4 A metallographic structure image of the TC4 titanium alloy obtained in Comparative Example 1 is shown in Figure 4. DETAILED DESCRIPTION

[0050] The technical solutions of the present application will be further described below through specific embodiments. Those skilled in the art should understand that the embodiments are only used to help understand the present application and should not be regarded as specific limitations on the present application.

[0051] In the following examples and comparative examples, the process parameters of the laser selective melting method are not specifically limited, and those skilled in the art can determine them according to the actual working conditions; the T β All are the beta phase transition temperature of the titanium alloy part; the air cooling is all air cooling after discharge.

[0052] Example 1

[0053] The present embodiment provides a post-processing method for laser additive manufacturing of TC4 titanium alloy, which comprises the following steps:

[0054] The TC4 titanium alloy part prepared by the laser selective melting method is heated to T β -200 for first annealing treatment and insulation for 2h, and then furnace cooling to room temperature, and then heated to T β +20℃ for β heat treatment and insulation for 60min, and then furnace cooling to room temperature, and then heated to T β -45℃ for hot isostatic pressing treatment and insulation for 3h, and then rapid cooling to room temperature by continuously inputting argon, and finally heated to T β -300)℃ for second annealing treatment and insulation for 2h, and then air cooling to room temperature.

[0055] The defect CT image and the metallographic structure image of the TC4 titanium alloy obtained in the example are shown in Figures 1-2 It can be known from Figures 1-2 that the TC4 titanium alloy has no internal metallurgical defects by CT observation, and the internal structure is a bimodal structure of lamellar α phase clusters and columnar β phase with unclear orientation.

[0056] Example 2

[0057] The example provides a post-treatment method for laser additive manufacturing of TC4 titanium alloy, which is the same as example 1 except that, after the hot isostatic pressing treatment, the part is cooled to room temperature before the second annealing treatment.

[0058] Example 3

[0059] The example provides a post-treatment method for laser additive manufacturing of TC4 titanium alloy, which is the same as example 1 except that, after the hot isostatic pressing treatment, the part is air cooled to room temperature before the second annealing treatment.

[0060] Comparative Example 1

[0061] The comparative example provides a post-treatment method for laser additive manufacturing of TC4 titanium alloy, which adopts a traditional stress relief annealing process, specifically including: annealing treatment in a vacuum environment at a heating rate of 10℃ / min to 800℃ and insulation for 2h, and then furnace cooling to room temperature.

[0062] The defect CT image and the metallographic structure image of the TC4 titanium alloy obtained in the comparative example are shown in Figures 3-4 It can be known from Figures 3-4 that the TC4 titanium alloy has internal metallurgical defects by CT observation, and the internal structure is acicular α' phase clusters and columnar β phase.

[0063] Comparative Example 2

[0064] The present comparative example provides a post-processing method for laser additive manufacturing of TC4 titanium alloy, which is the same as example 1 except that no β heat treatment is performed.

[0065] The TC4 titanium alloy obtained in the above examples and comparative examples is subjected to performance testing, wherein the tensile strength is tested according to ASTM E8 / E8M to obtain the stress-strain curve and the tensile strength, and the fracture toughness is tested according to ASTM E399, and the results are shown in Table 1.

[0066] Table 1

[0067] Tensile strength / MPa Fracture toughness / MPa-m 1 / 2 ]] Example 1 1100 120 Example 2 990 95 Example 3 1000 100 Comparative Example 1 1120 65 Comparative Example 2 1008 80

[0068] From Table 1, it can be seen that:

[0069] (1) The post-processing method provided by the present application realizes the synergistic improvement of the strength, toughness and damage tolerance performance of TC4 titanium alloy by combining the specific β heat treatment with the hot isostatic pressing treatment, and combining the regulation of the corresponding parameters to form the dual-state structure combined with the α cluster and the reconstructed β structure, so that the service scene can meet the static strength and fatigue damage tolerance requirements at the same time;

[0070] (2) As can be seen from the comparison of example 1 and example 2-3, when the cooling method after hot isostatic pressing treatment is furnace cooling or air cooling, the microstructure of the material is coarse due to the slow cooling rate, and the matching of tensile strength and fracture toughness is insufficient, so the application scene is limited; the present application adopts the method of continuously passing argon to rapidly cool to room temperature, so as to obtain the material performance with matching strength and toughness, and the service scene can meet the static strength and fatigue damage tolerance requirements at the same time;

[0071] (3) As can be seen from the comparison of example 1 and comparative example 1, when the laser additive manufacturing TC4 titanium alloy part is post-processed by using the traditional stress relief annealing process, although the tensile strength of the obtained material is better, there are dispersed metallurgical defects in the interior and the fracture toughness is poor, so the comprehensive improvement of strength, toughness and damage tolerance performance cannot be realized;

[0072] (4) As can be seen from the comparison of example 1 and comparative example 2, when no β heat treatment is performed, the size and morphology of the β structure do not change, and after the hot isostatic pressing treatment, the tensile strength of the material will be significantly reduced, and the α / β ratio cannot be further adjusted, resulting in a significant decrease in the tensile strength of the obtained TC4 titanium alloy, and the fracture toughness is not significantly improved, so the comprehensive performance is poor.

[0073] The applicant declares that the detailed structural features of the present application are illustrated by the above-mentioned embodiments, but the present application is not limited to the above-mentioned detailed structural features, i.e. it does not mean that the present application must rely on the above-mentioned detailed structural features to be implemented. It should be understood by those skilled in the art that any improvement of the present application, equivalent replacement of the components selected by the present application, addition of auxiliary components, selection of specific modes, etc. all fall within the protection scope and disclosure scope of the present application.

[0074] The preferred embodiments of the present application are described in detail above, but the present application is not limited to the specific details in the above-mentioned embodiments, and within the technical concept scope of the present application, various simple modifications can be made to the technical solutions of the present application, and these simple modifications all belong to the protection scope of the present application.

[0075] In addition, it should be noted that each specific technical feature described in the above-mentioned specific embodiments can be combined in any appropriate manner without contradiction, and in order to avoid unnecessary repetition, the present application will not further describe various possible combination manners.

[0076] In addition, various different embodiments of the present application can also be combined in any manner, as long as it does not deviate from the idea of the present application, and it should also be considered as disclosed by the present application.

Claims

1. A post-processing method for laser additive manufacturing of titanium alloy, characterized in that: The post-processing method comprises sequentially performing a first annealing treatment, a beta heat treatment, a hot isostatic pressing treatment and a second annealing treatment on the titanium alloy workpiece.

2. The post-processing method according to claim 1, characterized in that The titanium alloy includes TC4 titanium alloy; Preferably, the titanium alloy part is produced by a selective laser melting method.

3. The post-processing method according to claim 1 or 2, characterized in that: The heating rate of the first annealing treatment is 7-12°C / min; Preferably, the temperature rising end point of the first annealing treatment is (T β -250)~(T β -150)℃; where T β is the β phase transition temperature of titanium alloy parts; Preferably, the holding time of the first annealing treatment is 1 to 3 hours; Preferably, after the first annealing treatment, furnace cooling to room temperature is performed before the β heat treatment.

4. The post-processing method according to any one of claims 1 to 3, characterized in that: The heating rate of the β heat treatment is 7 to 12°C / min; Preferably, the temperature rise end point of the β heat treatment is (T β +15)~(T β +25)℃; Preferably, the holding time of the β heat treatment is 30 to 90 minutes; Preferably, after the β heat treatment, the steel is further furnace-cooled to room temperature before the hot isostatic pressing treatment.

5. The post-processing method according to any one of claims 1 to 4, characterized in that: The hot isostatic pressing treatment is carried out under an inert gas; Preferably, the pressure of the hot isostatic pressing treatment is 100-150 MPa.

6. The post-processing method according to any one of claims 1 to 5, characterized in that: The heating rate of the hot isostatic pressing treatment is 7 to 12°C / min; Preferably, the heating end point of the hot isostatic pressing treatment is (T β -50)~(T β -40)℃; Preferably, the heat preservation and pressure holding time of the hot isostatic pressing treatment is 2 to 4 hours.

7. The post-processing method according to any one of claims 1 to 6, characterized in that: After the hot isostatic pressing treatment, the second annealing treatment is preceded by continuous introduction of inert gas for rapid cooling to room temperature.

8. The post-processing method according to any one of claims 1 to 7, characterized in that: The heating rate of the second annealing treatment is 7 to 12°C / min; Preferably, the temperature rising end point of the second annealing treatment is (T β -350)~(T β -250)℃; Preferably, the holding time of the second annealing treatment is 1 to 3 hours; Preferably, the second annealing treatment is followed by air cooling to room temperature.

9. The post-processing method according to any one of claims 1 to 8, characterized in that: After the second annealing treatment, the internal structure of the titanium alloy part is a dual-state structure of a columnar β phase matrix and lamellar secondary α phase bundles.

10. The post-processing method according to any one of claims 1 to 9, characterized in that: The post-processing method comprises the following steps: The titanium alloy part prepared by laser selective melting was heated to (T β -250)~(T β The first annealing treatment was carried out at -150)℃ and kept at this temperature for 1-3h, then cooled to room temperature with the furnace, and then heated to (T β +15)~(T β After β heat treatment at 25°C and keeping the temperature for 30-90 minutes, the product is cooled to room temperature in the furnace, and then heated to (T β -50)~(T β -40)℃ for hot isostatic pressing and keep the temperature and pressure for 2-4h, then continue to pass inert gas to cool to room temperature, and finally heat up to (T β -350)~(T β The titanium alloy product is subjected to a second annealing treatment at -250)℃ and kept at this temperature for 1 to 3 hours, and then air-cooled to room temperature to obtain a titanium alloy product having an internal structure of a columnar β phase matrix and lamellar secondary α phase bundles.

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