Additive manufacturing TA15 alloy and low-temperature heat treatment method for improving strength of TA15 alloy

Abstract

The invention discloses an additive manufacturing TA15 alloy and a low-temperature heat treatment method for improving the strength of the additive manufacturing TA15 alloy, and relates to the technical field of alloy heat treatment, and the method comprises the steps that the additive manufacturing TA15 alloy is placed in a vacuum environment, heated to 500-575 DEG C at the heating rate of 10-20 DEG C / min, subjected to heat preservation for 2-4 h and then cooled to the room temperature, and the additive manufacturing TA15 alloy subjected to low-temperature heat treatment is obtained. According to the method, the dual purposes of fully eliminating the residual stress and finely regulating and controlling the microstructure are synchronously achieved in the single heat treatment step, so that the comprehensive mechanical property of the alloy is remarkably improved while deformation and cracking of the part are avoided.

Description

TECHNICAL FIELD

[0001] The application relates to a TA15 alloy and a low-temperature heat treatment method for improving the strength of the TA15 alloy, and belongs to the technical field of alloy heat treatment. BACKGROUND

[0002] TA15 (Ti-6.5Al-2Zr-1Mo-1V) titanium alloy is a near-alpha type high-temperature titanium alloy, which is favored due to its excellent comprehensive performance. The alloy has good thermal strength and weldability of alpha titanium alloy, and also has process plasticity close to (alpha+beta) two-phase titanium alloy through the addition of a small amount of beta stabilizing elements. The significant advantage is that the alloy can still maintain high strength, creep resistance and thermal stability under medium-high temperature (400-500 DEG C) conditions, and has low density and excellent corrosion resistance.

[0003] Based on these characteristics, the TA15 alloy is widely used in key load-bearing components in the field of aerospace, such as compressor discs, blades, casings of aero-engines, and structural parts such as aircraft fuselage frames and wall panels. Traditionally, these components are mainly manufactured by forging process, but in the face of increasingly complex structural design, the traditional manufacturing method often faces problems such as long process flow, low material utilization rate, and high manufacturing cost.

[0004] Selective Laser Melting (SLM) as a typical representative of additive manufacturing technology provides a revolutionary solution for realizing the "near-net forming" manufacturing of such complex titanium alloy components. SLM technology melts metal powder layer by layer through a high-energy laser beam to directly manufacture three-dimensional metal parts with high density and accurate size. It has the advantages of high design freedom, high material utilization rate, and short production cycle, and is especially suitable for rapid development and personalized manufacturing of small batch and complex structural parts in the field of aerospace. However, when the technology is applied to TA15 alloy, the process characteristics of rapid melting lead to coarse primary columnar beta grain boundaries and needle-like alpha' martensite structure, which makes the material strength close to that of forged parts, but difficult to further improve. There is a contradictory relationship between the strength and plasticity of metal materials. Traditional high-temperature annealing or solid solution aging treatment often sacrifices strength or plasticity while optimizing the structure. In addition, the extremely high temperature gradient and cyclic thermal history in the SLM manufacturing process also accumulate residual stress in the part, which causes the part to warp and deform or even crack, seriously affecting the forming accuracy and service reliability of the part, and the existing stress relief heat treatment process significantly reduces the strength of the titanium alloy.

[0005] In view of the above problems, the prior art still lacks a single heat treatment method that can synchronously and coordinately solve the above bottlenecks. The multi-step heat treatment scheme commonly used at present can improve the performance to some extent, but has the disadvantages of complicated process flow, long production cycle, high energy consumption and cost, and is difficult to meet the urgent needs of modern industry for economic and efficient manufacturing. Therefore, the industry urgently needs to develop an innovative integrated heat treatment new process, which synchronously realizes the dual purposes of fully eliminating residual stress and fine regulation of microstructure in a single heat treatment step, so as to significantly improve the comprehensive mechanical properties of the alloy while avoiding deformation and cracking of the parts. Developing such a process is expected to greatly simplify the post-processing process of SLM titanium alloy components, promote cost reduction and efficiency improvement, and promote the large-scale engineering application of additive manufacturing titanium alloy technology in the field of high-performance key load-bearing structures. SUMMARY

[0006] The purpose of the present application is to overcome the deficiencies in the prior art and provide a low-temperature heat treatment method for improving the strength of additive manufacturing TA15 alloy, which synchronously realizes the dual purposes of fully eliminating residual stress and fine regulation of microstructure in a single heat treatment step, so as to significantly improve the comprehensive mechanical properties of the alloy while avoiding deformation and cracking of the parts.

[0007] To achieve the above purpose, the present application is implemented by using the following technical solutions: On the one hand, the present application provides a low-temperature heat treatment method for improving the strength of additive manufacturing TA15 alloy, comprising: placing the additive manufacturing TA15 alloy in a vacuum environment, heating it to 500-575℃ at a heating rate of 10-20℃ / min, holding for 2-4h and then cooling to room temperature to obtain the low-temperature heat treated additive manufacturing TA15 alloy.

[0008] Further, the additive manufacturing uses a laser selective melting process.

[0009] Further, the process parameters of the laser selective melting process include a laser power of 220-340W, a scanning speed of 900-1350mm / s, a powder laying thickness of 30μm, a scanning line spacing of 0.1mm, a spot diameter of 75μm, preheating the substrate to 80℃, using a serpentine scanning strategy, and rotating the layers by 67°.

[0010] Further, the vacuum degree of the vacuum environment is less than 2.3×10 -3 Pa.

[0011] Further, the heating, holding and cooling to room temperature use a furnace temperature rising and falling mode.

[0012] In another aspect, the present application also provides an additive manufacturing TA15 alloy prepared by the low-temperature heat treatment method for improving the strength of the additive manufacturing TA15 alloy according to any one of the above.

[0013] Further, the additive manufacturing TA15 alloy has a yield strength of not less than 1180 MPa, a tensile strength of not less than 1230 MPa, an elongation after fracture of 6-10%, and a Vickers hardness of 380-420 HV.

[0014] Compared with the prior art, the present application has the following beneficial effects: The present application controls the heat treatment of the additive manufacturing TA15 alloy under high vacuum and low temperature conditions, promotes the incomplete decomposition of the non-equilibrium acicular a' martensite, and further enriches the micro-area rich in β-stable elements in the interior of the a' matrix through uphill diffusion to transform into the β phase, improves the stability of the a' matrix, produces a dispersion strengthening effect, fully eliminates the residual stress in the alloy, and makes the formed piece have excellent comprehensive mechanical properties. The present application adopts a single heat treatment step, simultaneously solves the problems of further strengthening treatment and residual stress of the additive manufacturing titanium alloy, significantly simplifies the heat treatment process of the additive manufacturing titanium alloy, greatly saves the production cost, improves the production efficiency, and has good potential for batch industrial application, is expected to greatly simplify the post-processing process of the SLM titanium alloy component, promote cost reduction and efficiency improvement, and promote the large-scale engineering application of the additive manufacturing titanium alloy technology in the field of high-performance key load-bearing structures. BRIEF DESCRIPTION OF DRAWINGS

[0015] Figure 1 The microstructure of the additive manufacturing TA15 alloy obtained after the low-temperature heat treatment of the comparative example 3 and the examples 1-3, comparative examples 1-2 of the present application is shown in the schematic diagram, wherein (a) is the microstructure of the original additive manufacturing TA15 alloy; (b) is the microstructure of the additive manufacturing TA15 alloy obtained after the low-temperature heat treatment of the example 1; (c) is the microstructure of the additive manufacturing TA15 alloy obtained after the low-temperature heat treatment of the example 2; (d) is the microstructure of the additive manufacturing TA15 alloy obtained after the low-temperature heat treatment of the example 3; (e) is the microstructure of the additive manufacturing TA15 alloy obtained after the low-temperature heat treatment of the comparative example 1; and (f) is the microstructure of the additive manufacturing TA15 alloy obtained after the low-temperature heat treatment of the comparative example 2. DETAILED DESCRIPTION

[0016] The present application will be further described below in conjunction with the drawings. The following examples are only used to more clearly illustrate the technical solutions of the present application, and cannot be used to limit the protection scope of the present application. Example 1

[0017] The embodiment of the present application provides a low-temperature heat treatment method for improving the strength of additive manufacturing TA15 alloy, comprising the following steps: TA15 alloy mechanical test bars are prepared by using a laser selective melting process, and process parameters are as follows: laser power 260 W, scanning speed 1200 mm / s, powder layer thickness 30 μm, scanning line spacing 0.1 mm, spot diameter 75 μm, titanium alloy substrate is selected, and preheating is performed to 80 DEG C to start printing, a serpentine scanning strategy is adopted, and interlayer rotation is 67 DEG.

[0018] TA15 alloy mechanical test bars are subjected to low-temperature heat treatment, the size of the test bar is ø13*80 mm, the test bar is placed into a high-vacuum annealing furnace, vacuum degree is extracted to be lower than 2.3*10 -3 Pa, heating is performed to 500 DEG C at a heating rate of 10 DEG C / min, 2h is kept, the furnace is cooled to room temperature, and additive manufacturing TA15 alloy after low-temperature heat treatment is obtained. Example 2

[0019] The difference from example 1 is that heating is performed to 540 DEG C at a heating rate of 10 DEG C / min. Example 3

[0020] The difference from example 1 is that heating is performed to 575 DEG C at a heating rate of 10 DEG C / min.

[0021] Comparative example 1: The difference from example 1 is that heating is performed to 650 DEG C at a heating rate of 10 DEG C / min.

[0022] Comparative example 2: The difference from example 1 is that heating is performed to 850 DEG C at a heating rate of 10 DEG C / min.

[0023] Comparative example 3: The difference from example 1 is that subsequent low-temperature heat treatment is not performed.

[0024] Microstructure observation is performed on additive manufacturing TA15 alloys obtained in examples 1-3 and comparative examples 1-3, as shown in the following table. Figure 1 Microstructures of the additive manufacturing TA15 alloys of comparative example 3, example 1, example 2 and example 3 all present basket organization appearance, and are mainly needle-shaped alpha prime martensite. Since low-temperature heat treatment can cause alpha prime martensite to decompose, beta stable element rich microzones in the interior are converted into beta phase, and the boundary of needle-shaped alpha prime martensite becomes blurred, and this phenomenon is most obvious in example 1. It can be seen from the microstructures of the additive manufacturing TA15 alloys of example 1, example 2 and example 3 that with the gradual increase of heat treatment temperature, the needle-shaped alpha prime martensite appears to be coarsened.

[0025] The microstructure of the additive manufacturing TA15 alloy obtained by the comparative example 1 has partially needle-like alpha prime martensite transformed into balanced lath-like alpha and a small amount of beta phase at the interface, and the organization coarsening is more obvious. The microstructure of the additive manufacturing TA15 alloy obtained by the comparative example 2 has been completely transformed into lath-like alpha + beta balanced organization, and the needle-like alpha prime martensite morphology has disappeared.

[0026] Then, the mechanical properties of the additive manufacturing TA15 alloys obtained by the examples 1-3 and the comparative examples 1-3 are tested, and the results are shown in Table 1: Table 1: Mechanical property test results of the additive manufacturing TA15 alloys obtained by the examples 1-3 and the comparative examples 1-3

[0027] According to the data in Table 1, the tensile properties, yield strength, tensile strength and Vickers hardness of the additive manufacturing TA15 alloys obtained by the examples 1-3 are 5-7% better than those of the comparative example 3 at room temperature, the plasticity is not reduced, and the overall performance is obviously better than that of the additive manufacturing TA15 alloys obtained by the comparative examples 1 and 2.

[0028] In summary Figure 1 According to the data in Table 1, the present application adopts low-temperature heat treatment at 500-575 DEG C, which promotes the incomplete decomposition of the non-equilibrium needle-like alpha prime martensite, and the micro-area rich in beta stable elements in the interior further enriches through uphill diffusion, and is transformed into beta phase, which improves the stability of the alpha prime matrix and produces a dispersion strengthening effect, significantly improving the yield strength and tensile strength of the alloy. In contrast, the two-phase zone annealing treatment used in the traditional heat treatment process is usually at a temperature higher than 600 DEG C for a long time, which causes the needle-like alpha prime martensite with high hardness to transform into lath-like alpha + beta balanced organization, and the microstructure will have a tendency to obviously coarsen, which greatly reduces the strength and hardness of the alloy and reduces the comprehensive mechanical properties of the alloy. In addition, the temperature used in the traditional heat treatment method is relatively high, which increases the production cost and operation difficulty.

[0029] The above only describes the preferred embodiments of the present application, and it should be noted that for ordinary skilled persons in the technical field, several improvements and modifications can be made without departing from the technical principles of the present application, and these improvements and modifications should also be considered as the protection scope of the present application.

Claims

1. A low-temperature heat treatment method for improving the strength of TA15 alloy in additive manufacturing, characterized in that, include: The additively manufactured TA15 alloy was placed in a vacuum environment and heated to 500-575°C at a heating rate of 10-20°C / min. After holding at this temperature for 2-4 hours, it was cooled to room temperature to obtain the additively manufactured TA15 alloy after low-temperature heat treatment.

2. The low-temperature heat treatment method for improving the strength of additive manufacturing TA15 alloy according to claim 1, characterized in that, The additive manufacturing process employs laser selective melting.

3. The low-temperature heat treatment method for improving the strength of additive manufacturing TA15 alloy according to claim 2, characterized in that, The process parameters of the laser selective melting process include a laser power of 220~340W, a scanning speed of 900~1350mm / s, a powder thickness of 30μm, a scanning line spacing of 0.1mm, a spot diameter of 75μm, a substrate preheating to 80℃, a serpentine scanning strategy, and an interlayer rotation of 67°.

4. The low-temperature heat treatment method for improving the strength of additive manufacturing TA15 alloy according to claim 1, characterized in that, The vacuum level of the vacuum environment is less than 2.3 × 10⁻⁶. -3 Pa.

5. The low-temperature heat treatment method for improving the strength of additive manufacturing TA15 alloy according to claim 1, characterized in that, The heating, heat preservation, and cooling to room temperature are carried out using the furnace heating and cooling method.

6. An additive manufacturing method for TA15 alloy, characterized in that, It is prepared by the low-temperature heat treatment method for improving the strength of additive manufacturing TA15 alloy as described in any one of claims 1 to 5.

7. The additive manufacturing TA15 alloy according to claim 6, characterized in that, The additively manufactured TA15 alloy has a yield strength of not less than 1180 MPa and a tensile strength of not less than 1230 MPa.

8. The additive manufacturing TA15 alloy according to claim 6, characterized in that, The additively manufactured TA15 alloy has an elongation after fracture of 6-10% and a Vickers hardness of 380-420 HV.

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