A method for the preparation of an ultrasonic wave assisted additive manufacturing titanium alloy material

Abstract

The application discloses a preparation method of ultrasonic wave assisted additive manufacturing of titanium alloy material, and the titanium alloy material substrate is subjected to ultrasonic vibration while electric arc additive manufacturing, the ultrasonic wave is transmitted to the molten pool through the substrate, and the cavitation effect and convection are utilized to promote the breaking of columnar crystals and the formation of equiaxed crystals. The application prepares a titanium alloy material with a bicrystal grain morphology by alternately using the method of ultrasonic vibration assisted additive manufacturing. The prepared titanium alloy can consider the plasticity and strength of the material to a certain extent, so that the TC4 titanium alloy with excellent comprehensive performance is obtained. As can be seen from the experimental results, the technical scheme of the application can control the grain morphology of the electric arc additive manufacturing TC4 titanium alloy, and provides a new way for improving the mechanical properties of the electric arc additive manufacturing TC4 titanium alloy.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of titanium alloy manufacturing, and in particular to a preparation method of a titanium alloy material prepared through ultrasonic wave assisted additive manufacturing. BACKGROUND

[0002] TC4 titanium alloy (Ti-6Al-4V) is a typical alpha + beta two-phase titanium alloy, which has high specific strength and good high-temperature and corrosion resistance. Its output has accounted for half of the total global titanium alloy output, and it has been widely used in the fields of aerospace, shipbuilding, military and the like. However, the TC4 titanium alloy has poor machinability and is difficult to prepare components with complex shapes. In recent years, the rapidly developing additive manufacturing technology has shown great advantages in solving this problem. Among them, the electric arc additive manufacturing technology has the advantages of high deposition rate, high raw material utilization rate and low cost, and thus is outstanding among many additive manufacturing methods. However, the unique thermal cycle and thermal history in the electric arc additive manufacturing process cause the grains to grow in the direction opposite to the maximum temperature gradient, which inevitably leads to the formation of coarse columnar crystals. This unique microstructure makes the mechanical properties of the components exhibit anisotropy, which limits the further application of the electric arc additive manufacturing TC4 titanium alloy in actual engineering. Therefore, how to inhibit the growth of columnar crystals so as to make the electric arc additive manufacturing parts obtain an ideal strength and plasticity combination has become the main problem currently faced.

[0003] Through literature retrieval of the prior art, it is found that Yandong Jing et al. published a paper entitled "Improved tensile strength and fatigue properties of wire-arc additively manufactured 2319 aluminum alloy by surface laser shock peening" in Materials Science and Engineering: A, 2023, 7: 144599. In the paper, laser shock peening (LSP) is used to post-process the electric arc additive manufactured 2319 aluminum alloy. The principle of LSP is that a high-intensity shock wave formed by plasma explosion on the metal surface is used to act on the metal surface through a high-energy pulsed laser. The characteristics of the technology are as follows: (1) the yield strength and tensile strength of the 2319 aluminum alloy treated by LSP are increased by 151.2% and 13.7%, respectively. (2) The total number of pores in the LSP affected layer is reduced by 65.3%. (3) The fatigue life of the electric arc additive manufactured 2319 aluminum alloy treated by LSP is greatly increased. However, the technology has a limited depth of action on the material, and cannot further strengthen the interior of the sample.

[0004] Further search found that Mingfang Xu published a paper entitled "Grain refinement and mechanical properties improvement of Inconel 625 alloy fabricated by ultrasonic-assisted wire and arc additive manufacturing" in Journal of Alloys and Compounds, 2022, 910: 164957, which used ultrasonic assistance in the process of arc additive manufacturing of Inconel 625 alloy based on the unique cavitation effect of ultrasonic waves, and high-frequency oscillation was performed on the liquid molten pool, which affected the grain formation process. The results of this technology show that: (1) ultrasonic waves significantly inhibit the growth of columnar crystals and promote the columnar-to-equiaxed transition (CET). (2) The cavitation effect and acoustic streaming reduce the temperature gradient and promote the reduction of harmful phase content. (3) Grain refinement significantly increases the tensile strength of the alloy. However, the refinement of the grains has an adverse effect on the elongation of the alloy, and the plasticity is only 76.16% of the original. SUMMARY

[0005] The purpose of the present application is to provide a preparation method of ultrasonic-assisted additive manufacturing of titanium alloy material. By arc additive manufacturing assisted by alternating ultrasonic vibration, titanium alloy with bimodal grain morphology of columnar and equiaxed crystals is prepared, so as to improve the comprehensive mechanical properties of arc additive manufacturing TC4 titanium alloy.

[0006] In order to achieve the above purpose, the present application is implemented according to the following technical solutions:

[0007] The present application applies ultrasonic vibration to the titanium alloy material substrate during arc additive manufacturing, and the ultrasonic wave is transmitted to the molten pool through the substrate, which promotes the breaking of columnar crystals and the formation of equiaxed crystals through cavitation effect and convection.

[0008] Specifically, the following steps are included:

[0009] S1: The titanium alloy material substrate is surface pretreated and then fixed using a tool clamp; the surface pretreatment is: after removing the surface oxide layer by using SiC sandpaper polishing, wiping and drying with acetone.

[0010] S2: The ultrasonic vibration head of the ultrasonic auxiliary system is fixed to the center position directly below the titanium alloy material substrate, and the ultrasonic vibration head and the welding torch of the ultrasonic auxiliary system are always in the same plane; preferably, the ultrasonic vibration head of the ultrasonic auxiliary system is pressed on the center position directly below the titanium alloy material substrate, and the pressure value is set to 0.2 MPa.

[0011] S3: Start the electric arc additive manufacturing system and the ultrasonic auxiliary system, and deposit the first layer on the titanium alloy material substrate by transporting the titanium alloy welding wire through the coaxial wire feeder;

[0012] S4: Turn off the ultrasonic vibration device, and after cooling, raise the welding torch for the deposition of the second layer;

[0013] S5: Repeat step S4, deposit layer by layer until the required titanium alloy thin-walled forming part is obtained, turn off the electric arc additive manufacturing system and the ultrasonic auxiliary system, and complete the preparation of the titanium alloy material after cooling.

[0014] Preferably, the titanium alloy material substrate is an annealed TC4 titanium alloy, which comprises Al 6.10%, V 3.90%, Fe 0.15%, C 0.08%, and Ti balance; the titanium alloy welding wire comprises Al 6.05%, V 4.0%, Fe 0.15%, C 0.02%, and Ti balance. The ultrasonic auxiliary system has an ultrasonic frequency of 20 kHz and an ultrasonic amplitude of 50 μm; the electric arc additive manufacturing system has a current of 130 A, a voltage of 11.7 V, a wire feeding speed of 5.3 m / min, a travel speed of 0.48 m / min, and an argon flow rate of 15 L / min. The cooling time of step S4 is 120 s. The welding torch of the electric arc additive manufacturing system is a single deposition welding torch. That is, the welding torch starts from the arc starting position and stops at the arc stopping position, and all the deposition layers have the same travel direction.

[0015] The beneficial effects of the present application are:

[0016] The present application is a preparation method of ultrasonic wave assisted additive manufacturing of titanium alloy material. Compared with the prior art, the present application prepares a titanium alloy material with a bicrystal grain morphology by alternately using the ultrasonic vibration assisted additive manufacturing method. The prepared titanium alloy can balance the plasticity and strength of the material to some extent, thereby obtaining a TC4 titanium alloy with excellent comprehensive performance. As can be seen from the experimental results, the technical scheme of the present application can control the grain morphology of the electric arc additive manufacturing TC4 titanium alloy, and provides a new way to improve the mechanical properties of the electric arc additive manufacturing TC4 titanium alloy. BRIEF DESCRIPTION OF DRAWINGS

[0017] Figure 1 It is a schematic diagram of the ultrasonic vibration assisted electric arc additive manufacturing process of the present application;

[0018] Wherein 1-welding gun, 2-welding wire, 3-nozzle, 4-substrate, 5-ultrasonic vibration gun;

[0019] Figure 2 For the macroscopic morphology of the TC4 titanium alloy thin wall prepared by alternately applying ultrasonic vibration assisted electric arc additive manufacturing according to the technical scheme of the present application;

[0020] Figure 3 For the hardness statistical column chart of different deposited layers;

[0021] Wherein 1, 3-applied vibration layer, 2, 4-unapplied vibration layer. DETAILED DESCRIPTION

[0022] The present application will be further described below in conjunction with the accompanying drawings and specific embodiments, wherein the illustrative embodiments and descriptions of the present application are used to explain the present application, but are not limiting to the present application.

[0023] The present application is based on the existing ultrasonic assisted additive manufacturing technology, and proposes a method for alternately applying ultrasonic vibration to assist electric arc additive manufacturing of TC4 titanium alloy. The specific idea is as follows: the deposited layer not subjected to ultrasonic vibration grows in a columnar crystal form, so as to ensure that the prepared TC4 titanium alloy has good plasticity; and the deposited layer subjected to ultrasonic vibration assistance presents an equiaxed crystal form under the action of ultrasonic waves, so as to promote the improvement of the strength of the prepared TC4 titanium alloy. By preparing a microstructure in which columnar crystals and equiaxed crystals coexist, an effective way is provided for simultaneously improving the strength and plasticity of the electric arc additive manufactured TC4 titanium alloy.

[0024] As shown in Figure 1 The present preparation method involves devices mainly including the following two systems.(1) Electric arc additive manufacturing system: the CMT TPS-4000 welding machine produced by Fronius Company is adopted in the embodiment of the present application, and a welding gun, a KUKA mechanical arm, a wire feeding mechanism and a circulating water cooling device are adopted.(2) Ultrasonic auxiliary system provided by Shandong Kai Ze Hengxin Machinery Co., Ltd., including an ultrasonic vibration gun and a workbench, an ultrasonic generator and an air compressor. The TC4 welding wire produced by Baoji Titanium Industry Co., Ltd. is selected, and the diameter is 1.2 mm, wherein the element composition ratio is as follows: Al 6.05%, V 4.0%, Fe 0.15%, C 0.02%, Ti balance. The annealed TC4 titanium alloy is selected as the substrate, and the size of the substrate is 200 mm*100 mm*3 mm, wherein the element composition ratio is as follows: Al 6.10%, V 3.90%, Fe 0.15%, C 0.08%, Ti balance.

[0025] S1: After polishing to remove the surface oxidation layer, wiping and drying with acetone, the substrate is fixed on the workbench through a fixture;

[0026] S2: The air compressor provides pressure to press the ultrasonic vibration gun against the center of the bottom of the substrate and keep it constant. The pressure value is set to 0.2MPa, and the welding gun is controlled to move above the substrate.

[0027] S3: Turn on the arc additive manufacturing system and ultrasonic-assisted system, set the current to 130A, voltage to 11.7V, wire feed speed to 5.3m / min, travel speed to 0.48m / min, argon flow rate to 15L / min, ultrasonic frequency to 20kHz, ultrasonic amplitude to 50μm, and interlayer cooling time to 120s. Deposition is performed layer by layer to obtain the desired TC4 titanium alloy part.

[0028] Before deposition, the ultrasonic vibrator is activated to ultrasonically vibrate the substrate. The first layer is then deposited according to the pre-set arc additive manufacturing parameters. Once deposition is complete, the ultrasonic vibrator is immediately deactivated. After a 120-second cooldown, the welding torch is raised 2mm to deposit the second layer, while the ultrasonic vibrator is deactivated. After another 120-second cooldown, the ultrasonic vibrator is reactivated to deposit the third layer. These steps are repeated until the desired thin-walled component is achieved.

[0029] The prepared TC4 titanium alloy thin-walled components were analyzed and tested. The specific implementation steps are as follows:

[0030] Wire cutting was used to select samples from the stable middle area of ​​the prepared TC4 titanium alloy thin-walled deposit layer, ensuring that the selected sample size included the deposited layer with or without vibration. The sample was mounted and polished with SiC sandpaper. It was then polished with a polishing machine until it finally showed a mirror effect and then etched. The etchant used was an etchant with a ratio of 41% HF: 68% HNO3: H2O = 1:3:27, and the etching time was 8 to 10 seconds. The microstructure of the deposited sample was observed using an MR5000 inverted optical microscope, and the hardness test was performed using a microhardness tester model 401MVD. The test load was 200g and the holding time was 10 seconds.

[0031] like Figure 2 、 3 As shown in the figure, the microstructure of the corroded samples was analyzed. In the deposited layer without ultrasonic assistance, the microstructure was dominated by coarse columnar crystals; in the deposited layer with ultrasonic assistance, a large number of equiaxed crystals appeared. Compared with the deposited layer without ultrasonic assistance, the ultrasonic vibration-assisted layer exhibited grain refinement and a corresponding increase in hardness. These results demonstrate that alternating ultrasonic vibrations during arc additive manufacturing can produce TC4 titanium alloy thin walls with a twinned morphology of columnar and equiaxed crystals.

[0032] In summary, the deposited layer subjected to the ultrasonic-assisted additive manufacturing mainly forms equiaxed crystals, and the deposited layer not subjected to the ultrasonic assistance forms a large number of columnar crystals. The formed part obtained by the improved method is subjected to experimental inspection, and it can be observed under a light microscope that the micro-morphology of the deposited layer subjected to the ultrasonic vibration presents equiaxed crystals, and the deposited layer not subjected to the ultrasonic vibration shows a typical columnar crystal morphology. The hardness test results show that the microhardness of the deposited layer subjected to the ultrasonic vibration is 305.98±14.99HV, and the microhardness of the deposited layer not subjected to the ultrasonic vibration is 272.86±13.06HV. It is indicated that the present application can regulate the microstructure morphology of the arc additive manufacturing TC4 titanium alloy, and significantly improve the mechanical properties.

[0033] The technical scheme of the present application is not limited to the above specific embodiments, and any technical transformation made according to the technical scheme of the present application falls within the protection scope of the present application.

Claims

1. A method for preparing titanium alloy materials by ultrasonic-assisted additive manufacturing, characterized in that: During arc additive manufacturing, ultrasonic vibration is applied to the titanium alloy substrate. The ultrasonic wave is transmitted to the molten pool through the substrate, promoting the breakage of columnar crystals and the formation of equiaxed crystals through cavitation effect and convection. The specific steps include: S1: The titanium alloy substrate is subjected to surface pretreatment and then fixed using a fixture; S2: The ultrasonic vibration head of the ultrasonic-assisted system is fixed at the center position directly below the titanium alloy material substrate, and the ultrasonic vibration head and the welding gun of the ultrasonic-assisted system are always in the same plane; the ultrasonic vibration head of the ultrasonic-assisted system is pressed at the center position directly below the titanium alloy material substrate, and the pressure value is set to 0.2 MPa; the titanium alloy material substrate is annealed TC4 titanium alloy, including Al 6.10%, V 3.90%, Fe 0.15%, C 0.08%, and Ti as a balance; the titanium alloy welding wire includes Al 6.05%, V 4.0%, Fe 0.15%, C 0.02%, and Ti as a balance; S3: Starting the arc additive manufacturing system and the ultrasonic-assisted system, feeding the titanium alloy welding wire through the coaxial wire feeder, and depositing the first layer on the titanium alloy substrate; the ultrasonic-assisted system has an ultrasonic frequency of 20 kHz and an ultrasonic amplitude of 50 µm; the arc additive manufacturing system has a current of 130 A, a voltage of 11.7 V, a wire feeding speed of 5.3 m / min, a travel speed of 0.48 m / min, and an argon gas flow rate of 15 L / min; the deposited layer assisted by ultrasonic vibration exhibits an equiaxed crystal morphology under the action of ultrasonic waves; S4: Turn off the ultrasonic vibration device, and after cooling, raise the welding gun to deposit the second layer; the cooling time is 120 s; the deposited layer not subjected to ultrasonic vibration grows in the form of columnar crystals; S5: Repeat steps S3 to S4, depositing layer by layer to obtain a titanium alloy thin-walled molded part with a double-grain morphology of columnar crystals and equiaxed crystals, turn off the arc additive manufacturing system and the ultrasonic auxiliary system, and complete the preparation of the titanium alloy material after cooling.

2. The method for preparing titanium alloy material by ultrasonic-assisted additive manufacturing according to claim 1, characterized in that: The surface pretreatment in step S1 is: using SiC sandpaper to polish and remove the surface oxide layer and then wiping and drying with acetone.

3. The method for preparing titanium alloy material by ultrasonic-assisted additive manufacturing according to claim 1, characterized in that: The welding gun of the arc additive manufacturing system is a single-phase deposition welding gun.

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