Ultrasonic-assisted SLM (selective laser melting) Ti-O alloy forming device and working method

Abstract

The invention relates to an ultrasonic-assisted SLM (selective laser melting) Ti-O alloy forming device and a working method.The ultrasonic-assisted SLM Ti-O alloy forming device comprises a sealed cavity used for being filled with high-purity argon, a base table is arranged in the sealed cavity, and an ultrasonic vibration integrated platform connected with an ultrasonic generator is mounted on the base table; a base plate located on the upper side of the ultrasonic vibration integration platform and used for laying powder is installed on the base table, a scraper powder laying mechanism is arranged on the upper side of the base plate, and a laser beam generating device used for acting on the powder is arranged above the base plate. According to the device and the method, the microscopic structure of the Ti-O alloy can be changed, so that the forming quality and the comprehensive mechanical property of the SLM formed Ti-O alloy are improved.

Description

Technical Field

[0001] The invention relates to a device and a working method for ultrasonic-assisted SLM forming of a Ti-O alloy. Background Art

[0002] Titanium and its alloys are widely used in the production and manufacturing of implants and dental implants for missing tissues such as medical hip joints, knee joints, shoulder joints, and skulls due to their low density, high specific strength, good corrosion resistance, and excellent biocompatibility. Among the existing medical titanium alloy systems, commercial pure titanium (CP-Ti) has excellent biocompatibility, but its mechanical properties are relatively low, and there is a risk of fracture under long-term loads in the human body. The mechanical properties of titanium alloys can be made to meet the requirements of use by adding elements. However, other alloying elements (such as Al, V, etc.) added will release metal ions during service in the human body, affecting the safety and biocompatibility of titanium alloys. At the same time, strengthening its mechanical properties by adding other non-toxic neutral metal elements such as Co, Mo, and Nb will increase its cost and the complexity of the preparation process, further limiting the wide application of titanium alloys. Therefore, by adding non-metallic elements such as oxygen, nitrogen, and carbon into the CP-Ti matrix in the form of interstitial atoms, the mechanical properties of CP-Ti can be significantly improved while maintaining low cost and excellent biocompatibility of the titanium matrix. This has become one of the important means for researchers to strengthen the mechanical strength of medical titanium alloys.

[0003] Existing research on solid solution oxygen strengthened titanium alloys is mainly based on preparation methods such as vacuum arc melting or powder metallurgy, and is further formed by cold working. However, since α-Ti has a typical close-packed hexagonal structure, its matrix material has a high work hardening rate and relatively poor thermal conductivity. The traditional method of processing titanium alloys has problems such as difficulty in cutting and plastic processing, serious heat accumulation in the local area of ​​deformation, and easy pollution of the material. Especially for Ti-O materials, their solid solution oxygen atoms significantly increase the strength and work hardening rate of the material, making its plastic processing more difficult, which limits the application of solid solution oxygen strengthened titanium alloys in the manufacture of medical implant devices.

[0004] Selective laser melting (SLM) is a powder additive manufacturing process that uses a computer-controlled laser beam to melt selected areas of a powder layer under a protective atmosphere to manufacture products. As one of the most popular additive manufacturing technologies, existing literature suggests that SLM-formed titanium alloys have high cleanliness, good forming accuracy, fine grain structure of formed components, excellent mechanical properties, and can directly form difficult-to-process metal material systems with complex shapes. Therefore, compared with traditional process paths, the preparation of customized medical titanium alloy implants by direct SLM forming has significant advantages. Another document pointed out that the tribological properties of titanium alloy specimens produced by SLM are better than those of cast specimens. Compared with cast specimens, SLM technology can easily and once manufacture customized specimens due to the high degree of design freedom brought by the principle of layer-by-layer forming, which greatly improves the material utilization rate of titanium alloys and shortens their manufacturing cycle. Furthermore, compared with traditional forming processing technology, SLM forming of titanium alloys is usually carried out in a laser working chamber filled with inert gases (such as helium and argon), which fully avoids the contamination of titanium alloys during the forming process. At the same time, the SLM forming process has the characteristics of rapid melting, cooling, and solidification, resulting in grain refinement, which makes SLM-printed titanium alloys have better comprehensive mechanical properties.

[0005] However, SLM-formed titanium alloys are prone to porosity defects inside the formed samples, including circular pores and irregular incomplete pores, which lead to low density and affect the comprehensive mechanical properties of the material. "The influence of layer thickness on the microstructure and properties of Ti-5Al-2.5Sn alloy formed by selective laser melting" explores the influence of SLM process on the actual shape, size and morphology of the surface texture of Ti-6Al-4V titanium alloy. It is found that due to the fixed laser power, with the increase of layer thickness and scanning rate, the laser body energy density continues to decrease, and porosity defects, including circular pores and irregular incomplete pores, appear inside the sample with low density.

[0006] A large number of existing studies have proposed the use of ultrasonic-assisted additive manufacturing of titanium alloys. Some literature has also proposed the introduction of high-intensity ultrasonic vibration into the TC4-DT titanium alloy wire arc direct energy deposition technology. It was found that ultrasonic-assisted vibration significantly improved the grain structure of the deposited component without introducing additional porosity. The yield strength and tensile strength of the alloy were increased by 22.23% and 15.06% respectively compared with the traditional wire arc direct energy deposition components. In addition, the difference in the lath-like α grain structure caused by the induced difference in fatigue crack propagation behavior. The disordered orientation of the lath-like α grains enhances the fatigue cracking resistance of the ultrasonic-assisted vibration wire arc direct energy deposition components. However, for ultrasonic-assisted additive titanium alloys, most of the research focuses on arc additive and laser wire preparation of titanium alloys. The molten pool behavior in the additive process is very different from that of SLM technology. There is little research on ultrasonic-assisted SLM preparation of titanium alloys, which is still in the development stage.

[0007] In summary, the combination of adding TiO2 particles and SLM technology can effectively improve the strength of Ti-O alloys. However, due to the defects of circular pores and irregular incomplete pores in the SLM process, the plasticity of Ti-O alloys will be adversely affected. In addition, the technology of preparing Ti-O alloys by ultrasonic-assisted SLM is still in the development stage. Based on the above shortcomings in the SLM technology for preparing Ti-O alloys, it is urgent to develop a working method for ultrasonic vibration-assisted SLM forming. Summary of the invention

[0008] The object of the present invention is to provide a device and a working method for ultrasonic-assisted SLM forming of Ti-O alloy, which are helpful to change the microstructure of Ti-O alloy, thereby improving the forming quality and comprehensive mechanical properties of SLM formed Ti-O alloy.

[0009] The technical solution of the present invention is: a device for ultrasonically assisted SLM forming of Ti-O alloy, comprising a sealed chamber for filling with high-purity argon gas, a base is arranged in the sealed chamber, an ultrasonic vibration integrated platform connected to an ultrasonic generator is installed on the base, a substrate located on the upper side of the ultrasonic vibration integrated platform and used for laying powder is installed on the base, a scraper powder laying mechanism is arranged on the upper side of the substrate, and a laser beam generating device for acting on the powder is arranged above the substrate.

[0010] Furthermore, an argon gas inlet pipe is provided on one side of the sealed cavity, and an input end of the argon gas inlet pipe is connected to a high-purity argon gas source.

[0011] Furthermore, the ultrasonic vibration integrated platform is fixed on a base, and both sides of the base plate are connected to the base via vertical portions respectively.

[0012] Furthermore, a layer of flexible foam cotton is filled between the bottom surface of the substrate and the ultrasonic vibration integrated platform.

[0013] Furthermore, the scraper powder spreading mechanism includes a scraper driven by a first driving mechanism to move laterally, and is provided with a second driving mechanism to drive the first driving mechanism to move up and down.

[0014] Furthermore, the laser beam generating device comprises a fiber laser, and the fiber laser is connected to a galvanometer-lens system acting downward on the upper surface of the substrate via a flexible optical fiber.

[0015] A working method for ultrasonic vibration assisted SLM forming of Ti-O alloy, using an ultrasonic assisted SLM forming device of Ti-O alloy, comprising the following steps: (1) CP-Ti powder and TiO2 powder are mixed in a certain proportion and mixed in a powder mixer to form TiO2 / Ti mixed powder; (2) High-purity argon gas is filled into the sealed chamber, and then the TiO2 / Ti mixed powder is spread on the substrate through a scraper powder spreading mechanism; (3) Turn on the ultrasonic generator and transmit the ultrasonic vibration to the spread TiO2 / Ti mixed powder on the substrate through the ultrasonic vibration integrated platform; (4) Turn on the fiber laser, and the emitted laser beam is transmitted by the flexible optical fiber to the galvanometer-lens system, and finally acts on the spread TiO2 / Ti mixed powder; while turning on the fiber laser, turn on the ultrasonic generator and use its acoustic cavitation effect to change the flow and solidification behavior of the molten pool, thereby changing the microstructure of the Ti-O alloy.

[0016] Furthermore, the powder mixer is a planetary ball mill.

[0017] Furthermore, the mixing time of the powder mixer is 110-130 min, and the rotation speed is 180-220 rpm / min.

[0018] Furthermore, in the stage of spreading TiO2 / Ti mixed powder, the power of ultrasound is 50~70W and the frequency is 25~35Khz; in the stage of SLM forming Ti-O alloy, the power of ultrasound is 110~130W and the frequency is 25~35Khz.

[0019] Compared with the prior art, the present invention has the following advantages: (1) Excellent performance: Ultrasonic vibration is used to assist SLM forming of Ti-O alloy. By utilizing its acoustic cavitation effect, ultrasonic assisted vibration with different process parameters is introduced during the powder laying stage and the SLM additive process to change the flow and solidification behavior of the molten pool, thereby changing the microstructure of the Ti-O alloy, thereby improving the forming quality and comprehensive mechanical properties of the SLM formed Ti-O alloy.

[0020] (2) The Ti-O alloy prepared by this method has excellent biocompatibility and mechanical properties, meeting the safety requirements of implants during their service in the human body.

[0021] (3) The device for ultrasonic vibration-assisted SLM forming of Ti-O alloy integrates the ultrasonic vibration integrated platform and the substrate for spreading powder. The device has a simple structure and is easy to implement. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 Schematic diagram of the ultrasonic vibration assisted SLM forming device of Ti-O alloy of the present invention; Figure 2 The working process of the device for ultrasonic-assisted SLM forming of Ti-O alloy in the present invention; Figure 3 is the element content of the Ti-O alloy of the present invention; Figure 4 is a microscopic photograph of the TiO2 / Ti mixed powder after being mixed in a ball mill according to the present invention; Figure 5 This is a scanning electron microscope photo of the ultrasonic assisted formed Ti-O alloy of the present invention after electrolytic polishing; Figure 6 This is a metallographic photograph of the microstructure of the ultrasonic assisted formed Ti-O alloy of the present invention; Figure 7 is the stress-strain curve of the ultrasonic assisted forming Ti-O alloy of the present invention; In the figure: 1-sealed chamber 2-base 3-ultrasonic vibration integrated platform 4-substrate 5-scraper powder spreading mechanism 6-galvanometer-lens system 7-fiber laser 8-formed Ti-O sample 9-ultrasonic generator 10-argon gas inlet pipe 11-high-purity argon gas source. DETAILED DESCRIPTION

[0023] In order to make the above features and advantages of the present invention more easily understood, embodiments are given below with reference to the accompanying drawings for detailed description, but the present invention is not limited thereto.

[0024] refer to Figures 1 to 7 A device for ultrasonic-assisted SLM forming of Ti-O alloy, comprising a sealed chamber 1 for filling with high-purity argon gas and capable of being sealed, a base 2 is arranged in the sealed chamber, an ultrasonic vibration integrated platform 3 connected to an ultrasonic generator 9 is installed on the base, a substrate 4 located on the upper side of the ultrasonic vibration integrated platform and used for laying powder is installed on the base, a scraper powder laying mechanism 5 is arranged on the upper side of the substrate, and a laser beam generating device for acting on the powder is arranged above the substrate, such as Figure 1 shown.

[0025] In this embodiment, an argon gas inlet pipe 10 is provided on one side of the sealed cavity, and the input end of the argon gas inlet pipe is connected to a high-purity argon gas source 11, so as to control the on-off of the high-purity argon gas.

[0026] In this embodiment, the sealed chamber is provided with a discharge window and is sealable so that the sealed chamber can be closed after the powder is placed on the substrate.

[0027] In this embodiment, the ultrasonic vibration integrated platform is fixed on a base, and both sides of the base plate are connected to the base via vertical portions respectively.

[0028] In this embodiment, a layer of flexible foam cotton is filled between the bottom surface of the substrate and the ultrasonic vibration integrated platform to prevent the attenuation of ultrasonic vibration.

[0029] In this embodiment, the scraper powder spreading mechanism includes a scraper driven by a first driving mechanism to move laterally, and a second driving mechanism is provided to drive the first driving mechanism to move up and down. Thus, the scraper is driven to move laterally and to be adjusted up and down. For example, the first driving mechanism can be a laterally arranged slide cylinder, and the scraper is installed on the slide of the slide cylinder and extends forward to the upper side of the substrate. The second driving mechanism can be a vertically arranged electric cylinder, and the telescopic rod of the electric cylinder is connected to the bottom surface of the slide cylinder, thereby driving the slide cylinder to drive the scraper to move up and down.

[0030] In this embodiment, the laser beam generating device includes a fiber laser 7, which is connected to a galvanometer-lens system 6 acting downward on the upper surface of the substrate via a flexible optical fiber, so that the laser beam emitted by the fiber laser 7 is transmitted by the flexible optical fiber to the galvanometer-lens system 6 and finally acts on the spread powder.

[0031] See also Figure 2 A method for ultrasonic vibration assisted SLM forming of Ti-O alloy, a device for ultrasonic assisted SLM forming of Ti-O alloy, comprising the following steps: (1) CP-Ti powder and TiO2 powder are mixed in a certain proportion and mixed in a powder mixer to form a uniformly mixed TiO2 / Ti mixed powder; Figure 3 and Figure 4 As shown; (2) High-purity argon gas is filled into the sealed chamber, and then the TiO2 / Ti mixed powder is spread on the substrate 4 by the scraper powder spreading mechanism 5; (3) Turn on the ultrasonic generator 9, transmit the ultrasonic vibration to the spread TiO2 / Ti mixed powder on the substrate 4 through the ultrasonic vibration integrated platform 3, and improve the spreading quality of the powder by introducing ultrasonic auxiliary vibration of a certain power and frequency; (4) SLM forming process of Ti-O alloy: Turn on the fiber laser 7, and the laser beam emitted by the fiber laser is transmitted by the flexible optical fiber to the galvanometer-lens system 6, and finally acts on the spread TiO2 / Ti mixed powder; while turning on the fiber laser, turn on the ultrasonic generator 9, and use its acoustic cavitation effect to change the flow and solidification behavior of the molten pool, change the microstructure of the Ti-O alloy, and thus obtain a Ti-O alloy with a finer microstructure and better comprehensive mechanical properties.

[0032] In this embodiment, the oxygen content of the Ti-O material is designed to be 0.10-0.30 wt.%.

[0033] In this embodiment, the powder mixer is a planetary ball mill, and a mixed powder with a uniform oxygen content distribution is directly obtained by using a mixing method using a planetary ball mill.

[0034] In this embodiment, the mixing time of the powder mixer is 110-130 min, and the rotation speed is 180-220 rpm / min. Specifically, for example, the mixing time is 110 min, and the rotation speed is 180 rpm / min; or the mixing time is 120 min, and the rotation speed is 200 rpm / min; or the mixing time is 130 min, and the rotation speed is 220 rpm / min.

[0035] In this embodiment, during the spreading of the TiO2 / Ti mixed powder, the ultrasonic power is 50-70W and the frequency is 25-35Khz, so as to improve the spreading quality of the powder. During the SLM forming of the Ti-O alloy, the ultrasonic power is 110-130W and the frequency is 25-35Khz, so as to change the microstructure of the Ti-O alloy.

[0036] For example, in the stage of spreading TiO2 / Ti mixed powder, the ultrasonic power is 50W and the frequency is 25Khz; or the ultrasonic power is 70W and the frequency is 35Khz. In the stage of SLM forming Ti-O alloy, the ultrasonic power is 110W and the frequency is 25Khz; or the ultrasonic power is 130W and the frequency is 35Kh.

[0037] Specifically, in a preferred embodiment, in the stage of spreading TiO2 / Ti mixed powder, the power of the ultrasonic wave is 60W and the frequency is 28Khz; in the stage of SLM forming Ti-O alloy, the power of the ultrasonic wave is 120W and the frequency is 28Khz. The surface quality of Ti-O alloy prepared by ultrasonic assisted SLM is as follows: Figure 5 As shown, the microstructure Figure 6 The stress-strain curve is as follows: Figure 7 shown.

[0038] The above description is only a preferred embodiment of the present invention. For ordinary technicians in this field, according to the teachings of the present invention, designing different forms of ultrasonic-assisted SLM forming Ti-O alloy devices and working methods does not require creative labor. Without departing from the principles and spirit of the present invention, all equal changes, modifications, substitutions and variations made within the scope of the patent application of the present invention should fall within the scope of the present invention.

Claims

1. A device for ultrasonic-assisted SLM forming of Ti-O alloy, characterized in that: It comprises a sealed chamber for filling with high-purity argon gas, wherein a base is arranged in the sealed chamber, an ultrasonic vibration integrated platform connected to an ultrasonic generator is installed on the base, a substrate located on the upper side of the ultrasonic vibration integrated platform and used for laying powder is installed on the base, a scraper powder laying mechanism is arranged on the upper side of the substrate, and a laser beam generating device for acting on the powder is arranged above the substrate.

2. The device for ultrasonic-assisted SLM forming of Ti-O alloy according to claim 1, characterized in that: An argon gas inlet pipe is arranged on one side of the sealed cavity, and an input end of the argon gas inlet pipe is connected to a high-purity argon gas source.

3. The device for ultrasonically assisted SLM forming of Ti-O alloy according to claim 1 or 2, characterized in that: The ultrasonic vibration integrated platform is fixed on a base, and two sides of the base plate are connected to the base via vertical parts respectively.

4. The device for ultrasonically assisted SLM forming of Ti-O alloy according to claim 3, characterized in that: A layer of flexible foam cotton is filled between the bottom surface of the substrate and the ultrasonic vibration integrated platform.

5. The device for ultrasonically assisted SLM forming of Ti-O alloy according to claim 1, 2 or 4, characterized in that: The scraper powder spreading mechanism comprises a scraper driven by a first driving mechanism to move laterally, and is provided with a second driving mechanism to drive the first driving mechanism to move up and down.

6. The device for ultrasonically assisted SLM forming of Ti-O alloy according to claim 1, 2 or 4, characterized in that: The laser beam generating device comprises a fiber laser, and the fiber laser is connected to a galvanometer-lens system acting downward on the upper surface of the substrate via a flexible optical fiber.

7. A method for ultrasonic vibration assisted SLM forming of Ti-O alloy, using the ultrasonic assisted SLM forming of Ti-O alloy device according to claim 6, characterized in that: The following steps are involved: (1) CP-Ti powder and TiO2 powder are mixed in a certain proportion and mixed in a powder mixer to form TiO2 / Ti mixed powder; (2) High-purity argon gas is filled into the sealed chamber, and then the TiO2 / Ti mixed powder is spread on the substrate through a scraper powder spreading mechanism; (3) Turn on the ultrasonic generator and transmit the ultrasonic vibration to the spread TiO2 / Ti mixed powder on the substrate through the ultrasonic vibration integrated platform; (4) Turn on the fiber laser, and the emitted laser beam is transmitted by the flexible optical fiber to the galvanometer-lens system, and finally acts on the spread TiO2 / Ti mixed powder; while turning on the fiber laser, turn on the ultrasonic generator and use its acoustic cavitation effect to change the flow and solidification behavior of the molten pool, thereby changing the microstructure of the Ti-O alloy.

8. The method for ultrasonic vibration assisted SLM forming of Ti-O alloy according to claim 7, characterized in that: The powder mixer is a planetary ball mill.

9. The method for ultrasonic vibration assisted SLM forming of Ti-O alloy according to claim 7 or 8, characterized in that: The mixing time of the powder mixer is 110-130 min, and the rotation speed is 180-220 rpm / min.

10. The method for ultrasonic vibration assisted SLM forming of Ti-O alloy according to claim 7 or 8, characterized in that: In the stage of spreading TiO2 / Ti mixed powder, the power of ultrasound is 50~70W and the frequency is 25~35Khz; in the stage of SLM forming Ti-O alloy, the power of ultrasound is 110~130W and the frequency is 25~35Khz.

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