Effects of Postweld Heat Treatment on Microstructure and Properties of Laser-Welded Ti-24Al-15Nb Alloy Joint
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JMEPEG https://doi.org/10.1007/s11665-019-04351-1
Effects of Postweld Heat Treatment on Microstructure and Properties of Laser-Welded Ti-24Al-15Nb Alloy Joint Lin Wang, Daqian Sun, Hongmei Li, and Chengjie Shen (Submitted February 20, 2019; in revised form August 21, 2019) The microstructure evolution and mechanical properties of laser-welded joints of Ti-24Al-15Nb alloy under different postweld heat treatment (PWHT) conditions were systematically investigated. The results show that the microstructure is very sensitive to PWHT temperatures. The weld zone consists of B2 and O phases after PWHT. With the PWHT temperatures increasing from 850 to 1000 °C, the amount of O phase decreases gradually, while the grains of O precipitates become coarser. After PWHT, there are some thin acicular O precipitates in heat-affected zone (HAZ), and the decomposition of a2-phase caused by niobium diffusion can be observed in the HAZ. The PWHT can significantly increase the microhardness of joints, resulting from O phase precipitation hardening effect. The tensile strength and elongation of joints can be remarkably improved after PWHT, which was closely related to the strengthening effect of O precipitates and slip transmission between O and B2 phases. In addition, the results indicate that the best mechanical properties can be achieved only when the number and size of O phase and B2 phase are the best match. Keywords
laser beam welding, mechanical properties, microstructure, postweld heat treatment, Ti-24Al-15Nb alloy
1. Introduction Ti3Al-based alloy is one of the potential structural materials for use at elevated temperature in space and aerospace fields because of its high specific strength, relatively low density, better fracture toughness, room temperature ductility and creep resistance, as well as good oxidation resistance and nonmagnetic properties (Ref 1-5). Most of the aerospace components are complex structures composed of sheet metal parts, ring parts, etc., so developing jointing techniques in order to manufacture high-quality jointed structures are indispensable to their extensive application (Ref 6). In order to develop a suitable welding method for Ti3Al-based alloys, some welding methods have been studied, including diffusion bonding (Ref 7), friction welding (Ref 8), brazing (Ref 9), electron-beam welding (Ref 10) and laser beam welding, and so on. However, the applications of solid-state welding and electron-beam welding are restricted by the dimensions of the workpieces. In addition, the solid diffusion bonding process, requiring a very high bonding temperature, causes excessive grain coarsening and results in a significant decrease in the elongation to failure. The laser welding, with high welding speed, high energy density, low heat input, low distortion, low residual
Lin Wang, Daqian Sun, Hongmei Li, and Chengjie Shen, Key Laboratory of Automobile Materials of Ministry of Education, School of Materials Science and Engineering, Jilin University, No. 5988 Renmin Street, Changchun 130025, China. Contact e-mails: wa
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