Effects of Postweld Heat Treatment on Microstructure and Properties of Laser-Welded Ti-24Al-15Nb Alloy Joint
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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 α2-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.
Keywordslaser beam welding mechanical properties microstructure postweld heat treatment Ti-24Al-15Nb alloy
The authors would like to thank the National Natural Science Foundation of China for financial support (51805205). And the work was also supported by “13th Five-Year” Science and Technology Project of Education Department of Jilin Province, China (No. JJKH20180126KJ) and Science and Technology Planning Project of Jilin Province, China (No. 20181312034ZG).They would also like to thank teacher Liu Guojun from Jilin University for his assistance in this experiment.
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