| Summary: | 碩士 === 義守大學 === 材料科學與工程學系碩士班 === 98 === To generate a rapid welding thermal cycle and eliminate the crystallization for a (Zr53Cu30Ni9Al8)Si0.5 bulk metallic glass (BMG) weld, the Nd:YAG single pulse laser welding process was used in this study.The test samples were welded with different parameters combinations, under the room temperature or lower initial temperatures. As the test accomplished, microstructure evolution in heat affected zone (HAZ) or weld fusion zone (WFZ) was studied by using OM, TEM, SEM, EDS or XRD.The results show that at room temperature with the single-pulsed laser welding approach, crystallization in the HAZ seems unavoidable while the WFZ appears crystal-free. As the initial temperature was decreased to 0oC, both WFZ and HAZ show the amorphous state. The crystallization phase was identified as Zr2Cu with crystal size from 50nm to 100nm.Furthermore, it was observed when the precipitates were greater in the HAZ, cracks were more likely to form, and hardness in the HAZ was decreased.Finally, using the optimal single pulse welding parameters, this study develops an innovated laser welding process to complete a continuous weld. Initially, this process finishes the odd numbers of single pulse weld. After that, every odd number weld was joined by the even numbers of single pulse weld. This approach can eliminate the pre-heat or post-heat effects on the weld which suppress the formation of the crystallization in the welds.Based on the above results, the effects of Nd:YAG laser welding parameters on the microstructure evolution and mechanical property for (Zr53Cu30Ni9Al8)Si0.5 BMG was established. Moreover, this results would be helpful to (Zr53Cu30Ni9Al8)Si0.5 BMG for the further applications.
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