A Study on Weldability of GTAW and CO2 LBW for Zirconium Alloy 702

• Main Authors: CHEN, Fei-Hsiang, 陳飛祥
• Other Authors: CHENG, Ching-Min
• Format: Others
• Language: zh-TW
• Published: 2009
• Online Access: http://ndltd.ncl.edu.tw/handle/4a73py

碩士 === 國立臺灣師範大學 === 工業教育學系 === 97 === Zirconium alloy 702 (UNS R60702) has excellent neutron and corrosion resistance and it is widely used in the nuclear power and chemical industry. Owing to the international price of defense industrial material such as Ni, Cr, Mo, Co, W,etc, is hiking gradually, it has caused a beneficial position to use Zirconium alloy and also there is a tendency to replace the use of Nickel-base alloy. Zirconium alloy 702 is a pretty active metal. It is easy to proceed under the vacuum chamber to do welding. However, its practical application is not so popular because the base metal dimensions are limited by the vacuum chamber. The objective of this research is to compare the mechanical properties of the Zirconium alloy 702 weldments using two different welding processes, Gas Tungsten Arc Welding (GTAW) and CO2 Laser Beam Welding (LBW). Mechanical properties test including microhardness test and tensile test were conducted. OM and SEM were also used for microstructure analysis. The content of alloy elements within the fusion zone was analyzed by EDS, XRD and EPMA analysis. The research mentioned above would enhance the internal welding technology of Zirconium alloys and improve the quality of industrial manufacturing technology. The result shows that Zirconium alloys 702 can be successfully welded by GTAW and CO2 LBW. The microstructure of Zirconium alloy 702 has been phase transformation (871°C), from α phase (HCP) transfer to β phase (BCC) and became Widmanstatten structure. In the hardness test, the hardness of fusion zone of GTAW and LBW was higher than base metal. All tensile test specimens were fracture at the base metal, According to the SEM observation, the ductile fracture feature was observed in all specimens. According to the EDS, XRD and EPMA analysis, the weldments of GTAW and CO2 LBW are no other elements in precipitation. It can be seen that Zirconium alloy 702 is a pure metal with very high purity. Keywords: Zirconium alloy 702 (UNS R60702), GTAW, CO2 LBW, Mechanical properties, EDS, XRD, EPMA