The Microstructures and Fatigue Crack Growth Properties in Ti-6Al-4V Laser Welds

• Main Authors: Tsay, Chan Yi, 蔡健益
• Other Authors: L.W. Tsay
• Format: Others
• Language: zh-TW
• Published: 1997
• Online Access: http://ndltd.ncl.edu.tw/handle/00003849064016698880

碩士 === 國立海洋大學 === 材料工程研究所 === 85 === The present work was undertaken to investigate the effects of microstructures on the mechanical properties and fatigue crack growth in Ti-6Al-4V plate and laser welds. Experimental results revealed Ti-6Al-4V alloy was heat-treated in vacuum at 950℃ for 40min and cooled subsequently by Ar quence. The microstructures is cosisted of refined lamellar α plus βin the base metal (BM). The results also indicates the microstructure of various aged specimens is almost similar. The presence of martensite in the narrow fusion zone (FZ), results in the tensile fracture of laser-welded specimens in the BM. The decomposition of martensite can account for the slightly hardening of laser welds after postweld heat treatments. The variation in tensile properties is minor for variously aged specimens. In addition, the welds aged at various temperatures show minor difference in tensile properties. The fatigue crack growth rates decreased at low ΔK range can be attributed to the presence of residual compressive stress in laser welds. The results reveal the FZ retards the crack growth most among various regions in a weld.