Effect of laser beam welding on fracture toughness of a Ti-6.5Al-2Zr-1Mo-1V alloy sheet

• Published in: Journal of materials science 2007-08, Vol.42 (16), p.6651-6657
• Main Authors: Shi, Yaowu, Zhong, Fei, Li, Xiaoyan, Gong, Shuili, Chen, Li
• Format: Article
• Language: English
• Subjects: Acicular structure; Applied sciences; Base metal; Brittle fracture; Compact tension; Crack initiation; Crack propagation; Cross-disciplinary physics: materials science; rheology; Dimpling; Ductile-brittle transition; Exact sciences and technology; Fracture mechanics; Fracture testing; Fracture toughness; Fractures; Heat affected zone; Heat treating; Intergranular fracture; Joining, thermal cutting: metallurgical aspects; Laser beam welding; Laser cooling; Lasers; Materials science; Mechanical properties and methods of testing. Rheology. Fracture mechanics. Tribology; Metal sheets; Metals. Metallurgy; Microstructure; Other topics in materials science; Physics; Post-weld heat treatment; Titanium base alloys; Weld metal; Welded joints; Welding
• ISSN: 0022-2461; 1573-4803
• DOI: 10.1007/s10853-007-1524-y

Investigation of fracture toughness on Ti-6.5Al-2Zr-1Mo-1V alloy thin sheet and its laser-welded joints has been carried out. In the test compact tension (CT) specimens and single specimen technology were used. In addition, hardness distribution and microstructure of the welded joints were examined. Fracture test indicates that brittle unstable fracture occurs after slow crack propagation for all the specimens, except that one heat affected zone (HAZ) specimen is brittle crack initiation. It is found that rolling directions have no obvious effect on fracture toughness of base metal. Moreover, fracture toughness of weld metal is obviously decreased in comparison with base metal whatever in as-welded condition or in stress relief condition. Post-weld heat treatment (PWHT) leads to fracture toughness of the welds further decreasing. Fractography observation shows that the fracture mode is predominantly dimpled in base metal. However, there exists intergranular fracture in the weld metal. Thus, the transition of fracture mode from both base metal and HAZ to weld metal may lead to dramatic decrease in fracture toughness. Microstructure examination reveals that the microstructure of weld metal consists of large grains with fine acicular structure. The formation of fine α acicular structure is due to rapid cooling during laser welding. After PWHT, the acicular structure is coarsened.