Effects of heat treatment on microstructure and microhardness of linear friction welded dissimilar Ti alloys
(1. AVIC Beijing Aeronautical Manufacturing Technology Research Institute, Beijing 100024, China;
2. School of Materials Science and Engineering, University of Science and Technology Beijing,
Beijing 100083, China)
2. School of Materials Science and Engineering, University of Science and Technology Beijing,
Beijing 100083, China)
Abstract: A detailed investigation for the influence of post weld heat treatment (PWHT) on the microstructure of TC4 and TC17 dissimilar joints was analyzed. The fully transformed microstructure in the as-welded zone indicated that the peak temperature exceeded the β-transus temperature at the weld interface during linear friction welding. TC4 side was mainly composed of martensite α′ phase with random distribution and it was single β for that of TC17. In the thermomechanically affected zones of TC4 and TC17, the structure undergoes severe plastic deformation and re-orientation, yet without altering the phase fractions. After PWHT, in the weld zone of TC4 alloy, the phase transformation α′→ α+β occurred and the acicular α was coarsened, which resulted in a decrease in hardness. In the weld zone of TC17 alloy, fine α phase precipitated at the grain boundary and within β grains, which resulted in a sharp increase in hardness.
Key words: linear friction welding; Ti alloys; heat treatments; microstructure; microhardness