High-Joint Efficiency of Vacuum Diffusion-Welded Dissimilar Rods of Ti-6Al-4V and 304L Stainless Steel Without Interlayer
摘要
The demand for lightweight structures in aerospace, nuclear, chemical, and other industries has sparked interest in the joining of titanium alloys and stainless steels. However, the disparities in their properties challenge to achieving reliable bonds. This study addresses these challenges through direct diffusion welding. These joints are suitable for a propellant tank for aerospace applications and a turbine blade for aeroengine components. Ti-6Al-4V is welded to 304L stainless steel under 5 MPa at 900 °C for 60 minutes without an interlayer in vacuum. The diffusion zone is wider on the Ti-6Al-4V side than on the stainless steel. As temperature increases, the diffusion zone expands and leads to the formation of intermetallics such as Fe2Ti, FeTi, Fe2Ti4O, and σ. The interface comprises austenite (~200 nm) with dislocations at 900 °C in stainless steel. Conversely, Ti-6Al-4V includes the alpha and beta phases, deformation twins and dislocations. The hardness is higher on the Ti-6Al-4V side and lower on the stainless steel. The joint (900 °C, 60 minutes) shows a 350 MPa strength (~60% joint efficiency based on stainless steel) and 8% elongation. As time increases, the joint's strength decreases. A brittle fracture is predominant at 850 °C, whereas the joint at 950 °C exhibits a brittle-ductile fracture.