Friction welding of TiNi alloy to stainless steel using Ni interlayer

Abstract

Friction welding was carried out between TiNi alloy and austenitic stainless steel with and without a Ni interlayer. When TiNi alloy was welded to stainless steel without the Ni interlayer, a large amount of brittle Fe₂Ti intermetallic compound was formed at the weld interface. The formation of this brittle compound led to degradation of the joint strength. The Ni interlayer changed the microstructures at the weld interface and improved the joint strength. A fracture occurred at the interface between Ni and TiNi. The interface between Ni and TiNi was free from Fe₂Ti and consisted of mainly TiNi₃ and TiNi. After TiNi₃ was formed as the reaction layer, a eutectic reaction occurred between the TiNi₃ and TiNi base alloy. A reaction layer with a eutectic structure tends to form at the periphery, where the temperature would be higher than that of the central region.