Element diffusion and microstructure evolution at interface of stainless steel/Ti alloy joint by laser welding with AgCuTi filler metal

Abstract

Joining of 304 stainless steel and TC4 titanium alloy was of great interest for applications in the marine, and aerospace fields. However, the direct welding process of steel and titanium will generate a large number of brittle Ti–Fe intermetallic compounds results in crack in joint. In this study, in order to avoid the formation of Ti–Fe intermetallic compounds, the connection between stainless steel and titanium alloy is successfully realized by adding AgCuTi filler metal. A section of unmelted stainless steel was retained by laser offset welding, and the filler was diffusion bonding with the base metals on both sides by heat conduction, ensuring that the filler was not melted. Since Fe and Cu elements have high solid solubility in liquid state, so the stainless steel and filler interface formed a good connection. There was no Ti–Fe intermetallic compounds found in the joint, and Ti2Cu and AgTi2 intermetallic compounds with better ductility was formed at the filler-TC4 interface. In order to further explore the element diffusion distribution at the interface of the joint. The temperature distribution model in the fusion zone was established, and obtained the temperature field of the joint. The diffusion coefficients of Fe, Cu and Ti elements were calculated by Arrehenius formula. It was verified that the diffusion of Ti elements in the filler resulted in the aggregation of Ti elements at the filler-TC4 interface. The microstructure mechanism for formation of the brazed weld was proposed.