Effect of vacuum brazing and rotary friction welding on microstructure and mechanical properties of laminated steel and nickel alloy joints

In this study, a joint between a vacuum brazed laminated bimetal material, consisting of steel and Inconel (R) alloy, and a solid material is investigated. This type of joint is applied in an Axially Laminated Anisotropic Synchronous Reluctance Machine (ALASynRM) rotor, where the laminated active section of the rotor is joined to solid supporting shafts either by rotary friction welding (RFW) or vacuum brazing. The test specimens were manufactured with different RFW parameters and parent material compositions to evaluate the joint behavior. The RFW friction pressure (104-155 MPa) and time (1.0-3.0 s) were varied to assess their impact on joint performance and composition, while other process parameters remained constant. The joint's alloy composition and microstructure were analyzed, and its mechanical performance was assessed using tensile tests. Additionally, molecular dynamics (MD) simulations were employed to understand the nanoscale phenomena that occur during RFW joint formation. In this study, the ultimate tensile strength (UTS) of the joint in all RFW samples surpassed that of the vacuum brazed laminated material, while the vacuum brazed joints did not achieve comparable UTS. Metallurgical analysis indicated good and consistent diffusion between laminated bimetal and solid materials, resulting in defect-free joints. The MD simulations were strongly correlated with the experimental results, further validating our findings.