On the laser gas (N₂) alloying in the welding of molybdenum alloy

Welded joints of molybdenum (Mo) and Mo alloy have high brittleness and low strength, which seriously limit its application as structural materials. In this study, Nitrogen (N) is used to strengthen the fusion zone (FZ) in the Mo laser beam welding joints and N is added into the FZ during a laser gas alloying process. The XPS and SEM confirm that many Mo₂N phase were distributed on the surface of the grain boundary. The EBSD results indicate that Mo₂N, which can be distributed at the grain boundary and inside the grain, tends to distribute more at the grain boundary. The tensile strength of joint by laser gas alloying is up to 382 MPa. Mo₂N in the FZ plays the role of second phase strengthening. The presence of Mo₂N in the FZ facilitates the second phase strengthening, allowing the application of Mo as a structural material.