Electron Beam Welding of TZM plates

Abstract

Recently, many efforts have been made to join molybdenum and its alloys, such as TZM, due to their interest for industrial applications. However, it has a poor weldability due to high thermal conductivity and high melting temperature, sensitivity to gas impurities and lack of solid state transformations leading to coarse grain formation. Electron beam welding (EBW) is a high energy density process, and welding TZM can result in a smaller fusion and heat affected zones. The aim of this study was to perform an exploratory investigation on the ability of EBW to weld TZM, focusing on the major process parameters, the clamping system and evaluate the effect on the weld tensile strength. The selection of the parameter values and their refinement was performed using design of experiments. Sound welds were obtained, free of pores, cracks and misalignments. A dedicated clamping system was designed, manufactured, and proved to be of major importance. Tensile strength was close to 80% of the base material, which is remarkably good for this alloy. Pre- and post-weld treatment had no significant effect on the welding strength. However, further work is needed to minimize grain coarsening, eventually by stirring the molten pool using beam deflection.