AES analysis of grain boundary segregation and precipitation in electron beam welded molybdenum and Mo-0.56% Nb alloy

Abstract Electron beam melted Mo and a Mo-0.56% Nb alloy have been welded using an electron beam welding technique. The microstructure, tensile properties and fracture behavior of these welds have been examined and compared with those of sintered welds between 77 and 1273 K. Tensile tests have revealed that the strength of the weld metal is equivalent to that expected for the recrystallized structure in the ductile region. Brittle behavior is observed with fracture initiating at grain boundaries and propagating by intergranular or transgranular mode below room temperature. Welds exhibited a general loss of ductility compared with the corresponding values for the base metals. Postweld heat treatment was found to enhance the ductility mainly because of the recrystallization of the base metal. Auger electron spectroscopy has eliminated oxygen, nitrogen or other impurities as sources of grain boundary embrittlement in welds. It was found that carbon precipitation was effective in enhancing the grain boundary cohesion in welds of melted materials.