Effect of rhenium content on microstructures and mechanical properties of electron beam welded TZM alloy joints

In order to strengthen weld zones of molybdenum-titanium-zirconium (TZM) alloy joints, electron beam welding experiments using rhenium (Re) addition into weld metals were conducted. The effect of Re content on the phase constitution, microstructural evolution, and mechanical properties of weld zone was investigated by optical microscope (OM), scanning electron microscope (SEM), electron backscattering diffraction (EBSD), transmission electron microscope (TEM), microhardness and tensile tests. Weld narrowing and grain refinement were produced in the welded TZM alloy joints by adding Re interlayers. Re-rich particles segregated in grain boundaries and led to the promotions of stress relaxation and cohesive forces of GBs. Besides, low-angle grain boundaries emerged and increased with Re contents in weld zones, which can hinder the initiations and expandings of microcracks. Consequently, the tensile strengths of the joints were enhanced with the increasing Re contents in weld zones. When the Re content in the weld zone reached 48.7 wt. %, the tensile strength of the joint can be up to 524 MPa and the fracture location was also transferred from weld zone to heat affected zone.