Microstructure and mechanical properties of WRe/GH3128 alloy electron beam welded joint

Abstract

This study investigates electron beam welding of WRe/GH3128 alloy, focusing on the microstructure, defects, mechanical properties, and fracture characteristics of the welded joint. Competitive grain growth within the weld, attributed to solidification rate and grain orientation, as well as the influence of electron beam keyhole oscillation on grain morphology, is analyzed. The study discusses the uneven distribution of solute concentration within the solid phase during the non-equilibrium solidification stage of the weld, along with dendritic segregation and phase transformation processes. Segregation of Cr, Re, and C elements in the interdendritic region results in abundant precipitation of σ phase and M6C. Non-equilibrium solidification phase fractions and phase transformation processes within the weld are calculated using JMartPro software. Furthermore, the potential relationship between the uneven diffusion of elements within the reaction layer and the formation of intermetallic compounds is discussed. XRD testing confirms the presence of Cr7Re3, Ni4W, Ni4Mo, and M6C within the reaction layer. The microhardness and tensile properties of the joints are evaluated, with a tensile strength of 600 MPa, representing 77% of GH3128's strength, while the elongation is only 2.5%. The increase in weld microhardness is attributed to changes in grain morphology and precipitation of M6C and σ phases, with M6C reducing joint plasticity. Cracks and defects are observed in the WRe heat-affected zone, and the role of metallurgical bonding and solid-state healing in crack repair is elucidated. Finally, an analysis is conducted on factors such as crystal microstructure defects that can lead to crack nucleation and propagation, providing separate explanations for intergranular fracture in the WRe base material and brittle fracture in the reaction layer.