The microstructure analysis, mechanical properties, and fracture behavior of electron beam welded C-103 niobium-based refractory alloy

Abstract

This study involves investigation of metallurgical and mechanical properties of C-103 niobium alloy welded by electron beam. ICP, XRD and EDS method were used to determine the composition and phase contents of the alloy. Electron beam welding was carried out on specimens with various currents and transverse speeds. To examine macro- and micro-structural characteristics of the welded samples, stereographic, optical, electron scanning microscopy and EDS methods were used. Also, mechanical properties including micro-hardness profile and tensile strength were measured. It was observed that C-103 alloy has HfO2 precipitates with two different morphologies of spherical coarse and fine particles. Within the weld zone, primary precipitates were dissolved and new nanometer-sized ones were formed regularly throughout this zone. Morphology of the formed precipitates was mostly spherical and rarely filament-like. Due to greater number and smaller size of precipitates in weld zone, hardness of weld zone was more than HAZ and base metal zone. Tensile strength of welded sample was 317.5 MPa which is equal to 55% of tensile strength of base metal. Fracture of all welded samples occurred within weld zone which can be referred to enlargement of grains in this zone. The features presented on fracture surface of unprocessed C-103 alloy, such as cross section reduction, formation of dimples, opaque appearance of fracture surface indicate ductile nature of fracture. However, emerging of relatively smooth and sharp surface, abundant vein patterns and cleavage planes obviously indicate brittle fracture. HfO2 precipitates, as well as dissolved oxygen in the matrix, significantly affected metallurgical and mechanical properties of welded C-103 alloy samples.