Microstructural and Mechanical Characterization of 1.6-mm-Thick Nimonic-75 Superalloy Welds

Abstract

Abstract Gas tungsten arc welding (GTAW) and electron beam welding (EBW) studies on thin Nimonic-75 sheets of 1.6-mm thickness have been carried out using butt-weld configuration. Manual GTAW was done using Inconel-718 filler wire with a two-pass welding and EBW was done by autogenous welding. The strength of both the weldments at ambient temperature is found to be marginally (~4%) higher than the base metal. Marginally higher strength in the case of GTAW joints was observed at ambient temperature and is attributed to the use of Inconel-718 filler wire, where the additional alloying elements (niobium, aluminum, molybdenum) and their contents in the weldment contribute to increase in strength. The microstructure of the fusion zone in EBW reveals a needle-shaped/acicular structure with fine dendrites, whereas the dendrites are coarser in the case of GTAW welds. At elevated temperatures (600°C–700°C), the strength of GTAW is similar to the base metal. However, EBW coupon exhibited higher strength (~20–45%) than GTAW coupon, indicating the beneficial role of faster heating/cooling in EBW leading to acicular microstructure.