Study of the Structure and Properties of EP718 Alloy Welded Joints Produced by Robotic GMA Welding

The article presents a study of the structure and properties of the welding zone and the weld-affected zone (WAZ) of the EP718 nickel alloy joints. The joints are obtained by robotic pulsed gas metal arc welding in argon (GMA welding) with transverse oscillations of the electrode. The studied macrosections of welded joints of high-temperature nickel alloys show an extremely atypical picture of the fine-grained structure of the WAZ with local grain growth regions, comparing to previous experiments using pulsed GMA welding. The welded joints of the EP718 alloy samples of 4 mm thickness obtained by pulsed GMA welding demonstrated the ultimate tensile strength of 1056 MPa. The short-term strength of welded joints of the EP718 alloy 4 mm thickness at 650 °C reached the value of 949 MPa. According to EDXS analysis, particles of the Ti_xN_y type and carbides of the M_xC_y type are distinguished along the boundaries of such areas. These particles are formed in the WAZ zone in the temperature range of 700–1200 °C. A detailed EDXS analysis of WAZ revealed an increased content of molybdenum and sulfur in certain sections with a simultaneous decreased content of niobium and iron, as well as sections with increased (by 50–70% compared to the initial alloy) concentrations of niobium and molybdenum.