Effect of two post-weld heat treatment on microstructure and mechanical properties of Incoloy 825 nickel base alloy argon arc welded joint

To tackle the issue of microstructural segregation in nickel-based alloy weldments and the consequent degradation of joint mechanical properties， this study delves into the impacts of two post-weld heat treatment schedules on the microstructural features and mechanical behavior of gas tungsten arc-welded Incoloy 825 nickel-based alloy joints.The results reveal that both heat treatment procedures lead to a notable coarsening of fine grain boundary carbides in the base metal （BM）. Moreover， the γ′ phase can be precipitated within BM grains through solution treatment combined with two-stage aging. Both post-weld heat treatments facilitate extensive precipitation of the δ and Laves phases in the WZ interdendritic zones， effectively alleviating segregation. Nevertheless， joints subjected to solution treatment and two-stage aging develop microcracks at the interface between the unmixed zone （UMZ） and the heat-affected zone （HAZ）， along with the formation of micropores within the HAZ. Mechanical characterization indicates a substantial increase in microhardness in the weld zone （WZ） after both heat treatment protocols. Solution treatment with single-stage aging maintains hardness levels in the HAZ and BM that are comparable to those in the as-welded state. Joints treated with solution treatment and single-stage aging show a marginal reduction in tensile strength， accompanied by a 9.2% improvement in uniform elongation， and fracture exclusively occurs within the BM. Conversely， the tensile strength of joints treated with solution treatment and two-stage aging significantly rises to 795 MPa， an increase of 17.3%， while the uniform elongation decreases. The fracture localization shifts to the UMZ/HAZ interfacial regions and adjacent HAZ areas， presenting a ductile-brittle mixed fracture morphology.