Effect of Widmanstätten η phase on tensile shear strength of resistance spot welding joints of A286 superalloy

Abstract

This work aims to study the effect of Widmanstätten η phase on tensile shear strength (TSS) of resistance spot welding joints (RSW) of A286 superalloy subjected to post-weld high temperature aging treatment. The tensile shear test specimens were welded in the solution treated condition, and then subjected to six different post-weld aging treatments (at an aging temperature of 840 °C for six different aging times). The as-cast dendritic microstructure of the weld nugget and the austenite equiaxed-grain microstructure of the base metal have a different response to the post-weld high temperature aging treatment. Growth of Widmanstätten η phase in the weld nugget is faster than in the base metal. While in the base metal the Widmanstätten η phase precipitates into the grain, in the weld nugget precipitates at the interdendritic region because of the segregation of Ti towards the last-to-solidify interdendritic regions (studied by performing SEM/EDX analysis). Although the hardness increases with the presence of Widmanstätten η phase, the increase in hardness does not necessarily imply an increase in the experimental TSS.