Maximizing the integrity of linear friction welded Waspaloy

Abstract

The Ni-base superalloy, Waspaloy, was linear friction welded (LFWed) under various processing parameters and then subjected to a post weld heat treatment (PWHT). Tensile testing integrated with the optical image correlation Aramis® system indicated that there is a critical axial shortening value (2mm) below which LFWed and post weld heat treated (PWHTed) Waspaloy exhibited weak integrity. At and above this critical shortening, the yield strength and ultimate tensile stress (UTS) values were more or less the same as for the parent material. However, total elongation continued to increase with axial shortening even above the critical value due to decrease in width of thermo-mechanically affected zone (TMAZ). The sample with the highest axial shortening (4.9mm) exhibited an elongation 91% of the parent material elongation. According to Aramis® data, the mixture rule can be used reliably to determine the contribution of TMAZ to the tensile elongation of PWHTed Waspaloy. Microstructure characterization across the weld in the as-LFWed and PWHTed conditions was carried out to correlate the process parameters and microstructural changes that affect the tensile properties. Weak integrity at axial shortening below 2mm was mainly due to lack of bonding and/or presence of oxides at the weld interface. In the as-welded condition, a loss in hardness was observed, and related to the extensive dissolution of strengthening phase (γ′) in the weld area. The applied PWHT restored the hardness in the weld region.