High temperature fatigue of friction welded joints in dissimilar nickel based superalloys

The high temperature fatigue performance of two dissimilar material joints made by inertia friction welding and linear friction welding is assessed in the present study. The fatigue strength of the welded joints is found to be comparable to that of the weaker parent material for the plainsided specimens. However, the fatigue crack growth resistance within the weld zone of both material systems is found to be reduced compared to that of parent material. This effect is more pronounced for high temperature Ni alloys than for the lower temperature nickel alloy. Environmental attack is confirmed to be the controlling failure! mechanism for acceleration of crack growth, but the extent to which it is observed is sensitive to local microstructure, i.e. to grain size, redistribution of the main strengthening phase gamma, and to the grain boundary carbide morphology. Such local microstructural variations are the result of welding and subsequent post-weld heat treatment procedures.