A comparison of inertia friction welds in three nickel base superalloys

In this paper the microstructure, mechanical properties and residual stresses are compared for three inertia friction welded nickel-base superalloys. In contrast to alloy 720Li and RR1000, for Inconel 718 welding produces a precipitation free region leading to significantly reduced strength near the weld line. As a result, for alloy 720Li the hoop stresses are 1.5 times, and in RR1000 two times, higher than the tensile hoop stresses for Inconel 718. The maximum tensile weld stresses in Inconel 718 and RR1000 are yield stress limited in the weld region. That stresses significantly below the yield stress are found near the weld for alloy 720Li may be because the inferior creep properties of alloy 720Li compared to RR1000 result in stress relief during cooling after welding.Post weld heat treatment at the standard maximum aging temperature for Inconel 718 (732 °C), relieved residual hoop stresses to below 400 MPa. To achieve a similar level of residual hoop stress, Alloy 720Li must be stress relieved at least 30 °C and RR1000 about 80 °C hotter.