Effect of solution treatment temperature on the γ′ precipitation distribution, high temperature tensile and fatigue properties of FGH96 joints prepared by inertia friction welding

Inertia friction welding (IFW) was conducted on FGH96 superalloy shaped in rings. After welding, the joints experienced solution treatment and aging-treated. There are 4 kinds of solution treatments including no solution treatment and solution treatment at 1050 °C, 1080 °C and 1120 °C, respectively. The grain size, γ′ precipitate distribution, tensile and fatigue properties at 700 °C were measured and analyzed at different solution treatments. The results shows that with the increasing of the solution treatment temperature (STT), the grain size went up slowly below 1080 °C and got a sudden growth from 1080 °C to 1120 °C. At the same time, the secondary γ′ precipitates (mainly containing Ti, Al and Ni with ordered L1₂ structure) became fine and the shape gradually transformed from sphere into elliptical and irregular, which was a mixture of cuboids with concave faces and octets. When the solution treatment changes from no solution to solution treatment at 1120 °C, the tensile strength gradually increases from 1243 MPa to 1337 MPa and then remains constant from 1080 °C to 1120 °C. However, the yield strength increases from 917 MPa to 990 MPa at 1080 °C and then decreases to 927 MPa at 1120 °C which is close related to the grain growth of welding nugget zone (WNZ). The change tendency of fatigue limit with STT is in agreement with that of yield strength. It reaches the maximum of 765 MPa at 1080 °C which is closely connected to the shape transition of γ′ precipitates in WNZ and the grain growth. Combining high temperature tensile properties with fatigue limit, the optimal STT is 1080 °C.