Impact of solution heat treatment on microstructure and creep behavior of a novel cast & wrought FGH4096 turbine disk alloy

By means of microstructural observation and creep tests, a study has been made into the effects of solution heat treatments on microstructure and creep resistance of a novel cast & wrought FGH4096 superalloy. The results show that grain size increases and the volume fraction of primary γ´ phase decreases with the increase of solution heat treatment temperature. The super-solvus solution heat treatment leads to an increase of the total volume fraction of secondary and tertiary γ´ phases, and superior creep property can be obtained. Various cooling rates from sub-solvus solution heat treatment are applied to gain cooling secondary γ´ phase with different sizes and morphologies. It is found that the solution cooling rate determines secondary γ´ morphology and particle distribution that develops. The alloy samples with fine γ´ particles obtained from the fast solution cooling rate possess narrow matrix channels, which can effectively enhance the Orowan resistance and hinder dislocation movement within the matrix and thus improve the creep resistance at 704 °C/690 MPa. The creep tests for three samples with different distribution of γ´ particles are interrupted when entering the third stage to investigate the corresponding dominant deformation mechanisms by transmission electron microscopy. It is indicated that partial dislocations shearing precipitates leaving abundant stacking faults behind is the dominant creep failure mechanisms for samples with coarser secondary γ´ particles and wide γ matrix channels. The main creep mechanism for the samples with fine secondary γ´ particles is microtwinning shearing both γ´ particles and matrix.