Deformation and damage mechanisms during stress rupture of Waspaloy after vacuum solution plus aging treatment

Abstract

The microstructure of vacuum solution-treated Waspaloy is investigated before and after a stress rupture test. The samples with trimodal and bimodal distributions of γ′ precipitates are produced by single-stage (760 °C/16 h) and standard two-stage (845 °C/4 h + 760 °C/16 h) aging treatments, respectively. Both kinds of samples deform mainly by the propagation of dislocations in the uniformly deformed region and then by a combination of dislocation slip and deformation twinning in the necked region. The secondary and tertiary γ′ precipitates are sheared by a/2 < 110 > dislocations, while stacking faults are created in the primary γ′ precipitates by shearing of a/3 < 112 > dislocations. The finer tertiary γ′ precipitates can more effectively impede the movement of dislocations than the secondary γ′ precipitates. Thus, the single-stage aged sample exhibits a longer stress rupture life and lower strain rate than the two-stage aged sample. For the damage mechanism, the fracture in the uniform deformation stage is generally intergranular given that the deformation is mainly concentrated around the grain boundaries. A mixed mode of transgranular and intergranular fracture occurs in the necked region due to the obvious grain boundary sliding and serious deformation within the grains.