Temperature Dependence of Tensile Deformation Mechanisms in the Pm Superalloy with Ta Addition

Abstract

To further develop Ni-based PM superalloys for aero-engines, it is critical to understand their deformation mechanisms at various service temperatures. For turbine disks, tensile strength and plasticity are critical indexes. The high strain rate in tensile deformation makes it essentially different from creep. In this paper, a high-performance PM superalloy with various Ta was evaluated by tensile tests at different temperatures from room temperature to 815 °C. The relationship between temperatures and plastic deformation mechanisms was explored from multiple scales using scanning electron microscopy and transmission electron microscopy. Whereafter, temperature dependence of deformation mechanism map was established. The results demonstrated that the main deformation mechanism gradually changes from antiphase boundary (APB) shearing to superlattice stacking fault (SSF) shearing as the temperature increases. The a/2<110> dislocations in matrix can pass through γ′ particles by dissociation or climbing at elevated temperature. In the temperature range of this study, {111}<110> and {111}<112> slips dominate the plastic deformation. The extended stacking fault (ESF) is the source of the microtwin, which crosses the individual grain and thickens with increasing temperature. In addition, a novel mechanism of ESF formation was observed, i.e., the Shockley shearing separated by one layer of atoms. Besides, the effect of Ta on tensile strength and plasticity in PM superalloys were discussed.

Keywords: PM Ni-base Superalloys, Tantalum, deformation mechanism, extended stacking fault, microtwin