Effects of initial δ phase on hot tensile deformation behaviors and fracture characteristics of a typical Ni-based superalloy

Uniaxial tensile tests of a typical Ni-based superalloy are conducted under the deformation temperature range of 920-1010 degrees C and strain rate range of 0.01-0.001 s(-1). The effects of initial delta phase (Ni3Nb) on the hot tensile deformation behaviors and fracture characteristics are discussed in detail. The results show that: (1) For the studied Ni-based superalloy with a large amount of delta phase, the flow stress curves are composed of three distinct stages, i.e., work hardening stage, flow softening stage and the final fracture stage. (2) The initial delta phase has significant effects on the deformation behaviors of the studied superalloy. delta phase can cause the obvious work hardening at the beginning of hot deformation, and then accelerates the flow softening by promoting the dynamic recrystallization with further straining. With the increase of initial delta phase, the strain rate sensitivity coefficient decreases firstly and then increases. (3) The combined effects of localized necking and microvoid coalescence cause the final fracture of specimens. The increase of initial delta phase increases the density of nucleus for the formation of microvoids, and promotes the nucleation and coalescence of microvoids. (C) 2014 Elsevier B.V. All rights reserved.