Superplasticity in a Recrystallized Ni<SUB>3</SUB>Al Polycrystal Doped with Boron

Abstract

Superplasticity in a recrystallized Ni3Al polycrystal doped with boron was investigated. Superplastic flow with a maximum elongation of 160% was observed under the condition of an ultra fine grain size (1.6 μm) at a low initial strain rate (≤1.04×10−4s−1) and 973 K. A low flow stress and a high strain-rate sensitivity index were attained under these conditions.The occurrence of a dynamic recrystallization (DR) was verified by a transmission electron microscope (TEM), and DR was believed to be an important mechanism in superplastic deformation as associated with a reduced cavitation. This limited cavitation was explained by considering that DR relieves stress concentrations arising from grain boundary sliding and dislocation piling-up at grain boundaries. In addition, DR played another important role in suppressing apparent grain growth during superplastic deformation.