Tensile deformation micro-mechanisms of a polycrystalline nickel base superalloy: From jerky flow to softening

Abstract

In this study, efforts were made to elucidate the tensile deformation micro-mechanisms of a polycrystalline nickel-base superalloy used for the fabrication of critical rotating and stationary components of the gas turbine engine under relevant service conditions. The microstructural evolutions during the investigated temperatures and strain-rates are explicitly indicating the divergence in associated tensile responses. The alloy exhibits serrated or jerky flow behavior at 300 and 400 °C, whereas, yield strength anomaly (YSA) is observed at 750 °C. With further increase in testing temperature, softening mechanisms start dominating and dynamic recrystallization occurs at 930 °C. TEM investigation revealed that the serration in the flow curve at 300 °C is attributed to the disordering of the secondary γ′-precipitates by the leading a/2 <110> dislocation super-partial and refurbishment of order through thermal activation before the trailing super-partial arrives. The YSA observed at 750 °C is essentially due to the cross-slip of dislocation super-partials and the presence of dislocation debris.