Plasticity of the Nb-rich {\mu}-Co7Nb6 phase at room temperature and 600 {\deg}C

TL;DR

This study investigates how composition and temperature affect the plasticity of the {b}-Co7Nb6 phase in superalloys, revealing temperature-dependent slip mechanisms and stress behaviors through micropillar tests and microscopy.

Contribution

It provides new insights into the temperature and compositional dependence of slip mechanisms in the {b}-Co7Nb6 phase, combining experimental and theoretical analyses.

Findings

High yield stresses at room temperature for Co-49Nb and Co-52Nb micropillars.

Transition to partial dislocation slip at higher Nb content and elevated temperature.

Significant decrease in critical resolved shear stress at 600b0C for Co-49Nb micropillars.

Abstract

The {\mu}-phase is a common precipitation phase in superalloys and it exists in a wide composition and temperature range. As such, we study the influences of composition and temperature on its plasticity by micropillar compression tests and transmission electron microscopy. The micropillars of the {\mu}-Co7Nb6 phase deform plastically by basal slip at either room temperature or 600 oC. At room temperature, the Co-49Nb and Co-52Nb micropillars show high yield stresses and an abrupt large strain burst at the onset of yielding regardless of orientation, whereas the Co-54Nb micropillars oriented for basal slip yield at much lower stresses and show intermittent small strain bursts during plastic deformation. While the Co-49Nb micropillars deform by full dislocation slip on the basal plane at room temperature, the Co-54Nb micropillars deform by partial dislocation slip on the basal plane. At 600 oC, the Co-49Nb micropillars oriented for basal slip show stable and continuous plasticity and their critical resolved shear stress decreases dramatically. The plastic deformation of the Co-49Nb micropillars occurs via partial dislocation slip on the basal plane at 600 oC. Based on the geometric {\gamma}-surfaces for all potential basal slip planes, we explore where and why the glide of full and partial dislocations on the basal plane occurs in the {\mu}-Co7Nb6 phase.