Dislocation evolution of a novel Co-Al-W based single crystal alloy with a -Co_SS/'-Co₃(Al, W) coherent microstructure around flow stress anomaly temperature from yielding to fracture

In this study, a novel single-crystal (SC) Co-9Al-9W-2Ta-0.02B-0.02Ce alloy with a growth direction of [001] was prepared by selecting crystal method (SCM). The tensile strength, ductility and dislocation evolution around temperatures of the flow stress anomaly from deformation to fracture were investigated. Aged at 900 degrees C for 100 h, the microstructure of the aged SC alloy is composed of Co solid solution gamma-Co-SS matrix and nano-scale cuboidal gamma'-Co-3(Al, W) intermetallic precipitates, while the two phases are coherent. The aged SC alloy exhibits tensile flow stress anomaly at 800 degrees C, with a peck 0.2% yield strength of 685 MPa. The SC alloy always shows strain-hardening state after yielding and excellent elongation larger than 18.9% from RT to 900 degrees C. At the stress anomaly temperature of 800 degrees C, the dislocation evolution is dominated by the < 001 > dislocation in the {001} plane of the gamma' phase pining back the dislocation in the {111} plane of the gamma' phase in a strain range of similar to 5%. With the further increase of the strain until fracture, the dislocation configuration is controlled by formation of the superlattice intrinsic stacking faults (SISF) through the frontal a/3 < 121 > dislocations extending in the.' phase. At 900 degrees C, the mobility of dislocation increases by the strong thermal activation and the Orowan mechanism appears due to the dislocations bowling the gamma' phase. Both subsequently, reduce the strength and the strain-hardening effect of the SC alloy.