Hot tensile properties and deformation reponse of a γ(Ni)/γ'(Ni3Al)--delta(Ni3Nb) eutectic composite

Three distinct regions of tensile, deformation and fracture behavior were observed in a 2.5 wt% Al γ/γ'-delta eutectic alloy as the testing temperature was varied. The major finding was an extraordinary ductility maximum at about 5500C. It was shown that this phenomenon is caused by the deflection of transverse cracks at the eutectic grain boundaries when yielding occurs. This delamination between eutectic grains caused by fracture of a γ' eutectic grain boundary film leads to a distinctly different ''wood-like'' fracture surface morphology. Above 6900C to 9260C, yield and tensile strength values decrease while ductility increases slightly. Cooperative twinning of both phases develops giving rise to block-like deformation of the microstructure quite in parallel to the behavior observed previously in the γ-delta system