Plastic deformation of Ni/Ni3Al-Ni3Nb directionally crystallized eutectics

The investigation concerned the dislocation structure of the γ/γ'-sigma eutectics resulting from its directed crystallization and also its evolution after tensile testing at room temperature. The mechanisms of plastic deformations of each of the phases and of the eutectics as a whole were explained. It was shown that residual stresses arising in a solidifying eutectic produce a complicated dislocation structure. The eutectic deformation curve features three stages: elastic, pseudoelastic and plastic. The plastic deformation in active tension is effected by an intensive twinning of plates of the sigma phase along planes [211] and [011] as well as slippage of dislocations in the γ phase along octahedral planes. The eutectics breaks up as a result of the association of microcracks on boundaries of crystal twin lamellae