In-situ SEM observation of tensile deformation in rapidly solidified Ni3Al ribbons

Mechanical properties of Ni3Al ribbons have been studied using in-situ SEM tensile tests between room temperature and 400°C, The onset of plastic strain of the annealed material is characterized, after exceeding the yield stress, by the appearance of a plastic instability region followed by the homogeneous deformation region. The slope of the serrated zone decreases with annealing temperature and increases with test temperature. However, ribbons in the as-rapidly solidified (RS) condition do not show the plastic instability zone. This different behavior is related to distribution, arrangement and density of dislocations generated during rapid solidification and to their evolution during thermal treatments. Serrated yielding takes place due to the nucleation and propagation of Lüders bands, which are nucleated in high stress concentration regions and subsequently propagate through the gauge length. A model is proposed in order to explain strain hardening in the serrated zone and its dependence on annealing temperature and test temperature.