MECHANISM OF INTENSE SHEAR FAILURE IN NI3AL SINGLE-CRYSTALS

Localized shear bands, with minute misorientations off the slip plane, cause sharp failures in Ni3Al single crystals that fail after elongat ion exceeding 70-80% in room-temperature tensile tests. An explanation for intense slip plane shear failure, consistent with prior experimen tal observations, is proposed. Prior electron microscopy evidence obta ined by Horton, Baker and Yoo of decreasing antiphase-boundary energy in highly deformed slip bands is employed to suggest a highly localize d order-disorder transition. This shear-strain-induced slip-plane diso rdering provides the essential mechanism to lower the work-hardening r ate to zero or negative values. A decreasing work-hardening rate susta ins persistent shear localization, ultimately leading to failure. This mechanism is suggested to be applicable to other ordered crystals.