The Origin of Deformation Twinning in Polycrystalline γ'Containing Nickel-Base Alloys

Abstract

As in certain other γ' containing nickel-base alloys, twinning is observed after the intermediate temperature deformation of polycrystalline IN-100, Figure 1. The presence of twinning is dependent upon grain orientation and is favored in grains oriented with an <011> pole near the tensile creep axis. (All foils were taken transverse to the tensile axis.) This is to be expected since <011> is near a single slip orientation of high Schmid factor for {111} <112> shear.Previously it had been suggested that the dislocations required for {111} <112>.shear and twinning were produced by interaction of 1/2 <110> dislocations. Yet, twinning is observed at the earliest stage of deformation in polycrystalline IN-100, Figure 2. Further examination demonstrated that the grain boundaries are sources for the initiation of twinning. A typical example is shown in Figure 3 where faulted configurations associated with twinning extend from the grain boundary into the γ' containing matrix.