Abstract
Twins have been studied in an undeformed sample of the ordered L12 alloy Ni-20Al-30Fe. One twin/matrix boundary was seen to have “steps”. A dislocation mechanism is proposed, whereby Shockley partial dislocations of three different types move in a coordinated manner on adjacent {111} type planes to form twins in Ni3Al; this glide plane is also the twinning plane. A local, but not global, stress is created by this type of dislocation motion. Preliminary measurements of the thickness of each of the “steps” have been made. It is proposed that the “steps” thicknesses correspond to the thickness of multiples of three {111} type planes.