Abstract
The structural change and the shape memory behavior in quenched Mn-(5–20) at%Cu alloys have been studied at both normal and elevated temperatures using X-ray and electron diffraction methods and electron microscopy supplemented by metallographic observations. Quenched alloys are tetragonal and show a banded surface relief due to transformation twinning parallel to {101} planes. These tetragonal alloys are transformed to a cubic structure by heating to moderate temperatures, and the transformation temperatures increase linearly with manganese content. The banded surface relief becomes attenuated with increasing temperature and disappears at the fct→fcc reverse transformation temperature. On subsequent cooling to room temperature a similar banded structure appears and the angle between the surfaces in neighbouring light and dark bands increases as the temperature decreases. Similar structural changes are observed by an electron microscope. The fcc\
ightleftharpoonsfct transformation is of diffusionless (martensitic) type and takes place over a small temperature range which is less than 1 K . All quenched alloys show an ordinary shape memory effect and also a reversible shape memory effect. The behavior of shape recovery both on heating and cooling is discussed on the basis of metallographic and electron microscopic observations, and it is suggested that the residual magnetic ordering is responsible for a reversible shape memory effect.
