Structure changes during pseudoelastic deformation of CuAlMn single crystals

Structure changes during pseudoelastic deformation of CuAlMn single crystals were investigated using in situ optical and high-voltage electron microscopy (HVEM). Several crystal orientations were investigated, from an irrational to [100] and [110] tensile axis and plane orientations in the case of thin foils. The composition of the alloy was chosen such as to obtain superelastic behavior at room temperature. Optical microstructures allowed to identify parallel plates at the beginning of the stress plateau, the number of which increased with strain. The stress/temperature phase diagram was established within the range of existence of gamma'(1) and beta'(1). During in situ HVEM deformation in the [100] direction of gamma'(1) plates nucleated on pre-existing ones. At later deformation stages 18R martensite was formed in stacks of narrow needles. The Following crystallographic relationship was observed: [001]beta(1) parallel to[010]beta'(1), gamma'(1) and [110]beta(1) parallel to[001]beta'(1), gamma'(1). A small permanent deformaticn observed after stress release was connected with the presence of residual martensite of a high random stacking fault density and consisting often of alpha'(1), gamma'(1) and beta'(1) martensite layers. During deformation in the (110) direction a larger permanent deformation and a density of dislocations was observed. Copyright (C) 1996 Acta Metallurgica Inc.