Optical and Electron Microscope Observations of Transformation and Deformation Characteristics in Cu-Al-Ni Marmem Alloys

Abstract

The shape memory effect is now generally known as the phenomenon that a specimen apparently plastically deformed at some lower temperature reverts to its undeformed original shape on heating to a somewhat higher temperature in virtue of the reverse martensitic transformation. This phenomenon is very peculiar compared to the ordinary plastic deformation behaviour. Thus, it has been of great interest for many workers of both academic and technological fields, and is now found in a lot of alloy systems as recently tabulated by Wayman and Shimizu (1) and Delaey et al. (2). A common property for all of the alloy system is that each alloy exhibits a martensitic transformation, and the shape memory effect is commonly observed when the alloy is deformed at a partly or wholly martensitic condition and then heated to the matrix phase (3, 4, 5). These common property and observation indicate that the shape memory effect is originated in the behaviour of materials upon martensitic transformation, deformation of the martensite and reverse transformation to the matrix phase. Therefore, in order to know the mechanism of the shape memory effect, the trans-formations and deformation characteristics must be clarified for alloy systems exhibiting the effect. In this paper, the term “marmem” (1) will be used as descriptive of the shape memory behaviour, since the martensite phase exhibits a memory except for the special case known as the two-way (2) or reversible (6) shape memory effect.