Shape memory effect in cryogenic Cu-Al-Mn alloys

Abstract

The most successful commercial applications of shape memory alloys are as pipe couplings and mechanical fasteners. By using these alloys as elements of the thermomechanical joints it is essential that-the installed parts remain austenitic throughout their service life. If they become martensitic, the recovery stresses will be reduced at least to the martensitic yield stress and the shape memory joint will be destroyed. In the past, this has mandated the use of cryogenic alloys (M{sub s} < 290K) which remain austenitic at all normal service temperatures. The aim of these investigations was the development of new cryogenic Cu-based shape memory alloys (SMA`s) which can be used for commercial pipe coupling applications instead of more expensive Ni-Ti alloys. In this context Cu-Al-Mn alloys have been investigated, the {beta} phase of which, likewise to Cu-Zn-Al and Cu-Al-Ni alloys, undergoes a thermoelastic martensite reaction. Cu-Al-Mn alloys seem favorable due to their low transformation temperatures, which can be influenced in a variety of ways by their composition. Apart from this, Cu-Al-Mn alloys have been shown to possess an appreciable shape memory effect.