ON THE INHIBITION OF STABILISATION OF MARTENSITE IN Cu-Zn-AI ALLOYS

A shape memory device, and thus the alloy, when not operating is generally held in the martensitic condition. Also the shape memory effect depends on the retransformation of the martensite to the parent phase (i). Use of an alloy in a temperature controlling device, therefore, demands reliability and reproducibility of this retransformation temperature with shape memory cycles and more particularly, with time of hold in the martensitic condition before the device is operating at any given time. Notably, the latter aspect is known to be a weakness of Cu-Zn-AI shape memory alloys, as they are vulnerable to ageing which shifts the retransformation temperature to higher values (2-4). The martensite is thus stabilised relative to the parent phase and a shape memory device where the martensite is stabilised is unreliable. This poses a problem in utilising Cu-Zn-AI alloys in applications requiring high retransformation temperatures, as ageing in martensite is more pronounced the higher the temperature.