2-WAY SHAPE-MEMORY SPRINGS WITH IMPROVED REPEATABILITY ON THERMAL CYCLING

The influence of pre-training heat treatments on the amount and repeat ability of the two way shape memory (TWSM) effect developed in Cu-Zn-A l shape memory compression springs is studied. Pre-training heat treat ments were achieved by flash heating in a fluidised bed for various ti mes at temperatures between 200 degrees C and 450 degrees C. Training was carried out by constraint ageing at temperatures between 100 degre es C and 150 degrees C. The TWSM was assessed by thermal cycling the s prings both unloaded and opposed by weights. TWSM was shown to be crit ically dependent on the flash heating temperature and time and also on the exact procedure used in the constraint ageing training treatment. Scanning electron metallography and Vickers microhardness measurement s were used to correlate TWSM with microstructure.