TRANSFORMATION SEQUENCE IN A Cu-Al-Ni SHAPE MEMORY ALLOY AT ELEVATED TEMPERATURES.

Precipitation sequences in a Cu-14 pct Al-4 pct Ni (wt pct) shape memory alloy were studied by means of transmission electron diffraction and microscopy as well as X-ray microanalysis techniques. On aging thin foil specimens up to 550 degree C in the electron microscope, an as-quenched sample having a mixture of 2H-type and DO//3-type metastable structures transformed to the stable simple cubic gamma //2 phase at or above 450 degree C. The remaining matrix either showed precipitates of the fcc alpha -phase on prolonged annealing at 500 to 550 degree C for a longer period, or transformed to martensite on cooling below the M//s temperature (approx. 150 degree C.