Microstructure and martensitic transformation of CuAlNi and CuAlNiZr melt spun ribbons with shape memory effect.

The reversible martensite transformation in CuAlNi and CuAlNiZr bulk alloy and melt spun ribbons was investigated using microcalorymetry and electron microscopy. The addition of Zr to CuAlNi resulted in precipitation of Cu2AlZr type phase containing 42.4at.%Cu, 12.5at.%Ni, 22.1at.%Al and 23.1at.%Zr. These precipitates lowered grain size in bulk and in ribbons down to 100 and 1 micrometer respectively. The higher cooling rate caused decrease of Ms in both alloys by 20 and 110 degrees centigrade respectively. Simultaneously, both the width of martensite plates and the diameter of (CuNi)2AlZr precipitates decreases down to 0.1-0.01 micrometer to 0.02 micrometer respectively. The martensitic transformation hysteresis in ribbons is wider than in bulk material.