By varying the Ni content from 4 to 10% in shape memory alloys, the effect of the Ni content upon the distribution of stacking faults and martensite plates could be studied by means of optical and transmission electron microscopy. After solution treatment, followed by water-quenching, martensite was already present in alloys which contained less than 9%Ni. However, the volume fraction of the martensite decreased markedly with increasing Ni content. Widely extended and densely overlapping stacking faults were observed in all of the investigated alloys. Their densities decreased with increasing Ni content. In addition to large stacking faults, many short and imperfectly overlapping stacking faults were observed to be uniformly distributed in 6%Ni alloy (where the maximum shape memory effect was observed). It was suggested that such imperfectly overlapping short segments of stacking fault might be the origin of the stress-induced martensite that was responsible for the shape memory effect.

H.Inagaki: Zeitschrift für Metallkunde, 1995, 86[4], 275-80