EFFECT OF QUENCHING RATE ON MARTENSITIC-TRANSFORMATION TEMPERATURE IN CU-AL-NI SHAPE-MEMORY ALLOYS

Experiments were carried out for Cu-xAl-5Ni-2Mn-1Ti shape memory alloys (x=11.45, 11.77, 11.88 mass%) in order to examine the effect of quenching rate on the transforation temperatures (M(s), M(f), A(s) and A(f)). The quenching rate was varried from 5 to 1x10(4) K/s by changing the temperature of quenching media. The transformation temperatures were determined by DSC measurements for all the samples quenched and are plotted as a function of quenching rate. It was found that all the transformation temperatures decreased by about 10 K, when the quenching rate was increased 10 times as large as its initial value. The reason was explained by considering the degree of order in the beta-phase. The primary alpha- and gamma(2)-phases do not precipitate even during air-cooling on quenching in the alloys with 11.77 and 11.88%Al, being close to the eutectoid composition. Therefore, no remarkable change in martensitic transformation temperature with reducing quenching rate was observed in these alloys. In other words, it can be concluded that these alloys are suitable for heat treatments in practice, where the specimens are cooled more slowly.