Martensitic Transformation in Ni-AI-Pt High Temperature Shape Memory Alloys

摘要

In alloys Ni-39(41)Al-xPt (x = 5,10,15,20 at.%) the alloying by Pt strongly increases the M_s point. There is no direct proportionality between the Pt content and the M_s point increasing. No traces of Ni_3Al were found in the alloys. The precipitation of Ni_5Al_3 was observed in Ni-39Al-15Pt alloy after cycling through the temperature range between the room temperature and 800°C. The effect of Pt alloying on the martensitic transformation and high temperature martensitic transformation stability is governed by the competition between the martensitic transformation and formation of the Ni_5Al_3 phase upon the cooling. Pt addition, instead of Ni, can resolve the problem of decomposition processes because the alloy composition is shifted out of the Ni_3Al domain on the phase diagram and it reduces the influence of the Ni_5Al_3 phase on the degradation of martensitic transformation.