MARTENSITIC-TRANSFORMATION IN FE-29 WT-PERCENT-NI ALLOY ULTRAFINE PARTICLES

The ultrafine-particle samples of Fe-29 wt% Ni alloy with different av erage particle sizes (12 to 100 nm) are prepared by the evaporation co ndensation method in N-2 atmosphere. They exhibit a mixture of martens ite alpha' (bcc) and austenite gamma (fcc) phases. Each individual par ticle is a single crystal (bce or fee). The volume fraction of martens ite increases markedly with the decrease of the average particle size. During heating, as the average particle size decreases, the temperatu re (A(s) and A(f)) for alpha'-->gamma reverse martensitic transformati on decreases, and the range (A(s)-A(f)) of reverse transformation temp erature becomes narrower, whereas during cooling (down to 77 K),we hav e not observed gamma-->alpha' martensitic transformation. The stabiliz ation of austenite and the growth mechanism of martensite and austenit e are preliminarily discussed in this paper.