Abstract: The ultrafine particle samples of Fe-29 wt% Ni alloy with different average diameters(12 to 100nm) are prepared by the evaporation condensation method in the atmosphere of N₂.They are a mixture of martensitio α'(bcc) and the austenite γ(fcc).Each individual particle is a single crystal (bcc or fcc). The volume fraction of martensite increases evidently with the decrease of the average diameter. During heating, as the average diameter decreases, the temperature (Aa and Af) for α'-γ reverie martensitic transformation comes down, and the range(As-Af) of the transformation temperature becomes narrower. However, during cooling (up to 77K), we have not found the martensitic transformation. The stabilization of the austenite and the growth mechanism of the martensite and austenite are preliminarily discussed in this Paper too.

Key words: evaporation condensation, ultrafine Particles, martensitic transformation