Abstract: The precipitation processes of Ti3Ni4 phase in Ti-51.8at% Ni alloy aged at 300 ~ 600℃ have been systematically studied by means of transmission electron microscope. It is found that the Ti3Ni4 precipitates nucleate homogeneously at the early stage of aging and appeal as fine dispersed particles . Upon the prolongation of aging time or temperature , the Ti3Ni4 precipitates become gradually the lenticular-like shape , and finally exhibit coarse plates. They are in good Coherence with the matrix. The contrast of the internal strain fields caused by the coherent Ti3Ni4 precipitates changes with their growth. When the Ti3Ni4 precpitates are coarsened enough, they lost in coherence with the matrix and produce dislocations about them . The Bagle's vectors for these dislocations are determined to be 1 / 2[111]B2 or 1 / 2[111]B2.

Key words: Ti3Ni4 phase, strain field contrast, TiNi alloy