Metallographic studies have been made of precipitation processes in Ti-50 pct Ni and Ti-52 pct Ni (at. pct) shape memory alloys. The eutectoid and peritectoid reactions previously reported for near-equiatomic and Ni-rich TiNi alloys were not observed for either composition. In the Ti-52Ni alloy, diffusional transformations take place, similar to those in supersaturated alloys. The precipitation sequence can be written as β 0 → Ti 11 Ni 14 → Ti 2 Ni 3 → TiNi 3 . The solidus line of the TiNi phase in the Ti-52Ni alloy lies at 812 ± 22 °C. Morphological characteristics of the various precipitate phases are described in detail.
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