EFFECT OF PRECIPITATES ON THE ELECTRICAL-RESISTIVITY TEMPERATURE CURVES IN AN AGED TI-51.8 AT-PERCENT-NI SHAPE MEMORY ALLOY

The electrical resistivity-temperature curves of an aged Ti-51.8at%Ni alloy may be classified as one of four typical types related to the precipitation processes of the Ti3Ni4 and Ti2Ni3 phases. The Ti3Ni4 precipitates are always in coherence with the matrix for specimens aged at a temperature below 873K for 10min-30h. Their internal strain fields appear as typical black/white lobe or displacement fringe images depending on the precipitation processes. The TR temperature is affected by the internal strain field from Ti3Ni4 precipitates, while the Ms temperature is mainly dependent on the amount of Ni in the matrix. Coarsening of Ti3Ni4 precipitates may give rise to an increase in the Mf temperature.