TEM AND HREM STUDY OF THE INTERPHASE INTERFACE STRUCTURE OF TI3NI4 PRECIPITATES AND PARENT PHASE IN AN AGED TINI SHAPE-MEMORY ALLOY

The structures of coherent and semi-coherent interphase interfaces bet ween Ti3Ni4 precipitates and parent phase in different aged Ti-51.5Ni (at.%) shape memory alloy have been studied by means of diffraction co ntrast analyses in transmission electron microscopy (TEM) and high res olution electron microscopy (HREM). When the alloy was aged at 723 K f or 3 h, very small Ti3Ni4 precipitates formed in the matrix with a coh erent interface to the parent phase. Very strong strain field was obse rved in this kind of coherent interface using TEM and HREM. When the a lloy was aged at 873 K for 20 h, large Ti3Ni4 precipitates formed in t he parent phase matrix possessing a semi-coherent interface. The dislo cation networks were observed in the semi-coherent interface. The Burg ers vectors of these sets of dislocations are determined to be [111](B 2) and [200](B2) types. Very weak strain field was observed in this ki nd of interface.