Selective variant growth of coherent Ti11Ni14 precipitate in a TiNi alloy under applied stresses

A coherent precipitate phase usually has a number of variants that are oriented in different but equivalent crystallographic directions. The distribution of the variants can be changed by applying stress during ageing. Under the stress constraint, the growth of differently oriented variants becomes selective, and this, in turn, varies the material's microstructure. The number of precipitate variants may be determined by decomposing the space group of the parent phase into the coset of the space group of the coherent precipitate phase; and which variants grow selectively is, however, dependent upon the coupling between the applied stress and the local strain of the variants. Selective variant growth of Ti11Ni14 precipitates in Ti-51.5 at% Ni alloy was investigated. A pole projection method was proposed and used to predict the selective variant growth of Ti-11/Ni-14 precipitates under the stress constraint. TEM observation was conducted to corroborate the prediction. A positive correlation between the theoretical analysis and the experiment was established. Copyright (C) 1997 Acta Metallurgica Inc. file.