For secondary reactions, the free energy calculations are significantly lower compared to those of the primary reactions, thus, formation of NiTi is weak reaction. It was found that elemental powder sintering of equiatomic composition did not result in single phase TiNi, instead, multi-phases including Ti2Ni, TiNi and TiNi3 were found to co-exist in the microstructure even after sintering to high temperatures for long durations implying, the stability of these phases. Quantitative phase fraction analysis revealed that NiTi volume fraction increased with time and temperature up to 1080°C, beyond which the amount of NiTi decreased while Ti2Ni and TiNi3 increased. No TiNi phase was observed to form in between Ti2Ni and TiNi3, implying that decomposition of TiNi into Ti2Ni and TiNi3 is not likely. No distinct peaks of martensitic transformation were observed on sintered Ni-Ti samples by DSC analysis. This is attributed to the high Ni contents (≥52at%) of the B2-NiTi phase formed...
|Publication status||Unpublished - 2011|