{'fraction_non_alphanumeric': 0.0078125, 'fraction_numerical': 0.0, 'mean_word_length': 5.788079470198675, 'pattern_counts': {'":': 0, '<': 0, '<?xml version=': 0, '>': 0, 'https://': 0, 'lorem ipsum': 0, 'www.': 0, 'xml': 0}, 'pii_count': 0, 'substrings_counts': 0, 'word_list_counts': {'cursed_substrings.json': 0, 'profanity_word_list.json': 0, 'sexual_word_list.json': 0, 'zh_pornsignals.json': 0}}
Martensitic phase transformations of nanocrystalline NiTi shape memory alloys processed by repeated cold rolling

Abstract The impact of grain size on the martensitic phase transformations of bulk nanocrystalline NiTi shape memory alloys processed by repeated cold rolling was systematically studied by differential scanning calorimetry and transmission electron microscopy. With decreasing grain size, the formation of the martensite is strongly suppressed and its thermal stability decreases. The effect of grain size on the intermediate R-phase is much smaller than that observed in the case of the martensite. Reversible and irreversible contributions to the Gibbs free energy of the martensite were obtained that are larger than those arising from the formation of martensite in coarse grains. Considering the dependence of the energy barrier on the transformation eigenstrain and the grain size, the experimental results were modelled within the general thermodynamic framework of the martensitic phase transformation.