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Analysis of Ti–Ni–Hf shape memory alloys by combinatorial nanocalorimetry / Yahya Motemani in Acta materialia, Vol. 59 N° 20 (Décembre 2011) 

Public ISBD [article]  in Acta materialia > Vol. 59 N° 20 (Décembre 2011) . - pp. 7602–7614 Titre : Analysis of Ti–Ni–Hf shape memory alloys by combinatorial nanocalorimetry Type de document : texte imprimé Auteurs : Yahya Motemani, Auteur ; Patrick J. McCluskey, Auteur ; Chunwang Zhao, Auteur Année de publication : 2012 Article en page(s) : pp. 7602–7614 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Thin  film  Calorimetry  Martensitic  transformation  Thermal  cycling  High-temperature  shape  memory  alloy Résumé : The martensitic transformation in Ti–Ni–Hf thin films with ultra-fine grain structure has been analyzed as a function of composition using a high-throughput array of nanocalorimeters. The martensite–austenite transformation temperature is significantly lower than in bulk Ti–Ni–Hf, but increases linearly with Hf content at a rate comparable to bulk Ti–Ni–Hf. The response to high-temperature cycling (22 °C < T < 850 °C) changes with Ni concentration. For Ni ⩽ 47 at.%, the transformation temperature increases during high-temperature cycling because precipitation of (Ti1−x, Hfx)2Ni enriches the surrounding matrix in Hf; for Ni ⩾ 47.7 at.%, precipitation of the same phase gradually suppresses the transformation. Low-temperature cycling (22 °C < T < 450 °C) causes the transformation temperature to initially decrease and then stabilize. Relaxation of internal stresses by dislocations generated during thermal cycling is suggested as the active mechanism. Thermal cycling stability of the films is improved compared to previous studies on bulk Ti–Ni–Hf. This is attributed to the very small grain size (18 ± 5 nm) of the samples. Alloys with superior thermal cycling stability are identified and the ability to control the transformation temperature through multiple thermal cycling is demonstrated. ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S135964541100601X [article] Analysis of Ti–Ni–Hf shape memory alloys by combinatorial nanocalorimetry [texte imprimé] / Yahya Motemani, Auteur ; Patrick J. McCluskey, Auteur ; Chunwang Zhao, Auteur . - 2012 . - pp. 7602–7614. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 59 N° 20 (Décembre 2011) . - pp. 7602–7614 Mots-clés : Thin  film  Calorimetry  Martensitic  transformation  Thermal  cycling  High-temperature  shape  memory  alloy Résumé : The martensitic transformation in Ti–Ni–Hf thin films with ultra-fine grain structure has been analyzed as a function of composition using a high-throughput array of nanocalorimeters. The martensite–austenite transformation temperature is significantly lower than in bulk Ti–Ni–Hf, but increases linearly with Hf content at a rate comparable to bulk Ti–Ni–Hf. The response to high-temperature cycling (22 °C < T < 850 °C) changes with Ni concentration. For Ni ⩽ 47 at.%, the transformation temperature increases during high-temperature cycling because precipitation of (Ti1−x, Hfx)2Ni enriches the surrounding matrix in Hf; for Ni ⩾ 47.7 at.%, precipitation of the same phase gradually suppresses the transformation. Low-temperature cycling (22 °C < T < 450 °C) causes the transformation temperature to initially decrease and then stabilize. Relaxation of internal stresses by dislocations generated during thermal cycling is suggested as the active mechanism. Thermal cycling stability of the films is improved compared to previous studies on bulk Ti–Ni–Hf. This is attributed to the very small grain size (18 ± 5 nm) of the samples. Alloys with superior thermal cycling stability are identified and the ability to control the transformation temperature through multiple thermal cycling is demonstrated. ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S135964541100601X