On the effect of alloy composition on martensite start temperatures and latent heats in Ni-Ti-based shape memory alloys
On the effect of alloy composition on martensite start temperatures and latent heats in Ni-Ti-based shape memory alloys
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DOI：
10.1016/j.actamat.2015.02.029
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发表时间：
2015-05-15
期刊：
影响因子：
9.4
通讯作者：
Eggeler, G.
中科院分区：
文献类型：
--
作者：
Frenzel, J.;Wieczorek, A.;Eggeler, G.
在本工作中，我们解释了ni - ti基形状记忆合金（sma）中马氏体起始温度（M-s）的浓度依赖性。我们简要回顾了目前的认识水平，并表明需要进一步的工作。然后，我们研究了二元Ni-Ti、三元Ni-Ti-X （X = Cr, Cu, Hf, Pd， V, Zr）和四元Ni-Ti-Cu-Y (Y = Co, Pd) sma中M-s对合金成分的依赖性。对于二元Ni- ti，我们将差示扫描量热实验与密度泛函理论（DFT）的应用结合起来，表明随着Ni浓度从50.0%增加到51.2%，相变热δ H降低。这导致奥氏体G(a)(T)和马氏体G(M)(T)的吉布斯自由能曲线发生位移，从而导致M-s温度降低。我们的DFT结果表明，δ H的强烈下降是由Ni对位原子周围的结构弛豫稳定B2相以及B19 '的逐渐不稳定引起的。二元、三元和四元ni - ti基sma的马氏体起始温度与相变潜热密切相关。当奥氏体和马氏体晶体结构的几何差异减小时，潜热减小。(C) 2015材料学报Elsevier Ltd.出版。版权所有。
In the present work we explain the concentration dependence of the martensite start temperature (M-s) in Ni-Ti-based shape memory alloys (SMAs). We briefly review the present level of understanding and show that there is a need for further work. We then investigate the strong dependence of M-s on alloy composition in binary Ni-Ti, ternary Ni-Ti-X (X = Cr, Cu, Hf, Pd, V, Zr) and quaternary Ni-Ti-Cu-Y (Y = Co, Pd) SMAs. For binary Ni-Ti, we combine differential scanning calorimetry experiments with insight gained through the application of the density functional theory (DFT) to show that heats of transformation Delta H decrease as Ni concentrations increase from 50.0 to 51.2 at.%. This causes a shift in the Gibbs free energy curves of austenite G(A)(T) and martensite G(M)(T), which in turn results in a lower M-s temperature. Our DFT results suggest that the strong decrease of Delta H is caused by a stabilization of the B2 phase by structural relaxations around Ni antisite atoms, together with a gradual destabilization of B19 '. The martensite start temperatures and the latent heats of transformation for binary, ternary and quaternary Ni-Ti-based SMAs are closely related. We observe smaller latent heats when the geometrical differences between the crystal structures of austenite and martensite decrease. (C) 2015 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.