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一定浓度的Pd掺杂能够有效地提高NiTi合金的相变温度, 并且降低热滞. 为了解其作用机理, 采用第一性原理计算方法, 对不同Pd掺杂浓度下NiTi合金(Ni24- nPdnTi24, n=2, 3, 4, 5, 6, 9, 12; 掺杂浓度分别为 4.2 at.%, 6.3 at.%, 8.4 at.%, 10.4 at.%, 12.5 at.%, 18.8 at.%, 25 at.%)的相稳定性和结构特性进行计算讨论. 马氏体相变温度可以通过奥氏体与马氏体两相能量差值进行分析, 且能量差越大相变温度越高; 相变过程中两相晶格常数之比越接近于1则热滞越接近于0. 计算结果表明: 当掺杂浓度小于10.4 at.% 时, B19'是最稳定的马氏体相, 体心四方(BCT)结构与B19'相的能量差随掺杂浓度的增加略有下降; 当掺杂浓度大于等于10.4 at.%时, B19相是最稳定的马氏体相, BCT与B19的能量差随着掺杂浓度增加显著升高. 这意味着在掺杂浓度大于等于10.4 at.%时相变温度随掺杂浓度的增加而显著增加. 用几何模型分析了马氏体相变的热滞, 结果表明掺杂浓度为10.4 at.% 时B2到B19相的相变过程热滞最小, 与实验结果一致.In this paper phase stability and functional properties of Pd-doped NiTi with different Pd concentrations (Ni24-nPdnTi24, n=2, 3, 4, 5, 6, 9, 12; CPd=4.2 at.%, 6.3 at.%, 8.4 at.%, 10.4 at.%, 12.5 at.%, 18.8 at.% and 25 at.%) are calculated by first-principles method. Results show that B19' is the most stable when CPd is less than 10.4 at.%, whereas B19 is the most stable for CPd is equal to or larger than 10.4 at.%. The formation energy decreases with increasing Pd concentration. With increasing CPd, the energy difference between austenite and martensite decreases slightly and increases for CPdCPdCPd=10.4 at.%, which agrees well with the experimental results.
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