变温下NiTi合金相变热力学特征

将试验测定的NiTi合金热容值用于计算不同电流值加热（不同的加热速度）的NiTi合金丝温度的变化历程，由于相变潜热的存在，当加热电流适当大时，会使升温工线产生拐点而形成台阶，实验发现加热速度的快民对合金相变所需要的时间影响很大，使用调制式差式扫描量热量研究了以不同速度加热或冷却合金时合金各相相变温度的变化情况，随着加热速度的增大，相变温度偏离平衡温度的趋势增大，经过数值处理之后，发现合金相变所需要的时间随加热或冷却速度的增大而呈指数关系递减。

Characteristics of Phase Transformation Thermodynamics for NiTi Wires underNon-Isothermal Conditions

The temperatures of NiTi wire, when heated by electric current, were calculated by using the specific heat capacities determined directly from experiment. Owing to the existence of the latent heat, there will be an inflection on the heating curve, resulting in the formation of a step. It is found that the time for phase transformation is greatly influenced by the heating rate. The phase transformation temperatures of NiTi wires were determined by employing the modulated differential scanning calorimeter (MDSC). The deviation of the transformation temperatures from the equilibrium temperature is higher with the increase of heating/cooling rate. It is found that the time for phase transformation declines exponentially upon the heating rate. Finally, the thermodynamic characteristics under non isothermal conditions were discussed.