NiTi形状记忆合金的相变温度滞后

用透射电镜、正电子湮没和电阻测量,研究了NiTi形状记忆合金的组织结构与相变滞后的关系结果表明,经不同制度时效处理的组织,其相变温度滞后大小的顺序是:片状马氏体>R相>束状马氏体。Ti_(11)Ni_(14)相质点周围的共格应力场对这些相的可逆转变起障碍作用。正电子湮没Doppler展宽能谱S参数值与试样的温度滞后值之间存在线性关系,从而确认Ti_(11)Ni_(14)相析出的错配位错密度及由此而建立的晶体中弹性应力场分布是决定NiTi合金相变温度滞后的主要因素。

HYSTERESIS OF PHASE TRANSFORMATION TEMPERATURE IN NiTi SHAPE MEMORY ALLOY

The relationship between structure and hysteresis of phase transformation tem-perature in NiTi shape memory alloy has been investigated by means of TEM observation, positron annihilation and electrical resistivity measurement. The sequence of hysteresis for the alloy aged under different regimes was found to be: plate martensite > R phase > tie--like martensite. The reversible displacement of phase boundaries of these transformations is blocked by the coherent stress field around Ti_(11)Ni_(14) phase particles. A linear relationship between Sparameter of positron annihilation and maximum values of temperature hysteresis showed that the mismatch dislocation and elastic stress field established by Ti_(11)Ni_(14) phase precipitation arethe main factor to determine the temperature hysteresis of phase transformation in NiTi shape memory alloy.