Composition Dependences of Entropy Change and Transformation Temperatures in Ni-rich Ti-Ni System
Composition Dependences of Entropy Change and Transformation Temperatures in Ni-rich Ti-Ni System
复制标题
DOI：
10.1007/s40830-015-0023-2
复制
发表时间：
2015-06-01
影响因子：
2.2
通讯作者：
Kainuma, R.
中科院分区：
文献类型：
--
作者：
Niitsu, K.;Kimura, Y.;Kainuma, R.
对富镍Ti-Ni合金的比热、电阻等物理性能进行了系统的研究。在Ni含量为49.98- 51.09%时，测定了B_2/B_19 '马氏体相变温度范围为180 - 373 K，当Ni含量大于51.23%时，马氏体相变突然消失，这也是文献报道的现象。还从差示扫描量热计测量评估了熵变，并且阐明了相对于To温度绘制的熵变示出了S形曲线，在约300 K处开始急剧减小。然后进行热力学方法试图确定转变消失的原因。由直接测量的51.75Ni（B_2）和50.92Ni（B_19 ′）的比热估算的熵变与实验数据更吻合，而不是基于Debye振动比热模型的计算曲线。在成分-温度系统中，母相和马氏体相之间的平衡服从Clausius-Clapeyron关系。利用所建立的成分-温度图，可以很好地理解Ti-Ni系马氏体相变的消失是由于低温下滞后的急剧增加。
For Ni-rich Ti-Ni alloys, physical properties such as specific heat and electric resistance were systematically investigated. The B2/B19' martensitic transformation temperatures ranging from 180 to 373 K were determined for Ni contents of 49.98-51.09 %, and a sudden disappearance of martensitic transformation was confirmed for Ni contents greater than 51.23 %, which has also been well reported in the literatures. The entropy change was also evaluated from differential scanning calorimeter measurement, and it was clarified that the entropy change plotted to T o temperature shows an S-shaped curve, starting to drastically decrease at about 300 K. Thermodynamic approaches were then carried out attempting to determine the reason for the disappearance of transformation. The entropy change estimated from direct measurements of specific heats for 51.75 Ni (B2) and 50.92 Ni (B19') was found to be more consistent with the experimental data, rather than the calculated curve based on the Debye model for vibration specific heat. It was proposed that the equilibrium between the parent and martensite phases obeys the Clausius-Clapeyron relationship in the composition-temperature system. Using the constructed composition-temperature diagram, the disappearance of martensitic transformation in the Ti-Ni system can be well understood as being due to the drastic increase of hysteresis at low temperature.