Effects of Ultra high-hydrostatic pressures on Crystallogaphy and Thermodynamics of Martensitic Transformations

研究了静水压力对长时效和短时效非因瓦Ti-51at%Ni形状记忆合金以及因瓦Fe-29.9at%Ni、Fe-31.9Ni-9.8Co-4形状记忆合金马氏体相变的影响。lTi （at%）和Fe-24。Oat%Pt合金，最后一种不同有序度的合金（s0, s>, s0.6, s0.8），在1.5GPa静水压力下进行电阻率测量和光学显微镜观察。结果发现，测量的因瓦合金转变温度与流体静压的依赖关系与使用Patel-Cohen方程计算的结果不太一致，尽管它与非因瓦合金的结果很一致。据此推测，因瓦尔合金的差异可能是由与因瓦尔性质有关的物理性质之一——自发体积磁致伸缩的存在引起的。然后，根据Parel和Cohen的方程，建立了一个包含由于s的项的新方程，并给出了对转变温度的静水压力依赖关系的估计。为了对新导出的方程进行评价，分别通过静水压力下的磁化测量和冷阶段的x射线衍射实验，得到了Fe-Ni和Fe-Pt （s0.6, s0.8）合金马氏体相变的体积变化s和未知物理量。然后，通过将测量到的物理量和已知的物理量（如体积模量和吉布斯化学自由能）放入新导出的方程中，计算出这些因瓦合金转变温度的压力依赖关系。结果表明，在实测静水压力范围内，英瓦尔合金的计算依赖关系与实测值完全吻合。由此得出结论，关于自发体积磁致伸缩效应的推测和推导的方程在定量上是正确的。光学显微镜观察表明，无论形成温度如何，Fe-Ni合金在静水压力下形成的马氏体与热马氏体的形貌是相同的。这一结果与本作者先前研究的Fe-Ni-C合金的结果一致。少

We have investigated the effect of hydrostatic pressures on martensitic transformations in non-invar Ti-51at%Ni shape memory alloys aged for a long time and a short time and in invar Fe-29.9at%Ni, assuaged Fe-31.9Ni-9.8Co-4. lTi (at%) and Fe-24. Oat%Pt alloys, the last alloy having different degrees of order (S 0, S>O, S 0.6, S 0.8), by carrying out electrical resistivity measurements under hydrostatic pressures up to 1.5GPa and optical microscopy observation. As a result, it was found that the hydrostatic pressure dependence of transformation temperatures measured for invar alloys was not in good agreement with the one calculated by using a Patel-Cohen's equation, although it was in good agreement for non-invar alloys. It was, then, speculated that the disagreement for the invar alloys might be caused by the existence of spontaneous volume magnetostriction, s, which is one of physical properties related to the invar nature. Then, a new equation including the term due to s has been der … More ived to estimate the hydrostatic pressure dependence of transformation temperature by referring to the Parel and Cohen's equation. In order to evaluate the newly derived equation unknown physical quantities involved in the equation, s and the volume change associated with the martensitic transformations for Fe-Ni and Fe-Pt (S 0.6, S 0.8) alloys, have been obtained by magnetization measurements under a hydrostatic pressure and x-ray diffraction experiments with a cold stage, respectively. The pressure dependence of transformation temperatures for those invar alloys has then been calculated by putting the measured physical quantities and the known ones, such as the bulk modulus and Gibbs chemical free energy, into the newly derived equation. Consequently, the calculated dependence for the invar alloys was in all good agreement with the measured one in the measured hydrostatic pressure range. It was, thus, concluded that the speculation as to the effect of spontaneous volume magnetostriction and the derived equation were quantitatively confirmed to be appropriate, optical microscopy observation showed that morphology of the martensities formed in the Fe-Ni alloy under hydrostatic pressure was the same as that of thermallymartensites irrespective of the formation temperature. This result is consistent with that in Fe-Ni-C alloys previously examined by the present authors. Less