Martensitic Transformation and its Composition Dependence in Ti-Ni-Cu Shape Memory Alloys

Ti_<50>Ni_<50-x>Cu_x合金作为一种高内耗的抗振材料，近年来受到了广泛的关注。这些合金在10=x=15时表现出B2-B19（正交）-B19 '（单斜）马氏体两阶段相变，但在x&gt;15时是否表现出两阶段相变尚不清楚。同时，首席研究员先前发现，当x&gt;15时，合金在250 K附近显示出非常高的内耗峰（Q^<-1>=0.2），称为“宽峰”。为了了解宽峰的起源，必须了解x&gt; 15的合金的马氏体相变特征。为此，我们在同步辐射装置（SPring-8）上进行了极高强度的X射线衍射实验。因此，我们证实了<nd>当x&gt;15时，也会发生第二阶段转变，并且我们可以确定转变温度。此外，还发现了非常奇特的特征， 关于我们 的样本显示<nd>12=x=20的2^变换。根据这些结果，可以分离多个内摩擦峰。因此，我们使用DMA进行了详细的内耗实验。因此，我们确认宽峰是一个弛豫峰，其激活能分别为：E=0.67eV（x=20），E=0.76eV（x=16）。此外，通过进行单晶实验，我们发现，宽峰消失，如果孪晶消除拉伸应力。这是双胞胎观察宽峰的必要性的直接证据。同时，也有一些报道指出，氢是观察宽峰所必需的。通过进行脱氢实验，我们也证实了宽峰通过脱氢而消失。从这些实验中，我们可以得出结论，孪晶界和H是必要的，以观察高宽峰。此外，我们发现脱氢后在178 K附近出现了一个新的弛豫峰。这些结果现在提交给Acta Materialia，包括对宽峰起源的讨论。少

Ti_<50>Ni_<50-x>Cu_x alloys attract much attention recently as vibration-proof materials with high internal friction. These alloys show 2-stage B2-B19(orthorhombic)-B19'(monoclinic) martensitic transformation for 10=x=15, but it is not clear whether they show 2-stage transformation for x>15 or not. Meanwhile, the head researcher previously found that for x>15 the alloys show very high internal friction peak (Q^<-1>=0.2) called "broad peak" at around 250K. In order to understand the origin of the broad peak, it is inevitable to understand the characteristics of the martensitic transformation of the alloys including the compositions x>15.For this purpose we carried out x-ray diffraction experiments with extremely high intensity at synchrotron facilities (SPring-8). Consequently we confirmed the 2^<nd> stage transformation also occurs for x>15, and we could determine the transformation temperatures. Furthermore, very peculiar characteristics were found such that only a very small fraction … More of specimens show the 2^<nd> transformation for 12=x=20. From these results it became possible to separate multiple internal friction peaks. Thus we carried out detailed internal friction experiments using DMA. Consequently we confirmed that the broad peak is a relaxation peak with the following activation energies ; E=0.67eV(x=20),E=0.76eV (x=16). Furthermore, by carrying out single crystal experiments, we found that the broad peak disappears if twins are eliminated by tensile stress. This is a direct evidence to show twins are necessary to observe the broad peak. Meanwhile, there are some reports that hydrogen is necessary to observe the broad peak. By carrying out de-hydrogenation experiments we also confirmed that the broad peak disappear by de-hydrogenation. From these experiments we can conclude that both twin boundaries and H are necessary to observe the high broad peak. Furthermore, we found that a new relaxation peak appears at around 178K after de-hydrogenation. These results are now submitted to Acta Materialia including the discussion of the origin of the broad peak. Less