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

Ti_<50>Ni_<50-x>Cu_x合金作为高内摩擦的防震材料近年来受到广泛关注。这些合金在10=x=15时表现为B2-B19（正交）-B19′（单斜）两阶段马氏体转变，但在x>15时是否表现为两阶段马氏体转变尚不清楚。同时，首席研究员先前发现，对于x >5合金在250K左右表现出非常高的内摩擦峰（Q^<-1>=0.2），称为“宽峰”。为了了解宽峰的成因，必须了解含成分x>15的合金的马氏体相变特征。为此，我们在同步加速器（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2^<和>阶段的转变也发生在x>15，我们可以确定转变温度。在12=x=20的条件下，大部分样品表现出2^<和>的转变。从这些结果可以分离出多个内摩擦峰。因此，我们使用DMA进行了详细的内摩擦实验。因此，我们证实了宽峰是一个松弛峰，其活化能如下：E = 0.67 ev (x = 20), E = 0.76 ev (x = 16)。此外，通过单晶实验，我们发现，如果拉应力消除孪晶，宽峰就会消失。这是一个直接的证据，说明双胞胎是观察宽峰的必要条件。与此同时，也有一些报道称，氢是观测宽峰所必需的。通过脱氢实验也证实了脱氢后宽峰消失。从这些实验中我们可以得出结论，孪生边界和H是观察高宽峰所必需的。此外，我们发现在脱氢后的178K左右出现了一个新的弛豫峰。这些结果现已提交给《材料学报》，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