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

Ti&lt；50&gt；Ni&lt；50-x&gt；Cux合金作为一种高内耗的耐振材料，近年来备受关注。这些合金在10=x=15存在两阶段的B2-B19(正交)-B19‘(单斜晶系)马氏体相变，而对于x&gt；15是否存在两阶段相变尚不清楚。同时，首席研究员此前发现，对于x&gt；15，合金在250K左右表现出很高的内耗峰(Q^&lt；-1&gt；=0.2)，称为“宽峰”。为了了解宽峰的起源，不可避免地要了解包括x&gt；15成分在内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，我们确认了x&gt；15也发生了2^&nD&gt；阶段相变，并确定了相变温度。此外，还发现了非常特殊的特征，以至于只有很小一部分…更多的样品显示了12=x=20的2^&nd&gt；相变。从这些结果中可以分离出多个内耗峰。因此，我们利用DMA进行了详细的内耗实验。因此，我们确认该宽峰是一个弛豫峰，其活化能为：E=0.67 eV(x=20)，E=0.76 eV(x=16)。此外，通过进行单晶实验，我们发现，如果通过张应力消除孪晶，则宽峰消失。这是一个直接的证据，表明双胞胎是观察宽峰所必需的。同时，也有一些报道称氢是观察宽峰所必需的。通过进行脱氢实验，我们也证实了脱氢使宽峰消失。从这些实验中我们可以得出结论，孪晶界和H都是观察高而宽的峰所必需的。此外，我们还发现在脱氢后的178K附近出现了一个新的弛豫峰。这些结果现已提交给《材料学报》，其中包括对宽峰起源的讨论。较少

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