Neutron-scattering and electron-microscopy studies of the premartensitic phenomena in NixAl100-x alloys.
Neutron-scattering and electron-microscopy studies of the premartensitic phenomena in NixAl100-x alloys.
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DOI：
10.1103/physrevb.44.9301
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发表时间：
1991-11
期刊：
影响因子：
--
通讯作者：
S. M. Shapiro;Baorui Yang;Yasutoshi Noda;Lee E. Tanner;D. Schryvers
中科院分区：
文献类型：
--
作者：
S. M. Shapiro;Baorui Yang;Yasutoshi Noda;Lee E. Tanner;D. Schryvers
在{ital x}=50、58、62.5和63.9 at时，对Ni{sub {ital x}}Al{sub 100{-}{ital x}}合金的立方相单晶进行了非弹性中子散射和电子显微镜研究。%。（110）-TA{sub 2}声子分支，对应于沿（{bar 1}10）方向的原子位移，显示出异常行为，因为整个分支对组成非常敏感，并且表现出扭结，其在{ital q}空间中的位置也对{ital x}敏感。在与扭结相同的{初始q}处也存在弹性漫射散射的峰值。振幅对比电子显微镜图像显示了许多马氏体相变材料特有的粗花呢图案。高分辨率（相衬）电子图像显示立方结构的微观偏差，可以视为低温（5,{bar 2}）马氏体相的胚胎。与这些变形相关的位移场被证明是实验中观察到的弹性中心峰的起源。温度依赖性研究表明，当{ital T}接近{ital T}{次{ital M}}（马氏体相变开始温度）时，扭结附近声子分支有明显的软化，弹性扩散散射增加。模式永远不会完全变软。此外，软化被狭窄地限制在与（110）垂直的（{bar 1}10）方向上。对单轴应力下声子色散曲线的研究表明，声子模式在扭结{ital q}值附近软化，这可以用Clapp提出的马氏体相变材料成核的局域软模式理论来解释。«少
Inelastic-neutron-scattering and electron-microscopy studies were performed on single crystals of the cubic phase of Ni{sub {ital x}}Al{sub 100{minus}{ital x}} alloys for {ital x}=50, 58, 62.5, and 63.9 at. %. The (110)-TA{sub 2} phonon branch, corresponding to atomic displacements along the ({bar 1}10) direction, is shown to exhibit anomalous behavior in that the entire branch is very sensitive to composition and exhibits a kink'' whose position in {ital q} space is also sensitive to {ital x}. A peak in the elastic diffuse scattering is also present at the same {ital q} as the kink. Amplitude-contrast electron-microscope images display a tweed'' pattern characteristic of many martensitically transforming materials. The high-resolution (phase-contrast) electron image reveals microscopic deviations of the cubic structure and can be viewed as embryos of the low-temperature (5,{bar 2}) martensitic phase. The displacement fields associated with these distortions are shown to be the origin of the elastic central peak observed in the experiments. Temperature-dependence studies show a substantial softening of the phonon branch in the vicinity of the kink and the elastic diffuse scattering increases as {ital T} approaches {ital T}{sub {ital M}}, the martensitic-transformation onset temperature. The mode never becomes completely soft. Furthermore, the softening is narrowly restricted tomore » the ({bar 1}10) direction, which is perpendicular to (110). Studies of the phonon dispersion curve under uniaxial stress show a softening of the phonon mode near the {ital q} value of the kink, which can be interpreted in terms of Clapp's proposed localized-soft-mode theory of nucleation of materials undergoing martensitic transformation.« less