3D in-situ characterization of dislocation density in nickel-titanium shape memory alloys using high-energy diffraction microscopy
3D in-situ characterization of dislocation density in nickel-titanium shape memory alloys using high-energy diffraction microscopy
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DOI：
10.1016/j.actamat.2024.119659
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发表时间：
2024-01
期刊：
影响因子：
9.4
通讯作者：
Wenxi Li;Sangwon Lee;Tianchi Zhang;Yuefeng Jin;Darren Pagan;Lee Casalena;Michael Mills;A. Bucsek
中科院分区：
文献类型：
--
作者：
Wenxi Li;Sangwon Lee;Tianchi Zhang;Yuefeng Jin;Darren Pagan;Lee Casalena;Michael Mills;A. Bucsek
功能疲劳-在循环加载过程中材料响应的变化-是形状记忆合金技术循环寿命要求的主要障碍。功能疲劳是由微观结构的永久变化引起的，例如在正向和反向马氏体相变期间产生位错。在这项工作中，远场和近场高能衍射显微镜（ff-和nf-HEDM）被用来表征局部积累的几何必要的位错（GND）密度在奥氏体相在原位和在3D整个散装Ni 49. 9 Ti 50. 1多晶形状记忆合金在负载偏置热循环。自定义nf-HEDM数据分析程序用于重建空间分辨的晶内取向不良图，然后将其转换为空间分辨的GND密度图。通过这种方式，GND密度在各个周期的单个颗粒中被跟踪。我们发现，无论是施密德因子，也不是最大的转换工作与GND密度演变在负载偏置的热循环过程中强烈相关。结果表明，空间分辨的GND密度分布不均匀，但在晶界附近、试样表面的晶粒中以及大体积晶粒中GND密度增加较快，表明这些区域/类型的晶粒将经历不同的功能疲劳行为。最后，研究了晶界和晶粒邻域对GND密度演化的影响，强调了晶界和晶粒邻域在GND密度演化中所起的作用。这项工作证明了nf-HEDM的效用，了解亚晶尺度塑性变形的演变，包括材料进行马氏体相变。
Functional fatigue—changes to the material response during cyclic loading—is a major barrier to the cycle lifetime demands of shape memory alloy technologies. Functional fatigue is caused by permanent changes to the microstructure such as the generation of dislocations during the forward and reverse martensitic phase transformation. In this work, far-field and near-field high-energy diffraction microscopy (ff- and nf-HEDM) are used to characterize the local accumulation of geometrically necessary dislocation (GND) density in the austenite phase in situ and in 3D across a bulk Ni49.9Ti50.1polycrystalline shape memory alloy during load-biased thermal cycling. A custom nf-HEDM data analysis procedure is used to reconstruct spatially-resolved intragranular misorientation maps that are then converted to spatially-resolved GND density maps. In this way, GND density is tracked in individual grains across cycles. We find that neither Schmid factor nor the maximum transformation work correlates strongly with GND density evolution during load-biased thermal cycling. The results show that the spatially-resolved GND density is distributed heterogeneously, but GND density increases faster near grain boundaries, in grains at the sample surface, and in grains with large volumes, indicating that these regions/types of grains will undergo different functional fatigue behaviors. Finally, the effect of grain neighborhood and grain boundaries on GND evolution are investigated, highlighting the role played by grain boundaries and the grain neighborhood in the evolution of GND density. This work demonstrates the utility of nf-HEDM for understanding the evolution of subgrain-scale plastic deformation, including materials that undergo a martensitic phase transformation.