Point Defects in Intermetallic Compounds

9313702利用微扰角相关技术，以原子尺度的分辨率检测高度有序金属间化合物中点缺陷的柯林斯浓度，这是一种能够清楚地区分缺陷的伽马射线谱。一个目标是确定各种化合物中的平衡和形变引起的缺陷。平衡(热)缺陷形成热焓和缺陷浓度是根据测量的探针-缺陷复合体的位置分数来确定的，方法是在以前的研究中开发的。利用PAC和穆斯堡尔谱技术，比较了形变引起的缺陷与热缺陷以及从探测原子的位置分数估算的浓度。第二个目标是研究材料在高能机械球磨下的微观结构演变。对晶界和表面的体位和探测位的缺陷进行了监测。分析了缺陷对失稳平衡相的影响。这里研究的材料缺陷会影响在各种应用中使用的先进材料中的相稳定性和扩散。***

9313702 Collins Concentrations of point defects in highly-ordered intermetallic compounds are detected with atomic-scale resolution using perturbed angular correlations (PAC), a gamma-ray spectroscopy capable of differentiating clearly between defects. An objective is to identify equilibrium and deformation-induced defects in a variety of compounds. Equilibrium (thermal) defect formation enthalpies and defect concentrations are determined from measured site fractions of probe-defect complexes using a methodology developed during previous studies. Deformation-induced defects are compared to thermal defects and the concentrations estimated from site fractions of probe atoms using PAC and Mossbauer techniques. A second objective is to examine the microstructural evolution of materials subjected to high energy mechanical milling. Defects in volume sites and probe sites at grain boundaries and surfaces are monitored. The effect of the defects on destabilizing equilibrium phases is assessed. %%% The material defects under study here affect phase stability and diffusion in advanced materials used in a variety of applications. ***