The Yield Strength Anomaly in B2 Compounds

B2 化合物的屈服强度异常

• 批准号: 9812211
• 负责人: Ian Baker
• 金额: $ 24万
• 依托单位: Dartmouth College
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 1998
• 资助国家: 美国
• 起止时间: 1998-09-01 至 2001-12-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=9812211&HistoricalAwards=false
• 关键词: Yield; Strength; Anomaly; B2; Compounds

9812211 Baker The aim of this research is to explore whether the vacancy- hardening model that explains the yield strength anomaly in FeAl is applicable to other B2 compounds that show a similar temperature dependence of yield strength. The model is general and could be applicable to a wide variety of crystal structures, which show a yield anomaly. The research involves single crystal growth, mechanical testing and slipline analysis, and transmission electron microscopy (TEM) of single crystals of CoTi, CoHf and CoZr. Measurements of vacancy concentrations are made for different annealing temperatures using the Simmons/Balluffi method, whereby the density measured by dilatometry is compared to that measured by x-rays. The activation enthalpies for both vacancy formation and vacancy migration are determined and compared with values obtained from the vacancy-hardening model. In order to determine the dislocation/vacancy interactions associated with the yield strength anomaly, TEM in-situ straining experiments are performed both as a function of temperature and on crystals containing different quenched-in vacancy concentrations. Mechanical testing includes determination of the tension/compression asymmetry of the yield stress as a function of temperature in single crystals of different orientations. The compression tests are performed in a wide range of strain rates with the very high strain rate tests being performed at Los Alamos National Laboratory. Specialized mechanical tests using a Gleeble test machine, which allows very rapid heating and quenching, are performed at Oak Ridge National Laboratory. This apparatus enables yield strength measurement to be performed at the yield strength peak temperature with different vacancy concentrations present. TEM examination of slip-plane- sectioned specimens rapidly-cooled after testing in the Gleeble allows dislocation structures truly representative of high temperature testing to be examined. %%% Intermeta llic alloys exhibit unique mechanical properties that could enable their use in high temperature structural applications. This research should advance understanding of the mechanical behavior of this important class of metal alloys.

小行星9812211 本研究的目的是探讨空位硬化模型，解释FeAl的屈服强度异常是适用于其他B2化合物，表现出类似的温度依赖性的屈服强度。 该模型是通用的，可以适用于各种各样的晶体结构，这表明产量异常。 研究内容包括CoTi、CoHf和CoZr单晶的生长、力学测试和滑移线分析以及透射电子显微镜（TEM）。 使用Simmons/Balluffi方法对不同退火温度下的空位浓度进行测量，由此将通过X射线测量法测量的密度与通过X射线测量的密度进行比较。 确定了空位形成和空位迁移的活化能谱，并与从空位硬化模型获得的值进行了比较。 为了确定与屈服强度异常相关的位错/空位相互作用，TEM原位应变实验作为温度的函数和包含不同淬火空位浓度的晶体上进行。 机械测试包括在不同取向的单晶中作为温度的函数的屈服应力的拉伸/压缩不对称性的确定。 压缩试验是在很宽的应变率范围内进行的，其中非常高的应变率试验是在洛斯阿拉莫斯国家实验室进行的。 在橡树岭国家实验室使用Gleeble试验机进行专门的机械试验，该试验机可快速加热和淬火。 该装置使得能够在存在不同空位浓度的屈服强度峰值温度下进行屈服强度测量。 在Gleeble中测试后快速冷却的滑移面截面试样的TEM检查允许检查真正代表高温测试的位错结构。 %金属间化合物合金具有独特的机械性能，使其能够用于高温结构应用。 这项研究将促进对这类重要金属合金的机械行为的理解。