Creep and Superplasticity in Materials with Ultrafine Grain Sizes

该基金研究了使用等通道角压（ECAP）通过严重塑性变形（SPD）处理铝和镁合金的加工和表征。第二相粒子的适当分散有望固定晶界，从而保持亚微米范围内的超细晶粒尺寸。相对较大的晶粒尺寸范围，从微米到纳米，将提供一个机会，明确地确定蠕变和超塑性性能，当晶粒尺寸非常小，并获得基本信息，将需要在长期内成功利用这些材料。该研究的目标是利用原子力显微镜等先进技术系统地研究ECAP后的空化和晶界滑动以及加工材料的变形。随着超塑性，扩散蠕变的潜在机制将被研究。从科学的角度来看，已有成熟的理论预测了金属在小晶粒尺寸时的塑性流动（或蠕变），但这些理论仍然存在相当大的猜测空间，并且对其一般有效性存在许多讨论和分歧。该研究有望填补空白，并提供在不同晶粒尺寸和应用应力和应变率范围内的变形机制的科学理解。此外，调查将有成形操作的技术应用。这项资助适用于研究生和研究生以及本科生高年级项目的参与。本项目由材料研究部金属项目和制造与工业创新部共同资助。

The grant investigates processing and characterization of aluminum and magnesium alloys via severe plastic deformation (SPD) using equal channel angular pressing (ECAP). Appropriate dispersion of second phase particles are expected to pin the grain boundaries thereby retaining ultra fine grain size in submicron range. The relatively large range of grain sizes, from micron to nanometers, will provide an opportunity to unambiguously determine the creep and superplastic properties when the grain sizes are extremely small and to obtain fundamental information that will be needed in the longer term for the successful utilization of these materials. A goal of the study is to utilize advanced techniques such as atomic force microscopy to systematically investigate cavitation and grain boundary sliding following ECAP as well as deformation of the processed materials. Along with superplasticity, the underlying mechanisms of diffusional creep will be investigated.From a scientific viewpoint, there are well-developed theories predicting the plastic flow (or creep) of metals when the grain sizes are small but these theories remain open to considerable speculation and there has been much discussion and disagreement concerning their general validity. The study is expected to fill in the gaps and provide scientific understanding of deformation mechanisms at varied grain sizes and in a range of applied stresses and strain-rates. In addition, the investigations will have technological applications for forming operations. The grant avails participation of graduate and post-graduate students along with undergraduate senior projects. The project is co-funded by metals program in the division of materials research and manufacturing in the division of manufacturing and industrial innovation.