Creep and Superplasticity in Materials with Ultrafine Grain Sizes

该基金研究采用等通道转角挤压(ECAP)进行严重塑性变形(SPD)的铝和镁合金的加工和表征。第二相粒子的适当分散有望钉扎晶界，从而将超细晶粒尺寸保持在亚微米范围内。相对较大的颗粒尺寸范围，从微米到纳米，将提供一个机会，以明确确定蠕变和超塑性性能时，颗粒尺寸非常小，并获得基本信息，将需要在较长的时间内，这些材料的成功利用。这项研究的目标是利用先进的技术，如原子力显微镜，系统地研究ECAP后的空化和晶界滑动以及加工材料的变形。除了超塑性，还将研究扩散蠕变的基本机制。从科学的观点来看，已有成熟的理论预测金属在晶粒度较小时的塑性流动(或蠕变)，但这些理论仍有相当大的猜测余地，对于其普遍有效性存在许多讨论和分歧。这项研究有望填补这一空白，并提供对不同晶粒度、不同施加应力和应变率范围内的变形机制的科学理解。此外，这些调查还将在成形操作中得到技术应用。该助学金有利于研究生和研究生以及本科生高级项目的参与。该项目由金属计划在制造和工业创新部门的材料研究和制造部门共同资助。

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.