A Microstructural Study of Wear Mechanisms in Nanocrystalline Metals

该项目的重点是纳米晶金属和合金的磨损。其目的是了解纳米晶金属和合金中的磨损机理和磨损率作为晶粒度的函数的精确模型。为此，将通过机械球磨粉末的等通道转角挤压来制备块体纳米晶Al和Al-Si。我们还将生产双峰颗粒结构，由纳米晶和常规颗粒材料的混合物组成，我们预计这种材料将具有高硬度和非常好的延展性。利用透射电子显微镜和X射线衍射仪对样品的微观结构进行了表征。这种块状纳米晶材料不应该受到解释涂层和改性表面层的磨损数据的困难，这些涂层和表面改性层的晶粒度和应变经常在各层中变化。力学性能将作为不同加载速率下拉伸下的颗粒尺寸的函数来测量。在室温空气、干氧和惰性气体中，对不同粒度的磨粒进行磨损试验。用透射电子显微镜、扫描电子显微镜、轮廓术和纳米压痕等手段研究了变形机制，并将结果与磨损试验结果和力学性能进行了关联。我们还旨在构建纳米晶材料的磨损机理图，这些图包括氧化起主要作用的条件以及变形机制控制磨损行为的条件。虽然这项工作侧重于特定的材料，但总体目标是了解纳米晶范围内的晶粒度对纳米晶金属和合金整体磨损率和磨损机理的影响。

This project is focused on the wear of nanocrystalline metals and alloys. The goal is to understand the wear mechanisms and model accurately wear rate as a function of grain size in nanocrystalline metals and alloys. To this end, bulk nanocrystalline Al and Al-Si will be produced by equal channel angular extrusion of mechanically milled powders. We will also produce bimodal grain structures consisting of mixtures of nanocrystalline and conventionally-grained material, which we expect will have high hardness yet very good ductility. The microstructures will be characterized using transmission electron microscopy and X-ray diffraction. Such bulk nanocrystalline materials should not suffer from the difficulties of interpreting wear data that occur for coatings and modified surface layers where the grain size and strain often vary throughout the layers. Mechanical properties will be measured as a function of grain size under tension at different loading rates. Wear tests will be performed for different grain sizes in air, dry oxygen and inert gas at room temperature. The deformation mechanisms will be examined using transmission electron microscopy, scanning electron microscopy, profilometry and nanoindentation, and the results will be correlated with the wear test results and mechanical properties. We also aim to construct wear mechanism maps for nanocrystalline materials, with the maps including the conditions when oxidation is of major importance as well as the conditions when deformation mechanisms control the wear behavior. While the work focuses on specific materials, the overall goal is to understand the effects of grain size in the nanocrystalline range on the wear rate and wear mechanisms of nanocrystalline metals and alloys as a whole.