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。 目的是了解纳米晶金属和合金的磨损机制，并准确地将磨损率建模为晶粒尺寸的函数。 为此，将通过机械研磨粉末的等通道转角挤压来制备块体纳米晶Al和Al-Si。 我们还将生产由纳米晶和常规晶粒材料的混合物组成的双峰晶粒结构，我们预计这种结构将具有高硬度和良好的延展性。 将使用透射电子显微镜和X射线衍射表征微观结构。 这种块体纳米晶体材料不应遭受解释涂层和改性表面层的磨损数据的困难，其中晶粒尺寸和应变通常在整个层中变化。 机械性能将被测量为在不同加载速率下的拉伸下的晶粒尺寸的函数。 将在室温下在空气、干燥氧气和惰性气体中对不同粒度的颗粒进行磨损试验。 变形机制将使用透射电子显微镜，扫描电子显微镜，轮廓术和纳米压痕检查，结果将与磨损试验结果和机械性能。 我们还旨在构建纳米晶材料的磨损机制地图，地图包括氧化是非常重要的条件，以及变形机制控制磨损行为的条件。虽然这项工作的重点是特定的材料，但总体目标是了解纳米晶范围内晶粒尺寸对纳米晶金属和合金整体磨损率和磨损机制的影响。

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.