Crystallographic Textures Induced by Dry Sliding Wear in Metals

该奖项由2009年美国复苏和再投资法案(公法111-5)资助。技术摘要：本项目研究金属元素和合金的干滑动磨损所产生的晶体织构。这些晶体织构在严重塑性变形(SPD)纳米颗粒层中发展，这些纳米颗粒层是由滑动表面下方的磨损产生的，并延伸到一微米量级的深度。与轧制、拉拔或挤压等金属成形工艺所产生的织构相比，关于磨损引起的织构的数据只是部分和零散的。这是尽管人们知道质地会影响摩擦和磨损的事实。本研究的主要目的是首先系统地研究载荷、滑动速度和温度等磨损参数以及孪晶倾向和初始晶粒度等材料参数对织构的影响。用扫描电子显微镜(SEM)和透射电子显微镜(TEM)中的电子背散射衍射仪对织构进行了表征。其次，由于标准方法不能直接测量由于颗粒破碎而导致的SPD层中的塑性应变，因此实施了一种特定的方法，其中使用预先存在的纳米级沉淀物作为标记。通过对析出物形态演变的透射电子显微镜表征，可以直接测量塑性应变。第三，通过压痕和划痕测试相结合的方法，利用纳米摩擦学在微米和纳米尺度上确定了织构纳米颗粒层的力学性能。所有这些结果的综合将有助于设计一种策略，通过利用滑动磨损诱导的晶体织构来选择具有更好的摩擦和磨损响应的材料。拟议研究的影响是通过开发和整合两个模块，一个关于磨损和另一个关于质地，并通过为本科生提供研究经验来扩大现有的高级实验室课程。这项研究还得益于与法国Chvalier教授在严重塑料变形引起的纹理方面的国际合作。非技术摘要：过早磨损是许多机械系统故障的主要原因，仅在美国就造成了约1000亿美元的损失。开发低摩擦系数和高耐磨性的材料可以减少这些损失，同时提高能源消耗。为此，本研究旨在发展对晶体织构的认识和理解，即通过金属材料中的干滑动磨损稳定的多晶材料中颗粒的晶体取向分布。虽然织构控制在工业中被广泛用于优化材料的加工和使用性能，但由于缺乏知识，到目前为止还没有应用类似的方法来指导耐磨材料的设计和选择。拟议的研究试图通过利用定向成像显微镜和透射电子显微镜等表征技术以及纳米级机械测试方面的重要进展来弥合这一知识鸿沟。这项研究将为一名研究生和三名本科生提供重要的穿戴技术领域的教育。将特别努力招收女性和代表性不足的少数民族学生。还将与谢瓦利埃教授(法国)开展国际合作。

This Award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5).TECHNICAL SUMMARY:The crystallographic textures generated by dry sliding wear in metallic elements and alloys are investigated in this project. These crystallographic textures develop in the severely plastically deformed (SPD) nanograin layers that are produced by wear just below the sliding surfaces, and extend over a depth of the order of one micrometer. In contrast to textures produced by metal-forming processes such as rolling, drawing, or extrusion, there is only partial and scattered data on wear-induced textures. This is despite the fact that texture is known to affect friction and wear. The main objectives of this research are firstly to investigate systematically the effects of wear parameters, such as load, sliding velocity, and temperature, and material parameters, such as twinning tendency and initial grain size, on texturing. Textures are evaluated by electron backscattering diffraction in scanning electron microscopy (SEM) and by transmission electron microscopy (TEM). Secondly, since standard methods do not provide a direct measurement of plastic strain in the SPD layer owing to grain fragmentation, a specific method is implemented where pre-existing nanoscale precipitates are used as markers. TEM characterization of the precipitate shape evolution provides direct measurement of plastic strain. Thirdly, the mechanical properties of the textured nanograined layers are determined by combining indentation and scratch tests, both at the micro and nanoscale using nanotribometry. Integration of all these results will contribute to designing a strategy to select materials with improved friction and wear response by taking advantage of the crystallographic texturing induced by sliding wear. The impact of the proposed research is broadened by developing and integrating 2 modules, one on wear and the other one on texture, into an existing senior laboratory course and by providing research experience for undergraduate students. The research also benefits from an international collaboration with Prof. Chevalier (France) on texture induced by severe plastic deformation.NON-TECHNICAL SUMMARY:Premature wear is the primary cause of failure of many mechanical systems, leading to losses estimated to well over 100 billion dollars in the U.S. alone. The development of materials with lower friction coefficient and improved wear resistance could reduce these losses as well as improve energy consumption. To that end, the present research aims at developing the knowledge and understanding of the crystallographic textures, i.e. the distribution of crystallographic orientations of grains in a polycrystalline material, that are stabilized by dry sliding wear in metallic materials. While texture control is widely used in industry to optimize the processing and the properties of use of materials, lack of knowledge has prevented until now the application of a similar approach to guide the design and the selection of wear resistant materials. The proposed research attempts to bridge this knowledge gap by taking advantage of important advances in characterization techniques such as orientation imaging microscopy and transmission electron microscopy, as well as in nanoscale mechanical testing. The research will provide education for one graduate and three undergraduate students in the important technological field of wear. Special effort will be made to recruit female and underrepresented minority students. An international collaboration with Prof. Chevalier (France) will also be established.