Crystallographic Textures Induced by Dry Sliding Wear in Metals

该奖项是根据2009年美国复苏和再投资法案（公法111-5）资助的。技术概述：本项目研究了金属元素和合金干滑动磨损产生的晶体织构。这些晶体结构在严重塑性变形（SPD）纳米颗粒层中发展，这些层是由滑动表面下方的磨损产生的，并延伸到一微米的深度。与诸如轧制、拉伸或挤压等金属成形工艺产生的织构相反，关于磨损引起的织构只有部分和分散的数据。这是无视事实，质地是已知的影响摩擦和磨损。本研究的主要目的是首先系统地研究磨损参数（如载荷、滑动速度和温度）和材料参数（如孪生趋势和初始晶粒尺寸）对织构的影响。利用扫描电子显微镜（SEM）和透射电子显微镜（TEM）对织构进行了评价。其次，由于颗粒破碎，标准方法不能直接测量SPD层中的塑性应变，因此采用了一种特定的方法，其中使用预先存在的纳米级沉淀物作为标记。TEM表征析出相的形状演变提供了塑性应变的直接测量。第三，利用纳米摩擦学技术，结合压痕和划痕试验，确定了织构纳米颗粒层的力学性能。综合所有这些结果将有助于设计一种策略，通过利用滑动磨损引起的晶体织构来选择具有改善摩擦和磨损响应的材料。通过开发和整合两个模块（一个关于磨损，另一个关于纹理）到现有的高级实验课程中，并为本科生提供研究经验，扩大了拟议研究的影响。该研究还得益于与Chevalier教授（法国）在严重塑性变形诱导的纹理方面的国际合作。非技术总结：过早磨损是许多机械系统失效的主要原因，仅在美国就造成了超过1000亿美元的损失。开发具有更低摩擦系数和更高耐磨性的材料可以减少这些损失，并改善能耗。为此，本研究的目的是发展对晶体织构的认识和理解，即多晶材料中晶粒的晶体取向分布，这些织构是由金属材料中的干滑动磨损稳定的。虽然织构控制在工业上被广泛用于优化材料的加工和使用性能，但迄今为止，缺乏知识阻碍了类似方法的应用，以指导耐磨材料的设计和选择。该研究试图通过利用表征技术的重要进展，如取向成像显微镜和透射电子显微镜，以及纳米级机械测试，来弥合这一知识差距。本研究将为一名研究生和三名本科生提供服装重要技术领域的教育。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Chevalier教授（法国）建立国际合作。

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.