This Award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5).
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.
