Designing superhard,self-toughening CrAlN coatings through grain boundary engineering |
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Authors: | Zhao Li Paul Munroe Zhong-tao Jiang Xiaoli Zhao Jiang Xu Zhi-feng Zhou Jian-qing Jiang Feng Fang Zong-han Xie |
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Affiliation: | 1. School of Materials Science and Engineering, Southeast University, Nanjing, Jiangsu Province 211189, PR China;2. Electron Microscope Unit, University of New South Wales, Sydney, NSW 2052, Australia;3. School of Engineering and Energy, Murdoch University, Perth, WA 6150, Australia;4. School of Engineering, Edith Cowan University, Joondalup, WA 6027, Australia;5. Department of Material Science and Engineering, Nanjing University of Aeronautics and Astronautics, Nanjing 210016, PR China;6. Department of Mechanical and Biomedical Engineering, City University of Hong Kong, Kowloon, Hong Kong, China;7. School of Mechanical Engineering, University of Adelaide, Adelaide, SA 5005, Australia |
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Abstract: | One of the toughest challenges that hinders the application of ceramic coatings is their poor damage tolerance. Addressing this problem requires the development of novel micro- or nanostructures that would impart to these coatings both high hardness and high toughness. In this paper, CrAlN coatings, with varying Al contents up to 30 at.%, were engineered onto steel substrates using the magnetron sputtering technique. Whilst the addition of Al does not significantly alter the columnar microstructure, it does change the preferred grain orientation and increase the compressive residual stress. Moreover, the hardness, elastic strain to failure (H/E) and plastic deformation resistance (H3/E2) of the resultant CrAlN coating with the highest Al content were found to increase ~47, ~29 and ~140%, respectively, as compared to CrN. Evidence collected from transmission electron microscopy and X-ray photoelectron spectroscopy experiments shows that AlN, existing in an amorphous state at the columnar CrN grain boundaries, has a crucial role in providing the unusual combination of high hardness and exceptional damage resistance. The results provide a new pathway to developing durable ceramic coatings suitable for applications involving severe loading conditions. |
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