Carbon nanofiber toughened nc-TiC/a-C nanocomposite coatings.
Date of Issue2010
School of Mechanical and Aerospace Engineering
Producing nanocomposite films with both high hardness and toughness is a tough job but of great scientific and technical interest. Carbon nanofibers (CNFs) toughening for hard coatings is promising. This project is to try to realize in-situ CNF toughened nanocrystalline titanium carbide (nc-TiC) and amorphous carbon (a-C) nanocomposite coatings with high hardness and at the same time high toughness. In-situ growth of CNFs in amorphous carbon (a-C) and nc-TiC involves sputtering and rapid thermal processing. Influence of CNF growth on microstructure, mechanical properties and tribological properties are studied in detail. The results show amorphous CNFs can be formed in a-C and nc-TiC to form CNF:a-C, and nc-TiC/CNF:a-C coatings by this sputter plus rapid thermal processing. CNF:a-C means CNF embedded in a-C; nc-TiC/CNF:a-C stands for into CNF and residual a-C matrix surrounding nc-TiC. A longer annealing time, a higher temperature and an Al2O3 barrier layer can promote CNF growth. CNF formation in a-C brought in toughness increase as a result of crack bridging. In-situ synthesis of nc-TiC/CNF:a-C nanocomposite coatings uniformly distributes CNFs and nano sized TiC crystallites. With inclusion of CNFs, the toughness of nc-TiC coating was increased by 87 % at an expense of 24 % hardness. CNF inclusion also reduces 50 % of the friction coefficient and 65 % of the wear rate. Mechanism studies confirm that the toughness is improved by crack bridging, crack deflection and fiber pullout.