Effects of Cr interlayer on mechanical and tribological properties of Cr-Al-Si-N nanocomposite coating

Cr-A1-Si-N coatings were deposited on SUS 304 substrate by a hybrid coating system. A Cr interlayer was introduced between Cr-A1-Si-N coating and SUS 304 substrate to improve the coating adherence. The effects of Cr interlayer on the microhardness, adhesion, and tribological behavior of Cr-A1-Si-N coatings were systematically investigated. The results indicate that the microhardness of the Cr-A1-Si-N coatings gradually deceases with increasing thickness of Cr interlayers. The adhesion between Cr-A1-Si-N and SUS 304 substrate is improved by addition of the Cr interlayers. A peak critical load of-50 N is observed for the coating containing Cr interlayer of 60 nm as compared - 20 N for the coating without Cr interlayer. The thicker Cr interlayers result in reduced critical load values. Moreover, the wear resistance of the Cr-AI-Si-N coatings is greatly enhanced by introducing the Cr interlayer with thickness of 60 nm in spite of the decreased microhardness. The friction coefficient of the coating system is also moderately reduced.

Effect of hexagonal-BN on phase transformation of additive-free Si_3N_4 /SiC nanocomposites prepared from amorphous precursor

Si3N4/SiC nanocomposites are well known and attractive for advanced ceramic applications due to excellent mechanlcal and thermal properties, which make them suitable for use in turbine engines, heat exchangers, and other sophisticated applications. However, without the presence of additives, the fabrication of Si3N4/SiC composites is difficult. The additives form a liquid phase during sintering and facilitate the densification of the composite. However, the additives present a drawback at high temperatures since they decrease the mechanical properties of the composites. Recently, Si3N4/SiC composites were fabricated via the polymer precursor route without any additives, using electric field assisted sintering （EFAS）. In this study, fully densified Si3N4/SiC nanocomposites incorporating hexagonal-BN were successfully fabricated by hot pressing without any additives at 1700 ℃ for 2 h under vacuum at a pressure of 50 MPa （via the amorphous precursor route）. Moreover, the incorporation of additives and h-BN is found to decrease the content of SiC. The phase transformation, densification, microstructure, and mechanical properties were discussed and presented.

Influence of Nitrogen Flow Ratio on the Microstructure, Composition, and Mechanical Properties of DC Magnetron Sputtered Zr-B-O-N Films

Nanocrystalline ZrB2 film and nanocomposite Zr-B-O-N films were prepared by non-reactive as well as re- active magnetron sputtering techniques, respectively. By means of X-ray diffraction analysis, electron probe microanalysis, X-ray photoelectron spectroscopy, and scanning electron microscopy, the influence of nitrogen flow ratio on the film microstructure and characteristics were investigated systematically, including the depo- sition rate, chemical compositions, phase constituents, grain size, chemical bonding, as well as cross-sectional morphologies. Meanwhile, the hardness and adhesion of above films were also evaluated by micro-indentation method and a scratch tester. With increasing the nitrogen flow ratio, the deposition rate of above films de- creased approximately linearly, whereas the contents of N and O in the films increased gradually and tended to saturation. Moreover, the film microstructure was also altered gradually from a fine columnar microstructure to a featureless glass-structure. As the nitrogen flow ratio was 11.7%, the Zr-B-O-N film possessed an typical nanocomposite structure and presented good mechanical properties. During the process of reactive sputtering of metal borides, the introduction of nitrogen can show a pronounced suppression of columnar grain growth and strong nanocomposite structure forming ability.