Effect of Silicon Content on the Microstructure and Mechanical Properties of Ti-Si-B-C Nanocomposite Hard Coatings
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HARD coating is one of the most versatile means to protect material from degradation and improve component performances, by reducing friction and improving wear resistance. The applications of hard coatings on several automobile parts, such as crankshafts, pistons, bearings, gears, and valves, have the major advantages of increased fuel efficiency and reduction of carbon dioxide emission due to such coatings. These coatings are also applied on movable parts such as turbine blades in aero engines and thermal power plants, cutting tools, die-casting, and punching tools. However, the emergence of newer challenges with the advent of new technologies and environmental regulations demands further improvement and optimization of these hard coatings. The performance of these hard coatings can be enhanced by changing the deposition process, parameters, and composition. Some of the widely studied hard coatings are TiN, SiC, WN, TiC, Si3N4, (TiAl)N, (Ti, Cr)N, CrN, WC, ZrB2, diamond, and diamondlike carbon.[1–7] The hardness in these compounds is higher due to higher bond energies between the different atoms,
DIVYA VERMA, D. BANERJEE, and S.K. MISHRA are with the CSIR-National Metallurgical Laboratory, Jamshedpur 831007, India. Contact emails: [email protected], [email protected] Manuscript submitted February 3, 2018. Article published online December 5, 2018 894—VOLUME 50A, FEBRUARY 2019
shorter bond length, and the close-packing structure. The covalent bond formed in these compounds leads to higher hardness. The hard coatings are either single phase or have multiple phases. Even though the single-phase hard coatings have excellent properties important for applications in industries, they still have limitations due to high brittleness, low fracture toughness, and poor stability at elevated temperatures. The more close-packed structure of the coatings leads to lesser toughness in them. Some of these limitations can be overcome using multicomponent nanocomposite hard coatings that possess high fracture toughness and stability at high temperatures. Normally, these multicomponent hard coatings are in ternary or quaternary systems such as Ti-Si-N, Ti-Al-N, Si-C-N, Ti-B-C, and Ti-C-N. In the nanocomposites where one side has higher hardness due to the decrease of the crystallite size, the Hall–Petch relation becomes active; on the other side, crack deflection can take place due to secondary phases and crack pinning at the amorphous-crystalline interface, leading to higher toughness. The addition of alloying elements in the Ti-N coatings has been studied extensively. In the case of Ti-Si-N coatings, with the addition of Si to the TiN system, two phases, namely, nanocrystalline TiN phase uniformly dispersed in the amorphous matrix of Si3N4, are observed, which enhances the hardness and wear resistance of the coating. Similarly, C was added to the TiN system to enhance its abrasion and wear resistance. Significant improvement in the oxidation resistance of METALLURGICAL AND MATERIALS TRANSACTIONS A
the coating has been reported
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