Growth and Properties of TiN/Al 2 O 3 /Ti(C, N)/TiN Multilayer CVD Coatings on Ti (C, N)-Based Cermet Substrates with Ni
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RODUCTION
NOWADAYS, chemical vapor deposition (CVD) multilayered tool coatings are being widely employed on cemented carbide tools to prolong the life of substrate materials because of the reduction of the friction coefficient and improved hardness and oxidation resistance compared with the substrate materials.[1,2] TiN-Ti (C, N)-Al2O3-TiN multilayers are often used.[3–6] The inner TiN layer is closest to the substrate system. The layer plays the role of improving the adhesion between the substrate and coatings. The Ti (C, N) layer provides hardness and abrasion wear resistance. The Al2O3 layer provides excellent thermal stability, wear resistance and oxidation resistance. The outer TiN layer is used for judging the tool’s wear status according to the obvious
JUNBO LIU, JI XIONG, ZHIXING GUO, CHENGTAO QIN, YA XIAO, and QIANBING YOU are with the School of Manufacturing Science and Engineering, Sichuan University, Chengdu, 610065, P.R. China. Contact e-mail: [email protected] Manuscript submitted July 20, 2019.
METALLURGICAL AND MATERIALS TRANSACTIONS A
golden color. Although the coatings have many advantages, modern trends in the metal cutting field require much higher speed, and in this case the cemented carbide substrates cannot support the coatings. Ti (C, N)-based cermet cutting tools have excellent oxidation resistance, and the high temperature hardness and wear resistance provide a new dimension for high-speed cutting processes.[7–9] Advancements in Ti (C, N)-based cermet cutting tools have provided an alternative substitute for cemented carbides as a substrate for the coatings. Ti (C, N)-based cermets consist of two phases. One is the binder phase; the other is the black core/gray rim phase. The binder phase is formed by metals responsible for the toughness. Undissolved Ti (C, N) cores and secondary carbide rims are formed via a dissolution-precipitation process in the binder phase, which provides superior wear resistance. The binder phase is critical for the synergic effect between the solubility and wettability during the metallurgical process, which determines the phase composition of cermets.[10–13] Thus, to obtain high performance of the substrates/coatings, it is essential to investigate the effect of the binder phase on the coatings.
In the present work, Ti (C, N)-based cermets with the three most typical binder phases, Ni/Co/Fe, were manufactured by traditional powder metallurgical techniques. Afterwards, TiN-Ti (C, N)-Al2O3-TiN multilayer CVD coatings were deposited on the cermets, and the growth properties of the coatings were studied.
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EXPERIMENTAL PROCEDURES
A. Preparation of the Ti (C, N)-Based Cermet Substrate The samples were produced by powder metallurgy routes. The cermets were designed to have a chemical composition of 75 wt pct Ti (C, N), 10 wt pct Mo2C and 15 wt pct Ni/Co/Fe binder phase. The mixed powders were ball-milled in steel jars using WC-8 wt pct Co balls with 10 mm diameter for 72 hours. Gasoline was used as the milling medium. Milling speed was set at 68 rpm. The weight ra
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