Adherent Ti(C,N) Coatings on Cemented Carbide Substrates with Fe/Ni/Co Binder
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INTRODUCTION
CEMENTED carbides consist of a large amount of carbide grains embedded in ductile binder. Because of their high hardness, refractoriness, and wear resistance, cemented carbides are the most important materials for cutting and mining tools. The combination of wearresistant hard coatings and cemented carbides substrates has brought about a quiet revolution in the metalcutting industry since 1971. It is estimated that 80 pct or more of the machining operations today are carried out using coated tools.[1] Therefore, both the surface coating technology and the innovation of the cemented carbide substrate attract worldwide interest. There are two well-established vapor processing routes for coating, namely chemical vapor deposition (CVD) and physical vapor deposition (PVD) (e.g. evaporation, sputtering, and ion plating). The PVD process is less widespread as CVD because of the relatively poor adhesion and high internal stress. However, conventional high-temperature CVD (HTCVD) process is usually carried out at temperatures above 1000 °C, which results in the formation of the g phase at the bonding and a decrease of transverse rupture strength (TRS).[2] In recent years, moderate-temperature CVD (MTCVD) is introduced to solve the problem of TRS decrease. The deposition temperature can be decreased to 700–800 °C because of the adoption of metal-organic compound such as acetonitrile instead of methane or nitrogen in the CVD process.[3] At present, the most common coatings on the market are TiC, TiN, Ti(C,N), TiAlN, and Al2O3. Ti(C,N) is a favorable coating that offers better hardness and abrasive wear resistance than conventional TiN coatings and excellent chemical stability superior to TiC.[4] ZHIXING GUO, JI XIONG, and SIQIN BI, Doctors, are with the School of Manufacturing Science and Engineering, Sichuan University, Chengdu 610065, P.R. China. Contact e-mail: submission000@ hotmail.com. MEI YANG, Doctor, is with the College of Materials and Chemistry & Chemical Engineering, Chengdu University of Technology, Chengdu 610059, P.R. China. Manuscript submitted November 14, 2008. Article published online August 26, 2009. METALLURGICAL AND MATERIALS TRANSACTIONS B
As for cemented carbide substrate, cobalt currently dominates the market as the binder of cemented carbide because of its unique properties.[5] However, the use of cobalt as a binder has several drawbacks related to its hexagonal close-packed structure.[6] Furthermore, because of the market price fluctuations and environmental toxicity of cobalt, it has for many years been a concern of the cemented carbide industry to seek elements other than cobalt as the binder metal. Since iron and nickel belong to the same group with cobalt in the periodical table, they are considered to act as alternative binders for cobalt. Prakash[7] reported that cemented carbides with Fe-rich binders had enhanced properties such as higher hardness, abrasive wear resistance, toughness, and strength compared with Co-bonded hard metals. Perter and Brabyn[8] did research on nickel
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