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Contributing Editor: Jürgen Eckert
I.
INTRODUCTION
With the development of high-speed cutting, dry and semidry cutting technology, the cutting tools with better performances are required, and the cemented carbide and high-speed steel cutting tool substrate coated with a layer of coating makes the coated cutting tools have higher hardness, wear resistance, and oxidation resistance than the original tools, and the coating would improve service life of the cutting tool effectively. TiN, as the first generation of tool nitride coating, is golden yellow with a hardness of 2300 HV, whose coefficient of friction (COF) reaches 0.45-0.52 under the highest working temperature of 500 °C, and can be used for general metal cutting.1TiAlN coating based on doping TiN coating by aluminum is the second generation of tool nitride coating with a hardness of 3400-3500 HV, whose COF against a quenched steel ball is about 0.5, and the highest working temperature is 800 °C. Because the atomic radius of Al is smaller than that of Ti, Al atoms exist in TiAlN in the form of replacing Ti atoms in TiN; the lattice distortion not only improves the hardness of TiAlN coating but also intensifies adhesive wear of the cutting tool, reducing the workpiece surface accuracy, which is not suitable for precision machining.2,3To further improve the wear properties of TiAlN coating at high temperatures, Cr element is added into TiAlN coating to form AlTiCrN coating, which belongs to the third generation tool nitride coating. The addition of Cr atoms change a part of the original hexagonal close-packed (Al, Ti)N phase into a harder cubic (Al, Cr)N phase, improving the wear and oxidation resistance of the coating with hardness of 3400-3600 HV, whose COF at room temperature against a ceramic ball is only 0.4. Due to the formation of stable dense [alpha]-(Al, Cr)2O3 when the coating works at the high temperatures, the working temperature of AlTiCrN coating can be improved.4,5At the same time, AlTiCrN coating can produce a lubricative oxide film at high temperatures, which is called a self-lubricating coating.6The microstructures, mechanical properties, friction and wear resistance, corrosion resistance, and machining applications of AlTiCrN coating were investigated by many researchers,7-10but...