Study On Performance Of Ultra-fine Co-based Series Cemented Carbide Coating

The ultrafine WC-Co cemented carbide, which features high hardness, high toughness and corrosion resistance, has been widely used in machining. The modern machining puts forward higher requirements on the performance of the cemented carbide cutting tool(properties including high cutting speed, high feed speed, reliability, long service time, high accuracy and good cutting controllability). By the coating method, on the premise of maintaining its original good mechanical properties, the cemented carbide can be further improved in hardness, toughness, and high temperature oxidation resistance, so as to adapt to the efficient processing environment for materials which are currently difficult to beprocessed. In this paper, high-energy ball milling was adopted to prepare the carbide substrates YG8 and YG6, the Ti AIN coating and the Ti CN-Al2O3-Ti N multi-layer composite coating of carbide cutting tools were respectively prepared through physical and chemical vapor depositions. X-ray diffraction, scanning electron microscopy, automatic scratch tester and micro-hardness tester were employed for structural analysis and performance testing of the coating.Results showed that, with the increase in Co level, the hardness of the YG series carbide was decreased but the flexural strength increased. With the increase in Al level, the Ti N level in the Ti Al N coating was gradually reduced. Moreover, as the coating was mainly the Ti3 Al N phase of the hexagonal wurtzite structure, with a(200) predominant orientation, the micro-hardness of the coating surface was increased to some extent. In the turning of 0Cr18Ni9 stainless steel with Ti Al N coated carbide cutting tools, the Ti Al N coating showed the best performance at line speed of 240 m/min, feed rate if 0.06 mm-rev, and cutting depth of 0.1 mm. Wear forms of the Ti Al N coated turning tools were mainly the micro chipping and flaking of the coating. The prepared Ti CN-Al2O3-Ti N multi-layer composite coating consisted of three layers, with Ti CN, Al2O3, and Ti N successively from the inner to the outer. The Al2O3 coating was mainly made of ?-Al2O3 crystal, which is conducive to grain refinement. The flaking of multi-layper composite coating occurred not only between the coating and substrate, but also between the coatings, as the ?-Al2O3 coating would lower the bonding strength between the coating and the substrate. In the milling of 0Cr18Ni9 stainless steel with multi-layer composite Ti CN-Al2O3-Ti N coated carbide cutting tools, when the substrate was WC-8Co-8(W, Ti, Ta) C coating, the carbide milling tool showed the best performance and a great overall brittleness, with mechanical and oxidation wears as the major wear forms.