Abstract
Abstract A bipolar pulsed d.c. PACVD technique was used to deposit crystalline Al2O3 coatings onto WC/Co cemented carbide cutting inserts and onto steel substrates using a gas mixture of AlCl3, H2, O2 and Ar. Different deposition conditions were tested, substrate temperatures (Ts) between 500 and 700°C and a gas mixture ratio O/AlCl3 in the range from 2 to 20. At Ts≥600°C transparent crystalline coatings of the γ-Al2O3 phase were obtained having the best crystallinity for O/Al ratio of 4 and 6. At a substrate temperature of 700°C and an O/AlCl3 ratio of 2, α-Al2O3 or a mixture of α- and γ-Al2O3 phases was formed. The microhardness HV[0.02] of the crystalline coatings was found to be in the range 19–23 GPa. The γ-Al2O3 layers appeared in most cases transparent with smooth surfaces. The wear properties of Al2O3-coated cutting inserts produced by the PACVD method were evaluated and compared with a thermal CVD κ-Al2O3 coating in a machining test in a ball bearing steel. From the test results it could be concluded that the PACVD Al2O3 coatings showed wear properties very similar to the thermal CVD κ-Al2O3 coatings.
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