SOLID PARTICLE EROSION OF HOT FLAME-DEPOSITED DIAMOND COATINGS ON CEMENTED CARBIDE

Diamond coatings were deposited on cemented carbide substrates using the flame technique developed by Hirose and Kondoh (Y. Hirose and N. Kondo, Proc. Japan Appl. Phys. Spring Meet., 1988, p. 434). The coatings were subjected to erosion testing with alumina particles at velocities of 46 and 72 m s-1. Cemented carbide, TiN/TiC- and Al2O3/TiC-coated cemented carbide were used as reference. The most important parameter controlling the erosion resistance is the diamond coating thickness. With a sufficient coating thickness (6 mum) the diamond-coated samples outperformed the reference materials whereas a too thin coating (1.5 mum) yielded a lower erosion resistance. The erosion process is initiated by the formation of a hole in the coating. Thereafter the erosion proceeds by a spalling mechanism. It is proposed that the initial holes are formed during deposition or by fragmentation due to point defects in the coating and that the driving force for the spalling is the relaxation of residual stresses in the coating by crack propagation in the coating and in the coating/substrate interface.