CRYSTAL-STRUCTURE AND SCRATCH TESTING OF KAPPA-AL2O3 ON WC-CO SUBSTRATES WITH A TIC INTERLAYER

The crystal structure of kappa-Al2O3, determined by electron and X-ray diffractions, was an orthorhombic structure with lattice constants of a=0.477 nm, b=0.83 nm and c=0.894 nm. The Vickers hardness of kappa-A l2O3 was about 1800. The adhesion strength between coatings and substr ate was estimated from the critical load of the scratch test with a py ramidal indenter as being about 80 kgf mm(-2) for the kappa-Al2O3/(WC- Co alloy) system with a chemically vapour-deposited TiC interlayer and 1 kgf mm(-2) for that system without a TiC interlayer.