Formation and Bonding Mechanism of Solution Derived -Al₂O₃ Coating on Carbide Substrate

Abstract

Ceramic coated cemented carbide cutting tools were prepared from an aluminium alkoxide solution and carbide substrates by a sol–gel route. Having been preprocessed, carbide substrates were coated with boehmite sol by a dip coating process and dried to produce the gel film. After heat treatment at 1200°C, a coating with a thickness of more than 6 µm could be obtained without any macroscopic defects. The coated cutting tools showed good performance in turning steel and hence the sol–gel route presents a novel and promising coating method for cutting tools. To determine the heat treatment schedule, boehmite gel was characterised by differential thermal analysis. The coating morphology was examined with the aid of scanning electron microscopy. The compositions of the coating and interface layer, as well as the crystal structure were characterised by X-ray diffraction (XRD). The elemental distribution near the interlayer was analysed by electron probe microanalysis. Cobalt was found to diffuse into the coating thus enhancing the bonding strength between the substrate and the coating.