Preparation of alpha alumina coating on carbide tools

Ceramic-coated cemented carbide cutting tools were prepared from aluminum alkoxide solution and carbide substrates by the sol-gel route. The carbide substrates were coated with boehmite sol by dip-coating process and dried to form a gel film. Multiple coatings were necessary for high quality and sufficient thickness of the coatings. After the heat treatment at 1200°C, a coating with a thickness up to more than 6 μm could be obtained without any macroscopic defects and showed good performance in turning steel, which presented a novel and promising coating method for cutting tools. To determine the heat treatment schedule, boehmite gel was characterized by differential thermal analysis (DTA). The coating morphology was examined by scanning electron microscope (SEM). The composition of coating and interface were characterized by X-ray diffraction (XRD). The elemental distribution near the interlayer was analyzed by electron probe microanalysis (EPMA). Cobalt was found to diffuse into the coating, which could enhance the bonding strength between the substrate and the coating.