Preparation of alpha-alumina coated carbide tools by the sol-gel process

Ceramic-coated cemented carbide cutting tools were prepared from aluminum a lkoxide solution and carbide substrates by the sol-gel route. The carbide s ubstrates was coated with boehmite sol by a dip-coating process and dried t o get gel film. Multiple coating was necessary for high quality and suffici ent thickness of the coatings. After heat treatment at 1200 degrees C, the coating with a thickness up to more than 6 mu m could be obtained without a ny macroscopic defect and showed good performance in turning medium carbon steel, which presented a novel and promising coating method for cutting too ls. To determine the heat treatment schedule, boehmite gel was characterize d by differential thermal analysis (DTA). The coating morphology was examin ed with the aid of a scanning electron microscope (SEM). The composition of the coating and interface layer was characterized by X-ray diffraction (XR D). The results suggested that the coating convert to alpha-alumina at abou t 1140 degrees C and sintered to a relatively high density at 1200 degrees C. The coating was polycrystalline and isotropic and there was no weak phas e in the interface layer. It was found in electron probe microanalysis (EPM A) that cobalt diffused into the coating, which would be conducive to enhan cing the bonding strength between the substrate and the coating. (C) 2000 E lsevier Science S.A. All rights reserved.