To improve the surface roughness of alumina substrates, the AlN precursor mixtures were coated on the alumina substrates. AlN precursor mixtures were coated on Al2O3 substrates using a sol-gel method. The AlN precursor mixtures were prepared using urea, aluminum nitrate, sucrose and a surfactant. The effects of calcination temperature and soaking time on the phase evolution, microstructure, mechanical properties and surface roughness of the coating layer were investigated. The phase evolution, microstructure and constitution of the coating layer after calcination were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), and electron spectroscopy for chemical analysis (ESCA). It was found that Al-N-O and Al2O3 phases can coexist at 1300 oC after soaking for ≤ 60 min in N2/H2 atmosphere. The adhesive strength of coating layer significantly increased with increasing calcination temperature. The surface roughness of Al2O3 substrates can be improved using AlN sol gel at 1300 oC. However, the surface roughness was obviously increased at 1500 oC.

Keywords: AlN coatings, Surface roughness, Ceramic substrates