Thermal stability of nc-TiN/a-BN/a-TiB2 nanocomposites prepared by plasma chemical vapor deposition at a total pressure of several mbar and deposition temperature of 570 degreesC with TiCl4, BCl3, N-2 and H-2 as reactants was investigated. It was shown that the thermal stability of nc-TiN/a-BN/a-TiB2 nanocomposite coatings is fairly high but lower than that of the nc-TiN/a-Si3N4 and nc-TiN/a-Si3N4/a-TiSi2 coatings. The loss of boron from the coating together with the diffusion of chromium and other elements from the steel substrate into the coating during annealing are limiting the thermal stability of these coatings. (C) 2004 Elsevier B.V. All rights reserved.