Structural characterisation of ZrB2/oxides nanocomposite ®lms synthesised in ¯owing Ar±BCl3 post-discharges

A chemical vapour deposition process enhanced by a ¯owing microwave Ar±BCl3 post-discharge has been carried out to synthesise at 733 K thin ®lms containing zirconium diboride. In this process, zirconium atoms diffuse from the substrate (Zircaloy-4) to the gas/®lm interface and react with boron-containing molecules to synthesise ZrB2. Secondary neutral mass spectroscopy analyses show that these ®lms contain oxygen also. Electron probe microanalysis results are not consistent with the possible de®ned compounds of the Zr±B±O system described in the literature. Thus, coatings obtained by post-discharge treatment are made of several phases, which are mixed: ZrB2, B2O3 and ZrO2. This point is con®rmed by X-ray photoelectron spectroscopy. However, electron diffraction analyses show that only ZrB2 is crystallised. Thus, these ®lms are composed of ZrB2 nanograins embedded in an amorphous solid solution of zirconium and boron oxides. These nanocomposite ®lms contain Zr(Fe,Cr)2 precipitates also, i.e. the same than those present in zircaloy-4 substrates. However, the precipitates size in the ®lm is about one order of magnitude higher than in substrates. According to the growth mechanism of the nanocomposite ®lms, we present a possible explanation on the occurrence and on the size of the Zr(Fe,Cr)2 precipitates. # 2001 Elsevier Science B.V. All rights reserved.