Thermal stability and crystallization studies of amorphous TM–C films

Abstract

During the last years, several binary transition metals (TM)–Carbon systems have been explored with the aim of, first obtaining amorphous alloys in a wide range of composition, especially towards the carbon-rich concentrations and second, studying the thermal stability and the crystallization of these new materials. Sputtering has been chosen as means of elaboration to obtain the films and electron probe microanalysis was used to determine the composition. The as-sputtered amorphous state was detected by electron diffraction and/or X-ray. For each amorphous film, the thermal stability was studied by differential scanning calorimetry and the crystallization was followed by hot-stage transmission electron microscopy. The products of crystallization were identified by electron diffraction. In this paper, we present a comparison of the main results we have got on amorphous and then crystallized films belonging to the well-known Fe–C, Mn–C and Cr–C systems. The thermal stability increases from Fe–C to Cr–C systems. Depending both on the carbon content and the nature of the transition metal, various unknown carbides form from the amorphous films. We find that they are often isomorphous with interstitial compounds already existing among borides, nitrides, carbonitrides and other carbides. The emphasis is put in their structural description. It is thus demonstrated that the new structures can offer either prismatic, octahedral or both sites to the C atoms. This suggests that more than one type of local orders may exist in the amorphous state for these TM–C systems.