Characterization of Al-Mg-B-C films based on experimental and first-principles investigations

Al-Mg-B and Al-Mg-B-C films were deposited by DC magnetron sputtering from the AlMgB14 and B4C targets on silicon substrates at different discharge power densities at both the targets. The deposited films were characterized by atomic force microscopy, X-ray diffraction, transmission electron microscopy, Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, nanoindentation, scratch and pin-on-disk testing. All the deposited films were found to be X-ray amorphous. The film roughness, nanohardness and elastic modulus increase with the discharge power densities at both targets. An introduction of carbon is accompanied by the formation of the strong C-B4 units that strengthen Al-Mg-B-C films. The films exhibit a coefficient of friction in the range of 0.09-0.20. First-principles calculations show that the amorphous AlMgB14-based materials consist of the fragments of boron icosahedra, for which reason they possess the hardness that is lower than the hardness of the crystalline counterparts. Based on experimental and theoretical results, it is assumed that the observed strength enhancement can be assigned to an improvement of the B-B icosahedron-like network and film densification.