Mechanical properties and structure of amorphous and crystalline B4C films

Amorphous and crystalline films were prepared by magnetron sputtering of hot-pressed B4C target. Hardness, elastic modulus (characterized by nanoindentation), intrinsic stress and structure (characterized by electron diffraction, Raman and optical spectroscopy) of the films were investigated in dependence on the substrate bias and deposition temperature. Electron diffraction and Raman spectroscopy show amorphous structure for all the films deposited at temperatures below 900 °C. Crystalline B4C phase appears at T > 900 °C. The hardness and elastic modulus of the films deposited on unheated substrates decrease with increasing negative substrate bias. These variations correlate well with those observed for compressive stress, argon content in films and intensity of Raman spectra.The hardness and elastic modulus of the films increase with increasing substrate temperature up to 940 °C but remain lower than those for the polycrystalline bulk B4C (∼ 41 GPa). The increase of deposition temperature up to 970 °C results in a growth of hardness that in some points (44–60 GPa) significantly exceeds that for the bulk B4C material. The scatter of values of hardness and elastic modulus of this film was higher than that of films deposited at lower temperatures. It may be related to specific local microstructure which consists of B4C crystallites and carbon clusters.