Characterization of nanocomposite coatings in the system Ti-B-N by analytical electron microscopy and X-ray photoelectron spectroscopy

Superhard nanocomposite coatings of different composition in the quasi-binary system TiN-TiB₂ were deposited onto stainless steel sheets by means of unbalanced DC magnetron cosputtering using segmented TiN/TiB₂ targets. The chemistry and microstructure of a TiB_0.6N_0.7 coating was investigated using X-ray and electron diffraction, photoelectron spectroscopy, energy-filtering transmission electron microscopy, and electron energy-loss spectrometry. High resolution elemental mapping of the elements Ti, B, N, and O with energy-filtering TEM reveals a homogeneous distribution on the nanometer scale. X-Ray and electron diffraction exhibit only TiN crystallites of nanometer size, but no information on the boron-rich phase. The near-edge fine structures of the BK and NK ionization edges in the EELS spectra of the Ti-B-N coatings were used to derive information on the phases by comparing the edges with those of reference compounds. It was found that the TiN nanocrystals occur together with TiO_x particles; the grains are embedded in a strongly disordered or quasi-amorphous matrix consisting mainly of TiB₂ particles and, near the steel substrate, also boron oxide (B₂O₃).