Chromium nitride

Abstract: Microstructure and macroscopic properties of droplet free CrN films deposited by the recently developed high power pulsed magnetron sputtering (HIPIMS) technique are presented. Magnetron glow discharges with peak power densities reaching 3000 W cm−2 were used to sputter Cr targets in both inert and reactive gas atmospheres. The flux arriving at the substrates consisted of neutrals and ions (approx. 70/30) of the sputtered metal and working gas atoms (Ar) with significantly elevated degree of ionization compared to conventional magnetron sputtering. The high-speed steel and stainless steel substrates were metal ion etched using a bias voltage of −1200 V prior to the deposition of CrN films. The film-to-substrate interfaces, observed by scanning transmission electron microscope cross-sections, were clean and contained no phases besides the film and substrate ones or recrystallized regions. CrN films were grown by reactive HIPIMS at floating potential reaching −160 V. Initial nucleation grains were large compared to conventional magnetron sputtered films, indicating a high adatom mobility in the present case. The films exhibited polycrystalline columnar growth morphology with evidence of renucleation. No intercolumnar voids were observed and the corrosion behavior of the film was superior to arc deposited CrNx. A high density of lattice defects was observed throughout the films due to the high floating potential. A residual compressive stress of 3 GPa and a hardness value of HK0.025=2600 were measured. A low friction coefficient of 0.4 and low wear rates against Al2O3 in these films are explained by the absence of droplets and voids known to contribute to extensive debris generation.

Abstract: Surface oxidation mechanisms of TiN and CrN films were studied by means of x-ray photoelectron (XPS) and absorption spectroscopy (XAS). In the N 1s XPS spectra of both the oxidized TiN and CrN films, a feature assigned to molecular nitrogen was observed in addition to a feature assigned to nitride. The assignment was confirmed by the N K-edge XAS spectra of the TiN and CrN films which exhibited a sharp feature at 401.4 eV. Besides these features, the N 1s XPS spectra of the oxidized TiN films showed a third feature, which was assigned to NX–Ti–OY like structures taking into account the change in the Ti 2p XPS spectra. However, no evident feature assigned to NX–Ti–OY like structures was observed in the XAS spectra because of the overlapping with the nitride features. The above results indicated that the CrN films directly changed to Cr2O3 with the formation of molecular nitrogen in the interstitial positions of the surface oxide layers, while the TiN films were oxidized to TiO2 through the formation of NX–...