Nanostructured coatings with variable contents of tungsten carbide (WC) and amorphous carbon (a-C) are prepared by controlling the sputtering power ratio using WC and graphite targets. XRD and TEM/ED analysis shows that increasing the C incorporation, the WC nanocrystalline phases evolve from γ-W 2 C to β-WC 1-x. Further C enrichment leads to a nanocomposite structure of small WC 1-x crystals dispersed in a-C matrix. The a-C at.% is estimated by XPS analysis and correlated with the observed tribo-mechanical properties. The hardness and friction properties vary from hard/high friction (36-40 GPa; µ=0.6-0.8) to moderate-hard/low friction (16-20 GPa; µ∼0.2) coatings depending on the film composition. The transition point is found for a-C content of 10 at.%. This correlates with a change from nanocrystalline WC to nanocomposite WC 1-x /a-C coatings. The overall study will help to understand the previous literature data and will serve as guide for a tailored synthesis of these WC/a-C nanocomposites.

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Magnetron sputtered chromium aluminium nitride films are excellent candidates for advanced machining and protection for high temperature applications. In this work CrAlNbased coatings including Y or Zr as dopants (2 at. %) are deposited by d.c. reactive magnetron sputtering on silicon substrates using metallic targets and Ar/N 2 mixtures. The hardness properties are found in the range of 22-33 GPa with H/E ratios close to 0.1. The influence of the dopant element in terms of oxidation resistance after heating in air at 1000ºC is studied by means of X-ray diffraction (XRD), cross-sectional scanning electron microscopy (X-SEM) and energy dispersive X-ray analysis (EDAX). The microstructure and chemical bonding are investigated using a transmission electron microscope (TEM) and electron energy-loss spectroscopy (EELS) respectively. The improvement in oxidation resistance as compared to pure CrN coating is manifested in the formation of a Al-rich outer layer that protects the underneath coating from oxygen diffusion. The best performance obtained with the CrAlYN film is investigated by in situ annealing of this sample inside the TEM in order to gain knowledge about the structural and chemical transformations induced during heating. *Manuscript with changes highlighted Click here to view linked References

In this work, a series of WC/C nanostructured films were deposited on silicon substrates by changing the ratio of sputtering power applied to graphite and WC magnetron sources (PC/PWC: 0, 0.1, 0.5, 1). The thermal stability of WC/C coatings was followed in situ by means of X‐ray diffraction measurements up to 1 100 °C in vacuum (10−1 Pa). Initially, the film microstructure is composed of nanocrystalline WC1−x and W2C phases. As the PC/PWC ratio increases the crystallinity decreases, and WC1−x becomes the predominant phase from PC/PWC = 0.1. The results show that the structural evolution with temperature of all studied layers depends essentially on their initial phase and chemical composition (determined by the synthesis conditions: ratio PC/PWC). The coating deposited at PC/PWC = 0 reveals a transformation of W2C phase into W and W3C phases at 400 °C. However, the samples with PC/PWC greater than 0 exhibits an improved thermal stability up to 600–700 °C where the WC1−x begins to transform into W2C and WC phases. At 900 °C, WC is the predominant phase, especially for those coatings prepared with higher ratios. Further annealing above 1 000 °C yields W as the foremost phase. The thermal behaviour was later studied by means of Raman spectroscopy measurements at certain temperatures where the main changes in phase composition were observed. Particularly, a fitting analysis was carried out on the D and G bands typical of disordered and amorphous carbon. The changes induced during heating are discussed in terms of the positions of D and G lines, and full width at half maximum (FWHM).