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Abstract: Thermal annealing has often been used to reduce residual stress and improve mechanical properties and performance of hard coatings. In this work, nanocomposite TiSiN coatings were engineered onto steel substrates by reactive unbalanced magnetron sputtering. Following deposition, thermal annealing was performed at temperatures up to 900°C. A marked decrease in residual stress was observed in the coatings with the increase of thermal annealing temperature. To ascertain the role of residual stress in the response of the coatings to contact damage, nanoindentation was used to probe the damage resistance of the coatings and Rockwell-C test used to evaluate their adhesion strength, as a function of thermal annealing temperature. A combination of high damage resistance and good adhesion strength was observed for the coating annealed at an intermediate temperature of 600°C. [Copyright &y& Elsevier]

Abstract In the present study, molybdenum doped chromium nitride coatings deposited onto silicon substrates via unbalanced magnetron sputtering, in as-deposited and annealed conditions, at 500–800 °C in steps of 100 °C, were studied to reveal their temperature dependent structural, morphological, optical and mechanical behaviors. An analysis of these features was carried out using X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), ultraviolet visible (UV–Vis) spectroscopy, nanoindentation and finite element modeling (FEM) techniques. XRD results exhibited a significant improvement in the crystallinity of the Molybdenum (Mo)-doped chromium nitride (CrN) coatings along (111) and (200) diffraction planes, as the annealing temperatures increased. The lattice parameters gradually decreased from 4.20 to 4.12 Å as the temperature increased. The same tendency was also observed for lattice microstrains and residual stresses. Smooth grain-like surfaces were observed by FESEM imaging techniques. At an annealing temperature of 700 °C, the spectral absorptance of Mo:CrN films attained its peak value (86%), whereas the energy band-gaps were reduced from 2.48 to 1.14 eV. The other optical parameters such as complex dielectric constants, Urbach energy values, and steepness parameters of these coatings were also discussed. The hardness and elastic modulus of the as-deposited Mo:CrN films were estimated to be 18.4 and 287 GPa, respectively. At a film thickness of 1.0 μm, the highest stress of 20 GPa was evaluated, via FEM studies, at the interface between the film and the substrate. As the film thickness was enhanced, the stress level decreased. At higher annealing temperatures, both the mechanical hardness (H) and the elastic modulus (E) of Mo-doped CrN coatings dwindled. Highlights • Mo:CrN sputtered films were studied for the opto-dielectric, and mechanical properties. • A high solar absorptance of 86% was attained by Mo:CrN coating annealed at 700 °C. • Mechanical studies show that hardness & elastic modulus increases with annealing. • Substrates with higher elastic modulus induces higher level of coating's stress. [ABSTRACT FROM AUTHOR]

Abstract: One of the toughest challenges that hinders the application of ceramic coatings is their poor damage tolerance. Addressing this problem requires the development of novel micro- or nanostructures that would impart to these coatings both high hardness and high toughness. In this paper, CrAlN coatings, with varying Al contents up to 30at.%, were engineered onto steel substrates using the magnetron sputtering technique. Whilst the addition of Al does not significantly alter the columnar microstructure, it does change the preferred grain orientation and increase the compressive residual stress. Moreover, the hardness, elastic strain to failure (H/E) and plastic deformation resistance (H 3/E 2) of the resultant CrAlN coating with the highest Al content were found to increase ∼47, ∼29 and ∼140%, respectively, as compared to CrN. Evidence collected from transmission electron microscopy and X-ray photoelectron spectroscopy experiments shows that AlN, existing in an amorphous state at the columnar CrN grain boundaries, has a crucial role in providing the unusual combination of high hardness and exceptional damage resistance. The results provide a new pathway to developing durable ceramic coatings suitable for applications involving severe loading conditions. [Copyright &y& Elsevier]

Abstract: Nanocomposite TiSiN coatings were deposited on tool steels. Detailed mechanisms that govern the corrosion of these coated steels were revealed, following immersion tests in a 70% nitric acid solution. Pitting originated preferentially from coating defect sites and expanded with increasing immersion time. Both Young’s modulus and hardness measured by nanoindentation decreased as the corrosion damage intensified. A thin oxide layer formed from the thermal annealing of the as-deposited samples at 900°C was found to be effective against corrosive attack. In addition, compressive residual stress was noted to suppress the propagation of corrosion-induced cracks. The role of residual stress in controlling the corrosion resistance of these ceramic-coated steels is clarified by finite element analysis. [Copyright &y& Elsevier]