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In the present study, (Cr,Al)N nanolayer coatings with different Al/Cr atomic ratios were deposited by magnetron sputtering on different substrate materials (H11 and D2 tool steel, alumina). To prepare the (Cr,Al)N coatings with different Al/Cr atomic ratios in the same batch, we used two targets composed of two triangle-like segments together with two standard Al and Cr targets. This approach enabled us to study the evolution of structural and mechanical properties in dependence on composition. The elemental composition of the coatings was determined by energy-dispersive X-ray analysis (EDS). The phase composition of the (Cr,Al)N coatings was determined utilizing X-ray diffraction (XRD), while scanning electron microscopy (SEM) was employed to assess their morphology and microstructure. The coating surface topography was analyzed by atomic force microscopy (AFM). In order to evaluate the effect of the Al/Cr atomic ratio on the oxidation behavior, the (Cr,Al)N coatings were oxidized in ambient atmospheres at temperatures between 700 and 850 °C and subsequently analyzed by means of cross-sectional SEM and transmission electron microscopy (TEM). The oxidation rate, determined by weight gain over time, was utilized to quantify the oxidation process. The oxidation tests showed that the Al-rich (Cr,Al)N nanolayer coatings exhibit a considerably better oxidation resistance than the Cr-rich ones. We found that the oxide scale formed on the Al-rich coating is composed of double layers: a Cr-oxide top layer and an inner (Cr,Al) mixed oxide layer. In contrast, the oxide scale of the Cr-rich coating mainly consists of the Cr2O3 layer. In particular, we focused on the oxidation process occurring at the locations of growth defects. We noticed that the first oxidation products on the coated substrate occurred at a temperature that was much lower than the temperature for the (Cr,Al)N coating oxidation initiation. These products (iron oxides) formed only at the sites of those growth defects that extended through the entire coating thickness. [ABSTRACT FROM AUTHOR]

Several chromium carbonitride (Cr&z.sbnd;(C,N)) coatings were prepared with different C:N ratios by varying the N2 and C2H2 flow. Chromium nitride (Cr&z.sbnd;N) and chromium carbide (Cr&z.sbnd;C) coatings were also prepared for comparison. The coatings were deposited in two different ion-plating systems: by reactive evaporation in BAI730M (Balzers) apparatus at high temperature (450 °C) and by reactive sputtering in plasma-beam Sputron (Balzers) apparatus at low temperature (200 °C). Among mechanical properties microhardness, adhesion (measured by scratch test) and surface roughness were evaluated. Oxidation of the coatings was carried out by heating the samples at temperatures of 750–900 °C in an oxygen atmosphere. Crystal structure and microstructure were studied by XRD, TEM and SEM. Chemical State of the elements was observed by XPS. The concentration and depth profiles of the samples oxidized at various temperatures were measured by AES, EDX and GDOES. [Copyright &y& Elsevier]

A series of chromium nitride, carbide and carbonitride coatings were prepared by ion plating using nitrogen and acetylene as reactive gases. The depositions were made at different partial pressures of the reactive gases while maintaining other parameters constant. The crystal structure and microstructure were studied by TEM. The CrN and Cr2N phases were detected in the chromium nitride coatings. In the carbide coatings, orthorhombic Cr7C3 and the metastable cubic CrC phase were confirmed. For oxidation studies, the samples were annealed at 750 °C. Afterwards, the depth profile was measured by glow discharge optical emission spectrometry (GDOES). A complex diffusion was observed involving outdiffusion of nitrogen and segregation of carbon at the substrate-coating interface. [Copyright &y& Elsevier]

We studied the oxidation resistance of CrVN single-layer, CrN/(Cr,V)N nanolayer and CrN/(Cr,V)N/VN nanolayer hard coatings with respect to the Cr:V atomic ratio. All the coatings were deposited by DC magnetron sputtering in an industrial deposition system. Using different target configurations we were able to prepare a series of samples with various Cr:V ratios. The following target arrangements were used: a) two sources with triangle-like, segmental Cr/V targets for depositing a single-layer CrVN coating with different Cr:V atomic ratios; b) two triangle-like, segmental Cr/V targets and two chromium targets for depositing the nanolayer CrN/(Cr,V)N coating; and c) two triangle-like, segmental Cr/V targets, one chromium and one vanadium target for depositing the nanolayer CrN/(Cr,V)N/VN coating. The analysis of the oxidation mechanisms for all three types of coatings showed that the formation of a thin chromium oxide layer slows down the diffusion of vanadium towards the surface. However, at the locations where the growth defects were present the vanadium kept diffusing at high rates and formed V 2 O 5 dendritic structures at the surface. Vanadium oxide is known to have good lubricating properties at elevated temperatures, thus (Cr,V)N-based hard coatings could potentially be useful for the protection of hot-forging tools operating at high temperatures. [ABSTRACT FROM AUTHOR]