Thermal treatment effect on structural and mechanical properties of Cr–C coatings

Abstract

In the present study, the effect of thermal treatment on the mechanical and structural properties of chromium carbide coatings with different thicknesses is evaluated. The coatings were deposited by cathodic magnetron sputtering on XC100 steel substrates. Samples were annealed in vacuum, at different temperatures ranging from 700 to 1000°C for 1 h, resulting in the formation of chromium carbides. X-ray diffraction (XRD), microanalysis X/energy-dispersive X-ray spectrometer (EDS), X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy analysis were used to characterise the samples. Mechanical properties were evaluated by nano-indentation tests and the residual stress was calculated with the Stoney formula. The XRD analysis suggests the formation of the Cr 7 C 3 , Cr 23 C 6 carbides at 900°C. For thin films, they transformed totally to ternary (Cr, Fe) 7 C 3 carbides and their partial transformation has been observed in the case of thick films at 1000°C, without the formation of Cr 3 C 2. The EDS and XPS showed the diffusion mechanism between the chromium film and the steel substrate for the Cr, Fe, C, O elements during the annealing treatment. The increase of chromium film thickness from 0.5 to 2.64 µm, contributed to the significant enhancement of mechanical properties such as hardness (H) (from 12 to 26.3 GPa) and Young's Modulus (E) (from 250 to 330 GPa), respectively.

Effect of annealing treatment on the microstructure, mechanical and tribological properties of chromium carbonitride coatings

“…In earlier experiments (to be published elsewhere) we found that our CreN [12] and CreC [6] films show rather high friction coefficients between 0.53 and 0.62 and correspondingly high wear rates. Therefore, in this paper, our objective is to improve the coating's mechanical and tribological behaviour by increasing the carbon content.…”

“…On the other hand, the transformation of chromium nitrides to chromium carbonitrides in the coatings from 900°C consolidates the properties of carbides and nitrides, which can be explained by the smallest carbon atomic radius among the other elements (Cr, Fe, and N). Moreover, the activation energy for carbon diffusion in polycrystalline chromium is 1.14 eV and that of carbon into iron is about 1.4 eV [6,22]. These values are less than the activation energy of nitrogen into chromium.…”

“…Every time the annealing temperature rises, we stimulate the migration of a greater amount of carbon atoms to the film, which leads to the observed increase of the (410) Cr 7 C 3 peak intensity. This carbide is the most stable and the hardest among all the other carbide phases, especially when it is used as a coating for high carbon steel [6,17,20]. From Fig.…”

“…Chromium thin films with exclusive super saturationed metalloid elements such as carbon or nitrogen have received wide technological interest due to their remarkable performance, such as high hardness, high elasticity modulus, good wear resistance and chemical stability under extreme conditions [1][2][3][4]. Nowadays, the most commonly used PVD coatings are chromium nitrides [5] and carbides [6]. These hard coatings (H = 15-40 GPa, E = 200-500 GPa) have a high wear resistance which is many times better than steel substrates.…”

“…Concerning the chromium carbide coating, the presence of carbon in the chromium-based metal coating increases hardness and wear resistance by a lubricating effect [7]. The Cr 7 C 3 is one of the Cr carbides having excellent corrosion and wear resistance and is used largely in severe environmental conditions [6][7][8]. Among the chromium nitrides, the CrN and Cr 2 N are widely used for industrial applications because of their good hardness, high chemical stability and toughness [9][10][11].…”