Alex Montagne

Characterisation of R.F. magnetron sputtered Cr-N, Cr-Zr-N and Zr-N coatings

Binary Cr-N, Zr-N and Cr-Zr-N films were synthesised using a R.F. reactive magnetron sputtering technique by co-sputtering Cr and Zr. The crystalline structure, morphology, mechanical and tribological properties of the films as a function of Zr content were characterised by X-ray diffraction, microanalysis X (WDS, EDS), X-ray photoelectron spectroscopy, scanning electron microscopy, atomic force microscopy, nanoindentation, scratch adhesion and pin-on-disc sliding wear tests. The residual stress was calculated with the Stoney formula. The Cr-Zr-N films exhibit a two-phase microstructure, containing a cubic (CrN, ZrN) with hexagonal (Cr2N, Zr2N) phases, as shown by X-ray diffraction. As the Zr content increased, a columnar and compact structure is developed with a low surface roughness. The results reveal that the mechanical and tribological properties of the films were found to depend on the Zr content and the hardness (maximum 26.3 GPa) is greatly improved in comparison with CrN and ZrN films, especially at 31 at.-% Zr. In the scratch test, the hardest film (Cr0.18Zr0.31N0.47) exhibited an adhesive failure at Lc2 = 34.3 N.

Structural and mechanical properties of Cr–Zr–N coatings with different Zr content

ABSTRACT Cr–Zr–N films have been synthesised using R.F reactive magnetron sputtering system on Si (100) wafer and XC100 steel substrate without heating. The structural, mechanical and friction coefficient evolution as a function of the Zr content were investigated by XRD, (EDS, WDS), WPS, XPS, SEM, AFM, nanoindentation, Scratch adhesion and pin-on-disc sliding wear tests. The results show, that, with increasing Zr content, the film structure changed with the coexistence of (Cr–N, Zr–N) crystallographic orientation mixture. The films formed a (Cr, Zr) N solid solution where Zr atoms substitute Cr atoms. CrN lattice parameter increased from 4.17 to 4.32 Å with the crystallite size refinement. The mechanical parameters (H, σ, E, H/E and H3/E2) were significantly improved in comparison to binary films, especially at 29 at.-% Zr. The friction and wear behaviour of the Cr–Zr (29 at.-% Zr)–N coating also showed a significant improvement.

Biocompatibility of sol-gel hydroxyapatite-titania composite and bilayer coatings

Titania-Hydroxyapatite (TiO2/HAP) reinforced coatings are proposed to enhance the bioactivity and corrosion resistance of 316L stainless steel (316L SS). Herein, spin- and dip-coating sol-gel processes were investigated to construct two kinds of coatings: TiO2/HAP composite and TiO2/HAP bilayer. Physicochemical characterization highlighted the bioactivity response of the TiO2/HAP composite once incubated in physiological conditions for 7days whereas the TiO2/HAP bilayer showed instability and dissolution. Biological analysis revealed a failure in human stem cells adhesion on TiO2/HAP bilayer whereas on TiO2/HAP composite the presence of polygonal shaped cells, possessing good behaviour attested a good biocompatibility of the composite coating. Finally, TiO2/HAP composite with hardness up to 0.6GPa and elastic modulus up to 18GPa, showed an increased corrosion resistance of 316L SS. In conclusion, the user-friendly sol-gel processes led to bioactive TiO2/HAP composite buildup suitable for biomedical applications.

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 Cr7C3, Cr23C6 carbides at 900°C. For thin films, they transformed totally to ternary (Cr, Fe)7C3 carbides and their partial transformation has been observed in the case of thick films at 1000°C, without the formation of Cr3C2. 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 Youngs Modulus (E) (from 250 to 330 GPa), respectively.

Hydroxyapatite-TiO2-SiO2-Coated 316L Stainless Steel for Biomedical Application

Abstract This study investigated the effectiveness of titania (TiO2) as a reinforcing phase in the hydroxyapatite (HAP) coating and silica (SiO2) single layer as a bond coat between the TiO2-reinforced hydroxyapatite (TiO2/HAP) top layer and 316L stainless steel (316L SS) substrate on the corrosion resistance and mechanical properties of the underlying 316L SS metallic implant. Single layer of SiO2 film was first deposited on 316L SS substrate and studied separately. Water contact angle measurements, X-ray photoelectron spectroscopy, and Fourier transform infrared spectrophotometer analysis were used to evaluate the hydroxyl group reactivity at the SiO2 outer surface. The microstructural and morphological results showed that the reinforcement of HAP coating with TiO2 and SiO2 reduced the crystallite size and the roughness surface. Indeed, the deposition of 50 vol pct TiO2-reinforced hydroxyapatite layer enhanced the hardness and the elastic modulus of the HAP coating, and the introduction of SiO2 inner layer on the surface of the 316L SS allowed the improvement of the bonding strength and the corrosion resistance as confirmed by scratch studies, nanoindentation, and cyclic voltammetry tests.

Mechanical properties of WC/Co-CNT HVOF sprayed coatings

ABSTRACT Coatings based on WC–12Co, with and without the reinforcement of carbon nanotubes (CNTs) have been deposited by means of the HVOF thermal spraying technique on a SAE 1020 steel substrate. The aim of the present study is to evaluate in detail the influence of the 36 h milling time on both feedstock powders, particularly on the mechanical properties of WC-12Co coatings, with (WCCNT) and without (WCCONV) CNTs addition. Properties such as hardness, apparent yield stress and fracture toughness were observed to exhibit an improvement due to CNTs addition, whereas the elastic modulus was found to be insensitive to the CNTs content. These findings could explain the enhancement of the wear resistance of the CNTs-reinforced coatings (WCCNT) reported in the literature.

Assessment of the mechanical and tribological performance of a ZrN PVD coating

ABSTRACT The present work has been conducted in order to assess the mechanical and tribological performance of a ZrN/Mo2N coating deposited onto a H13 steel by means of a closed field unbalanced magnetron-sputtering ion-plating process. The hardness and elastic modulus of the coated system have been determined employing nanoindentation techniques. Dry and wet (3.5 wt-% NaCl solution) sliding wear tests were carried out making use of an alumina ball as counterpart. It has been determined that, during testing under the corrosive solution, the coating experiences a severe abrasive wear mechanism, due to the combined action of the alumina ball, the hard ‘debris’ and a coating localised corrosion attack. On the other hand, it has been shown that the coated system is able to increase the wear resistance of the substrate by more than one order of magnitude, if the wear tests are carried out in air under the same conditions.

A new method to fabricate Fe-TiC composite using conventional sintering and steam hammer

The aim of this research paper is to fabricate a Fe-TiC composite by a novel and simple manufacturing method. The latter is based on two cumulative processes; a conventional sintering (transient liquid phase sintering) and a hot forging with steam hammer respectively. The blinder phase of the studied simples is varied from carbon steel to high alloy steel using alloying additive powders. The obtained outcomes showed that after the sintering process, the relative density of the performed simples is improved from 86% to 95.8% without any densification process. Otherwise, in order to ensure maximum densification and enhance in addition the solubility of the alloying additives the hot forging process is then applied. Indeed, the final obtained composite product is a TiC-strengthened steel with a relative density around 99% (about 6.5 g/cm3 of density) wherein 30% (wt.) of spherical and semi-spherical TiC particles are homogeneously distributed in the metal matrix.