FABRICATION AND CHARACTERIZATION OF NITRIDE COATINGS FOR MECHANICAL, TRIBOLOGICAL AND CORROSION APPLICATIONS

Abstract

Nowadays, superior surface properties of the materials are getting much attention such as: hard and super-hard protective coatings with hierarchical surface structures for a variety of applications including automotive, aerospace components, and machining industries have received a great deal of attention. Metal nitride coatings are suitable for adhering to metal surface such as steel and aluminium to improve surface properties. Recently, the family of nitride coatings has received a lot of attention for protecting materials and is also used in many mechanical, corrosion and tribological applications. The present work is to synthesize the reinforcement and coating materials with structural, and morphological evolution of h-BN different nanostructured (nanosheets and nanoflowers) successfully prepared using a very simple and cost-effective single step wet chemical reaction route. The effect of precursors, reaction annealing time on structural and morphological properties of the synthesized powders. Thereafter, hexagonal boron nitride (h-BN) target was prepared by two step wet chemical reaction method using a nontoxic starting material (urea and boric acid). Optimized annealing parameters (1600°C for 2 hr) and N2 environment are applied for pertinent growth of boron nitride nano powder. A mechanical procedure was acquired to convert this powder into pallet (target) for further analysis. The prepared target (white pallet) was used to fabricate the corrosion resisting h-BN nano-sheet coating using pulse laser deposition technique. A thick h-BN coating was deposited on SS 304 and Si substrates. X-ray diffraction (XRD) and field emission scanning electron microscopy (FE-SEM) were employed to characterize the coating for structural and morphological purpose. X-ray photoelectron spectroscopy (XPS), Atomic force microscopy (AFM), and energy-dispersive X-ray spectroscopy (EDXA) were employed to characterize the coating for surface properties and chemical composition purpose. However, contact angle and electrochemical work station were employed for wetting and corrosion analysis tests. Pulsed laser deposition (PLD) grown h-BN coating shows the hydrophobicity (132.4°) and reduce corrosion rate by one order of magnitude compared to bare SS. On the basis of these results, the h-BN nano-sheet coating may be a promising candidate for corrosion resist application in (3.5 % NaCl solution) salinity environment. The temperature-dependent morphological evolution of “in-situ” grown zirconium nitride (ZrN) coatings on a low carbon steel plate (LCSP) substrate has been examined using sputtering technique. An optimized gas mixture of Ar + N2 and different substrate temperatures (200 °C, 300 °C and 400 °C) in sputtering process is accountable for dissimilar hierarchal surface structure (nano-cauliflower, nano-pyramids and nano-flakes). The growth mechanism and physical properties of these surface structures were investigated, systematically. The mechanical properties of the as prepared samples (hardness, elastic modulus, toughness, and adhesion) were evaluated using a well-established nano-indentation method. It has been assessed how the friction coefficient varies with cycle time. The surface chemistry, structure and hardness of the coatings covering the surface effect wear volume and friction levels. The dominant wear mechanisms were identified using FE-SEM, EDX and XPS analyses. During the process of wear, zirconium oxynitrides (O-Zr-N) were formed in the ZrNNF coating, which can have a positive effect on automotive applications. The wear volume of the ZrN nanoflakes hard coating was lower compared to pristine samples. The nanostructures such as nano-cauliflower, nano-pyramids and nano-flakes can be a plausible explanation for the improved tribological performance. Moreover, the electrochemical and contact angle experiments were utilized to examine the wetting and corrosion characteristics of the as prepared samples. The obtained results revealed that the ZrN-based nano-flakes coating show maximum elastic modulus (335.195 ± 16.75 GPa), hardness (33.173 ± 1.65 GPa), hydrophobicity (~118.5°) and corrosion resistance in comparison of other samples. Therefore, the ZrN-based nano-flakes coating offer a toughest barrier in the path of corrosive species, resultant higher protection of the low carbon steel plate. A process describing the formation of corrosion initiation and products was also discussed in detail. Zirconium (Zr) and vanadium (V) doping can change the basic properties of titanium nitride (TiN) coatings prepared by the magnetron sputtering deposition technique, including microstructure, coating-substrate adhesion, friction and wear resistance. However, the specific effect of Zr and V doping level on the properties of TiN coatings and the mechanism needs further investigation. Using GI-Xray diffraction, field emission scanning electron microscopy, energy dispersive X-ray spectroscopy, and atomic force microscopy, researchers can identify the microstructure, morphology, chemical composition, phase composition, and roughness of coatings, respectively. The dominant preferred orientation for TiN is found to be (220) while TiVN and TiZrN are oriented along (111) and improve the metal surface life. The Zr doped deposited TiZrN coating show promising properties with higher texture coefficients, higher elastic modulus (351.017 ± 17.70 GPa) and higher hardness (36.925 ± 1.84 GPa) than those of TiN and TiVN specimens. With steel balls serving as the counter material, the friction as well as wear properties were examined and compared using the ball-on-disc technique at high speed. The findings demonstrated that Zr and V content TiN coatings (TiZrN and TiVN) present superior anti-wear properties with lower wear volume while TiN coated Al7079-BN showed a lower friction coefficient and higher wear volume. The Zr doped coating (TiZrN) showed improved mechanical and tribological properties as compared to other binary and ternary nitride coatings. Adhesive (TiN) to abrasive (TiZrN & TiVN) wear mechanism of coatings has been identified using an FE-SEM, EDS and XPS analyses.