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The service life of industrial components is limited predominantly by Chemical corrosion/mechanical wear. The project is concerned with the investigation of the capability of Ti(Al,O)/Al₂O₃ coatings to improve the service life of tool steel (H13) used for dies in aluminium high pressure die casting.

This paper gives a general review on the research work conducted at the University of Waikato on producing and evaluating the titanium/alumina based composite coatings. The powder feedstocks for making the composite coatings were produced by high energy mechanical milling of a mixture of Al and TiO₂ powders in two different molar ratios followed by a thermal reaction process. The feedstocks were then thermally sprayed using a high velocity air-fuel (HVAF) technique on H13 steel substrates to produce a Ti(Al,O)/Al₂O₃ composite coatings. The performance of the coating was assessed in terms of thermal shock resistance and reaction kinetics with molten aluminium. The composite powders and coatings were characterized using scanning electron microscopy (SEM), optical microscopy and X-ray diffractometry (XRD).

Ni–Co coatings are widely used due to their unique mechanical properties, high anticorrosion properties, good thermal stability and special magnetic properties. Ni–Co–xTiO₂ (x = 0–20 g/L in the electrolyte) composite coatings were fabricated by electrodeposition on mild steel. The effect of TiO₂ concentration on the microhardness, surface morphology and tribological behaviour has been studied. The results show that, comparing with pure Ni–Co coating, both microhardness and wear property of the Ni–Co–TiO₂ composite coatings were significantly improved. The microstructure and properties for the Ni–Co–TiO₂ composite coatings were varied following with the TiO₂ concentration. The mechanism of mechanical property improvement was also discussed.

Copper (Cu) is widely used as electrical conducting and contacting material. However, Cu is soft and does not have good mechanical properties. In order to improve the hardness and wear resistance of Cu, sol-enhanced Cu–Al₂O₃ nanocomposite coatings were electroplated by adding a transparent Al oxide (Al₂O₃) sol into the traditional electroplating Cu solution. It was found that the microstructure and mechanical properties of the nanocomposite coatings were largely influenced by the Al₂O₃ sol concentration. The results show that the Al₂O₃ nanoparticle reinforced the composite coatings, resulting in significantly improved hardness and wear resistance in comparison with the pure Cu coatings. The coating prepared at the sol concentration of 3.93 mol/L had the best microhardness and wear resistance. The microhardness has been improved by ~20% from 145.5 HV (Vickers hardness number) of pure Cu coating to 173.3 HV of Cu–Al₂O₃ composite coatings. The wear resistance was also improved by ~84%, with the wear volume loss dropped from 3.2 × 10^-3 mm³ of Cu coating to 0.52 × 10^-3 mm³ of composite coatings. Adding excessive sol to the electrolyte deteriorated the properties.

The microstructure, microhardness and wear property of electroplated Ni–ZrO₂ nanocomposite coatings with different ZrO₂ concentration were analyzed using SEM, microhardness and wear tests. It was found that in the composite coatings, incorporation of ZrO₂ particles improves the mechanical property of Ni coatings and the effect of ZrO₂ nanoparticles concentration on the surface morphology, microstructure and mechanical property of electroplated coatings was discussed. The mechanical properties of Ni–ZrO₂ coatings reach the optimum value when the ZrO₂ concentration is 10 g/L.

Recent developments of laser surface modification of titanium alloys for increasing their corrosion, wear and oxidation resistance are introduced. The effects of laser processing parameters on the resulting surface properties of titanium alloys are reviewed. The problems to be solved and the prospects in the field of laser modification of Ti alloys are discussed. Due to the intrinsic properties, a laser beam can be focused onto the metallic surface to produce a broad range of treatments depending on the input energy. Thus, composite strengthening coatings can be fabricated by the methods of laser alloying, cladding, pulse laser deposition (PLD), etc., which are promising techniques of producing a layer of new materials on the surface of titanium alloys.

Iron-based composite coatings reinforced with TiB₂–TiC multiple ceramic have been fabricated from a precursor of B₄C, TiO₂ and Al powders by laser cladding. The effect of TiO₂ and Al on the microstructure and wear properties of the coatings was investigated. The results showed that the volume fraction, type and size of the reinforcements were influenced by the content of TiO₂ and Al. TiB₂ and TiC were evenly distributed in the coating; however, most of Al₂O₃ were ejected from the coatings, only few of them retained in the coating acting as nucleation core of reinforcement or inclusion. The microhardness and wear resistance of the coatings were improved, whereas the friction coefficients of the coatings were considerably lower than that of substrate.

In situ synthesized VC–VB particles reinforced Fe-based composite coatings were produced by laser beam melting mixture of ferrovanadium (Fe–V) alloy, boron carbide (B₄C), CaF₂ and Fe-based self-melting powders. The results showed that VB particles with black regular and irregular blocky shape and VC with black flower-like shape were uniformly distributed in the coatings. The type, amount, and size of the reinforcements were influenced by the content of FeV₄₀ and B₄C powders. Compared to the substrate, the hardness and wear resistance of the composite coatings were greatly improved.

Microarc oxidation (MAO) composite coatings containing rutile TiO₂ were produced on 2024 aluminum alloy in an electrolyte with nanorutile TiO₂ particles. The microstructure and properties of the composite coatings were analyzed by SEM, EDS, laser confocal microscope, XRD, Vickers hardness tester, scratch test and friction test, respectively. The results showed that the composite coatings consisted of $\gamma$-Al₂O₃, $\alpha$-Al₂O₃, mullite and rutile TiO₂. With increasing concentration of rutile TiO₂ particles in the electrolyte, the compactness of the composite coatings was improved significantly. The abrasion performance of the microarc oxidation composite coatings containing rutile TiO₂ was better than that of MAO coatings without rutile TiO₂.

Ti6Al4V alloy of titanium is a significant biomaterial due to its biocompatible nature, but it lacks required bioactivity to make it mimic properties to a human bone. Thus, hydroxyl-apatite (HAp), an inorganic compound found in human bones, is generally coated onto Ti6Al4V substrates to improve their bio-characteristics. But, HAp itself lacks certain bio-functionalities, such as allowing tissue bone regeneration and poor binding to the Ti6Al4V substrate, which results in osteoporosis and reduced bioactivity of the bio-implant, respectively. The proposed way out for this is the further doping of HAp with Strontium (Sr) for enabling tissue bone regeneration as well as addition of Polydopamine (PDA) for improved adhesion of HAp-based coatings with the substrate. Moreover, PDA results in increased drug delivery area and thus can be used as a material for enhancing resistance to bacterial growth. The present study demonstrates an experimental work on deposition of HAp, HAp with PDA and HAp with PDA and Sr coatings deposited onto Ti6Al4V alloy by means of biomimetic coating technique. Initially the pure HAp coatings were deposited using 10 SBF (simulated body fluid) solution and optimized in terms of time duration for desired coating uniformity. Then, for the optimized coating duration, the PDA pretreated Ti6Al4V substrates were coated, utilizing HAp, and Sr (at two different compositions) combinations were deposited through modified 10 SBF solutions. The characterization involving microstructural analysis and phase detection was performed for all these coatings using Scanned Electron Microscopy (SEM), Energy Dispersive Spectroscopy (EDS) and X-Ray Diffraction (XRD) of the coated substrates and adhesion strength was calculated using a standard pull out adhesion test ISO 13779–4. The study showed an effective and comparatively cheap method of depositing organic coatings using biomimetic technique to obtain improved bio-functionalities in metallic implants at low temperatures.

In the current experimental study, grey cast iron (CI) substrate was coated with Inconel718-Al₂O₃ based composite coating with a high-velocity oxy-fuel technique. The effect of changing the Al₂O₃ content (10, 20 and 30 wt.%) on the microstructure, hardness, porosity and electrochemical corrosion performance of Inconel (INC718) coating was studied. Investigations on the corrosion behavior of uncoated and HVOF-coated substrates were carried out at room temperature at 3.5wt.% sodium chloride solution (NaCl) with the help of the potentiodynamic polarization approach. The surface morphologies and compositions of HVOF as-sprayed and electrochemically corroded coatings were studied through SEM and EDS techniques. The various phases existing in the INC718 and Al₂O₃ feedstock powders and HVOF-deposited composite coatings were determined by XRD analysis. The microhardness of INC718-based coatings was found to be increased with the increase in Al₂O₃ content. The highest average microhardness value of about $801\pm 40$HV${}_{0.2}$ was observed in INC718-30wt.% Al₂O₃ coating. The deposited coatings exhibited an increased porosity level with the increased amount of Al₂O₃ contents. However, the coating with 10wt.% Al₂O₃ content exhibited the maximum corrosion resistance. Its improved corrosion performance is attributed to low porosity levels, which causes the penetrating pathways of Cl⁻ ions to be blocked completely.

Metal-based functionally graded coatings have proven effectiveness in improving anti-wear properties and surface integrity of the substrates. The use of electrodeposition coating technique, considering the economics and versatility associated with this method, is a preferred technique of depositing metal-based composite coatings. Further, Ni-based composite coatings are proven for anti-wear applications, and addition of various reinforcement for developing functional coatings need to be evaluated for different applications. This study describes the development, analysis, and performance evaluation of Ni–TiN–AlN and Ni–SiC–Cr electrodeposited composite coatings on tungsten carbide (WC) tool substrates, to impart improved anti-wear properties during machining. The composite coatings were deposited and optimized for current density values of the electrodeposition process, which was identified as the most significant parameter in both the cases. The coatings were characterized using scanning electron microscope (SEM), energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD) for microstructural analysis. The results were further analyzed for tribological behavior through microhardness and adhesion strength tests of the deposited coatings, which are significant properties imitating anti-wear characteristics of the substrate. A significant increase of 47% and 36% in microhardness was obtained for Ni–SiC–Cr coated specimen and Ni–TiN–AlN coated specimen, respectively, compared to the uncoated WC substrates, accompanied with a good adhesion strength in both the cases. The microstructural analysis in both the cases revealed an increase in the deposited coating constituents with increasing current density, leading to a denser coating deposition up to the saturation point, and then beginning of coating delamination due to over-saturation with further increase in current density.

TiO₂/Fe composite coatings were prepared on Al₂O₃ balls by mechanical coating technique. SEM results showed that the composite coatings had a composite microstructure of discrete islands of TiO₂ deposited on Fe coatings. The loading amounts of TiO₂ in the composite coatings were increased by introducing Al₂O₃ impact balls. The degradation rate of methylene blue (MB) under UV irradiation was used to evaluate the photocatalytic activity of the composite coatings. Compared with TiO₂/Ti and TiO₂/Cu composite coatings made by this method, TiO₂/Fe composite coatings showed higher photocatalytic activity.

Ti6Al4V alloy of titanium is a significant biomaterial due to its biocompatible nature, but it lacks required bioactivity to make it mimic properties to a human bone. Thus, hydroxyl-apatite (HAp), an inorganic compound found in human bones, is generally coated onto Ti6Al4V substrates to improve their bio-characteristics. But, HAp itself lacks certain bio-functionalities, such as allowing tissue bone regeneration and poor binding to the Ti6Al4V substrate, which results in osteoporosis and reduced bioactivity of the bio-implant, respectively. The proposed way out for this is the further doping of HAp with Strontium (Sr) for enabling tissue bone regeneration as well as addition of Polydopamine (PDA) for improved adhesion of HAp-based coatings with the substrate. Moreover, PDA results in increased drug delivery area and thus can be used as a material for enhancing resistance to bacterial growth. The present study demonstrates an experimental work on deposition of HAp, HAp with PDA and HAp with PDA and Sr coatings deposited onto Ti6Al4V alloy by means of biomimetic coating technique. Initially the pure HAp coatings were deposited using 10 SBF (simulated body fluid) solution and optimized in terms of time duration for desired coating uniformity. Then, for the optimized coating duration, the PDA pretreated Ti6Al4V substrates were coated, utilizing HAp, and Sr (at two different compositions) combinations were deposited through modified 10 SBF solutions. The characterization involving microstructural analysis and phase detection was performed for all these coatings using Scanned Electron Microscopy (SEM), Energy Dispersive Spectroscopy (EDS) and X-Ray Diffraction (XRD) of the coated substrates and adhesion strength was calculated using a standard pull out adhesion test ISO 10779–4. The study showed an effective and comparatively cheap method of depositing organic coatings using biomimetic technique to obtain improved bio-functionalities in metallic implants at low temperatures.