Faiz Muhaffel

Characteristics of multi-layer coating formed on commercially pure titanium for biomedical applications

An innovative multi-layer coating comprising a bioactive compound layer (consisting of hydroxyapatite and calcium titanate) with an underlying titanium oxide layer (in the form of anatase and rutile) has been developed on Grade 4 quality commercially pure titanium via a single step micro-arc oxidation process. Deposition of a multi-layer coating on titanium enhanced the bioactivity, while providing antibacterial characteristics as compared its untreated state. Furthermore, introduction of silver (4.6wt.%) into the multi-layer coating during micro-arc oxidation process imposed superior antibacterial efficiency without sacrificing the bioactivity.

Fabrication of oxide layer on zirconium by micro-arc oxidation: Structural and antimicrobial characteristics

The aim of this study was to cover the surfaces of zirconium (Zr) with an antimicrobial layer for biomedical applications. For this purpose, the micro-arc oxidation (MAO) process was employed in a sodium silicate and sodium hydroxide containing base electrolyte with and without addition of silver acetate (AgC2H3O2). In general, synthesized MAO layers were composed of zirconium oxide (ZrO2) and zircon (ZrSiO4). Addition of AgC2H3O2 into the base electrolyte caused homogenous precipitation of silver-containing particles in the MAO layer, which exhibited excellent antibacterial efficiency against methicillin-resistant Staphylococcus aureus (MRSA) as compared to the untreated and MAO-treated Zr.

Effect of Annealing Temperature on the Corrosion Resistance of Electroless Produced Ni-B-W Coatings

The present work deals with the formation of Ni-B-W coating on steel by electroless plating process and evaluation of their corrosion resistance after applying heat treatments at different temperatures for 1 h. The Ni-B-W coating was prepared using alkaline borohydride- reduced electroless nickel bath. Scanning electron microscopy of the surface cross-sectional view of the electroless Ni-B-W coating was analyzed and layer characteristics was investigated. Coating structure was investigated using XRD. The study reveals that the Ni-B-W coating is amorphous in their as-plated condition and upon heat treatment at 400 0C for 1 h, Ni-B-W coating crystallize and produce nickel and nickel borides in the coatings. Annealing temperature dependence of the corrosion resistance of the coating was investigated by potentiodynamic polarisation measurements. These results show that the Ni–B-W coating annealed at 650 0C exhibit better corrosion resistance than those of coatings with other annealing temperature. The corrosion resistance increased after the crystallisation of the coating, due to factors like; decrease of porosity and internal stress and the formation of tungsten oxide on the surface acting as a protective layer.

Optimisation of micro-arc oxidation electrolyte for fabrication of antibacterial coating on titanium

Abstract This study has been carried out to optimise the silver (Ag) content of the coating synthesised on commercially pure titanium (Cp–Ti, Grade 4) for biomedical applications by micro-arc oxidation (MAO) process. The MAO process has been conducted in electrolytes containing silver acetate (AgC2H3O2) at different concentrations between 0 and 0·002 mol L−1. When compared to the base electrolyte, coatings synthesised in ≥0·001 mol L−1 AgC2H3O2 added electrolytes exhibited an antibacterial efficiency of 99·98% against Staphylococcus aureus (S. aureus). Detailed examination revealed that the presence of 0·001 mol L−1 AgC2H3O2 in the electrolyte resulted in incorporation of 1·14 wt-% Ag into fabricated coating consisting mainly of outer hydroxyapatite (HA) and inner titanium oxide (TiO2) layers. In comparison to the Ag-free coating, 1·14 wt-% Ag in the coating lowered the proliferation of SAOS-2 cells, which still tended to grow at a relatively low rate with increasing culturing time.

Heat Treated and As-Plated Electroless Duplex Ni-P/Ni-B Coatings: Evaluation of Hardness and Wear Resistance

The present work deals with the formation of NiP/NiB duplex coatings by electroless plating and evaluation of their hardness and wear resistance. The duplex coatings were prepared with Ni-P as the inner layer. To analyze the structure of the coatings, XRD analysis was carried out. According to the results, NiP and NiB coatings are amorphous in their as-plated condition and after applying heat-treatment at 450 °C for 1 h, both NiP and NiB coatings crystallize and produce nickel, nickel phosphide and nickel borides in the coatings. To determine the surface morphology and cross-section characteristics of the coatings, SEM observations were carried out and concluded that duplex coatings are uniform and good coherent exists between the duplex layers and the coatings are also connected closely to the substrate. The hardness of electroless nickel duplex coatings increased with applying heat treatment and reached maximum value at coatings annealed at 400 °C. To analyze the tribological properties, pin-on-disc tests were carried out. The wear track patterns on the coatings and on Al2O3 balls were then examined by optical microscopy and EDS. The friction coefficient and wear rate of the coatings were lower than the substrate steel. Friction coefficient decreased from 0.43 to 0.36 and wear resistance decreased from 11.3 to 6.4 by applying heat treatment at 450 °C for 1 h to duplex coatings.

Evaluation of Wear and Corrosion Resistances of Oxide Coatings Formed on Magnesium Alloys by Micro Arc Oxidation

In the present study, wear and corrosion resistances of magnesium alloys were analyzed after coated by micro arc oxidation (MAO) process for potential protection of gear component, which is the most wearing part of a conventional bicycle. Two of the most common magnesium alloys (AZ31 and AZ91) were used in the study and they were oxidized in three different electrolytes (aluminate-, silicate-and phosphate-based). Scanning electron microscopy (SEM) was utilized in order to analyze the coating morphology and wear tracks obtained during wear tests. Energy dispersive X-ray spectroscopy (EDS) analyses were implemented to determine the elemental composition of the coatings. Wear and corrosion tests were applied to compare the performances of the coatings. Experimental results showed that wear and corrosion resistances of the samples generally increased after coated by MAO process and the best protection against wear and corrosion related failures, was achieved by utilizing silicate-based electrolyte for MAO process of magnesium alloys under selected process parameters.

Influence of Pulse Time on the Structural and Tribological Properties of Micro Arc Oxidized AZ91D Magnesium Alloy

Micro arc oxidation process is recently developed as a promising surface modification technique applying high voltage and current density onto the light metals. The magnesium alloys exhibit nearly the lowest density among metallic structural materials but its poor characteristics in corrosion resistance, wear resistance, hardness and so on, limit its wide-range of applications. Through micro arc oxidation, thick and wear-resistant ceramic coatings are directly formed on the surface of magnesium alloys. In this study, oxide coatings were formed on AZ91D magnesium alloy in a silicate-based electrolyte by micro arc oxidation (MAO) process. MAO process was applied in an alkaline electrolyte with different pulse time and the contribution of applied pulse time in micro structural and wear resistance was systematically investigated. Structure, composition and tribological characteristics of the coatings were studied by scanning electron microscope (SEM), X-ray diffraction (XRD) and dry sliding reciprocating wear tests.

Effect of Voltage Parameters on Surface Morphology of Micro Arc Oxidized Cp Titanium

In this study, commercially pure titanium (Cp-Ti) was micro arc oxidized in an alkaline solution by using a bipolar power supply capable of applying square voltage pulses. In the oxidation process, voltage level and numbers of positive and negative pulses were varied, and the effect of such parameters on surface and cross sectional morphology of the coatings were evaluated. In characterization works, X-ray diffraction analysis (XRD), scanning electron microscopy (SEM), coating thickness measurements and surface roughness measurements were employed. Results generally showed that coating thickness and surface roughness greatly depend on the voltage level in that higher voltage levels give thicker coatings and rougher surfaces. When the number of successive positive voltage pulses is increased, more uniform surface appearance with well distributed and equal sized micro pores are obtained up to 400 V of positive voltage. When the oxidation is performed for positive and negative pulse numbers of 10-1 at higher voltage levels, the average pore size of the coating thickness increased and the number of pores decreased.