Murat Baydogan

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.

An energetic approach to abrasive wear of a martensitic stainless steel

Abrasive wear is the most common type of wear that causes failure of machine elements. Examinations of abraded surfaces revealed presence of embedded particles and grooves elongated along the sliding direction. This indicates that, there are two sequential stages of an abrasion process. In the first stage, asperities on the hard surface and/or hard abrasive grains penetrate into the soft material surface and then in the second stage, they grind the surface in the sliding direction. Therefore, indentation and scratching of an indenter, which can be realized by hardness and scratch tests, can simulate the damage produced on the abraded surface. On the basis of this simulation, an energetic model is proposed for abrasive wear in the present study. In this study, abrasive wear behavior of a martensitic stainless steel is examined by hardness and scratch tests. The results of tests were evaluated to estimate the work done during abrasion and to find out the dimensional wear coefficient according to the model proposed above.

High Cycle Fatigue Behavior of Thermally Oxidized Ti6Al4V Alloy

In this study, the effect of thermal oxidation on the high cycle rotating bending fatigue behavior of Ti6Al4V alloy was investigated. Oxidation, which was performed at 600°C for 60 h in air, considerably improved the surface hardness and particularly the yield strength of the alloy without scarifying the tensile ductility. Unfortunately, the rotating bending fatigue strength at 5x106 cycles decreased from about 610 MPa to about 400 MPa upon oxidation. Thus, thermal oxidation leaded a reduction in the fatigue strength of around 34%, while improving the surface hardness (HV0.1) and yield strength 85 % and 36 %, respectively.

Influence of retrogression and re-ageing on the mechanical and corrosion properties of 7039 aluminium alloy

The effect of T6 and retrogression and re-ageing (RRA) treatments on the corrosion and mechanical properties of a 7039 Al alloy was examined. T6- and RRA-tempered alloys exhibited a similar intergranular corrosion resistance for a retrogression time of 3 min at 220 °C. The results revealed that an RRA-tempered alloy (3 min retrogression at 220 °C followed by re-ageing) exhibited a higher hardness and strength and a lower ductility and toughness than a T6-tempered alloy with a significant improvement in the stress corrosion cracking resistance.

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.

Synthesis and Characterization of Ag Doped Hydroxylapatite as an Antibacterial Scaffolds Material

Not many studies have been found in the literature on the effect of Ag ions on the structure and phase stability of hydroxylapatite which may be recognized as important information in the scaffold fabrication. The objective of the current study is to develop a better understanding on the structure and behavior of the antibacterial Ag incorporated hydroxylapatite. In order to do this, Ag doped hydroxylapatite was made by a precipitation method, and sintered in air at 1300oC. The materials were characterized by X-ray diffraction (XRD), Fourier transforms infrared spectroscopy (FTIR), density measurements and scanning electron microscopy (SEM).

A novel fabrication method for a TiO2 layer over CoCr alloy

ABSTRACT This study has been initiated to form a TiO2 layer having enhanced biological properties on the surface of a CoCr alloy, which is mostly used in manufacturing of orthopaedic implants. As a novel approach, CoCr alloy samples were first coated with titanium and then oxidised in air at 600°C for 60 h. Surface characterisation of the samples were made by structural surveys (scanning electron microscopic examinations, X-ray diffraction analyses), roughness and hardness measurements, bioactivity and wear tests. Results of the experiments have showed that fabrication of TiO2 as the outermost surface layer caused remarkable increment in the wear resistance and the bioactivity of the CoCr alloy.

Micro Arc Oxidation of AZ91 Magnesium Alloy – Effect of Organic Compounds in the Electrolyte

AZ91 Mg alloy was micro arc oxidized under constant electrical parameters in silicate based and phosphate based electrolytes with and without addition of organic chemicals, namely Hexamethylenetetramine (HMTA), TRIS (hydroxymethyl) aminomethane (THAM) and Glycerol in two different concentrations. Following oxidation, samples were characterized by X-ray diffraction analysis (XRD), scanning electron microscopy (SEM), coating thickness measurements, hardness measurements and electrochemical corrosion tests. Results showed that coating layers mainly consisted of MgO, Mg2SiO4 and MgF2 for silicate based electrolytes, and MgO for phosphate based electrolytes. Incorporation of organic chemicals into electrolyte composition did not change the type of the phases in the coating. However, when they are added in silicate based electrolytes, pore density and coating thickness are reduced and pore size is increased. On the other hand, there is no significant change in surface morphology when organic chemicals are added in phosphate based electrolyte. In the view point of corrosion resistance, organic chemicals did not enhance corrosion resistance of the samples oxidized in silicate based electrolytes, but exhibited some increment in corrosion resistance of the samples oxidized in phosphate based electrolytes.

Service Life Estimation for a Reformer Tube against Creep Dominated Failure

Abstract Remaining service life of a petrochemical plant reformer tube, which has been exposed to water vapour at 540° C for 22 years under an internal pressure of 88 bar, was analysed via the Larson-Miller approach. Samples machined from the exposed and the original tubes were subjected to stress rupture tests at various stress levels and temperatures to determine the variation of the Larson-Miller parameter with the applied stress. At a service temperature of 540° C, the remaining service life decreased with increasing applied stress. For the stress of 42 MPa, which corresponded to the hoop stress generated on the tube during service, it was estimated that the tube has completed about 50 % of its actual service life.

Anti-Bacterial Microporous Ceramic Coating for Ti6Al4V Alloys

In this study, micro porous oxide layer was formed on a Ti6Al4V alloy by the micro arc oxidation process in an electrolyte containing (CH3COO)2CaH2O + Na3PO4 with appropriate amount of silver containing agent. A wide spectrum antibiotic was also applied to the surface. Samples were subjected to antimicrobial activity tests in accordance with JIS Z 2801 standard against E.coli and the results were compared with those of original Ti6Al4V sample. First experimental results presented here showed that the micro arc oxidation process improve the antibacterial activity of Ti6Al4V alloy surface and further improvement could be obtained upon antibiotic application in addition to the micro arc oxidation process.