Huseyin Cimenoglu

Residual stress estimation of ceramic thin films by X-ray diffraction and indentation techniques

Abstract The residual stresses in ceramic thin films obtained by the indentation method have been found to be three times higher than those of the X-ray diffraction method. This discrepancy can be eliminated by setting the geometrical factor for the Vickers pyramid indenter to 1 in the relevant equation of the indentation method.

Diffusion model for growth of Fe2B layer in pure iron

Abstract A simple diffusion model is proposed to estimate the growth kinetics of Fe2B layers created at the surface of pure iron. This model employs the mass balance equation at the Fe2B/substrate interface to evaluate the boron diffusion coefficient (DFe2B) in the boride layer. The Fe2B layers were formed using the paste boriding process, at four temperatures with different exposure times. Analysing the results, the evolution of the parabolic growth constant (k) of the Fe2B layer is presented as a function of boron concentration and boride incubation time [t0(T)]. Furthermore, the instantaneous velocity of the Fe2B/substrate interface and the weight gain of borided pure iron were estimated for different boriding temperatures. Finally, to validate the diffusion model, the boride layer thicknesses were predicted and experimentally verified for two boriding temperatures and for different treatment times.

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.

The effect of deformation before ageing on the wear resistance of an aluminium alloy

In this study, the effect of plastic deformation applied before ageing on the wear resistance of an Al–Mg–Si alloy was examined. Wear tests were performed by sliding the pin specimens, which were prepared from deformed and undeformed alloys prior to ageing, on M2 quality high speed tool steel (65 HRC) and 120 mesh Al2O3 abrasive band. Finally, it is concluded that plastically deformed solution treated alloy has higher wear resistance than undeformed alloy. The contribution of intermediate deformation to wear resistance was found to depend on the type of counterface (metal or abrasive).

Micro-scratch and corrosion behavior of functionally graded HA-TiO2 nanostructured composite coatings fabricated by electrophoretic deposition

In the present study, functionally graded coatings of HA/TiO2 nanoparticles and HA-TiO2 nanocomposite coatings with 0, 10 and 20 wt% of TiO2 were fabricated by electrophoretic deposition on Ti-6Al-4V substrate. The functionally graded structure of HA/TiO2 coatings was formed by gradual addition of HA suspension into the deposition cell containing TiO2 nanoparticles. Micro-scratch test results showed the highest critical distances of crack initiation and delamination, normal load before failure and critical contact pressures for functionally graded coating. It was observed that the improvement of adhesion strength and fracture toughness of functionally graded coatings would be due to the reduction of thermal expansion coefficient mismatch between Ti-6Al-4V substrate and HA. The results of potentiodynamic polarization measurements showed that the graded structure of the coating could efficiently increase the corrosion resistance of substrate.

Hardness characterisation of thin Zr(Hf, N) coatings

Abstract In this study, depth-sensing Vickers indentation tests were conducted on Zr(Hf,N) coatings, containing different amounts of Hf (0–21 wt.%). The coatings were deposited on hardened AISI D2 cold-work tool steel with a physical vapour deposition technique. Hardness characteristics of the coatings were analysed under six different indentation loads (0.01–0.1 N) according to load and energy methods. The same Vickers hardness numbers were obtained from the conventional load method under indentation loads that create indents having depths lower than 10% of the coating thickness. An energy method, which was derived from the work of indentation, gave similar Vickers hardness numbers over a wide range of indentation depths (up to 25% of the coating thickness). The hardness numbers of Zr(Hf,N) coatings calculated by these two methods, which are independent of the indentation depth, did not change with increasing Hf content of the coatings. The average Vickers hardness number obtained from the energy method is approximately half that from the load method. After correcting the conventional-load-method HV numbers according to the Oliver and Pharr procedure, the difference between HV numbers calculated by load and energy methods significantly decreased.

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 the particle size on the mechanical properties of 60 vol.% SiCp reinforced Al matrix composites

Abstract The effect of the reinforcing particle size on the mechanical properties of 60 vol.% SiC reinforced aluminium matrix composites produced by the pressure infiltration technique was examined by compression, impact and wear tests. The compression strength and the impact resistance decreased with increasing reinforcing particle size. The composites exhibited different abrasion behaviour depending on the size of abrasive Al2O3 grains. On fine abrasive Al2O3 grains (85 μm), the abrasion resistance increased with increasing reinforcing SiC particle size. The contrary result was obtained on coarse abrasive Al2O3 grains (250 μm). The wear tests conducted on M2 quality tool steel revealed that reinforcing of aluminium with coarse SiC particles has a very beneficial effect on the wear resistance with respect to fine reinforcing SiC particles.

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.

Characterisation of CoB–Co2B coatings by the scratch test

New results about the scratch practical adhesion-resistance of the CoB–Co2B/substrate system developed at the surface of CoCrMo (ASTM-F75) alloy were estimated. The boron diffusion on the surface of the cobalt alloy was conducted using the powder-pack boriding process at temperatures of 1223 and 1273 K with different exposure times for each temperature. The scratch tests over the surface of cobalt borided alloy were performed with a 200 micrometres Rockwell C diamond indenter considering a continuously increasing normal force for the entire set of experimental conditions of the boriding process. The worn tracks produced on the coating/substrate system were analysed by optical and scanning electron microscopy to estimate and identify the critical loads and failure mechanisms, respectively. The results indicated that the critical loads varied between 95 and 142 N as a function of the boride coating thicknesses with a development of various types of failure mechanisms over the surface of the coating/substrate system.