Eyup Sabri Kayali

Characterization of molybdenum nitride coatings produced by arc-PVD technique

Abstract Molybdenum nitride coatings were deposited onto high-speed steel (HSS) substrates by the arcPVD technique. It was possible to produce coatings with Mo2N and MoN structure by varying the nitrogen partial pressure between 0.4 and 1.5 Pa. The relationships between hardness, thickness, and crystallographic structure of the coating and the deposition parameters were investigated. Hardness of the coatings increased with the increase of nitrogen content of the coating. Tribological behavior of the coatings was determined by ball-on-disk wear tests. The wear behavior of Mo-N-coated HSS samples against alumina balls was better than that of TiN-coated ones. Electrochemical polarization experiments were conducted in 1 N sulfuric acid. The porosity of the sample was determined by the copper decoration test. The coating with the lowest nitrogen content showed the best corrosion protective properties in the electrochemical tests.

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.

The Improvement of Titanium Reinforced Hydroxyapatite for Biomedical Applications

Abstract The addition of different amounts of inclusions to brittle hydroxya patite (HA) gives the advantage of tailoring and predicting the possible mechanical proper ties of the biocomposite. Biocomposite materials have been developed in order to combine the propert ies of bioactive material with the better mechanical properties of a second phase. Titanium, having superior biocompatibility, mechanical properties and corrosion resistance, is suitable as a reinforcement phase for biomedical applications. This study focuses on the effect s of sintering temperature and the amount of reinforcement phase on the mechanical properties of HA-Ti composites. The HA material used was derived from freshly-extracted human teeth wi th calcination at 850°C. Titanium powders were mixed by 5 and 10 wt % with HA and have been subjected to sintering at 1200 and 1300C for three hours. Density, microhardness, and compressive strength m easurements have been carried out. Microstructures have been investigated by SEM and the phas an lysis has been determined by the x-ray diffraction analysis . The best mechanical properties have been obtained by sintering at 1300°C for three hours with the addition of 10 wt % Ti to HA.

The Influence of Sintering Temperature on Mechanical and Microstructural Properties of Bovine Hydroxyapatite

The influence of sintering temperature on densification, microstructure and the mechanical properties of bovine hydroxyapatite (BHA), produced by a calcination method, was investigated. Densification and mechanical properties increased over increasing sintering temperature in the range between 1000°C and 1300°C, and there are evidences of optimum sintering temperature at 1200°C. The measured mechanical properties indicate sintered BHA-bodies as interesting biomaterials for further investigation in biomedical applications.

Sintering Effect on Mechanical Properties of Composites of Hydroxyapatite Lanthanum Oxide (HA-La2O3)

Composites of calcinated bovine bone derived hydroxyapatite (HA) with 0.25, 0.5, 1, and 2 wt % La2O3 were prepared by sintering. The experimental results indicated that compression strength and microhardness of HA-La2O3 composites increase when the content of La2O3 and sintering temperature increase. The best mechanical properties were achieved after sintering at 1300°C. The results are in agreement with densification measurements and microstructure analysis.

Characterization of Plasma Sprayed Bioglass Coatings on Titanium

Bioglass, 45S5 containing 45 % SiO 2, 6 % P2O5, 24.5 % CaO and 24.5 % Na 2O all in weight percent, was plasma sprayed onto a titanium substrate with and without 60 Al 2O3 40 TiO2 as a bond coating. Mechanical properties were evaluated by followin g the ASTM C633 method and the microstructural characterization has been carried out by using scanning electron microscope. Results indicate that the bonding strength of bond coatings is three times higher than of the coatings that are directly applied to the surface. It has been observed that there is a uniform coating layer with a thickness of 110 μm and that there was not any reaction observed at the coating-met al interface.

Nano Calcium Phosphate Powder Production through Chemical Agitation from Atlantic Deer Cowrie Shells (Cypraea cervus Linnaeus)

The process is a simple chemical method and aims to produce nano-structured calcium phosphate powders from natural sources, for biomedical applications. For this purpose, Atlantic Deer Cowrie (ADC) shells (Cypraea cervus Linnaeus, 1771) were collected from a local gift store in Istanbul. The empty shells were cleaned and crushed then were ball milled and sieved under 100µm. The raw powders were suspended on a hotplate stirrer for a simple chemical agitation. The temperature was kept at 80°C for 15 min. and then appropriate amount of H3PO4 was added by titration into the prepared solution to form calcium phosphate precursors. The solution was stirred on a hotplate for 8 hours then dried at 100°C for 24 hours. Afterwards the resulting dried sediments were collected and heat treated between 400-800°C for 4 hours, dependent on the required specific calcium phosphate phase. X-ray diffraction (XRD) analysis and scanning electron microscopy (SEM) were carried out for identifying various hydroxyapatite (HA), tricalcium phosphate (TCP) and other calcium phosphate phases. Various particle sizes ranging from nano to micron, are obtained depending on the chemistry used and the processing technique applied during the production. A range of calcium phosphate phases can be obtained from ADC shells, by using a simple and economic conversion method. Proper cleaning methods developed and appropriate preparation techniques will enable us to use these nano calcium phosphate powders in orthopedic and dental applications.

Nano-Bioceramics Production from Razor Shell

The regeneration potential of human bone is limited in the cases of repairing large bone defects, such as those associated with comminuted fractures or bone tumor resection. In most cases, autogenous and allogenic bones are used as bone grafts. However, the amount of both of them is severely limited. Nowadays, natural biomaterials are in question, like corals, cuttlefish, and various nacre species, or hydroxyapatite (HA) made from egg shells. The present work aims at preparing inexpensive nano-sized HA and whitlockite particles from various raw materials of natural-biological origin. Razor shells (ensis ensis) were collected from beaches of Thessaloniki in Greece. Each sample was reduced to particle size <100 µm and DTA/TG was employed to determine their exact CaCO3 content. The suspended raw powders were put on a hotplate. The temperature was set to 80°C for 15 min. Then, equivalent amount of H3PO4 was added, drop by drop, into the solution. Different Ca/P ratios were tried. The reaction was ultrasonically assisted and continued for 8h. Then, to evaporate the liquid part, the mixture was put into an incubator at 100°C for 24 h and the resulting dried sediment was collected. The morphology of the produced powders was examined by SEM and revealed nano-sized particles. X-ray diffraction analysis indicated various Ca-phosphate phases, i.e. monetite and calcium phosphate hydrate. Thus, razor shells could be an alternative source for calcium phosphate ceramics production. In this study, long nacre shells were converted to various bioceramic structures with simple ultrasonic method without using hydrothermal method, which is carried out in a close vessel heated in a furnace and could cause accident if the vessel is worn. Chemical ultrasonic method is very safe and reliable method for bioceramic production from aragonite structures.

Sintering Effect on Mechanical Properties of Composites Made of Bovine Hydroxyapatite (BHA) and Commercial Inert Glass (CIG)

Composite biomaterials of calcinated bovine bone derived hydroxyapatite (HA) doped with 5 and 10 wt% commercial inert glass (CIG) were prepared by sintering. The production of HA from natural sources satisfies economic and time-saving aims, while the use of CIGs is directed by economic and ecological aspects. The produced composites were subjected to scanning electron microscopy (SEM) and X-ray diffraction analysis. Measurements of compression strength, microhardness, and density were also carried out. The experimental results and their discussion showed that the type and the composition of incorporated glass are of crucial importance. Consequently, provided that an optimum amount of glass is incorporated, the resultant materials can exhibit good values of compression strength and microhardness and hence they can be suggested for potential use in load-bearing biomedical applications.

Tribological Behaviour of Combined Coatings Deposited on Aluminium

In this paper the tribological performance of oxide (Cr2O3, ZrO2CaO and Al203) and combined coatings applied on a commercially pure aluminum sheet were presented. Combined coatings were produced by applying Polytetrafluoroethylene (PTFE) film on the oxide coatings. Among the oxide coatings Cr2O3 exhibited the highest and Al2O3 exhibited the lowest wear resistance, in accordance with their hardness. Combined coatings exhibited superior wear resistance than oxide coatings even at heavy wear testing conditions.