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In this work, the microstructure of titania coating fabricated on the surface of hydrostatically extruded titanium grade 4 with the use of the micro-arc oxidation method was studied. The surface topography and microstructure investigations performed with atomic force microscopy and scanning and transmission electron microscopy revealed that, by using an Na2HPO4 electrolyte, a well-adherent porous coating is produced on the top surface and side walls of the extruded rod. The distribution of chemical elements was analyzed by using energy dispersive X-ray spectroscopy. The chemical elements dissolved in the electrolyte i.e. (Na, P and O) incorporated into the coating. Sodium locates preferentially in the outer part of the coating, while phosphorus and oxygen are distributed throughout the whole coating. The most relevant finding shows that a grain refinement caused by a hydrostatic extrusion provoked an increase in density of high-angle grain boundaries (HAGB), which in turn secured the formation of a continuous amorphous layer close to the substrate. The presence of this layer compensates for the effect of anisotropic substrate, producing a comparable and homogenous microstructure with a large number of micropores.

Electron beam surface melting has been applied as a posttreatment to plasma-transferred, arc-deposited Stellite 6 hardfacing and its molybdenum-alloyed version. Molybdenum addition increase...

This work has been initiated with the aim of increasing the success of micro-arc oxidation coatings fabricated on aluminium alloys against degradation under sliding contact conditions at high temperatures. For this purpose, the 7075 Al alloy has been micro-arc oxidised in an aluminate-based electrolyte with or without the adding monoclinic ZrO2 particles. Microstructural analyses revealed that the coating synthesised in a ZrO2-added electrolyte consisted of a ZrO2 particles participated Al2O3-based outer layer and a monolithic Al2O3-based inner layer, which exhibited similar features with that of the synthesised in the ZrO2-free aluminate-based electrolyte. Moreover, the coating fabricated in the ZrO2-added electrolyte exhibited enhanced wear resistance during the dry sliding wear tests conducted at room temperature and had higher durability during the tests done at 300 degrees C. Since the examined coatings were worn by fatigue wear mechanism, their durability during high temperature wear tests was analysed by using the conventional stress-based fatigue approach. From the derived equations, the maximum contact pressures at which coatings can endure 106 contact cycles at 300 degrees C were estimated as 851 and 331 MPa for the coatings fabricated in the ZrO2-added and ZrO2-free aluminate-based electrolytes, respectively.

Tento článek si klade za cíl porozumět mikrostrukturním změnám v Plasma Transfer Arc (PTA) naneseném tvrdokovem z vysokorychlostní oceli (HSS) M2 po zabudování 10% hmotn. Mo legování během nanášení s následným tavením laserového povrchu. Tvrdé povrchové úpravy uložené PTA byly vyrobeny na 4140 oceli. Potom byly Mo legované a nelegované PTA depozity podrobeny procesu laserového povrchového tavení (LSM). U všech výsledných struktur byla provedena komplexní mikrostrukturální charakterizace. Ke zjištění struktury matrice a morfologie karbidů byla použita optická metalografie s použitím vhodných leptacích činidel a SEM mikroskopie ve spojení s technikami XRD. Mikrostruktura PTA byla blízká rovnovážné struktuře M2 HSS obsahující směs feritu / austenitu / martenzitu spolu skarbidy typu MC, M2C a M6C. Zatímco LSM M2 HSS způsobil vyšší podíl martenzitu a jemnějších zrn ve struktuře, což mělo za následek zvýšení tvrdosti. Přidání 10% hmotn. Mo mění karbidy z MC a prutů jako M2C na vláknité M2C a rybí kosti jako M6C. LSM depozit M2 HSS PTA legovaných Mo vedlo k celkovému snížení podílu karbidů M6C a vláknitých karbidů M2C doprovázených poklesem tvrdosti. The article aims to comprehend the microstructural changes, in Plasma Transfer Arc (PTA) deposited M2 high speed steel (HSS) hardfacings upon incorporation of 10wt% Mo alloying during deposition followed by laser surface melting. PTA deposited hardfacings were produced over 4140 steel. Then Mo alloyed and unalloyed PTA deposits were subjected to laser surface melting (LSM) process. A comprehensive microstructural characterization for all the resultant structures was carried out. Optical metallography using appropriate etching reagents and SEM microscopy in conjunction with XRD techniques were employed to ascertain the matrix structure and carbides morphology. The PTA microstructure was close to equilibrium structure of M2 HSS containing mixture of ferrite / austenite / martensite along with MC, M2C and M6C type carbides. While the LSM of M2 HSS caused higher fraction of martensite and finer grains in the structure resulting in increment in hardness. 10-wt% Mo addition changes the carbides from MC and rod like M2C to fibrous M2C and fishbone like M6C carbides. The LSM of Mo alloyed M2 HSS PTA deposits led to an overall decrease in the fraction of M6C carbides and fibrous M2C carbides accompanied by a decrease in hardness.

Aluminum doped zinc oxide (ZnO:Al) thin films via 1.2 at. % Al content was deposited on p-type silicon wafers by using sol-gel dip coating technique to compare the effect of post treatment ambient on electrical characteristics of ZnO:Al/p-Si heterojunction. The annealing environment treatment was performed at 700 °C for 60 min under various gas ambients such as, air, argon, nitrogen, and vacuum. The deposited heterojunction samples were characterised in order to clarified its morphology and crystalline structure. The films showed an orientation along c-axis and the best electrical properties (0.75 × 10 −4 Ω cm) were obtained for the sample prepared in vacum. The changes in electrical properties and current-voltage performance were compared with each other after p-n junction was annealed under different ambient conditions. The heterojunction electrical parameters were determined Therefore, it was possible to make an annealing ambient comparison of the heterojunction for the cost-effect production by using sol-gel dip coating technique to use as the diode in electronic devices.

This study focuses on the surface modification of a medical grade Co-Cr alloy via combining cold spray and thermal oxidation processes. After deposition of a Ti96-Al4 (wt.%) coating, samples were oxidized at 600 degrees C for 60h in air. Oxidation transformed the coating into a dual-layered structure comprising an outer oxide layer (mainly rutile) with a diffusion layer (mainly oxygen enriched titanium and Ti-Al intermetallics) beneath it. Formation of new phases made the diffusion layer brittle and prone to fracture during pull out tests. Scratch and Rockwell-C tests confirmed good adhesion between the oxide and underlying diffusion layers, having average hardness as 1297 HV and 387 HV, respectively. The dual-layer coating exhibited excellent wear performance in a 0.9wt.% NaCl solution against sliding action of alumina ball as compared to Co-Cr substrate, especially at contact pressures

This study focuses on the biological properties of Ti6Al4V after employing micro-arc oxidation in sodium phosphate- and calcium acetate-containing electrolyte with and without addition of silver acetate. After micro-arc oxidation process, structural features of the surfaces were analyzed by using an energy dispersive X-ray spectrometer equipped scanning electron microscope, an X-ray diffractometer and a Fourier transform infrared spectroscope. The micro-arc oxidation process generated multilayer coatings composed of carbonated hydroxyapatite and titanium oxide layers, while addition of 0·001 mol/l silver acetate into the electrolyte caused incorporation of 0·7 wt.% silver into the coating. The antibacterial activity of the coatings was analyzed by using the Streptococcus mutans American Type Culture Collection 25175 strain. The metabolic activity of the multilayers was evaluated in cultures of a human primary osteogenic sarcoma cell line (Saos-2). In short, incorporation of 0·7 wt.% silver in the form of agglomerated particles, mostly around the micropores of the titanium oxide layer, enhanced the antibacterial efficiency of the fabricated coating to some extent without altering the cell proliferation considerably.

Vliv legování (10 wt% Mo) a následného zpracování povrchu (laserové přetavení povrchu) na vlastnosti a chování byl hodnocen u PTA návaru oceli M2. Vlivem legování Mo došlo ke změně charaketru a povahy jak matrice, tak karbidů v povlaku M2. Naopak, laserové zpracování vedlo ke zjemnění struktury a potalčení precipitace karbidických částic. Navzdory zvýšení povrchové trvrdosti vykazoval povlak po laserovém zpracování pokles odolnosti proti opotřebení. Naopak, návar legovaný Mo zlepšil odolnost proti opotřebení, ačkoli jeho tvrdost poklesla. Důvodem byla tvorba oxidického tribofilmu typu Magneli v Mo legované oceli. The influence of alloying (10 wt% Molybdenum) and post deposition treatment (Laser Surface Melting) on the structural characteristics and wear performance of Plasma Transfer Arc deposited M2 hardfacings have been investigated. The nature of matrix and carbides of M2 hardfacing had changed upon Molybdenum addition while the Laser Surface Melting caused structural refinement and a decrease in carbide volume fraction. Despite an increase in hardness, Laser Surface Melting has resulted in reduction in sliding wear resistance against alumina counterface, while the Molybdenum enhanced the wear resistance even with decrease in hardness. This counter intuitive behaviour is attributed to Magnelli oxide containing tribo-oxide layer formation on the worn surface of Molybdenum alloyed hardfacings.

Laser surface melting (LSM) process has been applied on the plasma transferred arc (PTA) deposited Stellite 12 and 10 wt% Mo alloyed Stellite 12 in this study. Following the LSM process, structural and mechanical property comparison of the LSM’ed surfaces has been made. Hardness of the LSM’ed surfaces was measured as 549 HV and 623 HV for the Stellite 12 and Stellite 12 + 10 wt% Mo deposits, respectively. Despite their different hardness and structural features, the LSM’ed surfaces exhibited similar tribological performance at room temperature (RT), where fatigue wear mechanism operates. However, the wear at 500 °C promotes tribo-oxide layer formation whose composition depended on the alloying with Mo. Thus, addition of 10 wt% Mo into Stellite 12 PTA deposit has remarkably enhanced the high temperature wear performance of the LSM’ed surface as a result of participation of complex oxide (CoMoO4) in tribo-oxide layer.

Aiming at additional improvements in the properties of Stellite 12 PTA hardfacing alloy deposited on 4140 steel substrate, the authors have adopted a dual approach. During PTA deposition Stellite 12 hardfacing powder was alloyed with 10 wt-% Mo, followed by laser surface melting (LSM). Addition of 10 wt-% Mo, led to an increase in the volume fraction of Co and W-rich complex carbides. Later on LSM executed on the PTA led to the development of unique microstructure near the surface, characterised by the segregation of hard Cr-rich carbides. The resultant layers were subjected to mechanical characterisation, at room temperature, e.g. hardness and wear resistance. It was concluded that combining both approaches i.e. addition of Mo during the hardfacing process followed by LSM of deposited layer gave additional improvements in mechanical properties owing to evolution of a unique carbide structure.

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.

Micro-arc oxidation is a simple, single-step surface modification method used to produce coatings on titanium alloys for biomedical applications. The formation and properties of coatings can be widely controlled by adjusting process parameters such as applied voltage, frequency, processing time and electrolyte composition. In the present study, three different electrolytes were used to obtain well adherent, rough, porous, hydroxyapatite containing, oxide coating on Ti6Al7Nb alloy. Coatings were investigated in terms of their microstructure, chemical composition, roughness, hardness, adhesion strength and biocompatibility. Among the coatings produced in different electrolytes, one of them exhibited both good mechanical properties and bioactivity, while containing crystalline hydroxyapatite on the surface, whereas the other two coatings were mostly amorphous. Thereby, we have proposed an efficient electrolyte containing calcium and phosphorous species in order to modify titanium based alloys to improve their biocompatibility and osseointegration. Such properties are achieved by formation of a rough outer layer with open pores, providing high surface area for cells to adhere, proliferate and migrate into the coating, promoting firm anchorage of the coated implant in the bone.

This study compares the tribological behaviour, of cold sprayed (CS’ed), SiC particle (SiCp) reinforced Al-12Si matrix composite coatings deposited on 1050 grade aluminium, in two different testing environments (dry and water). The increase in hardness with incorporation of SiCp caused the coatings to exhibit lower wear rate and friction coefficient in both testing environments. As an indication of water lubricity, sliding in water imposed superior tribological performance (i.e. lower wear rate and lower friction coefficient) as compared to the dry sliding condition especially at lower wear testing load. In summary, finding of this study revealed that, water could be a promising lubricant for metallic engineering components after coating with SiCp reinforced Al-12Si matrix composites by CS process.

In this study, structural characteristics and tribological performance of the coatings deposited on a 1050 quality aluminium substrate by cold spraying of the feedstock consisting of 100% Al–12Si and 25 vol.% SiC + 75 vol.% Al–12Si powders were examined. Wear tests were conducted in air and in water against alumina ball under loads of 1 and 5 N by a reciprocating wear tester at room temperature. Presence of SiC particles in the structure enhanced the wear resistance of the Al–12Si coating both in air and water. As compared to the air testing condition, water containing media provided better tribological performance especially at the wear test load of 1 N. The findings of this study revealed potentiality of water to be used as a lubricant for SiC-reinforced Al–12Si matrix cold spray composite coatings at relatively low wear test loads.

Multi-layer coatings (composed of outer hydroxyapatite and inner titania layers) have been synthesized on Ti6Al4V alloy for biomedical applications by employing micro-arc oxidation at positive and negative voltages of 400 and 80, respectively. Addition of silver nitrate (at concentrations of 0.1 g/L and 0.4 g/L) into the calcium acetate hydrate and disodium hydrogen phosphate anhydrous containing base electrolyte provided an enhancement in bio- and antibacterial activities of the synthesized coating, while imposing precipitation of silver nanoparticles on the hydroxyapatite layer. It is finally concluded that addition of 0.1 g/L AgNO 3 into the base electrolyte is promising for MAO process of titanium-based implants, when the structural characteristics and risk of cytotoxicity are of concern for the synthesized multi-layer coatings.

This study reports on the consolidation of niobium boride powders by cold pressing/pressureless sintering (PS, with or without Co addition) and spark plasma sintering (SPS) techniques. Niobium boride powders (containing NbB, Nb3B4 and NbB2 phases) which were mechanochemically synthesized from Nb2O5, B2O3 and Mg blends and purified by HCl leaching were used as precursor material. The effects of different sintering techniques on the consolidation behaviour, microstructure, densification rate and mechanical properties (microhardness, wear characteristics, elastic modulus, indentation response and fracture toughness) of the bulk products were investigated. PS with Co addition resulted in superior properties than those yielded after PS without Co addition and SPS. Bulk niobium boride products having relative density of 93-98%, microhardness of 24-28 GPa, wear volume loss of 2.8-4.5 x 10(-4) mm(3), elastic modulus of 508-552 GPa and fracture toughness of 4.05-4.74 MPa m(1/2) were obtained by Co (2 or 5 wt.%) activated PS at 1500 degrees C., Scientific and Technological Research Council of Turkey (TÜBİTAK)

This work examines the role of counterface materials on the tribological behaviour of Mg alloys subjected to plasma electrolytic oxidation (PEO) process and focuses on reducing the sliding coefficient of friction (COF) values of PEO treated surfaces. Surfaces of AZ31 grade Mg alloy were subjected to a PEO treatment in a sodium metasilicate and potassium hydroxide containing electrolyte. Unlubricated sliding wear tests were conducted using counterfaces made of nitride based (N-based), TiN, TiCN, CrN and hydrogenated diamond-like carbon (H-DLC) coated as well as uncoated SAE 52100 grade bearing steel balls. MgO based coatings formed on the surfaces of samples during PEO process increased the wear resistance of AZ31, regardless of the type of counterface material used. Sliding the PEO treated surfaces against counterfaces made of uncoated steel and N-based coatings yielded high COF values of 0.6–0.8 that exceeded those of the uncoated AZ31 against the same counterfaces. During dry sliding of H-DLC counterface on the MgO coating, smooth and stable friction curves with a low steady state COF value of 0.13, were recorded. Therefore, a major drawback of PEO treatment that gives rise to surfaces with high COF could be addressed by running them against H-DLC coated counterfaces, a method that could be applied to development lightweight tribological components that are both sliding wear resistant and have low COF.

This study was initiated with the aim of extending the usage of magnesium alloys especially in corrosion and wear related engineering applications by coating their surfaces via micro arc oxidation (MAO). Considering the individual influence of phosphate-based and aluminate-based electrolytes on the corrosion and wear performances of the synthesized MAO coatings, respectively, AZ91 magnesium alloy has been subjected to MAO in aluminate-based reference electrolyte with and without additions of Na3PO4 at concentrations of 5 and 10 g/l. As opposed to dry sliding conditions, MAO coatings synthesized in the aluminate-based reference electrolyte did not provide good protection of AZ91 magnesium alloy against wear in corrosive media (0.9 wt% NaCl solution). This study revealed that, addition of 5 g/l Na3PO4 into this reference electrolyte was sufficient for enhanced resistance of MAO coating against chemical and mechanical degradations (i.e. corrosion-wear) without altering its features in terms of surface roughness and thickness.

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/substrat...

In this paper, diffusional surface hardening processes utilized to overcome the poor tribological performance of titanium and its alloys is briefly introduced. More specifically, surface treatments known as thermal oxidation, nitriding and boriding offering the advantage of producing graded surfaces comprising hard compound layer and diffusion zone by diffusion of interstitial atoms (oxygen, nitrogen and boron) are overviewed.

The ZnO:Al thin films were exposed to beta radiation at 0.65 kGy absorbed dose level using a Sr-90 radioisotope after the thin films derived by sol gel dip coating technique were annealed in the argon at 700 °C. The optical changes in the thin film were determined for the unirradiated and the irradiated states at four different Al concentrations (0.8, 1.0, 1.2 and 1.6 at.%). There was a relation between brightness and light reflectance in the ZnO:Al thin film. The characterization of the colour parameters was specified for the unirradiated and the irradiated states according to the standardization concept. Beta irradiation caused to changes in the electrical resistivity, the light absorbance, the brightness and the colour parameters with the slight variations of the grain height on surface of the film. The absorbed dose caused a slight decrease in the grain height of the ZnO:Al thin film after the irradiation. Besides, the surface roughness of the irradiated film increased slowly as the result of the agglomeration tendency on the surface of the film.

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 (4.6 wt.%) into the multi-layer coating during micro-arc oxidation process imposed superior antibacterial efficiency without sacrificing the bioactivity. (C) 2014 Elsevier B.V. All rights reserved.

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 99.8% against Staphylococcus aureus (S. aureus). Detailed examination revealed that the presence of 0.01 mol L-1 AgC2H3O2 in the electrolyte resulted in incorporation of 1.4 wt-% Ag into fabricated coating consisting mainly of outer hydroxyapatite (HA) and inner titanium oxide (TiO2) layers. In comparison to the Ag-free coating, 1.4 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.

Magnesium alloys are attractive materials for reducing the weight of the engineering components. Despite their high strength to weight ratio, poor corrosion and wear performances limit their extensive usage. In this respect, improvement of their wear and corrosion resistance by coating processes is a necessity for magnesium alloys. In this study, the wear and corrosion performances of AZ91D magnesium alloy have been examined after magnesia and alumina coatings. While micro arc oxidation (MAO) process was applied to generate a magnesia layer, cold spraying (CS) and MAO processes were combined to obtain novel alumina layer. CS was conducted to cover the substrate by depositing an aluminum layer (monolithic or composite). Afterwards, application of the MAO process produced an alumina layer on the deposited aluminum layer (monolithic or composite) forming a multi-layered coating on the examined magnesium alloy. Results of the experiments revealed that the alumina layer formed on the alumina reinforced aluminum matrix composite layer ensured superior protection for AZ91D alloy against mechanical and chemical degradations as compared to the magnesia layer.

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.

Commercial purity titanium samples were gas nitrided for 3, 5, 7 and 12 h at 1250°C. TiN layers with nitrogen diffusion zones were formed on the surfaces, which caused an increase in the surface hardness with respect to the processing time. In addition, nitriding provided a reduction in friction coefficient and an enhancement in wear resistance against an alumina ball under dry sliding conditions.

A ceramic composite constituting the formula 78 wt% WC–16 wt% TiC–6 wt% Co denoted as the 78WC–16TiC–6Co ceramic composite was fabricated using a powder metallurgy process, by utilising commercially available WC and Co powders, and laboratory produced TiC powders. TiC powders were produced from machining chips of Grade 4 Titanium. Five different procedures were followed for the manufacturing process by altering the amount of the binding agent (stearic acid) and/or compacting pressure and/or sintering regime (temperature and time) and/or mixing process (dry mixing and mechanical alloying). Characterisation investigations conducted on the sintered samples revealed that stearic acid as the binding agent resulted in the decrease of the relative density while mechanical alloying (MA) induced finer microstructures. The 78WC–16TiC–6Co composites manufactured from commercially available and laboratory produced TiC powders using similar process procedures (including MA) exhibited similar characteristics in terms of relative density, hardness, and wear performance.

Samples of a Ti6Al4V alloy were treated by thermochemical gas nitriding at 1120°C for 7 h. Gas nitriding provided formation of titanium nitride layer with a hardness over 1800 HV. The titanium nitride layer exhibited excellent wear resistance along with a lower coefficient of friction against alumina ball under dry sliding conditions when compared to the as-received state.

This study focuses on tribological performance of as-received and borided Ti6Al4V alloys against ceramic counterfaces (Al2O3 and Si3N4 balls) in water. The wear mode of the alloy changed from ploughing to polishing by achieving a remarkable reduction in wear loss upon boriding. On the borided surface, the destructive action of the Si3N4 ball was very limited, when compared to that of the Al2O3 ball.

AZ91 Mg alloy was subjected to the micro arc oxidation process by using different processing parameters. Following oxidation, surface topography and qualitative phase analysis were made by tabletop digital microscopy and X-ray diffraction (XRD) analysis. In order to evaluate the relative corrosion resistance of the samples that were oxidized in different parameters, the samples were immersed in a corrosive solution for 6 days and the weight losses before and after the corrosion tests were compared. Relative corrosion resistance of the samples was evaluated on the basis of surface topography.

Gas nitriding of a commercial purity Grade 4 titanium at 1120°C for 5 h formed hard TiN layer (2450 HV) on the surface with a thickness of about 35 m. When compared to the as-received state, nitrided titanium exhibited excellent wear resistance along with a relatively low coefficient of friction (CoF) against Al2O3 ball under dry sliding conditions.

Air oxidation behavior of a Ti6Al7Nb alloy was examined over the temperature range of 873 –1173 K for different time intervals ranging in between 12 and 72 h. The rate of oxidation evaluated according to the weight gain measurements, fitted parabolic kinetics by yielding oxidation activation energy of 226 kJ/mol. Rutile and anatase modifications of TiO2 formed on the surface as the result of air oxidation. Oxidation temperatures higher than 923 K encouraged rutile formation rather than anatase. As temperature of oxidation was increased, the thickness of the oxide layer increased. Thicker oxide layer provided higher surface hardness and better protection against a corrosive media (5 M HCl solution) was provided.

Air oxidation behaviour of a Ti–6Al–4V alloy was examined over the temperature range of 600–800 °C for different time intervals ranging between 0.5 and 72 h. In addition to the determination of the oxidation kinetics by weight gain measurements, oxygen diffusion zone (ODZ) depth and hardness measurements were conducted on the cross-sections of the oxidised alloys to investigate the diffusion kinetics of oxygen into the substrate. The rate of oxidation evaluated according to the weight gain measurements fitted parabolic kinetics between 600 and 700 °C and linear kinetics above 700 °C by yielding activation energies of 276 and 191 kJ/mol, respectively. Analysis of the ODZ depth and hardness measurements resulted in an activation energy of 202 kJ/mol for oxygen diffusion in Ti–6Al–4V alloy. Finally, the kinetics of oxidation and oxygen diffusion were evaluated by the analysis of the experimental data with respect to temperature-compensated time parameter.

The effect of retrogression and reaging (RRA) treatment on the hardness and stress corrosion cracking (SCC) susceptibility of 7075 aluminum alloy sheets was systematically investigated. The material in its as-received T6-temper state was retrogressed at 170 °C, 220 °C, 240 °C, and 380 °C for different durations between 15 seconds and 60 minutes. Subsequent reaging was performed at the T6 aging condition (120 °C for 24 hours). RRA-treated alloys exhibited a better combination of hardness and SCC resistance than the T6-temper state when retrogressed between 170 °C and 240 °C for short durations. However, a retrogression temperature of 380 °C resulted in considerable reduction in both hardness and SCC resistance. Among retrogression temperatures employed, 170 °C provided an optimum combination of hardness and SCC resistance, corresponding to 20 pct improvement in hardness and 85 pct improvement in SCC resistance. In this article, improvements in hardness and SCC resistance of 7075 alloy upon RRA treatment are discussed.

Tribological behavior of squeeze cast aluminum alloy (2618, 6082, 7012 and 7075) matrix SiC particle-reinforced (50 vol.%) composites was examined using a reciprocating wear tester by rubbing a 10 mm diameter Al 2 O 3 ball on the composite surfaces in air and in water. Wear tests conducted in air revealed that, at low test loads (≤3 N), the tribological performance of the composites were not remarkably influenced by the properties of the matrix alloy. At high test loads (≥4.5 N), where 7012 and 7075 aluminum alloy matrix composites exhibited superior tribological performance relative to 2618 and 6082 aluminum alloy matrix composites, the wear rate and coefficient of friction decreased with increasing matrix hardness. When compared to the sliding conditions during testing in air, the coefficient of friction and the wear rate of the composites were dramatically lower in water. Even at test loads as high as 24 N, tribological performance of composites tested in water was comparable to that of in air low load (≤4.5 N) testing conditions.

This study gives some information about the preparation of Glycidyl Methacrylate (GMA) microcapsules with Melamine Formaldehyde (MF) resin as a shell material (MF-GMA). Melamine formaldehyde resin containing hydroxyl groups was synthesized in the first step. Second step includes the addition of GMA monomer along with Sodium Dodecyl Benzenesulfonate (SDBS) and Polyvinyl Alcohol (PVA) aqueous solution for getting emulsible solution. The resultant MF-GMA microcapsules had good enclosing performance and thermal stability. The characteristic properties and the morphology of microencapsulated Glycidyl Methacrylate were examined by using FTIR analysis and their morphology was investigated by using optical microscope.

This study has been conducted to investigate the mechanical properties of aluminum matrix 50 vol.% SiC particle (SiCp) reinforced composites produced by a squeeze casting technique. Commercial 2618, 6082, and 7012 aluminum alloys were utilized as the matrix material. Composites were tested in as-cast and T6-tempered states. Mechanical properties of the composites were determined by hardness measurements and impact tests. As-cast composites exhibited lower hardness along with a better impact resistance than their T6-tempered states. After T6-tempering the hardness of 7012 matrix composite reached to a value of 324 HV2, which is comparable with the hardness of quenched and tempered steels.

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.

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.

In this study, the effect of cold working on the recrystallization and thermal oxidation behaviours of Grade 2 quality commercial purity titanium (CP-Ti) were examined. Recrystallization tests were carried out on the 23%, 35% and 50% cold worked samples at various temperatures in between 550 and 700 °C. Thermal oxidation of the cold worked samples was conducted at 600 and 650 °C. Recrystallization activation energy was calculated as 66–88 kJ/mol. Since thermal oxidation progresses by oxide layer growth and diffusion of oxygen into the substrate (oxygen diffusion zone formation), oxygen diffusion zone formation activation energies of 149–170 kJ/mol were calculated for the examined cold work ratios. These results indicate that when a cold worked CP-Ti was subjected to thermal oxidation treatment to improve its surface hardness and wear resistance, it loses its bulk hardness due to recrystallization.

In this study dry sliding and corrosion wear resistances and cavitation erosion–corrosion (CEC) behavior of T6 and “Retrogression and Reaging (RRA)” treated 7039 aluminum alloys were compared. Dry sliding wear performance of the alloy was examined in normal atmospheric conditions. CEC and corrosion wear tests were conducted in a “30 g/l NaCl+10 ml/l HCl” solution. The experimental results showed that the RRA treatment considerably improved the resistance of 7039 aluminum alloy to CEC and dry sliding wear. The RRA treated alloy exhibited lower corrosive wear resistance than the T6 treated alloy.

In this study, the effect of retrogression and reaging (RRA) treatment on dry sliding and corrosive wear properties of 7075 aluminum alloy, which was received originally in the T6 temper condition, has been investigated. Retrogression was carried out at four different temperatures between 170 and 380 °C for 60 s. Following the retrogression, alloys were reaged at 120 °C for 24 h. Wear tests were conducted on a ball-on-disc-type wear tester by rubbing Al 2 O 3 balls against the surfaces of the alloys. Corrosive wear tests were carried out in a 30 g/l NaCl+10 g/l HCl solution. Retrogression at 220 and 240 °C improved the dry sliding wear resistance when compared to the T6 temper. However, RRA-treated alloys exhibited higher corrosive wear rate than that of the T6-tempered alloy. Worn surface examinations revealed the wear mechanisms as adhesion for the dry sliding wear and abrasion for the corrosive wear.

In the present investigation, recrystallization of Grade-2 quality commercial purity titanium (CP-Ti) has been studied. CP-Ti was received as 4 mm thick plate having hardness of 202 HV0.3. Upon rolling about 55, 70 and 85 % at room temperature, the hardness increased to 268, 276 and 283 HV0.3, respectively. Cold rolled samples were then subjected to isothermal annealing in salt bath at 550-700°C. After measuring hardness, recrystallization curves were plotted for each annealing temperature. Recovery region was not clearly visible on the recrystallization curves. Heavily cold worked samples were soften rapidly and reached to the grain growth region at shorter annealing times. According to Arrhenius plot, recrystallization activation energy of CP-Ti was calculated in between 89,5 and 78,6 kJ/mol. The higher the cold working, the lower is the recrystallization activation energy.

In this study, comparative investigation of thermal oxidation treatment for Ti-6Al-4V was carried out to determine the optimum oxidation conditions for further evaluation of corrosion-wear performance. Characterization of modified surface layers was made by means of microscopic examinations, hardness measurements and X-ray diffraction analysis. Optimum oxidation condition was determined according to the results of accelerated corrosion tests made in 5m HCl solution The examined Ti-6Al-4V alloy exhibited excellent resistance to corrosion after oxidation at 600 degrees C for 60 h. This oxidation condition achieved 25 times higher wear resistance than the untreated alloy during reciprocating wear test conducted in a 0.9% NaCl solution.

WOS: 000184340800017, In this study, dry sliding and abrasive wear behaviour of Al - 70 vol.-%Al2O3 particulate composite alloyed with Mg was examined. The composites were produced by a pressure infiltration casting technique. The composition of the matrix varied between 0 and 8 wt-%Mg, and the diameter of the Al2O3 particulates was 60 mum. Dry sliding wear tests were carried out on an unlubricated M2 quality high speed tool steel disc by a pin on disc type wear tester. Abrasive wear tests were run by rubbing the composites on abrasive Al2O3 grains. The results of the wear tests revealed that, both dry sliding and abrasive wear resistance of the composites increased with increasing Mg content in the matrix. MST/5421 Mr Ahlatci. Mr Karakas and Professor Dr Cimenoglu are in the Department of Metallurgical and Materials Engineering, Istanbul Technical University, 34469 Maslak, Istanbul, Turkey (heimen@itu.edu.tr). Associate Professor Candan is in the Technical Education Faculty, Division of Metal Casting, Zonguldak Karaehnas University 78100 Karabuk, Turkey. Manuscript received 4 February 2002: accepted 27 August 2002. (C) 2003 IOM Communications Ltd. Published by Maney, for the Institute of Materials, Minerals and Mining.

ZnO:Al/p-Si heterojunctions were fabricated by solgel dip coating technique onto p-type Si wafer substrates. Al-doped zinc oxide (ZnO:Al) thin film on p-Si wafer was irradiated by reactor neutrons at ITU TRIGA Mark-II nuclear reactor. Neutron irradiation was performed with neutron/gamma ratio at 1.44 × 104 (n cm−2 s−1 mR−1). The effect of neutron irradiation on the electrical characteristics of the ZnO:Al thin film was evaluated by means of current–voltage (I–V) characteristics for the unirradiated and the irradiated states. For this purpose, the changes of I–V characteristics of the unirradiated ZnO:Al thin films were compared with the irradiated ZnO:Al by reactor neutrons. The irradiated thin ZnO:Al film cell structure is appropriate for the usage of solar cell material which is promising energy material.

The addition of 10 wt% Mo encouraged a eutectic reaction to form Co6Mo6C complex carbide and Co3Mo intermetallic in addition to Cr23C6 while causing solid solution hardening of the Co-rich dendritic matrix in the microstructure of the PTA deposited Stellite 12 coating. The addition of molybdenum not only imposed a higher hardness but also enhanced wear resistance. Under oxidation dominated wear conditions (500 and 700 degrees C), the addition of molybdenum provided a remarkable increase in wear resistance in comparison to the lower temperatures (RT and 300 degrees C), due to the development of a protective oxide film on the worn surface. (C) 2015 Elsevier Ltd. All rights reserved.