I. Ozdemir

The mechanical response of Al–Si–Mg/SiCp composite: influence of porosity

Abstract The effect of porosity on the mechanical and fracture behaviour in Al–Si matrix alloy and composites reinforced with SiC particles of 10 and 20 vol.% in the as-cast state and after extrusion process has been studied. Matrix alloy and composites were fabricated by compocasting and extrusion. Samples were characterized by optical microscopy, image analyzer, scanning electron microscopy and tensile tests. The results demonstrate that hot extrusion considerably reduces the porosity, while size and distribution of the reinforcement particles are also affected. In the point of fracture behaviour, the existence of large porosity is more effective.

Association between severity of lower urinary tract symptoms, erectile dysfunction and metabolic syndrome

Introduction. The purpose of this study was to investigate the association between severity of lower urinary tract symptoms (LUTS), erectile dysfunction (ED) and metabolic syndrome. Methods. Our study population included a consecutive series of 190 patients with LUTS (International Prostate Symptom Score-IPSS >7) with or without manifestations of the metabolic syndrome. The diagnoses of diabetes mellitus and hypertension were obtained from the patients medical history. Data on blood pressure, waist measure, body height and weight were collected and body mass index were calculated. Patients were assessed based on the International Index of Erectile Function (IIEF) for ED and IPSS and IPSS-Quality of Life for LUTS. Blood samples were drawn from fasting patients to determine, fasting blood glucose (FBG), triglycerides, HDL-cholesterol and serum total testosterone levels. Results. In severe LUTS patient group, IIEF erectile function domain scores were significantly lower than moderate LUTS patient group (p < 0.05). Multiple logistic regression analysis confirmed that presence of ED was the most predictor of severe LUTS. The prevalence of metabolic syndrome was higher in patients with severe LUTS (26%vs. 46%, p = 0.009). The severe form of the LUTS was significantly correlated with waist circumference >102 cm (p < 0.05), blood pressure ≥130/85 mmHg (p < 0.05) and FBG >110 mg/dl (p < 0.01). Conclusion. Obesity, high plasma level of FBG and hypertension constitute risk factors for the development of severe LUTS. Metabolic syndrome may play a key role in the pathogenesis in both ED and LUTS. Presence of ED is the most predictor of severe LUTS.

The effect of forging on the properties of particulate-SiC-reinforced aluminium-alloy composites

Abstract Composites of an aluminium–silicon alloy (Al–5%Si–0.2%Mg) containing different volume fractions of particulate silicon carbide reinforcement and unreinforced matrix alloy samples were produced by the permanent die casting technique. The cast ingots were cut into blanks to be forged in two steps to obtain rectangular plate-shaped samples. At each step of closed-die hot forging approximately 50% reduction in thickness was obtained. The microstructures and mechanical properties of the matrix alloy and the composite samples were investigated in the as-cast state and after the forging operation. The forged microstructures had a more uniform distribution of the SiC particles and the eutectic silicon in comparison to the as-cast microstructures. Evaluation of the mechanical properties showed that the forged samples had strength values superior to those of the as-cast counterparts. After forging, the yield strength of the matrix alloy and composite samples was increased by about 80%, and the improvement in tensile strength was about 40%.The addition of increasing amounts of particulate SiC decreased the ductility and increased the yield and tensile strength up to an optimum reinforcement volume fraction over which a decrease in strength and ductility was obtained.

Microstructures and age hardenability of AL-5%si-0.2%Mg based composites reinforced with particulate SiC

Abstract Composites of an Al-0.5%Si-0.2%Mg alloy reinforced with paniculate SiC have been produced by the compocasting route. The silicon carbide was oxidized at 900 °C for 2 h and mixed into the semi-liquid alloy by means of a special stirrer. The slurry was held at 750 °C for 5 min and cast into a permanent die preheated to different temperatures and composite ingots containing 9, 13, 17, 22, and 26 vol.% SiC were obtained. The distribution of SiC particles, the porosity content and the dendrite arm spacing of the composites were determined. The phases other than the matrix and the reinforcement were identified to be Mg 2 Si, MgAl 2 O 4 and FeSi 3 Al 9 . It was found that the oxidation of SiC and the presence of magnesium in the matrix alloy rendered easy incorporation without causing any significant magnesium depletion in the matrix. It was found that the composites produced were age hardenable. After prolonged exposure to temperatures above 500 °C in the solid state, no formation of additional phases was found to take place in the microstructures.

NiCr coatings on stainless steel by HVOF technique

This paper demonstrates the successful application of NiCr coatings on stainless steel substrates using a high velocity oxy-fuel technique for corrosion applications. We present preliminary results of fabrication and microstructural characterization of NiCr coatings. These coatings were characterized by means of an optical microscope, image analyzer, scanning electron microscope and X-ray diffraction (XRD). A microhardness tester was used in order to determine the mechanical properties of the coating. Microstructural observations pointed out that the NiCr layers possessed porosity, oxidized, unmelted and semimelted particles, and inclusions. XRD results indicated that the outstanding phase of NiCr powder and coating was Ni. It was also found that the microhardness values decreased from the coating to substrate.

Friction and wear properties of Mo coatings on cast-iron substrates

In order to protect machining parts against wear and corrosion in automotive, aerospace, pulp and paper industries, they are coated with Mo-based materials. For these specific applications, Mo coatings were fabricated on cast-iron substrates using an atmospheric plasma-spray system and their friction and wear behavior were evaluated. The Mo coatings were subjected to sliding wear against AISI 303 counter bodies under dry and acid environments. A pin-on-plate type of apparatus was used with normal loads of 49, 89 and 129 N, and sliding speed of 1 Hz. In the steady state, it was demonstrated that the Mo-coated samples under dry conditions had slightly higher wear resistance than under acid conditions tested under a load of 129 N. Several wear failure mechanisms, such as local plastic deformation, cracks, pits, debris, grooves, scratches and tracks, were identified after the tests.

Wear properties of functionally gradient layers on stainless steel substrates for high temperature applications

Abstract Metal substrate components have been coated with functionally gradient coatings (FGCs) to improve thermal barrier properties and heat efficiency of high temperature materials in gas turbine engines, nuclear fusion equipment, diesel engines, jet engines and space shuttles. In this study, functionally graded materials (FGMs), which contain NiCrAl, 75% NiCrAl+25% MgZrO 3 , 50% NiCrAl+50% MgZrO 3 , 25% NiCrAl+75% MgZrO 3 and 100% MgZrO 3 coating layers, have been produced onto stainless steel substrates via an atmospheric plasma-spray technique. The fabricated samples were characterized by means of an optical microscope, scanning electron microscope (SEM), X-ray diffraction and microhardness tester. The wear behaviour of the FGCs was evaluated under dry conditions using a pin-on-plate configuration. The surface morphologies of the FGM samples after wear experiments were examined by SEM. The wear mechanism of the FGCs is discussed based on SEM observation of the worn surface morphologies.

Modelled and measured residual stresses in a bimaterial joint

Abstract A finite element technique has been used to predict residual and thermal stresses due to welding. For this purpose, a steel–brass material couple was chosen and thin plates of the materials were hard brazed. The finite element study was carried out using two-dimensional models. After the temperature distributions as a result of welding were calculated, thermal and residual stress values obtained. Thermo-elasto-plastic formulations using a von-Mises yield criterion with linear isotropic-hardening were employed. For this deformation, the initial stress method was used and the kinematical Bauschinger effect was considered. The authors prepared all calculation programs using FORTRAN 77. To obtain residual stresses that occur during the welding, the hole-drilling strain-gage method was chosen and conducted in accordance with the ASTM Standard E 837-99. The agreement between the calculated results and the experimental data shows that the finite element analysis method is reliable.

Effects on performance of Cr2O3 layers produced on Mo/cast-iron materials

Abstract The principle aim of this paper is to investigate effects on performance of protective multilayer coatings with Cr 2 O 3 /Mo/cast iron architecture in order to use in an internal combustion engines. With this regard, Cr 2 O 3 powders were deposited on Mo coated cast iron substrates using an atmospheric plasma spray system. The coated samples were characterized by means of an optical microscope, image analyzer (LUCIA), scanning electron microscope (SEM) and X-ray diffraction. Mechanical properties of the multilayers were determined by using standard and dynamic ultra microhardness machines. Wear tests were conducted with the Cr 2 O 3 /Mo and Mo coated cast iron substrates at 89 N under dry sliding conditions through a pin-on-plate arrangement against AISI 303L steel counterbody. The microstructural analysis of worn surfaces were examined by SEM. Thermal behavior of the Cr 2 O 3 /Mo coatings was scrutinized using a thermal cyclic machine without external load. The microstructural observations showed that the multilayers contain some inhomogeneities such as porosity, crack-like defects, unmelted particles, oxides and inclusions. The structures with the inhomogeneities strongly influenced their mechanical, wear/friction and thermal properties. It was also found that Cr 2 O 3 layer significantly increased the performance of Mo coated cast iron substrate as a protective layer.

Plasma sprayed cast iron coatings containing solid lubricant graphite and h-BN structure

Water-atomized cast iron powder of Fe-2.17 at.%C-9.93at.%Si-3.75at.%Al were deposited onto an aluminum alloy substrate by atmospheric direct current plasma spraying to improve its tribological properties. Preannealing of the cast iron powder allows the precipitation of considerable amounts of graphite structure in the powder. However, significant reduction in graphitized carbon in cast iron coatings is inevitable after plasma spraying in air atmosphere due to the in-flight burning and dissolution into molten iron droplets. Hexagonal boron nitride (h-BN) powders, which have excellent lubricating properties like graphite, were incorporated into the cast iron powder as a solid lubricant by the sintering process (1300°C) to obtain protective coatings with a low friction coefficient. The performance of each coating was evaluated using a ring-on-disk-type wear tester under a paraffin-based oil condition in an air atmosphere. A conventional cast iron liner, which had a flaky graphite embedded in the pearlitic matrix, was also tested under similar conditions for comparison. Sections of worn surfaces and debris were characterized, and the wear behavior of plasma-sprayed coatings was discussed.