Umit Cocen

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.

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.

The production of AlSi alloy-SiCp composites via compocasting: some microstructural aspects

Abstract Aluminium silicon alloy (Al-5%Si-0.2%Mg) based composites containing different volume fractions of reinforcing SiC particles are produced using the compocasting route. The particles of SiC were incorporated by a special stirrer and the slurry was poured into a permanent die of certain dimensions, preheated to various temperatures, in order to obtain different cooling rates during the solidification of the composite ingots. The microstructural characteristics such as dendrite arm spacing, SiC particle distribution, porosity and phases present in the microstructures of the composites were investigated by using light microscope, scanning electron microscope with microprobe attachment and X-ray diffractometer. High incorporation levels were obtained by using reasonably short mixing times. The ingots cast into moulds having temperatures of 80°C and below showed homogeneous SiC particle distribution. The samples with SiC volume fraction lower than 17% contained little porosity, and no formation of harmful Al4C3 was observed in any of the samples produced.

Squeeze Casting of Ni Coated SiC Particle Reinforced Al Based Composite

An investigation was carried out on the production of electroless Ni coated 20vol% SiC particle reinforced composite by squeeze casting. The morphology of the coating, microstructural, interfacial, and mechanical properties of the composite were characterized by using an optical microscope, image analyzer, scanning electron microscope (SEM), energy dispersion spectrometer (EDS), and X-ray diffractometer (XRD). The evaluation of microstructure shows that the matrix phase exhibits a pore-free and dentritic structure, and particle segregation. Interfacial examinations indicate that electroless nickel coating has not degraded during the fabrication process and prevent the formation of Al4C3.

An Investigation of the Effect of SiC Reinforcement Coating on the Wettability of Al/SiC System

In this study, the wetting behavior of oxide and metallic coated SiC substrate with Al—Si—Mg alloy has been investigated. SiC substrate and particles were coated with SiO2, TiO2, and metallic Ni by using thermo-chemical treatment, sol-gel and electroless coating techniques, respectively. Also, the effect of doping elements (Ni, Cu and Fe in TiO2 coating) on the wettability has been investigated. Coatings were characterized by SEM, EDS, XRD, and by means of surface roughness. Contact angle results demonstrate that metallic Ni coating significantly improves the wettability. However, doping elements did not alter the results due to their detrimental effect on surface roughness.

The Effect of Si and Mg on Age Hardening Behavior of Al-SiCp Composites

An investigation was carried out to determine the effect of Si and Mg on ageing behavior of Al-7%Si-0.7%Mg matrix composites reinforced with SiC particles of 10 and 20 vol.% and unreinforced matrix alloy. The samples were produced by compocasting technique and extruded. The produced samples were characterized by optical microscope, image analyzer, scanning electron microscope and X-ray mapping. The obtained results were compared with the previous study, which was studied on Al-5%Si-0.2%Mg matrix alloy and composites. It has been found that, the formation of some reaction products, mechanical properties and age hardening behavior of the composites strongly depend on Si and Mg content of the matrix alloy. In addition, increasing the Mg and Si content from 0.2 and 5 wt.% to 0.7 and 7 wt.% respectively, increase the critical temperature and hardening efficiency values.

Production of A1 Based Composite Reinforced with SnO2 Coated SiC Particles

An investigation was carried out on SnO2 coating of SiC particles by sol-gel technique and the production of SnO2 coated 20 vol% SiC particle reinforced composite and unreinforced matrix alloy by squeeze casting. The morphology of the coating and microstructural, interfacial and mechanical properties of the composite were characterized by using an optical microscope, image analyzer, scanning electron microscope (SEM), energy dispersion spectroscopy (EDS), and X-ray diffraction (XRD). It has been found that the coating is not degraded during the fabrication process; in other words, SnO 2 coating by sol-gel technique is an effective way to improve the matrix/reinforcement interfacial properties.

In Vitro Biocompatibility and Antibacterial Activity of Electrospun Ag Doped HAp/PHBV Composite Nanofibers

The authors report herein in vitro antibacterial property and osteoblast biocompatibility of electrospun Ag doped HAp/PHBV (Ag-HAp/PHBV) composite nanofibers as an osteoconductive and antibacterial material for bone tissue engineering applications. Ag-HAp powders were synthesized and stable composite suspensions of Ag-HAp/PHBV were prepared with the aid of a cationic surfactant DTAB for the electrospinning process. Continuous and uniform composite nanofibers were generated within a diameter range of 400–900 nm. Obtained nanocomposite scaffolds provide a favorable environment for bone mineralization, SaOS-2 osteoblastic cell attachment and growth as well as they present antibacterial activity against E. coli and S. aureus bacteria without any noticeable cytotoxic effect. GRAPHICAL ABSTRACT