C. Tekmen

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.

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.

Corrosion Behavior of an Artificially Aged (T6) Al–Si–Mg-based Metal Matrix Composite

The influence of age hardening on the corrosion behavior of Al–Si–Mg-based metal matrix composites (MMCs) has been investigated in aerated and deaerated 3.5 wt% aqueous NaCl solutions. Silicon carbide particle (SiCp reinforced composites consisting of 10 and 20 vol% SiCp are produced by the compocasting technique. After the extrusion process, the composites are artificially aged (T6). The corrosion resistances of the aged composites are analyzed by measuring the cyclic potentiodynamic polarization. The surface morphology of the composites before and after the corrosion tests are determined by using metallographic methods and scanning electron microscopy (SEM). In addition, the X-ray diffraction technique (XRD) has been used to determine the phases that occur at the matrix–reinforcement interface. The results demonstrate that the Epit values of unreinforced matrix alloy and composites increase negatively with increasing aging time. It is also observed that corrosion preferentially starts at the interface of Al–Mg2Si and Al–SiCp.

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.

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.

Thermal behaviour of plasma-sprayed Mo coating on cast-iron substrate

Abstract In this study, Mo coatings were fabricated on cast-iron substrate using a plasma-spray technique for diesel engine motors. In order to undergo cyclic heating because of piston element in combustion chamber, thermal behaviour of these coatings were scrutinized through a thermal cycling machine. These Mo coatings were tested at temperature range of 47–600 °C for periods of 303 s under thermal cycling conditions. The effects of thermal cycling on the properties of the samples were characterized by using an optical microscope, image analyzer, SEM, X-ray diffraction (XRD), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC) and microhardness tester. Microstructural observations showed that the coatings possessed lamellae structure with boundaries. XRD, TGA and DSC results revealed that Mo coatings transformed to MoO and MoO 3 during the thermal cycling process. It was found that an increase in porosity and residual thermal stresses after thermal cycling influenced the hardness results of the samples considerably. It was also observed to be a delimination between coating and substrate after thermal cycling.

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.