Mehmet Gavgali

The effects of induction hardening on wear properties of AISI 4140 steel in dry sliding conditions

Wear behaviour of induction hardened AISI 4140 steel was evaluated under dry sliding conditions. Specimens were induction hardened at 1000 Hz for 6, 10, 14, 18, 27 s, respectively, in the inductor which was a three-turn coil with a coupling distance of 2.8 mm. Normalised and induction hardened specimens were fully characterised before and after the wear testing using hardness, profilometer, scanning electron microscopy and X-ray diffraction. The wear tests using a pin-on-disc machine showed that the induction hardening treatments improved the wear behaviour of AISI 4140 steel specimens compared to normalised AISI 4140 steel as a result of residual stresses and hardened surfaces. The wear coefficients in normalised specimens are greater than that in the induction hardened samples. The lowest coefficient of the friction was obtained in specimens induction-hardened at 875 °C for 27 s.

The effects of artificial aging on wear properties of AA 6063 alloy

Abstract Wear behaviour of age-hardened 6063 aluminium alloy was evaluated under dry sliding conditions. A certain part of the aluminium samples was solution treated at 510 °C for 2, 4, 6 and 8 h, water-quenched then aged at 180 °C for 4 h, and the other part was solution treated at 510 °C for 6 h, water-quenched then aged at 180 °C for 1, 2, 3, 4 and 5 h in a muffle furnace. The as-cast and the aged samples were fully characterised before and after the wear testing using hardness, profilometer, scanning electron microscopy (SEM), optical microscopy, X-ray diffraction, and energy dispersive detector (EDS). The wear tests using on a pin-on-disc machine showed that the aging treatments improved the wear behaviour of AA 6063 alloy compared to as-cast samples.

Influence of mineral admixtures on the mechanical properties and corrosion of steel embedded in high strength concrete

The corrosion rate of steel material in concrete is extremely low when the metal is in passive state at normal conditions. This situation is completely different in the regions where corrosive ions are available. Chlorine ions around steel, at the passive state, destroy the reinforced concrete. To improve the mechanical properties of concrete and to increase the corrosion resistance of steel embedded in concrete, silica fume (SF) and blast furnace slag (BFS) were used at different ratio instead of Portland cement (PC). The dry-unit weight, the compressive strength and the ultrasonic pulse velocity (UPV) of the samples without steel reinforcement were determined. The corrosion current densities of the samples with steel reinforcement in 5% NaCl solution were measured by the linear polarization technique on the 28th, 75th, 150th and 250th days. Finally, it was observed that the samples with 10% SF+20% BFS had the highest compressive strength, and that the concrete samples with 10% SF+40% BFS and 0.35 water-binder ratios had the lowest corrosion current density. As a result, it can be concluded that the mineral admixtures improved the compressive strength, UPV and corrosion current density.

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.

Synthesis of in situ TiC nanoparticles in liquid aluminum: the effect of sintering temperature

In this study, in situ TiC nanoparticles with a diameter range of 70—400 nm have been successfully synthesized in liquid aluminum by conventional hot-pressing method. The effect of production temperature on the formation of the TiC phase during sintering was investigated by differential thermal analysis, X-ray diffraction, and scanning and transmission electron microscopies. The results show that the synthesizing temperature has a great effect on the formation of the TiC. Also, increase of producing temperature accelerates the formation of in situ TiC nanoparticles and decreases the portion of Al3Ti intermetallic phase in the liquid aluminum.

Influence of mineral admixtures on the some properties and corrosion of steel embedded in sodium sulfate solution of concrete

Abstract The corrosion of steel reinforcement is the most significant factor of deterioration in reinforced concrete structures. Corrosion of embedded steel in concrete may occur as a result of the depassivating effects of sulfate ions. Corrosive ions around the steel, at the passive state, destroy the reinforced concrete. To improve the mechanical and physical properties of concrete and to increase the corrosion resistance of steel embedded in concrete, silica fume (SF) and blast furnace slag (BFS) were used at different ratios instead of portland cement (PC). The workability, dry unit weight, the compressive strength and capillarity coefficient of the samples without steel reinforcement were determined. The corrosion current densities were measured by the linear polarization technique on the 28th, 75th, 150th and 250th days. Finally, it was observed that the samples with 10% SF+20% BFS had the highest compressive strength and the lowest capillarity coefficient. The concrete samples with 10% SF+40% BFS and 0.35 water–binder ratios (W/C) had the lowest corrosion current density. As a result, it can be concluded that the mineral admixtures improved the compressive strength, capillarity coefficient and corrosion current density.

Corrosion behavior of 90%Cu-10%Ni alloy at different rotation speeds

In this study, the corrosion behavior of 90%Cu-10%Ni (C70600) cupronickel alloy in artificial seawater was investigated. The corrosion tests were conducted using a rotating cylindrical electrode at different speeds. In the experiments, free corrosion potential tests, electrochemical impedance spectrum (EIS) analysis, weight loss tests, and optic microscope observation were performed. The corrosion rate of 90%Cu-10%Ni alloy in artificial seawater increased with increasing rotation speed and time. Damage period was changed with rotation speed. It was also determined that the damage to the protective film began after 3 hours at the rotation speed of 1600 rpm, and after 3 hours at 2000 rpm, and increased with increasing time. It was determined that 1200 rpm rotation speed is better than both 1200 rpm and 1600 rpm for working conditions.