Ahmet Özel

Surface Modification of Medium Carbon Steel by Using Electrolytic Plasma Thermocyclic Treatment

In this work, using the electrolytic plasma thermocyclic treatment technique (EPTT), surface modification of medium carbon steel was carried out. The EPTT system was set as industrial scale. Na2CO3 was used as electrolyte in water. Various voltage and ampere values were performed to obtain good surface properties. Moreover, different impulse ratio and cooling rates were performed. Metallographic studies were carried out with an optical microscope, scanning electron microscope (SEM), energy dispersive spectrometer (EDS) to study the hardened and modified surfaces. Also microhardness and Rockwell hardness tests were performed. The reliable microstructure and hardness values were obtained on the surface of steel samples.

Surface Modification of AISI 4140 Steel Using Electrolytic Plasma Thermocyclic Treatment

Surface modification of AISI 4140 steel has been carried out by using electrolytic plasma thermocyclic treatment (EPTT). Cyclic voltage between 320 and 250 for stipulated period of 1, 2, 3, 4 s and 2, 3, 4, 5 s, respectively, has been performed. At the same time, the effect of average voltage and duration on process has been studied. Microhardness hardness profile measurements have been used before and after thermal treatment to analyze the hardened layer. Scanning electron microscopy (SEM), stereo, optical microscopy, and X-ray diffraction (XRD) have been employed to characterize microstructure and phase composition of the treated layer. The hardening layers are composed of martensite, fine pearlite, oxides with iron, such as FeCr2O4, Fe3O4, and FeO. According to the treatment parameters, max 770 HV hardness and fine martensite, transition zone, and fine pearlite phases have been examined from the surface to the bulk body. When the substrate has been processed at 300–320 V for 42 s, the highest thickness is about 10 mm, and the corresponding microhardness is HV 500–650, which is 4 or 5 times higher than that of the substrate. The depth of hardened layer can be 6–8 mm, depending on the EPTT conditions.

Friction and wear performance of glass fiber reinforced poly-ether-ether-ketone composite against different polymer counterparts

In tribological applications, because of the corrosive problems of the metals in water applications, poly-ether-ether-ketone (PEEK) and its composites are preferred for rubbing materials. As it is known PEEK is a high performance semi-crystalline thermoplastic polymer and has received significant attention in recent years. This is due to its high mechanical strength and elastic modulus, high toughness, chemical inertness, high melting temperature, easy processing, and wear resistance. Therefore, poly-ether-ether-ketone polymer material plays a more important role as a bearing and sliding material.1,2 Lots of studies on the tribological properties of PEEK have been reported.3–11 Most studies published in the literature were in the friction and wear of polymers sliding against steels in dry conditions. The coefficient of friction can, generally, be reduced, and the wear resistance can be improved by selecting the right material combinations.12,13 Usually, tribological phenomena lead to a loss of mechanical efficiency. So, the accurate knowledge of the influence of applied load, sliding speed and contact temperature on the friction and wear is extremely important.14 The purposes of this investigation are to clarify the tribological characteristics of 30wt.% glass fiber reinforced poly-ether-etherketone composite sliding against poly-tetra-fluoro-ethylene (PTFE) filled poly-ether-imide (PEI) blend and 40% glass fiber reinforced PPS composite under dry sliding conditions. Tribological tests versus PTFE filled PEI blend and 40% glass fiber reinforced PPS composite were carried out on a pin-on-disc arrangement. Tribological tests were at room temperature under 0.707MPa, 1.42MPa and 2.12MPa applied pressure and at 0.5m/s sliding speed. The specific wear rates were realized from mass loss and were reported.

Unnotched Charpy Impact Energy Transition Behavior of Austempered Engineering Grade Ductile Iron Castings

Unnotched Charpy impact energy transition behavior of five different engineering grade ductile iron castings, as specified by EN 1563 Standards, were examined in as-cast, as well as in austempered states. ADIs were produced with the maximum impact energy values permissible for the grades. Austempering treatment detrimented the sub-zero impact properties of the ferritic castings, but considerably enhanced those of the pearlitic–ferritic irons. The impact energy transition behavior of the austempered states of all the grades examined were noted to be determined by the progressive transformation of the unavoidable carbon-unsaturated and untransformed regions of the austenite remaining in the matrix of the austempered ductile iron to martensite with decreasing temperature.