SEARCH RESULT

This study aims to investigate the effect of reduced graphene oxide (rGO) on microstructure, hardness and electrochemical corrosion performance of pure iron. The microstructure investigations were carried by optical and SEM microscopes. The electrochemical corrosion tests were conducted by potentiodynamic polarization test in 3.5% NaCl solution. The results showed that rGO-reinforced sample showed slightly higher hardness value. On the other hand, the corrosion performance of pure iron was significantly improved by the addition of rGO due to the reduced reduction kinetics.

International Iron & Steel Symposium
UDCS

Hüseyin Zengin MUHAMMET EMRE TURAN

In this study, fatigue behavior of 55Cr3 metal alloy spring steel which is produced as hot and cold was examined. Fatigue samples with a diameter of 10 mm, extracted from 55Cr3 spring steel in accordance with ISO 1143 standard, were subjected to rotational bending fatigue testing of different masses under repeated bending stresses according to a continuous rotating neutral axis. As a result of the investigations, the fatigue strength of 55Cr3 spring steel decreased with hot process, while the cold process increased.

International Iron & Steel Symposium
UDCS

Esma KESKİN Hayrettin Ahlatçı Yunus Türen Hüseyin Zengin Mustafa Ali KÜÇÜK Yasin SUBAŞI

In this study, the effect of C addition on the corrosion behavior of wire rods of 5.5 mm in diameter was investigated. The horizontal and vertical cross sections of the wire rods with 0.7, 0.8, 0.9 C ratio were taken during the metallographical process. The microstructure of the examined specimens was examined by light optical (LOM) and scanning electron microscopy (SEM). Hardness test of steel containing 0.7- 0.9 C was carried out in shimadzu brand micro hardness tester. Corrosion tests of the prepared samples were evaluated according to both the weight loss and the Potentiodynamic Polarization measurements in 3.5% NaCl solution. Despite the increased hardness of the specimens examined, the corrosion resistance decreased. This can be caused by inclusions in the microstructure.

International Iron & Steel Symposium
UDCS

Medine Kilinc Gulheser Dogancik Yunus Türen Yavuz Sun Hayrettin AHLATCI İbrahim AFŞAR Serhat ÖZDEMİR Hüseyin Koymatcık Hüseyin Zengin

In this study, influence of grain size on degree of sensitization and susceptibility to intergranular corrosion of AISI 316 austenitic stainless steel was investigated. As-received AISI 316 austenitic stainless steel samples were first solution heat treated at 1050 oC for 0.5 h, 1.5 h and 3 h in order to obtain different grain sizes and then, each of them was heat treated for sensitization at 700 oC for 1h followed by water quenching. Grain size measurements of the first set of samples were performed by linear intercept method according to ASTM E112 standard and the degree of sensitization was measured by double loop electrochemical potentiodynamic reactivation (DLEPR) test. The results showed that grain size increased as the solution heat treatment time increased. A decrease in the degree of sensitization was observed for the samples having larger grains. That is to say, the increase in grain size improved intergranular corrosion resistance.

International Iron & Steel Symposium
UDCS

Hüseyin Zengin Yunus Türen Hayrettin Ahlatçı Yavuz Sun Burak Dursun Ünsever

Zinc (Zn) has been widely used as main alloying element in magnesium alloys. Zn improves corrosion resistance and strength of magnesium alloys by grain boundary strengthening, solid solution and precipitation hardenings [1,2]. Zn has 6.2 wt% maximum solid solubility in Mg and together with Mg can form binary coherent compounds [3].

International Symposium on Light Alloys and Composite Materials
UHAKS

Hüseyin Zengin Yunus Türen Hayrettin Ahlatçı Yavuz Sun Emre Öztürk

Magnesium alloys have great potential in aerospace, automotive and electronic industries due to high specific strength and low densities [1], [2]. Because high specific strength and lightweight materials are needed to improve energy efficiency [3],[4]. However, magnesium alloys have poor mechanical properties, so this situation limits the usage of magnesium in practical applications. There have been a lot of attempts by researchers to overcome deficiencies of magnesium alloys, especially for decades. Researchers develop mechanical properties of magnesium by incorporating reinforcement materials. Micron size reinforcements are generally preferred but nowadays, nano-size materials especially carbon based are becoming popular subject for researchers. In this study, graphene nanoplatelets (GNPs) which is an allotrope of carbon is used as a reinforcement material for magnesium matrix composite. Aluminum was also used to evaluate its binding effects on Mg-GNPs composite. Pure Mg, Mg-0.25 wt.% GNPs, Mg-3Al-0.25 wt.% GNPs and Mg- 9Al-0.25 wt.% GNPs composites were fabricated using semi powder metallurgy technique. GNPs was exposed to ultrasonication process in ethanol for an hour in order to break Vander Waals bonding between carbon atoms. Mg-Al powder (mixed in Turbula mixer for two hours) was added to GNPs/Ethanol solution. Powders were mixed using magnetic stirrer which is connected to the vacuum distillation system. Process was continued until the ethanol removed from the system. Then obtained powder was dried in vacuum drying oven. Dried powders were compacted in graphite mold under 50 MPa applied load in hot pressing device. Argon was used to prevent oxidation and pressing, and sintering temperatures were chosen as 550 ºC. Experimental densities were calculated by Archimedes technique. Microstructures of produced samples were characterized using X-ray diffraction and Scanning Electron Microscope (SEM). Hardness test was applied according to the Vickers test method. Compression tests were performed for all samples to investigate mechanical effects of aluminum and GNPs on magnesium-based composite. Results show that uniform distribution of carbon atoms is seen for GNPs reinforced composites. Figure 1 shows SEM images of Mg-3Al-GNPs and Mg-9Al-GNPs composites. Microstructures are free of macro porosities. As shown in Table 1, hardness of pure magnesium is significantly improved with the addition of Aluminum and GNPs. It can be concluded that reinforcement materials may restrict the dislocation motion and aluminum can exhibit lubricant effect between matrix and GNPs. Compression tests reveal that 0.2% Compression Yield Strength (CYS) and Ultimate Compression Strength (UCS) are enhanced with the addition of reinforcement. Thus, mechanical properties of pure magnesium were significantly improved even low content of carbonaceous reinforcement.

International Symposium on Light Alloys and Composite Materials
UHAKS

MUHAMMET EMRE TURAN Yavuz Sun Fatih AYDIN Hüseyin Zengin Yunus Türen Hayrettin Ahlatçı

Abstract Rare earth (RE) additions can improve mechanical properties at room and elevated temperatures, formability and castability of magnesium alloys [1-3]. Recently, numerous studies have been conducted about wrought Mg-Zn-Zr- RE alloys due to their excellent strength and great potential for further development. In this study, microstructure, mechanical and corrosion properties of as-cast and as-extruded Mg-6Zn-0.5Zr (wt%) alloy, also denoted as ZK60, with minor La addition were investigated. Mg-6Zn-0.5Zr-0.2La magnesium alloy was produced by low-pressure die casting method under a protective argon gas atmosphere. Pure Mg (99.9%) ingots were melted at 750 °C and pure Zn (99.7%), Mg-30 wt% Zr and Mg- 30 wt% La master alloys were added into the molten Mg. The melt was held at this temperature for 30 min and stirred for 15 min to ensure a full dissolution of alloying elements. After applying a pressure of 2 bar into the air tight electric resistance furnace, the melt was transferred from the crucible to the steel mould preheated to 250 °C through the rising steel tube and cylindrical ingots with a diameter of 34 mm and length of 190 mm were obtained. After casting, the as-cast alloys were homogenized at 400 °C for 24 h and water quenched. Then, each homogenized billet was machined into cylindrical bar with a diameter of 32 mm and length of 30 mm. For extrusion process, the machined billets and the extrusion die were preheated to the target temperature for 40 min and directly extruded at an initial temperature of 300 °C with an extrusion ratio of 16:1 and a ram speed of 0.3 mm.s-1. Microstructure characterizations were conducted by a Nikon optical microscope (OM) and a Carl Zeiss Ultra Plus field emission scanning electron microscope (SEM) equipped with an energy dispersive spectroscopy (EDS). The constituent phases in the as-cast alloy and the macro-texture of the extruded alloy were characterized by X-ray diffraction (XRD-Rigaku Ultima IV). Tensile tests were conducted on a Zwick/Roell Z600 universal testing machine at a strain rate of 1.67 x 10-3 s-1 at room temperature (RT). The samples for immersion corrosion test (Φ 5 mm x 15 mm) were cut from the half radius of the alloys, followed by grinding and polishing. Then, the samples were immersed in 3.5 wt% NaCl solution at room temperature for 72 h. The electrochemical corrosion tests of the alloys were also performed in 3.5 wt% NaCl solution at room temperature by a Gamry model PC4/300 mA potentiostat/galvanostat with DC105 corrosion analysis.

International Symposium on Light Alloys and Composite Materials
UHAKS

Hüseyin Zengin Yunus Türen MUHAMMET EMRE TURAN Hayrettin Ahlatçı Yavuz Sun