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Öğe Characterization of armour steel welds using austenitic and ferritic filler metals(Springer India, 2022) Gürol, Uğur; Karahan, Tuba; Erdöl, Sevim; Çoban, Ozan; Baykal, Hakan; Koçak, MustafaIn this study, fillet welding processes were performed on high strength Miilux Protection 500 (MIL-A-46100) steel, which is used as armour material in defence industry, using GMAW method with austenitic ER307 and ferritic ER110S-G filler metals. The characterization of welded structure was carried out by performing elemental mapping processes as well as microstructural examination and microhardness tests. Results showed that hardness of weld metal was found to be 46% and 78% of the base metal hardness for austenic and ferritic filler metal, respectively. The fine-grained heat-affected zone was found to be the highest hardness while intercrital heat-affected zone was found to be lowest hardness through heat-affected zone. The smoother decrease was obtained in the softening zone with austenitic filler metal due to lower thermal conductivity. Consequently, the hardness values at a distance of 6 mm from the plate edge for both filler metals reached the hardness of base metal and both welded structures met the minimum requirements of the military standards.Öğe Dalış sistemlerine farklı ve yenilikçi bir yaklaşım(Beykent Üniversitesi, 2017) Urcan, Kerem; Karahan, Tuba; Özbek, SunullahSCUBA ve Satıhtan İkmalli Dalış Sistemlerinin (SİDS) avantajlarından faydalanarak askeri, kurtarma, ticari ve rekreasyonel dalış operasyonlarında kullanılmak üzere yeni dalış sistemlerinin geliştirilmesi amaçlanmaktadır. Var olan dalış sistemlerinin avantajlarını kullanarak, mevcut kısıtlamaların üstesinden gelebilmek için yenilikçi çözümler sunarak yeni dalış sistemleri geliştirilmesi kapsamında çalışmalar yapılması önem arz etmektedir. Bu kapsamda mevcut dalış sistemlerin teknik yeterlikleri ve çalışma prensipleri sergilenmeye çalışılmıştır. Bununla beraber mevcut dalış sistemleri karşılaştırılmış ve avantajları göz önüne alınarak günümüz ihtiyaçlarına uygun yeni dalış sistemlerinin geliştirilebilmesi için farklı yaklaşımlar ortaya konulmuştur.Öğe Evaluation of microstructural and mechanical properties of dissimilar Inconel 625 nickel alloy-UNS S32205 duplex stainless steel weldment using MIG welding(Springer Heidelberg, 2020) Tümer, Mustafa; Karahan, Tuba; Mert, TolgaInconel 625 nickel alloy and UNS S32205 duplex stainless steel (DSS) were welded with ER2209 filler metal using MIG (Metal Inert Gas) welding method. The weld metal obtained by DSS filler metal was subjected to mechanical and microstructural evaluation. Toughness and hardness properties had been examined by mechanical and microstructural characterization of weld metal, fusion line, and HAZ (Heat Affected Zone) region, and precipitations were investigated by light microscopy (LM), scanning electron microscopy (SEM), and energy-dispersive spectrometry (EDS). Corrosion behavior of base metals and face and root of weld metal were examined by using potentiodynamic polarization test. Additionally, detailed elemental analysis and mapping of weld metal with both optical emission spectrometer (OES) and X-Ray spectrometer were attained. Results demonstrate a significant decrease in toughness of the welding due to the presence of Nb and Mo rich intermetallic precipitations in the Inconel HAZ and root region, although there is no significant increase in hardness. Potentiodynamic polarization test shows that the dilution-induced microstructural transformation in the root of weld has the worst corrosion resistance in the weld metal. Therefore, this dissimilar welding does not have optimum properties for neither toughness nor corrosion.Öğe Investigation of microstructure, mechanical, and corrosion behavior of nickel-based alloy 625/duplex stainless steel UNS S32205 dissimilar weldments using ERNiCrMo-3 filler metal(Springer Heidelberg, 2021) Tümer, Mustafa; Mert, Tolga; Karahan, TubaIn this study, nickel-based alloy 625 and duplex stainless steel (DSS) UNS S32205 (2205) dissimilar pairs were welded with metal inert gas (MIG) welding process. Weld metal, obtained with the utilization of ERNiCrMo-3 filler wire, was subjected to mechanical, microstructural, and corrosion investigations. V-notch impact tests and micro hardness measurements were realized on dissimilar weld metal. Microstructural changes in weld metal, fusion line, and heat-affected zone were examined using optical, scanning (SEM), and transmission electron microscopes (TEM) with energy-dispersive spectrometry (EDS). Phase precipitations rich of Nb and Mo were detected among dendritic austenite arms in the weld metal. It was observed that ERNiCrMo-3 filler metal had sufficient toughness because of high nickel content. Corrosion tests revealed that weld metal face pass is the least corrosion-resistant zone in weld metal unlike weld root. This is mainly because more intense intermetallics formed in weld metal face compared with the middle of the weld and the root.Öğe Oxidation mechanism of W substituted Mo-Si-B alloys(Elsevier Sci Ltd, 2017) Karahan, Tuba; Ouyang, Gaoyuan; Ray, Pratik K.; Kramer, Matthew Joseph; Akınç, MüfitThe oxidation mechanism of a Mo55W15Si15B15 alloy was established, and the effects of W content, oxidation temperature and microstructural length scale were determined. In addition to influencing the oxidation mechanism, the addition of W also destabilized the A15 phase which is consistent with our previous experiments in ternary Mo-W-Si alloys [1]. Microstructural investigation of the oxidized alloy revealed entrapped tungsten oxides at temperatures below 1300 degrees C, which volatilize above 1400-1500 degrees C. The presence of WO3 in the oxide scale interrupts the surface coverage by the glassy borosilicate, thereby adversely affecting the oxidation behavior. In order to determine the effects of length scale, the microstructural evolution during the transient oxidation of cast and sintered alloys, with different microstructural length scales, was studied at 1100 and 1400 degrees C. Finer microstructure promoted faster borosilicate surface coverage at 1400 degrees C.Öğe Strengthening of AISI 2205 duplex stainless steel by strain ageing(Elsevier Sci Ltd, 2014) Karahan, Tuba; Ertek Emre, Hayriye; Tümer, Mustafa; Kaçar, RamazanIn this study, static strain ageing behavior of commercially available and solution heat treated duplex stainless steel was investigated and the effect of static strain ageing on the mechanical properties was also determined in detail. Some of as-received duplex stainless steel test specimens were pre-strained in tension by 5% and then aged at 100 degrees C, 200 degrees C, 300 degrees C, 400 degrees C, 500 degrees C and 600 degrees C for 30 min in furnace. Some of duplex stainless steel test specimens were solution heat treated at 1050 degrees C for 30 min, water quenched and then pre-strained for 5% in tension shortly after the solution heat treatment. In order to identify the effect of static strain ageing on the mechanical properties, the tensile strength, the change in the strength due to ageing (Delta Y), elongation fracture and hardness were determined. The test results showed that the mechanical properties were affected by static strain ageing mechanism which was applied at different temperatures for same time interval.
