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Öğe The corrosion behaviour of as-welded and post-weld heat treated Ti6Al4V alloy in simulated body fluid(Elsevier, 2019) Emre, Hayriye ErtekIn this study, the corrosion behavior of Ti6Al4V alloy base metal, laser welded and post-weld heat treated (PWHT) samples in simulated body fluid was investigated. The potentiodynamic polarization curves of the as-welded and PWHT samples were compared with each other and with the base metal. Surface morphologies of samples were evaluated. The polarization curves indicate that, the lower corrosion resistance obtained for as-welded samples as compared to base metal. The corrosion resistance of welded joints improved with increasing welding speed. PWHT process has positively affected to the corrosion properties of the laser welded Ti6Al4V joints. (C) 2019 Elsevier B.V. All rights reserved.Öğe Development of weld lobe for resistance spot-welded TRIP800 steel and evaluation of fracture mode of its weldment(Springer London Ltd, 2016) Emre, Hayriye Ertek; Kacar, RamazanThe weld lobe in spot welding provides an indication of good quality joining and the tolerance of the weld schedule in production stage. In this study, TRIP800 steel was used for the experiments, and welding times of 5, 10, 15, 20, and 25 cycles were selected with welding currents ranging from 1 to 7 kA with an interval of 2 kA and from 7 to 10 kA with an interval of 1 kA. The effect of heat input associated with welding current and welding time on nugget geometry, such as diameter, height, nugget size ratio, and electrode indentation, was determined by optical microscope. The welded specimens were exposed to tensile shear tests. Tensile shear strength and failure mode associated with nugget geometry and electrode indentations were also evaluated and weld lobe was drawn accordingly. It was found that the nugget diameter and nugget size ratio of TRIP800 steel spot welds should be at least 4.5aet and 0.15-0.30, respectively, for pullout failure mode, acceptable shear strength, and surface quality.Öğe Effect of bright annealing process on the properties of TIG welded duplex stainless steel tube(Inderscience Enterprises Ltd, 2015) Kacar, Ramazan; Emre, Hayriye ErtekPassivation is the process of forming a protective oxide film on stainless steel. It is accomplished through an appropriate inline bright annealing process. Duplex stainless steel exhibits optimum mechanical and corrosion properties with the austenite-ferrite phase balance in its structure. However, the ferrite-austenite equilibrium in duplex structure can also be affected by inline bright annealing process, in which the heating of stainless steel to a suitably high temperature in a reducing atmosphere takes place. For this reason, the effect of inline bright annealing process on the microstructure and mechanical properties of TIG welded AISI2205 stainless steel tube was evaluated in this study. The results point out that the structure and mechanical properties of the duplex stainless steel tube are affected by the inline bright annealing process. In light of foregoing findings, the sample that was inline bright annealed in reducing nitrogen gas atmosphere has given optimum mechanical properties.Öğe Effect of Cr-Ni coated Cu-Cr-Zr electrodes on the mechanical properties and failure modes of TRIP800 spot weldments(Pergamon-Elsevier Science Ltd, 2020) Emre, Hayriye Ertek; Bozkurt, BatuhanResistance spot welding (RSW) is a highly preferred welding process in the automotive and other industries because of its faster and economical processes and also it has higher quality. However, during the joining process, the temperature at the electrode tip reaches the highest value and, in the meantime, electrode tips are deformed. For this reason, the electrode wears down with increasing weld numbers, which changes the thermal, electrical, and mechanical contact conditions at the electrode and sheet interfaces. The coating is generally applied onto the surface of Cu-Cr-Zr electrodes for extended electrode life during RSW process. In this study, the tip surfaces of the electrodes were coated with Cr-Ni filler metal by using electro-spark deposition (ESD) coating method under 40, 80, and 120 V. Consequently, the effects of the coating on electrode characteristics and properties of the TRIP800 resistance spot weldment are investigated. The mechanical behaviors of the joined samples under static load were investigated by applying a tensile shear test and cross tension test. Tensile-shear strength, cross-tension strength was determined, and the failure modes of the samples was investigated. The nugget size was measured by stereo microscope. Microstructure investigations have also been carried out by optic microscope and scanning electron microscopy (SEM).Öğe Effect of Laser Welding on In-Vitro Bioactivity Properties of Ti6Al4V Joints(Korean Inst Metals Materials, 2022) Emre, Hayriye Ertek; Arslan, SennurIn this study, the Ti6AI4V alloy, which is used as an implant material in the medical field, was joined with the laser welding method at different welding speeds. The bioactivity features of the Ti6AI4V alloy and its samples joined at different welding speeds were determined by immersing in a simulated body fluid (SBF) for 1, 7, 14, 21 and 28 days. The hydroxyapatite (HA) formation on the surfaces of the samples was determined by calculating the weight gain. The weight loss was calculated by removing the HA from the surface after bioactivity testing. The corrosion rates of the samples were also determined according to the weight loss. In addition, the characterization of the HA formed on the surfaces of the samples was performed. As a result of the investigations, it was determined that the increase in laser welding speed, and therefore the decrease in heat input, positively affected the bioactivity and biocorrosion features of the Ti6Al4V laser welded joints. It was determined that the particle sizes of the HAs of the laser weldments increased with lower heat inputs. It was also observed that the amount of HA nucleated on the laser-welded samples increased in accordance with the increase in the laser welding speed. The laser welded samples that were welded at higher welding speeds and therefore at lower heat inputs, exhibited better biocorrosion behaviors.Öğe Effect of laser welding on microstructure and mechanical properties of biomedical Ti6Al4V(Springer Heidelberg, 2019) Emre, Hayriye Ertek; Arslan, SennurTi6Al4V titanium alloys are usually used in chemical industry and biomedical sectors as an implant material. In this study, the effect of laser welding on mechanical and microstructural behavior of biomedical Ti6Al4V sheets with different welding speeds was investigated in detailed. The mechanical properties of laser welded joints are investigated by tensile test and hardness measurements. Fracture morphologies and microstructure evaluations are also investigated. It was found that the laser-welded joints have lower tensile strength and elongation as compared to the base metal. The maximum tensile strength was obtained at 250 cm/min welding speed for laser welded joints. The metallographic investigation revealed that weld metal decorated by coarser acicular alpha ' martensite microstructure within the finer prior-beta grains and grain boundary alpha at higher welding speeds.Öğe Effect of Post Weld Heat Treatment Process on Microstructure and Mechanical Properties of Friction Welded Dissimilar Drill Pipe(Univ Fed Sao Carlos, Dept Engenharia Materials, 2015) Emre, Hayriye Ertek; Kacar, RamazanIn this study, N80-42CrMo4 dissimilar drill pipes were welded by a roto-friction welding machine. A set of welded samples were tested as-welded condition. Another set of welded samples were post weld heat treated (stress relief annealing) at the temperature of 600 degrees C, for 20 min. and then tested. The microstructures of the as-welded and stress relief annealed samples were examined by optical microscope and SEM. The properties of the all welded samples were determined by hardness measurement, tension and V notch-impact tests. The high hardness especially in the weld interface resulted in low toughness. As a conclusion, the stress relief annealing treatment caused a little decrease in yield strength and ultimate tensile strength, but increase in the elongation. The ductility of samples also increased after annealing treatment which is very important for static and dynamic loads.Öğe Effect of static strain aging on the fatigue behavior of S275JRC steel(Carl Hanser Verlag, 2017) Bulbul, Ahmet; Kacar, Ramazan; Emre, Hayriye ErtekIn this study, the effect of static strain aging on the fatigue behavior of a mild steel (S275JRC) was evaluated. For this purpose, the 5 % prestrained mild steel was aged at a temperature of 160 degrees C for different intervals. The aging behavior was determined primarily for the as-received (AR) as well as in the homogenization and normalizing heat treated (H+N heat treated) condition. The yield stresses before and after aging process as well as the hardness values of the aged steels were measured for the assessment of the strain aging progress. The dynamic mechanical behavior of strain aged samples was also determined by fatigue test under the dynamic loads. An increase in the yield strength due to strain aging and hardness induced improvement in fatigue strength of the steel were observed.Öğe Effects of welding methods on the mechanical properties of joining dissimilar steel couple(Gazi Univ, Fac Engineering Architecture, 2018) Kacar, Ramazan; Emre, Hayriye Ertek; Isineri, Ali Umit; Najafigharehtapeh, AsgharIn this study, the weldability of wear resistant hardox steel to austenitic stainless steel with shielded metal arc welding (SMAW) and gas metal arc welding (GMAW) methods was investigated and an effect of welding method on the mechanical properties and microstructure of weldment was examined. According to standard, welding groove was prepared for Hardox 400-AISI 304 steel couple that was multi pass welded in butt position by using GMAW and SMAW methods. The mechanical properties of the weldments were determined by tensile, three point bending and V-notch impact tests. In addition, hardness measurement and microstructure evaluation was carried out on the cross section of weldment. According to findings; the tensile strength, weld metal notch impact toughness and ductility of the samples joined with the GMAW method were determined higher than those joined with SMAW.Öğe Mechanical properties of plasma arc welded AISI304LN austenitic stainless steel at various temperatures(Taylor & Francis Ltd, 2023) Kacar, Ramazan; Emre, Hayriye Ertek; Nohutcu, SametAISI 304 grade austenitic stainless steels are widely used in a wide variety of fields such as chemical, automobile, food industries, etc. due to their good mechanical properties and corrosion resistivity. In this study, AISI 304LN austenitic stainless-steel couples were joined with plasma arc welding. The effect of temperature on the mechanical properties, formability and fracture morphologies of joints was evaluated. For this purpose, tensile testing of the joints was carried out in the temperature range of -50 degrees C, and 25 degrees C-850 degrees C. Thus, the ultimate tensile strength, (UTS), yield strength, (YS) and elongation (EL%) amounts of welded joints were determined. The fracture morphologies of the tensile test samples were examined. It was observed that the rupture (except 850 degrees C) occurred from the weld metal. The highest formability was obtained in the samples tested at 850 degrees C. In addition, the existence range of dynamic strain aging (DSA) of the plasma arc welded samples was also investigated. The unsteady plastic flow between the yield and the ultimate tensile of the sample subjected to the tensile test at 250-550 degrees C are evaluated as signs of DSA.Öğe Petrol sondaj borusu çeliklerinin sürtünme kaynak kabiliyetlerinin araştırılması(Karabük Üniversitesi, 2012) Emre, Hayriye Ertek; Kaçar, RamazanSürtünme kaynak yöntemi son yıllarda kullanım alanı bulmaya başlayan ve günümüzde de uygulama alanı genişleyen katı hal kaynak yöntemidir. Bu kaynak yöntemi ilk başlarda içi dolu aynı veya farklı cins malzemelerin kaynaklı birleştirmeleri için kullanıldı. Son zamanlarda boru, profil kesitli ve çubuk malzemelerin birleştirmelerinde de kullanılmaya başlanmıştır.Günümüz endüstrisinde petrol ve doğal gaz kuyularında, jeotermal kaynakların çıkarılmasında, maden endüstrisinde, inşaat sektöründe, zemin etütlerinde, içme ve sulama su kuyularının açılmasında sondaj yöntemi sıklıkla kullanılmaktadır. Belirtilen alanlarda sondaj işlemlerinde genellikle API (American Petroleum Institute) tarafından sınıflandırılarak standardize edilen J55, K55, N80, C75, C95, H40, P1 10 N80, J135) gibi petrol boru çelikleri kullanılmaktadır. Bu boruların birbirlerine alın alına birleştirmelerinde önceleri GMAK (Gaz metal ark kaynak) yöntemi kullanılmaktaydı. Ancak GMAK yönteminde meydana gelen gaz boşlukları,köpürme ve termal çevrimden dolayı meydana gelen çarpılma (distorsiyon) gibi kaynak hataları sebebiyle endüstride tercih edilmemektedir. Bunun yerine alternatif olarak sürtünme kaynaklı birleştirmeler tercihen kullanılmaya başlanmıştır. Ancak, aynı ve farklı cins petrol boru çeliklerinin sürtünme kaynak kabiliyetleri hakkında önemli bir literatür bilgisine rastlanmamıştır.Bu amaçla; çalışmada aynı cins ve farklı cins sondaj borularının sürtünme kaynak kabiliyetleri araştırılmıştır. Servis şartları da göz önünde bulundurularak numunelerin mikroyapı incelemeleri ve mekaniksel özellikleri belirlenmiştir. İlave olarak; kaynak sonrası bağlantıya gerginlikleri giderme ısıl işlemi uygulanmıştır. Böylece kaynak sonrası ısıl işlemin mekanik özellikler ve mikroyapı üzerindeki etkisi araştırılmıştır. Sonuç olarak; sürtünme kaynağı sonrası numunelere uygulanan gerilim giderme ısıl işleminin tüm birleştirmelerin mekanik ve mikroyapısal özelliklerini önemli ölçüde etkilediği tespit edilmiştir.Öğe Properties of Resistance Spot-Welded TWIP Steels(Mdpi Ag, 2017) Zeytin, Havva Kazdal; Emre, Hayriye Ertek; Kacar, RamazanHigh manganese TWIP (twinning-induced plasticity) steels are particularly attractive for automotive applications because of their exceptional properties of strength combined with an excellent ductility. However, the microstructure and properties of TWIP steels are affected by excessive thermal cycles, such as welding and heat treatment. This paper deals with characterization and understanding the effect of welding current and time on the mechanical properties and microstructure of the resistance spot welded TWIP steel. For this purpose, weld nugget diameter was evaluated and the hardness, tensile shear strength of the weldment, and failure mode of samples were also determined. It has been found that the tensile shear strength of the samples increased with increasing welding current and welding time without expulsion, which reduces the strength of the weldment. Tensile shear samples failed by a partial interfacial fracture mode for low-heat input welds. The pullout fractures were observed with a sufficient heat input without expulsion.Öğe Resistance Spot Weldability of Galvanize Coated and Uncoated TRIP Steels(Mdpi, 2016) Emre, Hayriye Ertek; Kacar, RamazanIn this study, the resistance spot weldabilty of zinc galvanize-coated and uncoated TRIP800 steels was investigated in detail. Depending on the welding parameters such as welding current and welding time, the effects of zinc coating on the weld nugget geometry, the tensile shear strength, the failure modes, the hardness, and the microstructure of the resistance spot-welded sample were studied, and the results are compared with that of uncoated weldment. The coating on the surface of the TRIP steel causes a decrease in the weld nugget size and tensile shear strength of the weldment, and it changes to failure mode of the test sample from pullout to interfacial or partial interfacial fracture. As compared with the uncoated sample, the galvanized TRIP800 steel weldment has required a larger critical nugget size for achieving the desired pullout fracture mode and acceptable tensile shear strength.Öğe Strengthening of AISI 2205 duplex stainless steel by strain ageing(Elsevier Sci Ltd, 2014) Karahan, Tuba; Emre, Hayriye Ertek; Tumer, Mustafa; Kacar, 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. (C) 2013 Elsevier Ltd. All rights reserved.Öğe TRIP800 çeliğinin nokta direnç kaynak kabiliyetinin araştırılması(Karabük Üniversitesi, 2016) Emre, Hayriye Ertek; Kaçar, RamazanTRIP çelikleri otomotiv endüstrisinin ihtiyaçlarını karşılamak için geliştirilmiş ileri yüksek mukavemetli çeliklerin en yeni türüdür. Bir otomobilin üretiminde yüzlerce farklı tipte işlem gerçekleştirilmektedir. Bu işlemlerden belki en önemlisi, araç kalitesini %40 oranında etkileyen, aracın gövdesinin ortaya çıkarıldığı kaynak işlemidir. Otomotiv endüstrisinde kullanılan kaynak yöntemleri arasında nokta direnç kaynak yöntemi, robot uygulamalarında son derece gelişmiş ve önemli bir konumdadır. TRIP çeliklerin nokta direnç kaynağı çalışmaları ise, kaynaklanabilme yeteneklerinin düşük olması sebebiyle incelenmekte ve kaynak sırasında oluşan kötü kaynak özelliklerinin iyileştirilme çabaları devam etmektedir. Bu çalışmada, otomotiv endüstrisinde yaygın kullanım alanı bulmaya başlayan 1.5 mm kalınlığındaki TRIP 800 çelik sacın ticari olarak temin edildiği şekliyle (kaplamalı, kaplamasız) ve belirli bir oranda (%10) soğuk deforme edildikten sonra nokta direnç kaynak kabiliyeti araştırılmıştır. Bu amaçla; birleştirmelere çekme-makaslama ve çapraz-çekme testleri uygulanarak mekanik özellikleri incelenmiş, kaynak çekirdek boyutları hesaplanmış ve kaynaklı bağlantıların sertlik ölçümü yapılmıştır. Kaynaklı bağlantıların çekme-makaslama dayanımı ve çekirdek geometrilerinden yararlanılarak kaynak edilebilme diyagramı oluşturulmuştur. Kaynaklı numunelerin metalografik incelemeleri optik mikroskop, SEM, XRD ve EDS vasıtasıyla incelenmiştir. Ayrıca birleştirmelere endüstriyel kullanım şartları göz önünde bulundurularak gerilme giderme ısıl işlemi ve otomotiv sanayinde kullanılan boyama sonrası kurutma ısıl işlemi uygulanarak, ısıl işlemin birleştirme mekanik özellikleri ve mikroyapısına etkisi de araştırılmıştır.
