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Öğe Characterization of mechanically alloyed and pressureless sintered Al-7 wt% Si-2 wt% LaB6-2 wt% (MoSi2, WSi2) hybrid composites(Elsevier, 2019) Tekoglu, Emre; Yürektürk, Yakup; Agaogullari, Duygu; Ovali, Didem; Mertdinc, Siddika; Ovecoglu, M. LutfiThe purpose of this research is to investigate the dual effect of silicide (MoSi2 or WSi2) and LaB6 reinforcing particles on the microstructural and mechanical properties of Al-7 wt% Si (Al7Si) matrix. Hypoeutectic Al7Si blends prepared from elemental Al and Si powders were mechanically alloyed (MA'd) for 12 h in a planetary ball mill (at 300 rpm). Afterwards, 2 wt% silicide reinforcements (MoSi2 or WSi2) with various particle size distributions (micron, bimodal, submicron) were separately added into these MA'd Al7Si powders together with 2 wt% of LaB6 particles. Powders having compositions of Al7Si, Al7Si-2 wt% LaB6, Al7Si-2 wt% LaB6-2 wt% MoSi2 and Al7Si-2 wt% LaB6-2 wt% WSi2 were milled for 30 min using a high-energy ball mill (at 1200 rpm) in order to obtain homogeneous distribution throughout the microstructure. Compositional, microstructural and mechanical characterization studies were performed on the sintered samples. The results showed that high-energy ball milling ensured the homogeneous distribution of micron-sized MoSi2 and WSi2 particles within the matrix rather than those of bimodal and submicron-sized ones. Micron-sized MoSi2 and WSi2 reinforced hybrid composites displayed dramatically higher hardness and wear resistance than those of composites reinforced with different size of MoSi2 and WSi2 particles. The striking point of the study was the remarkably higher hardness and wear resistance properties of the hybrid composites compared to those of un-reinforced and only LaB6-reinforced ones. As a conclusion, hybrid composites extremely displayed promising mechanical properties. (C) 2019 The Society of Powder Technology Japan. Published by Elsevier B.V. and The Society of Powder Technology Japan. All rights reserved.Öğe Effect of diffusion annealing on duplex coated pure titanium produced by hot-dip aluminizing and micro-arc oxidation(ELSEVIER SCIENCE SA, 2022) Yürektürk, YakupIn the present study, an Al2O3 ceramic coating was formed on a pure titanium surface with the application of the duplex coating technology produced by combining hot-dip aluminizing (HDA) and micro-arc oxidation (MAO) processes. Due to the porous nature of MAO coating with the structural and mechanical differences between the MAO (Al2O3) and HDA layers (Al, Al3Ti), diffusion annealing treatment was applied to duplex coated (HDA + MAO) titanium samples. With the diffusion annealing treatment, a composite layer with a thickness of about 125 mu m was formed beneath the modified MAO coating, which showed a denser structure by penetrating TiO2 into the MAO. MAO coatings with and without diffusion annealing exhibited compressive residual stresses with values of-1530 and-850 MPa, respectively. Microhardness and elastic modulus of the diffusion annealing-treated MAO coating reached 1230.1 HV and 241.3 GPa, respectively. The diffusion annealing-treated MAO coating provided-29% less coefficient of friction and-8.4 times greater relative wear resistance than that of MAO coating without diffusion annealing.Öğe Impact performances and failure modes of glass fiber reinforced polymers in different curvatures and stacking sequences(SAGE Publications Ltd, 2022) Kaboğlu, Cihan; Eken, Taha Yasin; Yürektürk, YakupRecently, glass fiber reinforced polymer composites have been increasingly used in applications which are exposed to impact loads due to their high strength, low weight, and corrosion resistance properties. Therefore, the effect of curvature of composite laminate on their impact resistance is important. In this study, the mechanical properties of three curvature diameters and two stacking sequences, which have not been compared before, were examined and compared. The diameter of curved composites is 760 mm, 380 mm, and 304 mm and flat designated as A, B, C, and D, respectively. The fiber stacking orders are [0/0/-45/+45/90/90]S and [90/90/-45/+45/0/0]S designated as Type 1 and Type 2, respectively. The drop-weight impact tests were performed and failure modes of composites were examined. It was observed that the impact resistance decreases with the increase of curvature, where 760 mm diameter and Type 2 composites had the highest strength in all of the composites. In addition, delamination, fiber breakage, and matrix cracking failure modes were observed in the composites after impact. The reason why the strength decreases as the curvature of the composite increases is that the curved areas create an effect that increases the external force applied. The reason why Type 2 stacking order is more durable than Type 1 stacking order is that the 90° fiber direction in the bottom layer has a damping effect on the applied force. According to the results of this study, composite materials with larger diameter and stacking order starting with 0° provides more mechanical strength. (Figure presented.)Öğe Influence of Electrolyte Compositions and Electrical Parameters on Thermal Properties of Micro-Arc Oxidized AZ91 Alloy(Springer, 2021) Selvi, Ekin; Muhaffel, Faiz; Yürektürk, Yakup; Vanli, Ali Serdar; Baydogan, MuratIn this study, AZ91 Mg alloy was micro-arc oxidized using different voltages in silicate- and aluminate/phosphate-based (dual) electrolytes that included K2ZrF6 or Na2ZrO3 as the Zr source for synthesizing ZrO2 in the micro-arc oxidation (MAO) coatings. Structural characterizations were done by using scanning electron microscopy and x-ray diffraction techniques. MAO coating characteristics of different samples were compared by measuring coating thickness, surface roughness, average pore size, and total pore fraction. Both hardness and pull-off tests were conducted to characterize the mechanical properties of the coatings. Thermal conductivity measurements and thermal shock tests were also carried out to evaluate the effect of the electrolyte composition and the type of Zr containing compound. It was found that the equivalent thermal conductivity of the MAOed samples can be reduced up to 30% compared to the bare AZ91 alloy. The decrease of the thermal conductivity was mainly attributed to formation of a thicker and denser MAO coating, and the incorporation of ZrO2 phase into the fabricated MAO coating. Finally, increased thermal shock resistance was strongly correlated with a lower hardness and higher cohesive strength of the MAO coating, which also leads to smaller crack formation and spallation-free surface characteristics.Öğe Investigation of indentation and dry sliding wear behaviour of Al-12.6 wt.% Si-10 wt.% TiB2 composites produced by sequential milling and pressureless sintering(Carl Hanser Verlag, 2019) Tekoglu, Emre; Yürektürk, Yakup; Agaogullari, Duygu; Dilawary, Shaikh Asad Ali; Baydogan, Murat; Ovecoglu, M. LutfiThe main purpose of this study is to comprehend the effects of cryomilling (CM) time on dry sliding wear behaviour of 10 wt.% TiB2 reinforced Al-12.6 wt.% Si metal matrix composites (MMCs). The MMCs were synthesised via sequential milling (mechanical alloying + cryomilling) and pressureless sintering. Indentation tests performed at a maximum load of 200 g showed that the Young's modulus and hardness of the composites increased up to 20 min of CM time. The effects of CM time and load on the composites were examined based on their tribological properties. Based on the results, the 4 h mechanical alloyed (MA'd) and 30 min CM'd sample showed the lowest wear rate under the normal load of 1 N, with its wear mechanism being predominantly oxidative. However, for the normal load of 4 N, the lowest wear rate was found in the 4 h MA'd composite, in which the dominant wear mechanism was abrasion.Öğe Investigation of the effects of hot dip aluminizing and diffusion annealing on microstructural and tribological properties of dual phase (DP800) steels(Pamukkale Üniversitesi, 2024) Yürektürk, Yakup; Çeltik, CansuIn this study, the effects of hot dip aluminizing (HDA) (90 s at 725°C) and diffusion annealing on the microstructural and tribological properties of DP800 steel were investigated. After HDA treatment, one of the sample was left to cool in air (HDA-1) and the other one left to cool in air after being subjected to a diffusion annealing for 1 hour in an oven set at 300°C (HDA-2). Evolution in mechanical and tribological properties depending on the developments in the coating microstructure investigated in terms of hardness and wear behaviour, respectively. Mechanical characterization results show that diffusion annealing increases the hardness value of hot dip aluminized steel to 1100 HV values. Considering the wear ball volume and friction coefficients, the most advanced tribological properties were observed in the diffusion-annealed HDA process (HDA-2).Öğe Modification of Cold-Sprayed Aluminum Coating on Nickel-Aluminum Bronze by Micro-Arc Oxidation(Springer, 2021) Yürektürk, YakupThis study aims to improve the wear resistance of nickel-aluminum bronze (NAB) substrates by micro-arc oxidation (MAO). As this treatment is difficult to apply to NAB surface, cold spraying (CS) was first used to deposit aluminum with a purity of 99.5% onto the NAB substrates. The aluminum-coated substrate was then treated by MAO to convert the aluminum layer into Al2O3 coating in order to enhance the wear resistance. The tribological behavior of NAB substrates with or without the alumina coating was evaluated with a dry sliding wear test using a ball-on-flat reciprocating tester with varied testing loads ranging from 1 to 5 N. The results demonstrated that the oxide layer (Al2O3) formed on the aluminum layer enhanced the wear resistance of NAB alloy against 100Cr6 steel ball. Compared to uncoated NAB alloy, the wear resistance (inverse of wear rate) of the NAB alloy with the MAO coating was at least nine times higher than that of the uncoated NAB alloy at all testing loads.Öğe Sıcak daldırma alüminyumlama (SDA) ve difüzyon tavlaması ile yüzeyi modifiye edilmiş Ti-6Al-4V alaşımının karakterizasyonu(2023) Yürektürk, YakupBu çalışmada, Ti6Al4V alaşımı önce sıcak daldırma alüminyumlama (SDA) işlemine ardından difüzyon tavlamasına tabi tutulmuştur. SDA 750°C'de 3 dk. uygulanmış ve bu işlemin uygulanmasıyla yüzeyde en üst tabaka bir Al ile Al3Ti difüzyon tabakasından bir kaplama oluşturulmuştur. Difüzyon tavlaması (DT) için sıcak daldırma alüminyumlanmış numuneler ısıtma hızı <12°C/s olan bir rezistans fırınında 1000°C'ye yükselecek şekilde ayarlanmış ve bu sıcaklıkta 1 saat tutulmuştur. Difüzyon tavlamasından sonra yeni bir formda Al3Ti ve oksit fazlarından (Al2TiO5, Al2O3) oluşan bir kompozit tabaka oluşmuştur. DT işlemi sonrasında oluşan kompozit kaplamanın yapısı incelendiğinde genel olarak üniform ve yoğun bir görünüm sergilediği, belirgin bir çatlak ve boşluk içermediği görülmektedir. Numunelerin yapısal, mekaniksel ve aşınma özellikleri SEM-EDS, XRD, sertlik ve kuru ortam “ball-on disc ” konfigürasyonunda tribometre testleri kullanılarak karakterize edilmiştir. Ti-6Al-4V alaşımı üzerine uygulanan SDA ve difüzyon tavlaması ile sertlik sadece SDA uygulanmış numuneye kıyasla ~11 kat ve başlangıç haline kıyasla ~1,4 kat yükselmiştir. Aşınma testi sonuçlarına göre, numuneler arasında en iyi aşınma direncini SDA ve ardından difüzyon tavlaması uygulanmış numune göstermiştir.
