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Öğe AA7075 alüminyum alaşımlarının farklı tip yüzey işlemleri ile yorulma davranışlarının iyileştirilmesi(Karabük Üniversitesi, 2018) Efe, Yusuf; Ünal, OkanBu çalışmada, AA7075 alüminyum alaşımlarına mekanik yüzey işlemleri olarak aşırı bilyalı dövme işlemi (ABD) ve ultrasonik nanokristal yüzey modifikasyonu işlemi (UNYM) uygulanmıştır. İşlemler sırasıyla aşırı bilyalı dövme işlemi, UNYM işlemi, ABD sonrası UNYM işlemi ve UNYM işlemi sonrası ABD işlemi olarak belirlenmiştir. Mekanik yüzey işlemlerinin uygulanmasından sonra, numunelerin mekanik ve tribolojik özelliklerini belirlemek için yorulma, aşınma, kalıntı gerilme, mikro sertlik, XRD ve yüzey pürüzlülüğü testleri gerçekleştirilmiştir. Aşınma testleri oda sıcaklığında kuru kayma koşullarında gerçekleştirilmiştir. Yorulma testleri oda sıcaklığında eksenel gerilmeli yorulma test cihazında gerçekleştirilmiştir. Ayrıca, numunelerin yüzeyine dik kesit bölgelerinden optik mikroskop ve SEM görüntülerine bakılmıştır. Genel olarak tüm yüzey işlemlerinin malzemelerin yüzeyinde tane boyutunu incelttiği, yüzeyde deformasyon sonrası mikroyapıda önemli değişimler meydana getirdiği, yüzeyde sertlik artışına neden olduğu ve artık basma gerilmesi oluşturduğu dikkat çekmektedir. Yorulma özellikleri UNYM sonrası en etkili sonuçlar elde edilirken çift katmanlı yüzey işlemi olan UNYM+ABD işlemi sonrası en etkili aşınma özellikleri dikkat çekmektedir.Öğe Effects of conventional shot peening, severe shot peening, re-shot peening and precised grinding operations on fatigue performance of AISI 1050 railway axle steel(Elsevier Sci Ltd, 2022) Unal, Okan; Maleki, Erfan; Karademir, Ibrahim; Husem, Fazil; Efe, Yusuf; Das, TuranIn this study, effects of conventional shot peening, severe shot peening, re-shot peening and precised grinding were performed to AISI 1050. By two-stage operations (SSP + RSP), residual stress depth and the magnitude on the surface were quite high. While deepest compressive stress was measured in A24 + G, maximum stress was observed in A24 + N14. Grinding and re-shot peening powerfully reduced the roughness. The increase in SP intensity improved the hardness considerably, besides the most effective hardness depth was observed after A36. N7 and N14 contributed effective results in the low cycle fatigue, whereas A24, A18, A18 + N14 and A36 in high cycle fatigue.Öğe Effects of static load on microstructural and mechanical performance of AISI 1050 medium carbon steel subjected to ultrasonic nanocrystal surface modification(Elsevier Science Sa, 2022) Unal, Okan; Husem, Fazil; Maleki, Erfan; Karademir, Ibrahim; Efe, Yusuf; Das, TuranIn this study, the effects of mild (M1, M2, M3), moderate (O1,O2), and severe (S1, S2, S3) static loads of ultrasonic nanocrystal surface modification (UNSM) on AISI 1050 steel were investigated. The layer affected by severe plastic deformation at moderate and severe static loadings became much thicker and the nanocrystalline layer became dominant around the surface region. The layer thickness influenced by the UNSM reached approximately 350 mu m. UNSM had a positive effect on the surface roughness and morphology via reducing the Ra between 0,3 mu m and 0,8 mu m excluding the highest static loads. Oxidation formation was observed on the surface at severe static load conditions. The microhardness showed a significant improvement independently of static loads, and the hardness depth reached up to approximately 250 mu m after the UNSM. Remarkable alteration in surface hardness was observed by increasing static load. Higher static loads ensured both deposition the compressive residual stress to the surface and propagation towards interior. The compressive stress of-700 MPa and a stress depth of over 1 mm were obtained by severe static loading. The processes implemented by moderate and severe static loads showed better performance over both low and high-cycle fatigue behavior.Öğe Enhancement in microstructural and mechanical performance of AA7075 aluminum alloy via severe shot peening and ultrasonic nanocrystal surface modification(Elsevier, 2020) Efe, Yusuf; Karademir, Ibrahim; Husem, Fazil; Maleki, Erfan; Karimbaev, Ruslan; Amanov, Auezhan; Unal, OkanIn this experimental study, AA7075 aluminum alloy was subjected to pure severe shot peening (SSP), pure ultrasonic nanocrystalline surface modification (UNSM) and the combination of these two treatments. The treated specimens were analyzed with detailed microstructure analysis, micro-hardness, surface roughness, XRD investigations and wear-friction tests. The results demonstrated that UNSM exhibited fine surface finish and provided minimum surface roughness with the Ra value of 0.8 limo Moreover, UNSM played an important role in the reduction of Ra as a secondary treatment. Electron back scatter diffraction (EBSD) analysis, full width at half maximum (FWHM) evaluations and compressive residual stress (CRS) measurements showed that the deformed layer structure was converted into a nanocrystallized and compressively stressed zone via SSP and UNSM. The hardness on the topmost layer was effectively enhanced by UNSM + SSP and SSP + UNSM processes. The wear and friction performance were particularly improved by two-stage operations of UNSM + SSP and SSP + UNSM. The performance was also compatible with the hardness, residual stress and nanocrystallization investigations.Öğe The formation of gradient nanostructured medium carbon steel via mild, moderate, and severe ultrasonic nanocrystal surface modification options: Assessment on wear and friction performance(Elsevier, 2022) Unal, Okan; Maleki, Erfan; Karademir, Ibrahim; Husem, Fazil; Efe, Yusuf; Das, TuranIn this study, the effect of UNSM applied under different static loads on the microstructure and friction-wear performance were detected. A significant correlation was noticed between the increase of the static load and nanocrystalline layer thickness. Both nanocrystallization layer and deformation depth increased significantly after UNSM. The grain size was measured under 500 nm for M series and 100 nm for O and S series of UNSM static loads. Surface integrity improved remarkably after mild (M) and moderate (O) UNSM (Ra values are 0.25 mu m and 0.7 mu m, respectively). The roughness was achieved approximately under 1 mu m for M and O types and 2 mu m for S types of operations. A 65% increase in hardness emerged by severe UNSM with a surface hardness of approximately 375-430 HV. UNSM demonstrated remarkable results on friction-wear performance by providing higher microhardness and residual compressive stress improvements with lower surface roughness.Öğe Surface Severe Plastically Deformed Nanostructured AA7075 Alloy: Assessment on Tribological and Axial Fatigue Behaviors(Springer, 2020) Efe, Yusuf; Karademir, Ibrahim; Husem, Fazil; Maleki, Erfan; Unal, OkanAA7075 alloy is exposed to severe shot peening (SSP) with an Almen intensity of 20A. The microstructure is analyzed via FEGSEM and EBSD microscopy. X-ray diffraction (XRD) analysis is used to evaluate the crystallite size in terms of FWHM measurements. The residual stress measurements show a thicker compressed layer (600 mu m) formed by SSP. Microhardness improvements are observed as 30% on topmost surface and releases substantially after 600 mu m. Coefficient of friction (COF) of treated material remains higher throughout the sliding distance, however, is reduced particularly in the early stage of sliding distance for the wear load of 20 N. The effect of SSP is vanished particularly at lower loads with longer sliding distances. Besides, improvement on fatigue behavior is observed after SSP despite the increase of roughness remarkably.
