Yazar "Amanov, Auezhan" seçeneğine göre listele

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    Effect of combined shot peening and ultrasonic nanocrystal surface modification processes on the fatigue performance of AISI 304
    (Elsevier Science Sa, 2019) Amanov, Auezhan; Karimbaev, Ruslan; Maleki, Erfan; Unal, Okan; Pyun, Young-Sik; Amanov, Tileubay
    In this study, the fatigue performance of AISI 304 subjected to shot peening (SP), ultrasonic nanocrystal surface modification (UNSM) and the combination of SP + UNSM processes was systematically assessed by rotary bending fatigue (RBF) tester at different stress levels. The purpose of combining SP and UNSM processes is to find out whether SP following UNSM process can further improve the fatigue life of AISI 304 in comparison with the SP and UNSM processes alone. Interestingly, the fatigue strength of AISI 304 was deteriorated by the combination of SP + UNSM processes in comparison with the UNSM process alone, but the combination of SP + UNSM processes demonstrated a higher fatigue strength in comparison with the SP process alone.
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    Effects of constrained groove pressing, severe shot peening and ultrasonic nanocrystal surface modification on microstructure and mechanical behavior of S500MC high strength low alloy automotive steel
    (Elsevier, 2021) Karademir, Ibrahim; Celik, Mustafa B.; Husem, Fazil; Maleki, Erfan; Amanov, Auezhan; Unal, Okan
    S500MC high strength low alloy automotive steel is exposed to bulk severe plastic deformation (SPD) via constrained groove pressing (CGP) and surface severe plastic deformation (S2PD) via severe shot peening (SSP) and ultrasonic nanocrystal surface modification (UNSM). SSP and UNSM could create a nanocrystallization layer till 50-100 mu m away from outmost surface. EBSD investigations showed average nano-grain size obtained via SSP and UNSM was found to be below 100 nm regime. The strength was improved via 1st to 4th pass of CGP, but elongation percentage decreased abruptly. UNSM achieves both strength-ductility improvement with gradient structure. SSP improves the total elongation however a slight decrease on strength is observed. SSP and UNSM showed better wear and friction resistance particularly at lower loads compared to CGP and untreated specimens. Nevertheless, wear and friction behavior at higher loads showed better responses for Bulk-SPD applications regardless of pass numbers. The frictional load increase played a detrimental role in removing a nano crystallization surface layer and diminishing the positive influence of SSP and UNSM.
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    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, Okan
    In 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.
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    Fatigue crack growth rate of AISI 4140 low alloy steel treated via shot peening and plasma nitriding
    (Pergamon-Elsevier Science Ltd, 2023) Ozturk, Mehmet; Husem, Fazil; Karademir, Ibrahim; Maleki, Erfan; Amanov, Auezhan; Unal, Okan
    In this study, the effects of conventional shot peening (CSP), severe shot peening (SSP), and plasma nitriding (PN) on the fatigue crack growth (FCGR) of AISI 4140 low alloy steel were investigated. FCGR tests were performed on axial fatigue equipment, associated with slow-motion camera and COD gauge. As a result of the experiments, an improvement of 8% in CSP, 15% in SSP, and 5,5% in the PN operations were observed on the number of cycles of all specimens at 30 mm crack length. Particularly for SSP treatments, hardness, compressive stresses, and the creation of nano-crystallization on the surface provide the most effective improvement in FCGR behavior. Additionally, for PN, formation of nitrogen diffusion and effective hardness improvement showed positive results in FCGR behavior. CSP and SSP (particularly SSP) behaved dominant on the improvement of FCGR performance compared to PN treatment. The formation of two-phase brittle structural white layer on the surface prevented the effective FCGR improvement.
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    An improvement in fatigue behavior of AISI 4340 steel by shot peening and ultrasonic nanocrystal surface modification
    (Elsevier Science Sa, 2020) Karimbaev, Ruslan; Pyun, Young-Sik; Maleki, Erfan; Unal, Okan; Amanov, Auezhan
    Individual and synergy effects of shot peening (SP) and ultrasonic nanocrystal surface modification (UNSM) on rotary bending fatigue (RBF) behavior of AISI 4340 steel were systematically investigated at various bending stress levels in the range of 275-600 MPa. The results revealed that the fatigue behavior of the as-received sample was enhanced by SP and it was further enhanced by SP and UNSM combination, while the UNSM-treated one exhibited the highest enhancement in fatigue behavior. The fatigue behavior of the SP + UNSM sample was enhanced after SP, but it was found to be detrimental after UNSM. Apart from RBF experiments, individual and synergy effects of SP and UNSM on surface roughness, hardness, residual stresses and grain size were analyzed as well. Fractography of the samples was characterized by scanning electron microscope (SEM) and fatigue mechanisms of each sample were discussed based on the obtained observations. The finest grain size and highest compressive residual stress (CRS) obtained by UNSM in comparison with those of the SP and SP + UNSM was responsible for the best fatigue performance.
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    Novel experimental methods for the determination of the boundaries between conventional, severe and over shot peening processes
    (Elsevier, 2018) Maleki, Erfan; Unal, Okan; Amanov, Auezhan
    Shot peening process is one of the severe plastic deformation methods which is well-recognized for the surface layer integrity of the components. This process, according to its energy level, can be categorized into three different cases of conventional, severe, and over shot peening. The aforementioned types of shot peening have positive and/or negative effects on their related performing conditions. In this study, the boundaries between these processes were determined for the first time by presenting novel approaches. The foundations of the presented approaches are microstructural investigations. The microstructures were characterized using optical microscopy, scanning electron microscopy, field emission scanning electron microscopy, and high resolution transmission electron microscopy observations and X- ray diffraction analysis. In addition, micro-hardness, residual stress measurements, and fatigue tests were carried out to study the effects of those three different shot peening processes.