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    Effect of severe vibratory peening on microstructural and tribological properties of hot rolled AISI 1020 mild steel
    (Elsevier Science Sa, 2020) Das, Turan; Erdogan, Azmi; Kursuncu, Bilal; Maleki, Erfan; Unal, Okan
    In this study, microstructural and mechanical performance of AISI 1020 were investigated after severe vibratory peening (SVP) for emerging the potential and performance of this novel treatment among surface severe plastic deformation (SSPD) methods. The specimens were subjected to SVP treatment of V1, V2, and V3 conditions at 20, 40 and 60 min. durations, respectively. Optical microscope (OM) and SEM images demonstrated two layered gradient structure. XRD analysis showed the oxide layer was completely vanished besides surface nanocrystallization by severe plastic deformation (SPD). The microhardness test revealed an average improvement of 48% compared to the untreated specimen. SVP caused raising of hardness from surface to a depth of approximately 900 mu m. In wear tests, the volume loss after SVP were less. The hardness improvement due to deformation overcame the negative effect caused by roughness increase. However, the friction coefficient of the unpeened specimen was the lowest at all loads.
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    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, Turan
    In 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.
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    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, Turan
    In 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.
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    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, Turan
    In 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.