Browsing by Subject "Surface nanocrystallization"

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    Surface nanocrystallization of SAE 1008 steel by single and multipass thread rolling process; [Nanokristallisierung der Oberfläche von SAE 1008 Stahl durch Ein- und Mehrfach-Gewindewalzen]
    (Wiley-VCH Verlag, 2017) Kahraman F.; Gençer G.M.; Kahraman A.D.
    In this study, the layers are investigated which are obtained on the surfaces of the single and multi-pass thread rolled screws. It is observed that deformation is more homogenous depending on the pass number and thread laps failure do not form on the 3-passed threads. A nanocrystallized layer that thicknesses and size depends on deformation amount is determined on the surfaces of the thread rolled SAE 1008 steel. While top of this layer has finer grain sizes, depending on the deformation amount grains coursed and oriented by the deformation direction. The finer grains are observed in the single pass thread rolled sample as size of 136 nm at the 15 μm inside from the surface of the root of the thread. Compared with bulk material, significant hardness increase is observed on the surfaces of the all thread rolled samples. The effect of pass number on the hardness is very low, increases of the pass number, hardness increases slightly. But thicknesses of layer are enhanced to increase the pass number. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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    Effect of the surface nanocrystallization on tribological behavior of the Cu based bimetallic materials (CuPbSn)
    (Institute of Physics Publishing, 2019) Gencer G.M.; Yolcu C.; Kahraman F.; Saklakoǧlu N.
    In this study, ultrasonic impact treatment was used to improve the tribological behavior of copper-based bimetallic materials that are used in internal combustion engine bearings and bushes. Bimetallic materials were obtained by coating three different CuPbSn alloys by sintering on the material surfaces of carbon steel substrate. After the sintering process, bimetallic materials were treated by ultrasonic impact process. As a result of the metallographic examination, sintered layers have uniform structure along the cross-section of the bimetallic materials. In addition, it was determined that the porosity of sintered materials decreased after the ultrasonic impact treatment. Due to the grain refinement and work hardening, higher hardness was obtained in the fine-grained layer. The hardness of the ultrasonic impact treated samples always higher than the untreated material. Because of the high surface hardness, ultrasonic impact treated samples showed higher wear resistance. The highest wear resistance was detected in the samples with the highest Sn content. Because Sn and Cu combine to form Cu3Sn intermetallic phase in Cu-Pb alloys and Cu3Sn increases the strength of the Cu-Pb alloys. Thus, increasing the Sn content in the Cu-Pb alloy resulted in the wear resistance increase. Furthermore, the formation of the SnO2 intermetallic phase on the sample surface has a significant effect on the wear resistance increase by preventing adhesion. © 2019 IOP Publishing Ltd.