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Öğe Effect of precipitation on mechanical and wear properties of ultrafine-grained Cu-Cr-Zr alloy(Elsevier Science Sa, 2014) Purcek, G.; Yanar, H.; Saray, Onur; Kraman, I.; Maier, H. J.The effect of an ultrafine-grained (UFG) microstructure and subsequent aging treatment on the mechanical and wear behavior of a Cu-Cr-Zr alloy was investigated. The results indicate that the precipitates dispersed within the UFG matrix significantly enhance the strain hardening, resulting in improvement of hardness, strength and wear resistance of the alloy, without notably sacrificing the elongation to failure and electrical conductivity, due to the combined effect of grain refinement and precipitation. The wear behavior of Cu-Cr-Zr alloy was found to be strongly dependent on its strength and hardness. The minimum weight loss (or the highest wear resistance) was obtained when the sample was processed by equal channel angular extrusion (ECAE) through an additional aging treatment, as this resulted in ultra-high strength and hardness. The wear results also indicate that the wear behavior of Cu-Cr-Zr alloy in all processing conditions is consistent with the Archard approach. Complex wear mechanisms such as adhesive, oxidative and abrasive wear, and delamination were found to be operative in the differently processed Cu-Cr-Zr alloys. It is to be concluded that the use of a two-step process, the first resulting in an UFG microstructure and a subsequent aging treatment provides a simple and effective procedure for extraordinary increase in strength, hardness and wear resistance of Cu-Cr-Zr alloys without modification of the chemical composition. (C) 2014 Elsevier B.V. All rights reserved.Öğe Effect of two-pass friction stir processing on the microstructure and mechanical properties of as-cast binary Al-12Si alloy(Elsevier Science Sa, 2015) Aktarer, S. M.; Sekban, D. M.; Saray, Onur; Kucukomeroglu, T.; Ma, Z. Y.; Purcek, G.The effect of two-pass friction stir processing (FSP) on the microstructural evolution, mechanical properties and impact toughness of as-cast Al-12Si alloy was investigated systematically. Severe plastic deformation imposed by FSP resulted in a considerable fragmentation of the needle-shaped eutectic silicon particles into the smaller ones. The length of eutectic Si particles decreased from 27 +/- 23 mu m to about 2.6 +/- 2.4 mu m. The average aspect ratio of 6.1 +/- 5.1 for eutectic Si particles in the as-cast state decreased to about 2.6 +/- 1.0 after FSP with a corresponding increase in their roundness. The hardness, strength, ductility and impact toughness of the alloy increased simultaneously after two-pass FSP. The increase in the yield and tensile sirength values after FSP was about 20% and 29%, respectively. The FSPed alloy exhibited 25% elongation to failure and 15% uniform elongation which were almost seven times and five times higher, respectively, than those of the as-cast alloy. The hardness of the alloy increased from 58 Hv0.5 for the as-cast state to about 67 Hv0.5 after FSP. The absorbed energy during impact test increased to about 8.3 J/cm(2) after FSP, which is about seven times higher than that of the as-cast alloy. Improvements in all mechanical properties were mainly attributed to the radical changes of the shape, size arid distribution of the eutectic silicon particles along with the breakage and refined of the large alpha-Al grains during two-pass FSP. (C) 2015 Elsevier B.V. All rights reserved.Öğe Formability of friction stir processed low carbon steels used in shipbuilding(Journal Mater Sci Technol, 2018) Sekban, D. M.; Akterer, S. M.; Saray, Onur; Ma, Z. Y.; Purcek, G.The stretch formability of a low carbon steel processed by friction stir processing (FSP) was studied under biaxial loading condition applied by a miniaturized Erichsen test. One-pass FSP decreased the ferritic grain size in the processed zone from 25 mu m to about 3 mu m, which also caused a remarkable increase in strength values without considerable decrease in formability under uniaxial loading. A coarse-grained (CG) sample before FSP reflected a moderate formability with an Erichsen index (EI) of 2.73 mm. FSP slightly decreased the stretch formability of the sample to 2.66 mm. However, FSP increased the required punch load (F-EI) due to the increased strength by grain refinement. FSP reduced considerably the roughness of the free surface of the biaxial stretched samples with reduced orange peel effect. The average roughness value (Ra) decreased from 2.90 in the CG sample down to about 0.65 mu m in fine-grained (FG) sample after FSP. It can be concluded that the FG microstructure in low carbon steels sheets or plates used generally in shipbuilding provides a good balance between strength and formability. (C) 2017 Published by Elsevier Ltd on behalf of The editorial office of Journal of Materials Science & Technology.Öğe Improvement of formability of ultrafine-grained materials by post-SPD annealing(Elsevier Science Sa, 2014) Saray, Onur; Purcek, G.; Karaman, I.; Maier, H. J.Ultrafine-grained (UFG) IF-steel, as an example of an essentially single phase UFG microstructure, was annealed at different temperatures and time intervals in order to improve its formability by achieving a good strength-ductility-formability balance. In general, annealing increased the ductility and formability of UFG steel. Annealing at temperatures inside the recovery region caused a limited improvement in the formability of UFG steel due to the relief of internal energy without considerable grain coarsening. As the grain size increased to above 4 mu m by annealing at temperatures inside the partially recrystallization region, the formability of UFG steel in the uniform region increased considerably, and localized deformation with early necking changed to a homogeneous mode as revealed by increased uniform thinning and enlargement of the membrane straining regime. Further grain coarsening resulted in a slight increase in uniform elongation both in uniaxial and biaxial tests. The UFG microstructure reduced the roughness of the free surface of biaxially stretched samples by decreasing the non-uniform grain flow, which leads to the so-called orange peel effect. Annealing of UFG microstructure did not degrade this positive effect due to the formation of sharp recrystallization textures although the annealed microstructures have relatively coarse grains. It can be concluded that a good balance between strength and uniform formability without an orange-peel effect can be achieved in UFG microstructures by well-design annealing processes. (C) 2014 Elsevier B.V. All rights reserved.Öğe Microstructure, mechanical properties and formability of friction stir processed interstitial-free steel(Elsevier Science Sa, 2015) Sekban, D. M.; Saray, Onur; Aktarer, S. M.; Purcek, G.; Ma, Z. Y.The microstructure, mechanical properties and stretch formability of fine-grained (FG) interstitial-free steel (IF-steel) formed by friction stir processing (FSP) was investigated systematically. One-pass FSP drastically refined the microstructure with aid of dynamic recrystallization (DRX) mechanism during processing and formed volumetric defect free basin-like processed region (PR) with a mean grain size of 5 mu m (initial grain size was 40 mu m). This microstructural evolution brought about a considerable increase in both hardness and strength values of IF-steel without considerable decrease in ductility values. Also, strain hardening dominated deformation behavior was obtained with the FSPed samples as an essential property for the engineering application. Coarse-grained (CG) IF-steel demonstrated high formability with an Erichsen index (El) of 2.88 mm. Grain refinement by FSP yielded very close El value of 2.80 mm with increasing punch load (F-El). Force-displacement curves obtained in each process conditions reflected a similar membrane straining regimes where samples uniformly thinned under biaxial tension loads with aid of strain hardening capability. The formation of FG microstructure by FSP reduced the roughness (orange peel effect) of the free surface of biaxial stretched sample by decreasing the nonuniform grain flow leading to the so-called orange peel effect. It is concluded that a good balance of strength, ductility and strain hardenability along with equivalence formability to CG condition can be achieved by FSP as a single step practical procedure. (C) 2015 Elsevier B.V. All rights reserved.Öğe Room temperature superplasticity in fine/ultrafine-grained Zn-Al alloys with different phase compositions(Trans Tech Publications Ltd, 2018) Demirtas, M.; Yanar, H.; Saray, Onur; Purcek, G.Three Zn-Al alloys, namely Zn-22Al, Zn-5Al and Zn-0.3Al, were subjected to equal-channel angular pressing (ECAP), and the effect of ECAP on their microstructure and room temperature (RT) superplastic behavior were investigated in detail referring to previous studies reported by the authors of the current study. ECAP remarkably refined the microstructures of three alloys as compared to their pre-processed conditions. While the lowest grain size was achieved in Zn-22Al alloy as 200 nm, the grain sizes of Zn-5Al and Zn-0.3Al alloys were ~540 nm and 2 µm, respectively, after ECAP. After the formation of fine/ultrafine-grained (F/UFG) microstructures, all Zn-Al alloys exhibited superplastic behavior at RT and high strain rates. The maximum superplastic elongations were 400%, 520% and 1000% for Zn-22Al, Zn-5Al and Zn-0.3Al alloys, respectively. It is interesting to point out that the highest RT superplastic elongation was obtained in Zn-0.3Al alloy with the largest grain size, while Zn-22Al alloy having the lowest grain size showed the minimum superplastic elongation. This paradox was attributed to the different phase compositions of these alloys. The formation of Al-rich ?/? phase boundaries, where grain boundary sliding is minimum comparing to Zn-rich ?/? and ?/? phase boundaries of Zn-Al alloys, is the lowest level in Zn-0.3Al alloy among all the alloys. Therefore, it can be concluded that if it is desired to achieve high superplastic elongation in Zn-Al alloys at RT, keeping Al content at a possibly minimum level seems to be the most suitable way. © 2018 Trans Tech Publications, Switzerland
