Yazar "Purcek, G." seçeneğine göre listele

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    Effect of Chemical Composition and Grain Size on RT Superplasticity of Zn-Al alloys processed by ECAP
    (Russian Acad Sciences, Inst Metals Superplasticity Problems, 2015) Demirtas, M.; Purcek, G.; Yanar, H.; Zhang, Z. J.; Zhang, Z. F.
    Dilute Zn-0.3Al, eutectic Zn-5Al and eutectoid Zn-22Al alloys were processed by multi-pass equal channel angular pressing (ECAP) in order to achieve fine grained (FG) or ultrafine-grained (UFG) microstructure and room temperature (RT) superplasticity. ECAP refined the microstructure of Zn-0.3Al and resulted in a FG Zn-rich.-matrix with an average grain size of 2 mu m and homogeneously distributed nano-sized Al-rich a-particles with the grain sizes in the range of 50-200 nm. A bi-modal microstructure was achieved in Zn-5Al alloy with UFG Al-rich a-and FG Zn-rich.-phases having mean grain sizes of 110 nm and 540 nm, respectively. ECAP brought about an agglomerate-free UFG microstructure in Zn-22Al alloy with an average grain size of 200 nm which is the lowest one obtained so far for this alloy after ECAP processing. The maximum RT superplastic elongations of 1000%, 520% and 400% were achieved for Zn-0.3Al, Zn-5Al and Zn-22Al alloys, respectively. Considering the RT superplasticity in Zn-Al alloys, it was found that lower Al content results in higher superplastic elongations even if the alloy has relatively larger grain size. Grain boundary sliding (GBS) was found to be the main deformation mechanism in region-II as the optimum superplastic region during RT deformation for all three Zn-Al alloys with the strain rate sensitivity factor ranging between 0.25-0.31.
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    Effect of long-term natural aging on microstructure and room temperature superplastic behavior of UFG/FG Zn-Al alloys processed by ECAP
    (Russian Acad Sciences, Inst Metals Superplasticity Problems, 2018) Demirtas, M.; Yanar, H.; Purcek, G.
    Two potential superplastic compositions of Zn-Al alloy systems, Zn-22Al and Zn-0.3Al alloys, were chosen and processed by equal-channel angular pressing /extrusion (ECAP /E) in order to achieve high strain rate (HSR) superplasticity at room temperature (RT). ECAP-processed samples of both alloys were then subjected to long-term natural aging up to 1100 days to evaluate the effect of long-term natural aging on their microstructures and superplastic behaviors. Before natural aging, the maximum elongations to failure at RT were 400 % for ultrafine-grained (UFG) Zn-22Al at the strain rate of 5 x 10(-2) s(-1) and 1000 % for fine-grained (FG) Zn-0.3Al at the strain rate of 1 x 10(-4) s(-1). Long-term natural aging did not cause a significant change in the elongation of UFG Zn-22Al alloy with 355 % maximum elongation. However, optimum strain rate giving the maximum elongation decreased to 3 x 10(-3) s(-1). On the other hand, Zn-0.3Al alloy lost more than half of its superplastic elongation and showed an elongation to failure of 435 % at the end of the natural aging period of 1100 days. Microstructural analyses show that grain boundary corrosion occurred in dilute Zn-0.3Al alloy during the natural aging process. Corroded grain boundaries resulted in cavity nucleation during the tensile tests and some of these cavities attained large sizes and caused premature failure.