Yazarlar

• Demirtas, M.(2)
• Purcek, G.(2)
• Yanar, H.(2)
• Demirtas, Muhammet(1)
• Department of Mechanical Engineering, Ibaraki University, 4-12-1 Nakanarusawa, Hitachi, 316-8511(1)
• Graduate School of System Design, Tokyo Metropolitan University, 6-6 Asahigaoka, Hino,Tokyo, 191-0065(1)
• Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency, 3-1-1 Yoshinodai, Chuo, Sagamihara, Kanagawa, 252-5210(1)
• Itoh, G.(1)
• Itoi, T.(1)
• Kawasaki, M.(1)
• Kitazono, K.(1)
• Kobayashi, J.(1)
• Morita, K.(1)
• National Institute for Materials Science, 1-2-1 Sengen, Tsukuba, 305-0047(1)
• Purcek, Gencaga(1)
• Sato, E.(1)
• Takayama, Y.(1)
• Yanar, Harun(1)
• Zhang, Zhe-Feng(1)
• Zhang, Zhenjun(1)

• MakaleAçık Erişim2018Scopus SJRQ3/r/bayburt/13676
  Effect of long-term natural aging on microstructure and room temperature superplastic behavior of UFG/FG Zn-Al alloys processed by ECAP

  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 × 10 −2 s −1 and 1000% for fine-grained (FG) Zn-0.3Al at the strain rate of 1 × 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 × 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.

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• MakaleYalnız künye2018Scopus SJRQ1/r/bayburt/12479
  High temperature superplasticity and deformation behavior of naturally aged Zn-Al alloys with different phase compositions

  Demirtas, M.; Kawasaki, M.; Yanar, H.; Purcek, G.

  Two Zn-Al alloys, eutectoid Zn-22Al and dilute Zn-0.3Al, were processed through equal-channel angular pressing (ECAP). The ECAP-processed alloys were subjected to long-term natural aging at room temperature for 120 days in order to investigate the effect of long-term natural aging on high-temperature superplasticity and the deformation behavior of these alloys. The grain size of the Zn-22Al alloy increased from 200 nm after ECAP to 400 nm after the natural aging process. The Zn-0.3Al alloy with a grain size of 1.3 µm after ECAP demonstrated a reasonably stable microstructure with the grain size of ~ 1.7 µm after long-term natural aging. The naturally aged ultrafine-grained (UFG) Zn-22Al alloy showed an excellent superplastic elongation of about 1800% at 200 °C. Grain boundary sliding was determined as the dominant deformation mechanism in this alloy. On the contrary, a considerably low elongation to failure of 230% was recorded in the naturally aged fine-grained (FG) Zn-0.3Al alloy at 150 °C, and dislocation creep was evaluated as the main deformation mechanism for this alloy. Detailed microstructural analyses showed that the FG Zn-0.3Al alloy was exposed to grain boundary corrosion during the natural aging process due to the presence of Al precipitates at grain boundaries whereas such formation was not observed in the UFG Zn-22% Al alloy. Grain boundary sliding was hindered by grain boundary corrosion and the cavity nucleation at the corroded grain boundaries caused a premature failure leading to such a low elongation in the Zn-0.3Al alloy.

  AtıfScopus30·WoS30·OpenAlex33

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• BildiriAçık Erişim2016Scopus SJRQ3/r/bayburt/13869
  Effect of natural aging on RT and HSR superplasticity of ultrafine grained Zn-22Al alloy

  Demirtas, Muhammet; Purcek, Gencaga; Yanar, Harun; Zhang, Zhenjun; Zhang, Zhe-Feng; Sato, E.; Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency, 3-1-1 Yoshinodai, Chuo, Sagamihara, Kanagawa, 252-5210; Itoh, G.; Kobayashi, J.; Department of Mechanical Engineering, Ibaraki University, 4-12-1 Nakanarusawa, Hitachi, 316-8511

  Zn–22Al alloy was processed using a well-designed two-step equal channel angular extrusion/pressing (ECAE/P), and ultrafine-grained (UFG) microstructure with 200 nm grain size was achieved. UFG Zn-22Al was subjected to long-term (up to 60 days) aging at room temperature (RT) and it was seen that natural aging caused limited grain growth in the microstructure. Grain sizes of about 300 nm, 350 nm and 350 nm were measured after 15, 30 and 60 days aging, which mean that UFG Zn-22Al alloy has a good microstructural stability at RT up to 60 days. ECAPed Zn-22Al alloy showed a maximum elongation of about 400% at a high strain rate of 5×10-2 s-1 and maximum elongation decreased with increasing grain size. Elongation to failures of ~375% and ~350% were obtained with the samples having 300 nm and 350 nm grain sizes, respectively. In addition, natural aging slightly decreased the strain rate at which superplastic region formed. While the maximum elongation occurred at the strain rate of 5×10-2 s-1 in ECAPed UFG alloy, it took place at lower strain rate of 1×10-2 s-1 after aging for all time periods. Also, flow stress of the alloy increased with increasing grain size during natural aging.

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