Yazarlar

• Demirtas, M.(4)
• Purcek, G.(4)
• Yanar, H.(4)
• Bochvar, N.R.(1)
• Demirtas, Muhammet(1)
• Department of Mechanical Engineering, Ibaraki University, 4-12-1 Nakanarusawa, Hitachi, 316-8511(1)
• Dobatkin, S.V.(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)
• 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)
• Shangina, D.V.(1)
• Takayama, Y.(1)
• Yanar, Harun(1)
• Zhang, Z. F.(1)
• Zhang, Z. J.(1)
• Zhang, Z.F.(1)
• Zhang, Z.J.(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.

  AtıfScopus4·WoS4·OpenAlex4

  İncele
• MakaleYalnız künye2018Scopus SJRQ1/r/bayburt/12525
  Influence of high pressure torsion-induced grain refinement and subsequent aging on tribological properties of Cu-Cr-Zr alloy

  Purcek, G.; Yanar, H.; Shangina, D.V.; Demirtas, M.; Bochvar, N.R.; Dobatkin, S.V.

  Effects of ultrafine grain formation via high pressure torsion (HPT) and precipitation during aging on the microstructure, mechanical and tribological properties of a Cu-Cr-Zr alloy have been investigated systematically. HPT results in the formation of ultrafine-grained (UFG) structure in the alloy with an average grain/subgrain size of 155 nm which leads to remarkable improvement in its hardness and strength along with a reduction in elongation to failure. Aging of UFG alloy brings about further strengthening due to the precipitation. UFG formation by HPT increases substantially the wear resistance of Cu-Cr-Zr alloy and reduces the friction coefficient. The highest wear resistance and the lowest friction coefficient are obtained on the sample processed by HPT and subsequent aging. The dominant wear mechanism of the alloy varies depending on the applied processes. Adhesion with smearing is the predominant wear mechanism for the initial (warm extruded) samples having coarse-grained (CG) structure. UFG samples show less adhesional effect with less smearing, and a higher tendency to the formation of cracks, abrasion and delamination seem to be dominant in those samples. Oxidative wear mechanism is also operative in both CG and UFG alloy samples. It may be concluded from this study that a combined process including UFG formation by HPT and subsequent precipitation by artificial aging provides a simple and effective processing procedure for improving the strength, hardness and wear resistance of Cu–Cr–Zr alloys without modification of the chemical composition.

  AtıfScopus96·WoS91·OpenAlex99

  İncele
• 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.

  AtıfScopus7·OpenAlex8

  İncele
• MakaleYalnız künye2015Scopus SJRQ3/r/bayburt/14130
  Effect of Chemical Composition and Grain Size on RT Superplasticity of Zn-Al alloys processed by ECAP

  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.

  AtıfWoS19

  İncele
• MakaleAçık Erişim2015Scopus SJRQ1/r/bayburt/12532
  Improvement of high strain rate and room temperature superplasticity in Zn-22Al alloy by two-step equal-channel angular pressing

  Demirtas, M.; Purcek, G.; Yanar, H.; Zhang, Z.J.; Zhang, Z.F.

  The Zn-22Al alloy was subjected to equal-channel angular pressing (ECAP) to improve its high strain rate (HSR) superplasticity at room temperature (RT). A well-designed two-step ECAP process formed an ultrafine-grained (UFG) microstructure with an average grain size of 200nm as the lowest one obtained so far after ECAP processing of this alloy. Also, agglomerate- and texture-free microstructure with UFG Al-rich α- and Zn-rich η-grains separated mostly by high-angle grain boundaries (HAGBs) was produced by this process. The maximum RT elongation was achieved to be 400% with a strain rate sensitivity of 0.30 at a very high strain rate of 5×10-2s-1 after the two-step ECAP process. This elongation value is the highest one obtained at RT and at all strain rates for this alloy up to now. The current results demonstrate that such an improvement in superplasticity of Zn-22Al alloy after the two-step ECAP process can enhance its applications where RT and HSR superplasticity are strongly needed.

  AtıfScopus48·OpenAlex48

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