Sürdürülebilir Kalkınma Amaçları

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• MakaleYalnız künye2020Scopus SJRQ3/r/bayburt/14089
  Effect of resin content on tribological behavior of brake pad composite material

  Yanar, Harun; Ayar, Hasan Huseyin; Demirtas, Muhammet; Purcek, Gencaga

  Purpose This paper aims to investigate the effect of straight phenolic resin content on the fade behavior, frictions and wear characteristics of pre-determined brake pad composite matrix having specific amount of barite (BaSO4), rock wool, Kevlar, graphite and magnetite. Design/methodology/approach Different amount of resin ranging between 16 and 20 wt. per cent were added by changing only the filler (barite) content of composite matrix. Subsequently, friction and wear behavior of the composite samples were analyzed using a special pin-on-disc type test system developed for brake pad sample. The worn surfaces were investigated by SEM and three-dimensional (3D) surface profilometer. Findings The average coefficient of friction (CoF) of composite samples and temperature of the disc surface showed a linear increase with decreasing the resin content. The sample having 20 wt. per cent resin showed the minimum wear rate with smooth worn surface. But the amount of fade is quite high in that sample. Decreasing resin content decreased the fade formation, and the composite with 16 per cent resin brought about the minimum fade formation. As the fade formation is unwanted in brake pad applications, the composite with 16 wt. per cent resin was proposed as the most appropriate one considering the performance parameters related to friction and wear. Originality/value This paper optimizes the resin content of composite brake pad materials to achieve the best combination of its tribo-performance and mechanical properties and provides valuable information for scientists and engineers working in that area.

  AtıfWoS8·OpenAlex15

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• MakaleAçık Erişim2018Scopus SJRQ2/r/bayburt/13764
  Effect of grain refinement and phase composition on room temperature superplasticity and damping capacity of dual-phase Zn-Al alloys

  Demirtas, Muhammet; Atli, Kadri C.; Yanar, Harun; Purcek, Gencaga

  The effects of grain refinement and phase composition on superplasticity and damping capacity of eutectic Zn-5Al and eutectoid Zn-22Al alloys were investigated. For grain refinement, equal-channel angular pressing (ECAP) was applied to these alloys. ECAP completely eliminated the as-cast lamellar microstructures of both alloys and resulted in ultrafine-grained structures along with room temperature superplasticity. Furthermore, these microstructural changes with ECAP increased the damping capacity of both alloys in the dynamic hysteresis region, where damping arises from viscous sliding of phase/grain boundaries. Dynamic recrystallization at the surface and thermally activated viscous motion of grain/phase boundaries at the subsurface of the samples of both alloys were proposed as the damping mechanisms in the region where the alloys showed combined aspects of static/dynamic hysteresis damping behavior. Although the grain size is larger in Zn-5Al compared to Zn-22Al, it showed higher damping capacity due to the different sliding characteristics of its phase boundaries.

  AtıfScopus14·WoS11·OpenAlex14

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• 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

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• 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

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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 Erişim2018Scopus SJRQ3/r/bayburt/12241
  Room temperature superplasticity in fine/ultrafine-grained Zn-Al alloys with different phase compositions

  Demirtas, Muhammet; Yanar, Harun; Saray, Onur; Purcek, Gencaga

  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 α/α phase boundaries, where grain boundary sliding is minimum comparing to Zn-rich η/η and η/α 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.

  AtıfScopus6·OpenAlex5

  İncele
• MakaleAçık Erişim2017Scopus SJRQ1/r/bayburt/13748
  Enhancing the Damping Behavior of Dilute Zn-0.3Al Alloy by Equal Channel Angular Pressing

  Demirtas, M.; Atli, K.C.; Yanar, H.; Purcek, G.

  The effect of grain size on the damping capacity of a dilute Zn-0.3Al alloy was investigated. It was found that there was a critical strain value (≈1 × 10−4) below and above which damping of Zn-0.3Al showed dynamic and static/dynamic hysteresis behavior, respectively. In the dynamic hysteresis region, damping resulted from viscous sliding of phase/grain boundaries, and decreasing grain size increased the damping capacity. While the quenched sample with 100 to 250 µm grain size showed very limited damping capacity with a loss factor tanδ of less than 0.007, decreasing grain size down to 2 µm by equal channel angular pressing (ECAP) increased tanδ to 0.100 in this region. Dynamic recrystallization due to microplasticity at the sample surface was proposed as the damping mechanism for the first time in the region where the alloy showed the combined aspects of dynamic and static hysteresis damping. In this region, tanδ increased with increasing strain amplitude, and ECAPed sample showed a tanδ value of 0.256 at a strain amplitude of 2 × 10−3, the highest recorded so far in the damping capacity-related studies on ZA alloys.

  AtıfScopus8·WoS7·OpenAlex7

  İncele
• BildiriAçık Erişim2017/r/bayburt/13716
  Optimization of RT superplasticity of UFG Zn-22Al alloy by applying ECAP at different temperatures and phase regions

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

  Zn-22Al alloy was subjected to either one-step or two-step equal channel pressing (ECAP) to investigate the effect of processing temperature on its microstructure and room temperature (RT) superplasticity. In one-step ECAP processes, 4 passes ECAP were applied to the alloy at different temperatures: RT, 100°C and 250°C in two-phase region below eutectoid temperature and 350°C in single-phase region above eutectoid temperature. In two-step ECAP processes, one-step ECAP-processed samples were subjected to four more passes ECAP at RT. Considering the one-step ECAP processing, RT superplasticity increased with decreasing ECAP temperature as expected, and the highest RT superplasticity was achieved as 350% after 4 passes ECAP at RT. On the other hand, application of 4 more passes ECAP at RT to the sample showing the lowest superplastic elongation after one-step ECAP (the sample processed at 350°C) resulted in the maximum RT elongation of 400% at a high strain rate of 5×10-2 s-1. These results suggest that first step temperature of two-step ECAP process is needed to increase above the eutectoid point of Zn-22Al alloy to achieve high RT superplasticity. These results were attributed to the changes in microstructure inside the single-phase and two-phase regions during the processes.

  AtıfScopus12·WoS10·OpenAlex9

  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

  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 künye2016Scopus SJRQ1/r/bayburt/13857
  Optimization of strength, ductility and electrical conductivity of Cu-Cr-Zr alloy by combining multi-route ECAP and aging

  Purcek, G.; Yanar, H.; Demirtas, M.; Alemdag, Y.; Shangina, D.V.; Dobatkin, S.V.

  Properties of Cu-Cr-Zr alloy with ultrafine-grained (UFG) structure produced by equal-channel angular pressing (ECAP) via different routes have been investigated. Special attention was paid to the optimization of multi-functional structural, thermal, electrical and mechanical properties of the alloy by aging of UFG one. Multi-pass ECAP via different routes gives rise to the formation of a deformation-induced submicrocrystalline structure with the grain (subgrain) sizes in the range of 200-300. nm depending on applied routes which leads to high hardness and strength in the Cu-Cr-Zr alloy with reduced ductility. Amongst the applied routes, route-Bc was found to be the best processing path for achieving the lowest grain size, the highest hardness and strength. Aging of 8Bc-processed UFG samples increases the hardness and strength of Cu-Cr-Zr alloy while retaining an electrical conductivity comparable to that of aged coarse-grained (CG) one. A satisfactory electrical conductivity of 71%IACS without considerable loss of peak hardness was achieved after aging of 8Bc-processed UFG alloy at 425. °C for 240. min. The precipitation strengthened UFG alloy remains its stable behavior at elevated temperatures up to 450. °C.

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  AtıfScopus164·WoS147·OpenAlex151

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