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    Effect of grain refinement and phase composition on room temperature superplasticity and damping capacity of dual-phase Zn-Al alloys
    (Cambridge University Press, 2018) Demirtas M.; Atli K.C.; Yanar H.; Purcek G.
    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. © 2018 Materials Research Society.
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    Enhancing the Damping Behavior of Dilute Zn-0.3Al Alloy by Equal Channel Angular Pressing
    (Springer Boston, 2017) 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 tan? of less than 0.007, decreasing grain size down to 2 µm by equal channel angular pressing (ECAP) increased tan? 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, tan? increased with increasing strain amplitude, and ECAPed sample showed a tan? 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. © 2017, The Minerals, Metals & Materials Society and ASM International.