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    Effect of precipitation on mechanical and wear properties of ultrafine-grained Cu-Cr-Zr alloy
    (Elsevier Science Sa, 2014) Purcek, G.; Yanar, H.; Saray, Onur; Kraman, I.; Maier, H. J.
    The effect of an ultrafine-grained (UFG) microstructure and subsequent aging treatment on the mechanical and wear behavior of a Cu-Cr-Zr alloy was investigated. The results indicate that the precipitates dispersed within the UFG matrix significantly enhance the strain hardening, resulting in improvement of hardness, strength and wear resistance of the alloy, without notably sacrificing the elongation to failure and electrical conductivity, due to the combined effect of grain refinement and precipitation. The wear behavior of Cu-Cr-Zr alloy was found to be strongly dependent on its strength and hardness. The minimum weight loss (or the highest wear resistance) was obtained when the sample was processed by equal channel angular extrusion (ECAE) through an additional aging treatment, as this resulted in ultra-high strength and hardness. The wear results also indicate that the wear behavior of Cu-Cr-Zr alloy in all processing conditions is consistent with the Archard approach. Complex wear mechanisms such as adhesive, oxidative and abrasive wear, and delamination were found to be operative in the differently processed Cu-Cr-Zr alloys. It is to be concluded that the use of a two-step process, the first resulting in an UFG microstructure and a subsequent aging treatment provides a simple and effective procedure for extraordinary increase in strength, hardness and wear resistance of Cu-Cr-Zr alloys without modification of the chemical composition. (C) 2014 Elsevier B.V. All rights reserved.
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    Improvement of formability of ultrafine-grained materials by post-SPD annealing
    (Elsevier Science Sa, 2014) Saray, Onur; Purcek, G.; Karaman, I.; Maier, H. J.
    Ultrafine-grained (UFG) IF-steel, as an example of an essentially single phase UFG microstructure, was annealed at different temperatures and time intervals in order to improve its formability by achieving a good strength-ductility-formability balance. In general, annealing increased the ductility and formability of UFG steel. Annealing at temperatures inside the recovery region caused a limited improvement in the formability of UFG steel due to the relief of internal energy without considerable grain coarsening. As the grain size increased to above 4 mu m by annealing at temperatures inside the partially recrystallization region, the formability of UFG steel in the uniform region increased considerably, and localized deformation with early necking changed to a homogeneous mode as revealed by increased uniform thinning and enlargement of the membrane straining regime. Further grain coarsening resulted in a slight increase in uniform elongation both in uniaxial and biaxial tests. The UFG microstructure reduced the roughness of the free surface of biaxially stretched samples by decreasing the non-uniform grain flow, which leads to the so-called orange peel effect. Annealing of UFG microstructure did not degrade this positive effect due to the formation of sharp recrystallization textures although the annealed microstructures have relatively coarse grains. It can be concluded that a good balance between strength and uniform formability without an orange-peel effect can be achieved in UFG microstructures by well-design annealing processes. (C) 2014 Elsevier B.V. All rights reserved.