Issue 19

L. Kunz et alii, Frattura ed Integrità Strutturale, 19 (2012) 61-75; DOI: 10.3221/IGF-ESIS.19.06 61 Mechanical properties of copper processed by Equal Channel Angular Pressing – a review Ludvík Kunz Institute of Physics of Materials, Academy of Sciences of the Czech Republic, Czech Republic. Luca Collini Department of Industrial Engineering, University of Parma, Italy. A BSTRACT . The Equal Channel Angular Pressing is a hardening treatment with which ductile metals can be processed to refine their grain and sub-grain structure. This process enhances the mechanical strength of metals in terms of tensile strength, stress-controlled fatigue strength, and fatigue crack growth resistance. In this paper the authors draw a review of the major results of a wide research activity they carried out on a copper microstructure processed by Equal Channel Angular Pressing. The essential results are that tensile and fatigue strengths of the so obtained refined structure are improved by a factor of two with respect to the original coarse-grained metal. The fatigue crack initiation mechanism and the stability of the refined microstructure under cyclic loading are topics also discussed, evidencing the essential role of the process and of the material parameter, as the content of impurities in the microstructure. In this review, the authors also underline some critical aspects that have to be more investigated. K EYWORDS . Ultrafine-grain structure; Equal Channel Angular Pressing; Copper; fatigue; fatigue crack resistance. I NTRODUCTION ankind has used copper since the ancient times. Its mechanical properties and structure are well explored and known. Application of copper in many branches of industry, e.g. in production of wires, copper-based solar power collectors, integrated circuits and generally in electronics, is intensive and has been steadily increasing in recent decades. Copper can be also recycled very effectively and represents a relevant engineering material also for the future. Copper belongs to the most thoroughly investigated metals. Detailed studies of the relation of mechanical properties and microstructure have been already performed in the second half of the last century [1]. The effort of increasing the mechanical properties of engineering materials, led in the last two decades to the development of the so-called severe plastic deformation (SPD) processes, resulting in fine-grained structures that exhibit improved mechanical properties. Cu was again a material which was used in the early studies as a model material. This work briefly summarises the mechanical behaviour of ultrafine-grained (UFG) Cu prepared by one of the SPD methods, namely by Equal Channel Angular Pressing (ECAP). This method enables the production of the UFG Cu in bulk, which is favourable from the industrial point of view. The emphasis in this work is put on the fatigue properties and their relation to the UFG microstructure, even if discussion of recent - and in some cases inconsistent - results on UFG Cu published in literature, is accentuated. However, also the tensile properties, the relation of the cyclic softening/hardening to the stability of UFG structure, the mechanism of the cyclic slip localization and initiation and propagation of fatigue cracks are the topics reviewed in this work. M