Acta Metallurgica Slovaca, Vol. 17, 2011, No. 3, p. 158-162 158 MICROSTRUCTURAL STABILITY OF ULTRAFINE GRAINED COPPER AT ELEVATED TEMPERATURE L. Pantělejev 1 , O. Man 1 , L. Kunz 2 1 Brno University of Technology, Faculty of Mechanical Engineering, Technická 2896/2, Brno, 616 69, Czech Republic 2 Academy of Science of the Czech Republic, Institute of Physics of Materials, Žižkova 22, Brno, 616 62, Czech Republic Received 28.07.2011 Accepted 13.09.2011 Corresponding author: doc. Ing. Libor Pantělejev, Ph.D., Brno University of Technology, Faculty of Mechanical Engineering, Institute of Materials Science and Engineering, Technická 2896/2, 616 69 Brno, Czech Republic, tel.: +420514143188, fax.: +420541143439, E-mail: pantelejev@fme.vutbr.cz Abstract Thermal stability of ultrafine grained (UFG) structure of 99.9% pure copper produced by eight equal channel angular pressing (ECAP) passes was studied. The annealing experiments were conducted at temperature range from 180 °C to 300 °C in a tube furnace under argon as a protecting gas. The dwell times were in the range from 10 min to 300 min. The electron backscattering diffraction (EBSD) analyses were performed before and after annealing at exactly the same area in order to quantify the changes of UFG structure. More advanced analysis of the EBSD results based on kernel average misorientation (KAM) parameter was performed. Keywords: ultrafine grained microstructure, copper, microstructural stability, electron backscattering diffraction (EBSD) 1 Introduction Microstructural stability of ultra-fine grained materials prepared by severe plastic deformation (SPD) is one of the most discussed problems. It was found that the grain boundary structure of different materials is sensitive to elevated temperatures [1]. However, information about the stability of UFG microstructures is still poor; there is a number of opened questions about the details of grain coarsening mechanisms. At elevated temperature, the grain coarsening of UFG structures generally occurs [2]. Changes in grain size and formation of bimodal structures, as well as changes of amount of low angle boundary (LAB) and the high angle boundaries (HAB) were reported [3, 4]. Evolution of bimodal structure results in changes of mechanical properties like tensile characteristics, microhardness and fatigue properties [4-6]. Susceptibility to temperature activated processes leading to grain coarsening (normal or abnormal) depends on the level of strain introduced during SPD process. Currently, there is no sufficient description of the effect of elevated temperature on the microstructure of UFG materials, especially those prepared by SPD techniques. One of the factors frequently deemed as influencing the high temperature behaviour of UFG materials is the materials’ purity, which is based on a fact that alloys have higher thermal stability than pure