Repetitive grain growth behavior with increasing temperature and grain boundary roughening in a model nickel system

In conjunction with a previous investigation [Jung SH, Yoon DY, Kang SJL. Acta Mater 2013;61:5685], we have investigated the correlation between grain boundary structure and grain growth behavior in a model Ni system. Ultrafine Ni powder compacts of 180 nm size were sintered in a wide range of temperatures from 500 to 1150 degrees C and for various times in wet H-2. Between 500 and 600 degrees C, abnormal grain growth (AGG) readily occurred, with the formation of cube-shaped grains. Between 650 and 900 degrees C, grain growth behavior was stagnant up to 6000 min due to impingement of rapidly grown abnormal cube-shaped grains during heating. At 950 degrees C, some of the impinged abnormal grains suddenly grew after 20 min, showing secondary AGG behavior. As the sintering temperature was increased further, the grain growth behavior became quite normal. These changes in grain growth behavior with increasing temperature were accompanied by the structural transition of grain boundaries from fully faceted to partially faceted and defaceted. The observed grain growth behavior with respect to the grain boundary morphology is explained in terms of a coupling effect of the maximum driving force for grain growth and the critical driving force for appreciable migration of faceted boundaries. The present experimental results appear to support the validity of the previously suggested mixed control model of grain growth and the principle of microstructural evolution in polycrystals. (c) 2014 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.