Correlative deformation mechanisms in NixCo1-xO/ZrO2(CaO) directionally solidified eutectic composites with a confined metallic interphase

NixCo1-xO/ZrO2(CaO) directionally solidified eutectic composites have been previously shown to form Ni(Co) metallic interphases mediating NixCo1-xO and ZrO2(CaO) phases upon chemical reduction of the composite at high temperatures. Vickers and nanoindentation experiments indicate characteristics of toughening enhancement in the reduced composite due to plastic deformation of the confined metallic interphase. This paper reports on the effect of size scale and chemistry of the metallic interphase on the phenomenological aspects of deformation behavior and the extent of plasticity at different length scales in the reduced eutectic model system. Transmission electron microscopy observations clearly show that a size-dependent deformation mechanism operates within the metallic interphase. A decrease in the extent of strain energy absorption, dislocation activity and twinning propensity is observed within the ductile interphase with decreasing size scale. In addition, a transition is observed in the small-scale deformation mechanism of the metallic interphase with changes in the composition of the interphase. (C) 2008 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.