Indentation size effect and energy balance issues in nanomechanical behavior of ZTA ceramics

Abstract It is well known that physical, structural, mechanical as well as other functional properties change drastically at the nanoscale, thereby giving rise to size effects in all materials, especially ceramics. Therefore, it is extremely relevant today to understand the basic scientific issues involved in the development of size effects in materials, particularly ceramics which are characteristically brittle in nature. Hence, to be able to design better contact resistant ceramics; it is of significant importance to understand the genesis of indentation size effect (ISE) in the nanomechanical response of structural ceramics like zirconia toughened alumina (ZTA). Here we report the first-ever systematic study on ISE in nanoindentation behavior of 10, 20 and 40 volume% (vol%) ZTA. The nanoindentation experiments were conducted at an ultra low load range of 1–1000 mN. As the experimental data showed the presence of strong ISE, the efficacies of existing models in explaining the same; were critically examined. Among existing models, the strain gradient plasticity model provided the real physical reason for the genesis of ISE in ZTA and hence, explained the data the best. Similarly, existing models were used to predict the variations in experimentally measured ratios of plastic to total energy spent in the nanoindentation process. The results showed that the Malzbender model predicted experimental data the best. This observation implied the best efficacy of the internally expanded cavity concept in explaining the nanoindentation response of the present ZTA ceramics. In addition, the other possible mechanisms of ISE in ZTA were discussed. Finally, the linkage of microstructural parameters to ISE in ZTA was explored.