Grain boundary and grain interior strengthening in nano-micron grain sized Cu-1wt.%Al₂O₃ composite

A bulk Cu-1 wt%Al2O3 composite was synthesised to 97-99% theoretical density by mechanical alloying and spark plasma sintering to get varying grain sizes in the range 70 nm-2 mu m. Tensile tests were done at room temperature, and the substructure evolution was examined as a function of the grain size and strain. The flow property revealed bilinear Hall-Petch relationship with a transition at 0.55 mu m grain size. The stress-strain curves were found to follow the Hollomon-type relationship exhibiting an increase in strength coefficient and a decrease in strain hardening exponent with decreasing grain size. The variations in flow stress with grain size and strain delineate equivalent effects. The inter-dependence between the grain size and strain is explained by the substructure evolution and its contribution to the partitioning of work hardening between the grain interior and grain boundaries.