Grain boundary and grain interior strengthening in nano-micron grain sized Cu-1wt.%Al<inf>2</inf>O<inf>3</inf> 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 µm. 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 µm 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.