Copper-alumina nanocomposites derived from CuAlO2: Phase transformation and microstructural coarsening

Partial reduction of bulk CuAlO2 results in hierarchical structures wherein thereare copper-alumina regions with widely differing morphologies and scale. At thefinest level, the distribution of the 2 phases is at the nanoscale. By means ofatomic resolution STEM and electron diffraction, the nanocomposite regions wereshown to consist of a dense array of metallic copper platelets dispersed in amatrix of h-Al2O3. The copper nanoplatelets were single crystal, and they allexhibited the same orientation relationship with the matrix, namely [110]Cu//[010]h-Al2O3, (111)Cu//(4 0 2)h-Al2O3. It was shown that the 2-phase regions wherethe copper exhibited a significantly coarser, globular morphology, resulted fromdiscontinuous coarsening. Interestingly, a change in the matrix phase from h- tod-alumina was also observed as a result of the coarsening reaction. It is believedthat in the nanocomposite regions, the h-alumina phase was stabilized by thelower interfacial energy between the copper (110) platelets and the matrix.