Microstructure of Al-Al2O3 nanocomposite formed by in situ phase transformation during Al nanopowder consolidation

► Al-Al2O3 nanocomposites were formed by in situ phase transformation during consolidation of high purity Al nanopowder. ► During HIP process at 550 °C, the native amorphous layer on the initial powder transformed into nanocrystalline alumina that was dispersed in the Al matrix. ► Final microstructure can be characterized as an Al matrix containing both ultrafine and coarse grains as well as embedded nanosized alumina dispersoids. ► The coarse grains in the matrix stopped the crack propagation during deformation thereby increasing the toughness of the composite. ► Filaments were formed between the fracture surfaces when the sample failed during compression at 200 °C in air, probably as a result of melting of aluminum due to oxidation.