Effect of heat treatment on the hardness and microstructure in Co–3Al–1.5Y2O3–1.2Hf ODS alloy

An oxide dispersion strengthened (ODS) Co-based alloy was fabricated by mechanical alloying (MA) and spark plasma sintering (SPS). The sintered sample consisted of hard and soft regions. The hard region consisted of nanocrystalline fcc-Co (γ-Co) grains with the dense dispersion of nano-scale oxide particles, and coarse hcp-Co (ε-Co) and fcc-Co grains were present in the soft region. The nanocrystalline grain structure and oxide particle dispersion in the hard region is attributed to the high hardness of 410 VHN in the as-sintered sample. The high hardness was maintained after annealing at 1000 °C for 240 h indicating the excellent stability of the fine grain structure due to the grain boundary pinning by the oxide particles.