Oxide dispersion strengthened nickel based alloys via spark plasma sintering

Oxide dispersion strengthened (ODS) nickel based alloys were developed via mechanical milling and spark plasma sintering (SPS) of Ni-20Cr powder with additional dispersion of 1.2 wt% Y2O3 powder. Furthermore, 5 wt% Al2O3 was added to Ni-20Cr-1.2Y2O3 to provide composite strengthening in the ODS alloy. The effects of milling times, sintering temperature, and sintering dwell time were investigated on both mechanical properties and microstructural evolution. A high number of annealing twins was observed in the sintered microstructure for all the milling times. However, longer milling time contributed to improved hardness and narrower twin width in the consolidated alloys. Higher sintering temperature led to higher fraction of recrystallized grains, improved density and hardness. Adding 1.2 wt% Y2O3 to Ni-20Cr matrix significantly reduced the grain size due to dispersion strengthening effect of Y2O3 particles in controlling the grain boundary mobility and recrystallization phenomena. The strengthening mechanisms at room temperature were quantified based on both experimental and analytical calculations with a good agreement. A high compression yield stress obtained at 800 °C for Ni-20Cr-1.2Y2O3-5Al2O3 alloy was attributed to a combined effect of dispersion and composite strengthening.