Mechanical properties and microstructural analysis of ultra-fine grained Ni-based ODS alloy processed by powder forging

In the present study powder forging was employed to consolidate mechanically alloyed Ni-20Cr-20Fe-0.6Y2O3 Ni-based ODS powder. A mild steel can was filled with the mechanically alloyed powder and heated to 1200 oC in a Ar+H2 (90:10) atmosphere and hot forged in a channel die. The forged slab was characterized in terms of residual porosity, microstructure, oxide particle size and mechanical properties at room as well as elevated temperatures. The forged slab exhibited close to full density (> 99%), ultra-fined grain size of ~503 nm and an average oxide particle size of 25.6 nm. Enhanced mechanical properties at room and elevated temperatures were obtained due to a combination of ultra-fine grains and uniform distribution of oxide particles. The high strain rates involved during powder forging cause the breaking or shearing out the oxide layer, oxide particles, and other prior particle boundary (PPB’s) forming compounds present on the surface of the particles and dispersing them into the grains interior and along the grain boundaries. The exposed material and sliding due to shear stress also enhances strong metallurgical bonding across collapsed interfaces and consequently improves mechanical properties. The absence of prior particles boundaries (PPB) network, nearly isotropic properties and almost full density indicated that the powder forging route can emerge as an alternative consolidation technique to HIP and hot extrusion for the consolidation of powder metallurgy ODS superalloys.