Mechanical alloying and direct powder forging of Ni–20Cr–20Fe-0.08C alloy

Abstract

In the present work Ni–20Cr–20Fe-0.08C nickel-based alloy was prepared by mechanical alloying followed by direct powder forging. Mechanical alloying (MA) of the elemental powders corresponding to a starting composition of Ni–20Cr–20Fe-0.08C (without process control agent) was carried out in a high energy attritor mill (Simoloyer). X-ray diffraction studies indicated that a single phase (γ) solid solution was obtained at 8 h of milling. The crystallite size of the milled powder decreased significantly while lattice strain, lattice parameter, and dislocation density increased with milling time. Dynamic recrystallization was evident after 4 h of milling; as a result, a slight increase in crystallite size and a slight decrease in lattice strain and dislocation density were observed. The 8 h MA powders were further filled into a mild steel can and placed in a tubular furnace to carry out the loose sintering at 1150 °C after which they were hot forged. The forged slab exhibited almost full density, near isotropic properties, ultrafine equiaxed grained structure and minimised prior particles boundaries (PPB). This suggests that powder forging has a potential to be an alternative processing method to hot isostatic pressing (HIP), hot powder extrusion and additive manufacturing (AM) for the processing of powder metallurgy nickel based alloys.