The formation of the complex oxide in Ni-based alloy powder during mechanical milling and heat treatment

Abstract

Ni-based oxide dispersion strengthening (ODS) alloys fabricated by mechanical alloying (MA) and hot isostatic pressing (HIP) improve mechanical properties by adding yttria as a dispersoid. The evolution of the additive Y2O3 particles was studied by scanning electron microscope (SEM) for the powder milled for 5 h, 20 h, 40 h, and the un-milling powder. The samples of powders after the mechanical milling and the heat treatment at 1175 °C for 3 h corresponding to HIP were observed by high-resolution transmission electron microscopes (HRTEM). In the process of the mechanical alloying, the Y2O3 crystallites underwent dispersion, dissolution, and partly transformed into YCrO3 and Y2Ti2O7 particles. A small amount of the complex oxide particles could be produced in the process of mechanical milling. A high number density of complex oxide particles precipitated and coarsened in the powder after the heat treatment. Mechanical milling could induce the formation of complex oxide particles because of their formation energies. The difference in size of YCrO3 and Y2Ti2O7 particles in the powder after the heat treatment mainly attribute to diffusion coefficient, solubility, and the interfacial energy.