Formation of Nano-Sized Y₂O₃ Dispersoids in Mechanically Alloyed Ni–(Cr, Y₂O₃, Y) Alloys During Heat-Treatments

Abstract

In the present work, the evolution of nanoparticles during annealing and hot-consolidation in mechanically alloyed Ni-22Cr-1.5Y, Ni-22Cr-1.5Y2O3 and Ni-3% Y2O3 was examined. The high-energy ball-milling of elemental powders resulted in the complete dissolution of the constituent Cr, Y, or Y2O3, forming a Ni-based solid solution. During the subsequent annealing, however, oxide particles precipitated from the solid solution. In the case of mechanically alloyed Ni-22Cr-1.5Y2O3, over-grown Cr2O3 precipitated at a temperature as low as above approximately 500 degrees C and ternary YCrO3 particles precipitated at 1100 degrees C. In the case of mechanically alloyed Ni-22Cr-1.5Y, on the other hand, the binary Y2O3 phase precipitated at 1100 degrees C during spark plasma sintering. The presence of Cr in the alloy composition facilitated the formation of Cr2O3 or YCrO3, and the precipitated oxides were highly prone to grain growth during hot-consolidation, sometimes reaching several micrometers. In Cr-exempt Ni-3%Y or Ni-3% Y2O3, however, the growth of nanodispersoids was restrained even at temperatures as high as 1000 degrees C and the resulting dispersoid was only nano-sized Y2O3.

Characterization of Oxide Nanoparticles in Al-Free and Al-Containing Oxide Dispersion Strengthened Ferritic Steels

“…[1][2][3][4][5] From the viewpoint of oxide nanoparticles, they are dissolved into the steel during mechanical alloying and such dissolved oxides are re-formed as nano-sized complex oxide particles in the steel matrix during consolidation or heat treatment. [6][7][8] The oxide nanoparticles in ODS steels are expected to improve their strength and irradiation resistance, because the dispersed oxide particles are very stable even at a temperature close to the melting point of the steel and can be effective barriers to the motion of dislocations during tensile deformation. 1 9 The overall macroscopic behavior of ODS steels can be affected significantly by the structure of metal/oxide interfaces.…”