Influence of Iron Oxide Particles on the Strength of Ball-Milled Iron

Detailed microstructural and mechanical property studies of ball-milled iron, in the powder and consolidated states, are reviewed and assessed. The analyses cover three and one-half orders of magnitude in grain size (from 6 nm to 20 (mu)m) and focus on the influence of oxide particles on the strength. The study includes the early work of Jang and Koch, Kimura and Takaki and continues with the more recent work of Umemoto et al. and Belyakov, Sakai et al. It is shown that the major contributors to strength are the nano-oxide particles. These particles are created by adiabatic shear banding during ball-milling leading to a bimodal distribution of particles. The predicted strength from particles, (sigma)p, is given by (sigma)p=B·(Ds*)^-1/2 where Ds* is the surface-to-surface interparticle spacing, and B=395 MPa.(mu)m^1/2. A model is proposed that accounts for the influence of the bimodal particle size distribution on strength.