The effect of particle size on the yield stress of Cu-Al 2O 3 crystals

Abstract

The tensile behaviour of internally oxidized coppers-aluminum alloy single crystals has been studied as a function of oxide particle size and volume fraction. The results indicate that crystals containing only small ( <150 A ̊ ), coherent oxide particles, exhibit tensile characteristics comparable to precipitation-hardened systems containing deformable coherent particles. The yield stress data obtained for crystals containing large triangular non-coherent alumina platelets (400–800 Å) agree well with the theoretical predictions of the Orowan mechanism. However, crystals containing the same volume fraction of much smaller particles exhibit yield stresses an order of magnitude lower than required by the Orowan mechanism. It is concluded that the small, coherent, alumina particles are sheared or fractured at yield. The larger, noncoherent, alumina platelets are by-passed by dislocations, consistent with the Orowan yield criterion for non-deformable particles.