Plastic deformation of Cu 3Au single crystals containing alumina particles

Abstract

The plastic deformation of ordered and disordered Cu 3Au single crystals with and without a dispersion of alumina particles was investigated by stress-strain measurements and slip-line studies using optical microscopy. The dislocation microstructure was studied as a function of shear strain by transmission electron microscopy. The yield stress of disordered Cu 3Au-Al 2O 3 crystals is given by the sum of the matrix flow stress ( τ 1) and the particle bypassing stress ( τ 2) indicating that this is a system containing a low density of strong obstacles and a high density of weak obstacles. In the ordered Cu 3Au-Al 2O 3 crystals, the experimentally observed yield stress gives a better agreement with √ τ 1 2 + τ 2 2 than with τ 1 + τ 2, showing that this system contains obstacles of equal strength or a combination of strong and medium strength obstacles. Orowan by-passing and cross-slip occur at the dispersed particles during tensile deformation by unit dislocations in the disordered and by superdislocations in the ordered Cu 3Au-Al 2O 3 single crystals. The work hardening behaviour of ordered and disordered Cu 3Au-Al 2O 3 crystals result from the superposition of contributions from geometrically necessary dislocations and statistically stored dislocations as well as the characteristic distribution of these dislocations. Whereas the initial stage of deformation is dominated by geometrically necessary dislocations in ordered Cu 3Au-Al 2O 3 crystals, it is dominated by statistically stored dislocations arranged in dipole and multipole arrays in disordered Cu 3Au-Al 2O 3 crystals. In both systems the later stages of deformation are controlled by the statistically stored dislocations.