CRSS of disordered and ordered Cu₃Au single crystals containing SiO₂ particles Correlation with the Orowan stress

Abstract

Single crystals of Ou₃Au containing SiO₂ particles, oriented for single slip on (111)[101], and suitably heat-treated to have either an ordered or a disordered matrix, have been tested in compression in the range of temperatures 77–373 K. The quenching stresses generated at the particles, owing to the differences in the thermal expansion coefficients of Cu₃Au and SiO₂, were shown to have a significant effect on the CRSS of the disordered crystals, leading to an apparent temperature dependence of the Orowan stress. The effect was much less pronounced for the ordered crystals. After calculating the magnitude of this effect for the disordered samples, good agreement was obtained between the experimentally observed increment in the CRSS and the theoretically predicted Orowan stress. The agreement between theory and experiment for the ordered crystals was also satisfactory, assuming that the superlattice dislocations bypass the particles as a unit. TEM examination of (111) sections showed Orowan-type bowing of dislocations between the particles and resultant Orowan loops in the disordered single crystals, and Orowan-type bowing of superdislocations in the ordered single crystals, confirming that the initial yield stress in both the disordered and ordered alloys is controlled by the Orowan process.