The flow stress in Cu3Au

Ordering and disordering treatments have been given to an alloy of composition corresponding to Cu₃Au to produce a range of order and domain size values not obtainable by any other technique. Flow stresses in polycrystalline materials have been obtained for a range of grain sizes, and the results examined in terms of several previously suggested models of strengthening. While the model of Stoloff and Davies based on the transition from single dislocations to superlattice dislocations appears to be best capable of explaining the results, the agreement is little better than qualitative.     

Work hardening in the Cu3Au superlattice

Single crystals of a fully-ordered Cu₃Au alloy were deformed in compression at room temperature on a single glide system to a very high degree of plastic strain in Stage II. Transmission electron microscopy observations showed a very high density of superlattice screw dislocations which had cross-slipped onto {100} type planes. These cross-slipped superlattice dislocations were for the most part arranged as plus-minus pairs,i.e. multipoles. It is this large density of cross-slipped superlattice dislocations which is believed responsible for the high rate of work hardening observed in ordered Cu₃Au alloys. J. CZERNICHOW, formerly Research Assistant, Engineering Materials Group and Department of Mechanical Engineering, University of Maryland, College Park, Md.     

Effect of excess Au on antiphase domain growth in Cu3Au

The kinetics of antiphase domain growth have been studied in three nonstoichiometric Cu₃Au alloys containing nominally 26, 28, and 31.5 at. pct Au. During isothermal annealing of disordered samples below the critical temperatures, the domain growth in all of the alloys initially followed the samet ^1/2 dependence found previously for stoichiometric Cu₃Au. At long times, the two alloys furthest off stoichiometry reached limiting domain sizes which decreased with increasing Au content. Although the role of the excess Au in determining these limiting sizes is not clear, it is evident that most of the excess Au is accommodated within the domains. The antiphase domain size distributions in the alloys agree with those found for the stoichiometric alloy.     

Effect of deformation on the structure of an ordered and disordered alloy with composition in the vicinity of Au3Cu

The effect of deformation on the degree of long-range order in an alloy near Au₃Cu in composition has been studied by the method of x-ray diffraction. It was established that plastic deformation causes an order-disorder transformation which proceeds heterogeneously, and is accompanied by fragmentation of the antiphase domains and increase of the lattice parameter. Heterogeneity of the deformational order-disorder transformation is associated with the localization of strain produced by the deformation process. Tomsk State Architectural Design Academy. Translated from Poroshkovaya Metallurgiya, Nos. 3–4, pp. 33–37, March–April, 1997.