The substructure of Cu3Au after tensile deformation and shock loading

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Department of Materials Science and Engineering


A recent investigation by Beardmore et al. (Trans. Met. Soc. AIME 230, 725 (1964)) showed a sharp rise in resistivity and stored energy in the range 290-370 kb on shock-loading initially ordered Cu3,Au, but not with the initially disordered alloy. Using samples from that investigation, optical and transmission microscopy and X-ray diffraction were employed to study the substructure. Specimens were also deformed in ordinary tension at 77°K and 298°K for comparison. There was no sudden increase in the dislocation densities or marked change in dislocation arrangement in the shock-loaded specimens corresponding to the rise in energy and resistivity. The dislocation densities for both initial states were similar and of the order of 1011 per cm2 after a shock of 370 kb, only about 30 per cent greater than the densities found in ordinary tensile testing of Cu3Au to the same strain. Antiphase domain boundaries were created in the ordered alloy on both {001} and {111} planes, with about equal probability during shock loading, and the probabilities of these boundaries were an order of magnitude greater than after ordinary tension to the same strain. After tensile testing at 77°K the antiphase boundaries were primarily on {111}, but at 298°K these were primarily on {001}. The degree of long-range order was 0.6 after 25 per cent strain by shock loading, but 0.95 after tensile deformation to this strain. Disordering was due to the creation of these boundaries. Work hardening was not affected by them. Local order was reduced by shock loading the initially disordered specimens. There was local order among the atoms misplaced by deformation in the initially ordered specimens. Twins were identified in the specimens shocked at 290 kb and higher. These were finer and more randomly dispersed for the initially ordered state. No twins or appreciable concentrations of stacking faults were found in the tensile specimens. The interplanar spacing decreased at {001} antiphase boundaries, but increased at {111} boundaries. This indicates that the second-neighbor energy has the same sign as the first in this system.

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Acta Metallurgica