Polycrystalline specimens of α-phase copper–aluminium alloys of varying composition, amalgamated with mercury, have been deformed in tension in a soft tensile machine. In all cases, brittle intergranular failure occurred at stresses and strains below those required for fracture in air, the degree of embrittlement increasing with increasing aluminium content. The alloys having stacking-fault energies less than '~8 erg/cm2 were found to obey quite well the Petch–Stroh relation:[Formula: see text]The other alloys showed deviations from this relation which became more marked with increasing stacking-fault energy. Values of the fracture energy, varying from ~48 erg/cm2 for pure copper to ~470 erg/cm2 for Cu −8 wt.% Al, have been obtained for all of the alloys. These values are only applicable for relatively small grain sizes.The deviation from the Petch–Stroh relation in the high stacking-fault energy alloys is thought to be due to their tendency to show cross-slip and cellular-network formation, rather than coplanar arrays of dislocations as required by the Stroh model. The low stacking-fault energy alloys typically show well-defined pileups and so obey the Petch–Stroh relations, as expected.
Generalised stacking fault energies of copper alloys - density functional theory calculations
