Stacking fault densities in hexagonal (ξ phase) copper - germanium alloys

A Geiger counter x-ray diffractometer has been employed to record the line profiles of the (101), (102) and (103) fault-affected reflections together with the profiles of the (100), (002), (110) and (004) fault-unaffected reflections from cold-worked hexagonal close-packed copper-germanium alloys. The composite broadening has been attributed to three causes: particle size, lattice strain and presence of stacking faults. These quantities have been separated by Fourier analysis of the line shapes. The stacking fault probability has been found to be greatest for the alloy composition which is nearest that of the primary face-centred cubic phase boundary and the fault probability decreases in a roughly parabolic manner as the solute content in the alloys is increased. The behaviour has been qualitatively interpreted in terms of the difference in free energy between the hexagonal and face-centred cubic phases.