Stacking Faults and Dislocations in Copper-Aluminium and Cobalt-Nickel Alloys

Stacking fault densities α' in heavily cold-worked powders of copper-aluminium and cobalt-nickel alloys have been measured from the peak shifts, using Paterson's theory. The Fourier coefficients of the broadening function due to faults are calculated for the {111} and {200} powder lines, assuming equal densities of faults on all {111} planes, and these enable the strain broadening function to be evaluated from the measured coefficients. This function has approximately a Cauchy shape. Dislocation densities ρ estimated from the strain breadth ξ and mean square strain < S 2 >, vary much less with composition than does α'. Faults and dislocations disappear together on annealing, so that there is a linear relation between ρ and α'. It is nevertheless suggested that the stacking fault diffraction effects cannot be attributed to the fault ribbons in extended dislocations, as previously stated.