Abstract
A field-ion microscope study has been made of the early stages of coarsening of gold precipitates in solution-treated, quenched, and aged Fe-12 wt.-% Au, where the hardness of the alloy ranges from pre-peak to just beyond peak and the particles are from 2 nm (20 Å) to 20 nm in size. The precipitates were plate-like, lying on {100} ferrite planes. They were preferentially nucleated on grain boundaries and imperfections, and were partially coherent. Sizes (i.e. the length of the plate diagonal) were obtained from field-evaporation sequences of specimens. The mean particle size corresponding to maximum hardness was ∼ 7 nm. The square of the mean particle size varied linearly with time, suggesting an interface-controlled mechanism of coarsening, the activation energy for which was determined as 130 kJ/mol.
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