Abstract
The isothermal age-hardening behaviour of a multi-purpose dental casting gold alloy was investigated by means of hardness testing, X-ray diffraction study, scanning electron microscopic observations and energy dispersive spectroscopy. By ageing of the solution-treated specimen at 400∼500°C, two phases of the Au-rich α1 phase with an f.c.c. structure and the α2 phase with an ordered f.c.c. structure based on Pt3In were transformed into three phases of the α1 phase, the α2 phase and the β phase with an ordered f.c.t. structure based on PtZn. Hardening was attributed to the fine nodular precipitation resulting from the formation of the β phase in the α1 matrix. Softening was due to the coarsening of the fine nodular precipitates as the result of consumption of the α2 phase.
