A high-gold content ceramo-metal alloy (85 wt% Au, 5 wt% Pd, 5 wt% Pt) was selected for a definitive study of the hardening reactions. Specific points of concern included the hardening phase, hardening mechanism, and reaction kinetics to provide an understanding of the hardness development during the porcelain firing cycle. Contrary to previous reports, it is shown that ordering of a submicron FePt-type intermetallic phase is responsible for the observed aging behavior. Hence, it is concluded that through proper alloy design the hardening reaction can be made insensitive to variation in porcelain firing cycles.
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