Ductility of a dental Ag-Pd-Cu-Au alloy

Abstract

A silver-palladium type of dental alloy for fixed restorations has been investigated with regard to the ability of the material to be plastically deformed in uniaxial tensile testing after two different age-hardening treatments. A certain degree of ductility is required for the burnishing of the margins. Aged to peak hardness at 350°c after solid-solution annealing at 900°c., the material was found to be brittle owing to a reaction zone along the grain boundaries, promoting an intergranular fracture. When the age-hardening temperature was lowered to 275°c., a less pronounced reaction zone along the grain boundaries could be observed. The accompanying mechanical properties after precipitation hardening at 275°c are probably an acceptable compromise between mechanical strength and ductility. Small particles along grain boundaries and brittleness were also found after solid-solution annealing at 900°c and quenching. It is suggested that the improved ductility after subsequent aging at 275°c is due to a coarsening of these small particles. In the as-cast condition the alloy was softer and more ductile than in the age-hardened state.

Key Words:

• Age-hardening
• elongation
• grain boundary failures
• tensile testing