Pd and Au have complete solid solubility at all temperatures and compositions. Adding 20 wt.%Pd to Au increases the solidus temperature from 1064Ë C to 1250Ë C, which is hot enough to allow an Al2O3-based ceramic veneer to be fired at 1200Ë C around a Au-20Pd alloy stump for a dental implant. The coefficient of thermal expansion of this ceramic is 7.3 x 10-6 CË-1.
(a) Use the rule of mixtures to estimate the coefficient of thermal expansion of the Au-20Pd alloy.
(b) The Au-Pd stump is a solid, 3mm diameter cylinder with a roughened surface to assure strong bonding to the ceramic. Assuming the ceramic-metal interface remains well bonded during cooling to room temperature, will the ceramic veneer have a residual tensile or compressive hoop stress near the ceramic-metal interface?