[Thermal expansion of Au-Pd-Ag system alloys. Casting stress and deformation of addition of Sn and In].

To study the dimensional changes due to the release of casting stress in metal-ceramic alloys, a wheel-like pattern in which casting stress is liable to occur and rod- and barrel-like wax patterns in which the likelihood of such stress is low, were investigated with a phosphate-bonded investment compound. Furthermore, simultaneous casting was done using Au-Pd-Ag system alloys, 21 types of mother alloys and alloys with tin or indium or both, and accurate determinations of the thermal expansion rate with increased or decreased temperature were carried out. The results obtained were as follows. The mean thermal expansion rates of the mother alloys and the alloys with tin and indium upon increase and decrease of temperature were lowest for the large wheel-like pattern, followed by the small wheel-like pattern, rod-like pattern and barrel-like pattern, in that order. The mean thermal expansion rates of the mother alloys and the alloys with tin or indium or both were decreased when the palladium content was increased, but tended to increase when the silver content was higher. Gold had no influence on the thermal expansion rate. When the temperature decreased, the complex addition of tin and indium provided alloys showing only a slight deformation.