Fatigue studies of high-palladium dental casting alloys: Part II. Transmission electron microscopic observations.

The microstructures of two representative high-palladium dental alloys, a Pd-Cu-Ga alloy and a Pd-Ga alloy, which had been subjected to cyclic fatigue in uniaxial tension were investigated by transmission electron microscopy (TEM). Two different mechanisms were found to dominate microplastic deformation during fatigue: twinning in the Pd-Cu-Ga alloy, and planar slip of dislocations in the Pd-Ga alloy. In addition, stress-induced precipitation occurred in the Pd-Ga alloy during cyclic loading. Heat treatment simulating the firing cycles for dental porcelain resulted in the formation of a previously unreported bcc phase in the Pd-Cu-Ga alloy, and in the elimination of the characteristic tweed structure found in the Pd-Ga alloy for the as-cast condition.