Age-hardening behavior in a palladium-base dental porcelain-fused alloy

Age hardening in a Palladium-base porcelain-fused alloy was investigated by hardness tests, x-ray diffraction, scanning, and transmission electron microscopy. In the early stages of aging, a metastable ordered phase with a face-centered tetragonal structure based on Pd 3In was formed within the grains. Hardening was due to coherency strain between the metastable structure and the matrix with a face-centered cubic structure. In the later stages, a lamellar structure, consisting of a stable ordered phase with a face-centered tetragonal structure based on Pd 3In and a stable phase with a face-centered cubic structure, grew from the grain boundaries. Finally, the lamellae covered the whole grain and resulted in softening.