TEM analysis of tweed structure in high-palladium dental alloys

Transmission electron microscopy and convergent-beam electron diffraction w ere used to study three high-palladium dental alloys: an as-cast Pd-Ga allo y, a cast Pd-Cu-Ga alloy aged at room temperature for over 5 years, and a c ast Pd-Cu-Ga alloy annealed at 1023 K for 2 h and slowly cooled to room tem perature. Bands containing a tweed structure in the Pd-Ga alloy were 120 de grees twins with (1 (1) over bar 0) mirror planes. Within these bands the a lloy had a face-centered tetragonal structure with a c/a ratio of 1.03. The aged Pd-Cu-Ga alloy contained a larger amount of tweed structure than the original as-cast alloy, along with randomly oriented bands and thin lath-li ke regions. The annealed Pd-Cu-Ga alloy contained rectangular particles of a secondary phase that may be Pd2Ga, Pd5Ga2 or Pd13Ga5. The microtwinned ba nd structure relieves the strain energy arising from transformation of the f.c.c. palladium solid solution on cooling. (C) 1999 Kluwer Academic Publis hers.