Age-hardening mechanisms in a commercial dental gold alloy containing platinum and palladium.
The age-hardening mechanism of a commercial dental gold alloy containing platinum and palladium (in wt.%, 15 Cu, 6 Ag, 5 Pt, 3 Pd, 3 Zn, with the balance as gold) was elucidated by means of electrical resistivity, hardness tests, x-ray and electron diffraction and electron microscopy, as well as high-resolution electron microscopy. The sequence of phase transformations during isothermal aging below the critical temperature, Tc = 825 K, was described as follows: disordered solid solution alpha 0 (FCC)----metastable AuCu I' ordered phase (FCT)----metastable alpha 2 disordered phase (FCC) equilibrium AuCu I ordered phase (FCT) + equilibrium alpha 2 disordered phase (FCC). The hardening was due to the introduction of coherency strain at the interface between the AuCu I' platelet and the matrix. These ordered platelets had mutually perpendicular c-axes to compensate for the strain introduced by their tetragonality. A loss of coherency at the interface brought about softening of the alloy, i.e., over-aging.
Department of Dental Materials Science, Nagasaki University School of Dentistry, Japan.
T
T
Tani
K
K
Udoh
K
K
Yasuda
G
G
Van Tendeloo
J
J
Van Landuyt
D004553:Electric Conductivity; D006047:Gold Alloys / Q000032:analysis / Q000737:chemistry*; D006244:Hardness; D006245:Hardness Tests; D008854:Microscopy, Electron; D010165:Palladium / Q000032:analysis / Q000737:chemistry*; D010984:Platinum / Q000032:analysis / Q000737:chemistry*; D011199:Potentiometry; D013499:Surface Properties; D013696:Temperature; D013997:Time Factors; D014961:X-Ray Diffraction
D006047:Gold Alloys; D010984:Platinum; D010165:Palladium