|
The Ag-Pd-Cu alloys containing a small amount of Au is commonly used for dental purposes, because this alloy is cheaper than Au-base alloys for clinical use. However, the most important characteristic of this alloy is age-hardenability, which is not exhibited by other Ag-base dental alloys. The specimens used were Ag-Pd-Cu ternary alloys and Au addition alloy. These alloys were melted and casted by induction electric furnace and centrifugal casting machine in Ar atmosphere. These specimens were solution treated for 2hr at 800% and were then quenched into iced water, and aged at 350~550℃. Age-hardening characteristics of the small Au-containing Ag-Pd-Cu dental alloys were investigated by means of metallurgical microstructures, X-ray diffraction and electron microscope observations, energy dispersed spectra and electron probe microanalysis. Principal results are as follows : The case of hardening in stage Ⅰ was due to the formation of the L1o type face-centered tetragonal PdCu-ordered phase in the grain interior and hardening in stage I was affected by the Cu concentration. In stage Ⅱ, decomposition of the αsolid solution to a PdCu ordered phase(L1o type) and an Ag-rich α₂ phase occurred and a discontinuous precipitation occurred at the grain boundary. From the electron microscope study, it was concluded that the cause of age-hardening in this alloy is the precipitation of the PdCu ordered phase, which has AuCu Ⅰ type face-centered tetragonal structure. Precipitation procedure was α→α＋α₂＋PdCu→α₁＋α₂＋PdCu at Pd/Cu ＝1. Ag-Pd-Cu alloy is more effective dental alloy as ageing treatment and is suitable to isothermal ageing at 450℃.
|