The hardness, mirostructure, and corrosion resistance of two commercial low-gold dental casting alloys were studied by microhardness tester, optical microscope, SEM, and potentiostat after the heat treatments.
Stabilor NF IV alloy (55.0 wt.% Au-29.0 wt.% Ag-9.9 wt.%a Pd-4.0 wt.% In) and Duallor G Alloy (55.0 wt.% Au-25.0 wt.% Ag-7.9 wt.% Pd-11.6 wt.% Cu) were selected for the study.
Softening heat treatment for Stabilor NF IV alloy and Duallor G alloy was done at 800°C for 15 min., and followed by quenching in ice brine._ Hardening heat treatment for Stabilor NF IV alloy was done at500°Cfor.:15 min., and followed by air-cooling. Hardening heat treatment for Duallor G alloy was done at 350C for 15 min., and followed by air-cooling.
The results were as follows:
1 By hardening heat treatment after softening heat treatment, the microstructure of Stabilor NF IV showed lump-like lamellar structure at the grain boundaries and fine precipitates in the grains, that of Duallor G showed shoebrush-like lamellar structure along the grain boundaries and increased fine precipitates in the grains, which were arranged with regular directions.
2 Vickers hardness value of Stabilor NF IV was increased from 142 to 241 and that of Duallor G was increased from 93 to 304, according to hardening heat treatment after softening heat treatment.
3. Hardening heat treatment in both alloys produced a more inhomogeneous structure, resulting in a lower corrosion resistance, but was not largely effective in altering the corrosion resistance. I think this insignificant effect on the corrosion resistance is due to the nobility which was not lower and the heat treatment in the dentistry which could not significantly affect the microstructure.
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