Niemi L, Holland R I
J Dent Res. 1984 Jul;63(7):1014-8. doi: 10.1177/00220345840630070401.
The correlation between microstructure, tarnish, and corrosion behavior of a commercial dental Ag-Pd-Cu-Au casting alloy after various heat treatments was studied. The attacked structural components were identified by comparing SEM micrographs with light optical micrographs taken after exposure of the alloy to a 2% Na2S solution and after dynamic polarization in de-aerated artificial saliva. The characteristic dynamic polarization curves for the alloy after the heat treatments were established. The results were verified by analogous testing of two experimental alloys with compositions similar to those of the analyzed components in the commercial alloy annealed at 600 degrees C for seven wk. The matrix of the commercial alloy was decomposed, according to the heat treatments, into varying proportions of a tarnish- and corrosion-resistant Cu- and Pd-rich component (A) and a nonresistant Ag-rich component (B). The presence of A considerably increased the tarnish rate of B, due to galvanic coupling. Age-hardening of the alloy increased the proportion of the tarnish- and corrosion-prone component B.
研究了一种商用牙科银钯铜金铸造合金在不同热处理后微观结构、变色和腐蚀行为之间的相关性。通过将扫描电子显微镜（SEM）微观照片与该合金在2% Na2S溶液中暴露后以及在脱气人工唾液中动态极化后拍摄的光学显微镜照片进行比较，确定了被侵蚀的结构成分。建立了热处理后该合金的特征动态极化曲线。通过对两种实验合金进行类似测试验证了结果，这两种实验合金的成分与在600℃退火7周的商用合金中分析成分相似。根据热处理情况，商用合金的基体分解为不同比例的抗变色和抗腐蚀的富铜和富钯成分（A）以及不耐蚀的富银成分（B）。由于电偶耦合，A的存在显著提高了B的变色速率。合金的时效硬化增加了易变色和易腐蚀成分B的比例。
