Development of 12%Au-20%Pd-Ag casting dental alloy

本研究的目的是研制一种新型牙科合金，使铜含量提高到共晶区，强度大大提高，韧性不低于金合金。相关结果表明，抑制β相的体积比可以阻止疲劳性能的恶化。为进一步了解该合金，为下一步工作做好准备，本年度的工作是继续上一年的工作，对铸造的12%Au-20%Pd-Ag合金进行常压下的疲劳试验，从铸造缺陷与疲劳强度关系的角度探讨疲劳断裂机理。在1073K空冷条件下，合金铸件的低周和高周疲劳强度均明显低于空冷后的疲劳强度。然而，在所有的铸件冷却方案中，1123K水冷的铸件在高周率区的疲劳强度最高，这表明合金的抗疲劳性能不容易受到铸造过程中伴随的体积收缩的影响。在高载荷低周次区，体积收缩率越高，铸件的疲劳强度越低，而在低载荷高周次区，收缩的影响非常有限，几乎可以忽略收缩对疲劳裂纹扩展的影响。上述事实表明，在1123K对铸件进行固溶处理，可以减小铸造缺陷对疲劳强度的影响，提高疲劳强度。

It is aimed in this study to create a new dental alloy, which copper content is raised up to the eutectic zone, strength is increased greatly and toughness is not lower than that of gold alloys. It had been shown by the relative results that inhibiting the volume rate of the β phase can block the degradation of the fatigue property. To acquire further understanding to the alloy for next-step efforts, the work of the present year, the continuance of the last-year operations, was to conduct fatigue tests of casting 12%Au-20%Pd-Ag alloy in ambient atmosphere, and to look into the mechanism of fatigue fracture from the angle of the relation between casting defects and fatigue strength.1. The casting products of the alloy show apparently lower fatigue strength than that of the working products by air-cooling at 1073K both in low and high cycle regions. The casting of water cooling at 1123K, however, among all the casting cooling plans, brings the highest fatigue strength for the relevant casting product in the high cycle region, indicating the fact that the fatigue-resistant property of the alloy is not prone to be affected by volume shrinkage accompanying in the casting process.2. In the zone of high loads combining low cycles the higher volume shrinkage rate is the lower the fatigue strength of the casting products is, but in the zone of low loads combining high cycles the effect of shrinkage is so limited that one can almost neglect the influence of shrinkage on the growth of fatigue cracks.The above facts indicate that diminishing the effect of casting defects on the fatigue strength and increasing the fatigue strength are available by solution treating the casting materials at 1123K.