牙科用银钯合金时效处理后的晶相结构变化与显微硬度的关系研究

Effects of metallographic changes on the micro-hardness of an Ag-Pd dental casting alloy after different age hardening treatments

目的探讨牙科银钯合金不同时效处理后金相结构的变化与材料显微硬度差异的相互关系。方法牙科标准失蜡铸造程序制作10mm×10mm×1mm的片状银钯合金试样88个(n=4),经过淬火冷却固溶处理后,合金分别在400℃、459℃、600℃等温强化处理1min、2min、5min、10min、20min、50min和100min并立即冰水淬冷,固溶处理组作为对照组。进行显微硬度测试以及金相显微镜观察,分析合金的显微结构变化与硬度变化的相互关系。结果时效温度越高,合金硬度值的增加速度越快。400℃组硬度随强化处理时间增加单调增加;459℃组开始随时间增加而增加,20min后下降,50min后上升,100min后又降低;600℃时效处理组合金硬度开始迅速上升,2min后快速下降,在20min后逐渐稳定。不同时效处理后样本的金相结构出现显著差异,晶界处出现新的沉积相,并随处理条件出现变化,金相结构变化与硬度的改变具有很好的相关性。结论不同时效处理后合金晶界处新的沉积相出现和晶枝结构变化与硬度的改变具有相关性。

Objective To study the effects of metallographic changes on the micro-hardness of an Ag-Pd dental casting alloy after different age hardening treatment under and above the phase transformation temperature of the alloy.Methods 88 square specimens（n=4） with a size of 10mm×10mm×1mm were fabricated according to a standard dental casting procedure.After solution treatment heating by heating the specimen to 900℃ and immediately quenched into ice-water,The specimens were iso-thermally age-hardened at 400,459 and 600℃ for 1minute,2minutes,5minutes,10minutes,20minutes,50minutes and 100minutes respectively,then followed by immediate ice-water quench.The solution treated specimens without age hardening were taken as control.The Vickers＇ micro-hardness of the specimens was tested and the metallographic structures of specimens were observed.Results The micro-hardness values of the alloy after thermal treat under 400℃ increased with treating time,while those values treated under 459℃ fluctuate with treating time： increased initially,decreased after 20min and increased after 50min,then decreased again after 100min.For specimens treated under 600℃,the hardness increases initially,then decreased with treating time more than 2min,and remained stable after 20min.Metallographic observation revealed that thermal treat resulted in microstructure change of the ally,new phases formed in the interstitial interface of the crystalline.The changes in micro-hardness could be correlated to the micro-structure changes of the alloy.Conclusion The change of micro-hardness was correlated with the phase transformation of the alloy after thermal treat.The formation and dendrite growth of the new phase in the alloy could account for the changes of the hardness.