Cai Z, Brantley W A, Clark W A, Colijn H O
Section of Oral Biology, College of Dentistry, Texas A & M University System, Dallas, USA.
Dent Mater. 1997 Nov;13(6):365-71. doi: 10.1016/s0109-5641(97)80108-x.
The purpose of this study was to use transmission electron microscopy to examine four representative high-palladium alloys and gain insight into possible strengthening mechanisms.
Castings of two Pd-Cu-Ga alloys and two Pd-Ga alloys were thinned by jet polishing and ion milling, followed by plasma cleaning, to yield foil specimens. Multiple specimens were prepared for each alloy. Bright-field images, dark-field images and selected-area electron diffraction patterns for the alloys in the as-cast condition, after simulated porcelain-firing heat treatment, and after annealing at 980 degrees C were analyzed by standard transmission electron microscope (TEM) techniques. The overall compositions of the ultrastructures for the specimen foils were determined by conventional standardless energy-dispersive spectroscopic analyses with the TEM, and mean values of the elemental compositions were compared to the nominal alloy compositions provided by the manufacturers.
There was generally good agreement (differences less than 2 wt%) between the overall ultrastructure composition and each nominal alloy composition, except for Protocol from which in may have been lost during casting or formed intermetallic compounds that were not detected by TEM. The same fine-scale tweed structure within parallel bands of approximately 100-200 nm width was observed for all four alloys in the as-cast condition and after simulated porcelain-firing heat treatment. The persistence of the ultrastructure in the specimens of the two Pd-Cu-Ga alloys annealed at 980 degrees C and quenched in ice water indicated very rapid formation from the palladium solid solution. The presence of ¿100¿ and ¿110¿ forbidden reflections for the <001> zone suggested that the tweed structure is ordered, although further research is necessary to establish this conclusion.
The presence of a similar tweed structure in both the Pd-Cu-Ga alloys and the Pd-Ga alloys of substantially lower hardness shows that some other strengthening mechanism accounts for the high hardness and strength generally observed for Pd-Cu-Ga alloys.
本研究旨在利用透射电子显微镜检查四种具有代表性的高钯合金，并深入了解可能的强化机制。
通过喷射抛光和离子研磨将两种钯 - 铜 - 镓合金和两种钯 - 镓合金的铸件减薄，随后进行等离子清洗，以制备箔片试样。每种合金制备多个试样。采用标准透射电子显微镜（TEM）技术分析铸态、模拟烤瓷热处理后以及在980℃退火后的合金的明场图像、暗场图像和选区电子衍射图样。通过TEM的常规无标样能量色散光谱分析确定试样箔片超微结构的总体成分，并将元素组成的平均值与制造商提供的标称合金成分进行比较。
总体超微结构成分与每种标称合金成分之间通常具有良好的一致性（差异小于2 wt%），但对于Protocol，可能在铸造过程中损失或形成了TEM未检测到的金属间化合物。在铸态和模拟烤瓷热处理后的所有四种合金中，均观察到宽度约为100 - 200 nm的平行带内存在相同的精细尺度花呢结构。在980℃退火并在冰水中淬火的两种钯 - 铜 - 镓合金试样中，超微结构的持续存在表明其从钯固溶体中非常快速地形成。<001>晶带中“100”和“110”禁戒反射的存在表明花呢结构是有序的，尽管需要进一步研究来证实这一结论。
在硬度明显较低的钯 - 铜 - 镓合金和钯 - 镓合金中均存在类似的花呢结构，这表明其他一些强化机制导致了钯 - 铜 - 镓合金通常所观察到的高硬度和高强度。
