Application of Ion-etching to Metallography

The present paper has revealed the difference of microstructural characteristics between the metallurgical structure formed by discrepancies of sputtering yield in the ion-etching and that formed by differences of the electrochemical potential in the chemical etching on precious metals and alloys, and appreciated superiorities or inferiorities of the ion sputtering as an etching technique in metallography.The contrast in an optical micrograph arises mainly from a preferential attack of the grain boundary in the chemical etching, while in the ion-etching it is produced by the steps of the grains which are parallel to the polishing surfaces and are dependent on crystal orientation and composition. In the optical microscopic observation, the ion-etching method can obtain the clear contrast which is not at all inferior to that of the chemical etching. Besides its usefulness as an etching method for the specimens which can not etch chemically, the method can control easily amounts of etching, has good reproducibility of the etching images, and does not require proficient and empirical techniques in comparison with the chemical one.