Improved Metallography of Zirconium alloys

Several procedures for the metallographic preparation and viewing of zirconium alloys have been developed in recent years which broaden the ability of the metallographer to more totally describe the morphology of these materials. For most detailed studies, it is not possible to describe with a single method the structure of commercial materials. Features found to be present by one technique may be completely missed or inconclusively revealed by other techniques. Anodizing a metallographically prepared sample of a zirconium alloy in a phosphoric acid solution results in color contrast between retained intermetallic compounds and the matrix. While this method is not new, its application to evaluation of low-solubility compounds is described herein. A color contrast is also observed between various types of intermetallic compounds by the nature of their different anodizing characteristics. A technique for metallographic preparation and anodizing is described. The resultant microstructure with typical carbide, phosphide, and silicide intermetallics in zirconium and zirconium alloys is shown with color photomicrographs. Characteristics of each of these three types of intermetallic compounds are described. A technique for heat tinting metallographic samples of Zircaloy-2 and Zircaloy-4 to show alloy microsegregation is also described. This method is complementary to anodizing and conventional etching methods. Subtle compositional variations, such as the tin distribution in the Zircaloys, can be revealed by heat tinting techniques. Such variations are not apparent with other techniques.