Scanning electron microscopy in the study of the structures of eutectic alloys of iron and chromium with refractory borides

Abstract

A comparative analysis of the capabilities of the traditional method of metallographic analysis of the structure of metals and alloys and topographic analysis of the surface of deeply etched alloys is carried out, from which one of the components (for example, metal) of the structure has been removed by the chemical method. The potential capabilities of scanning electron microscopy in the secondary electron mode are indicated due to the high resolution and depth of field. It is shown that the application of both methods is complementary and significantly increases the information of the real structure of the phase crystals that make up the alloy. By the example of the investigated alloys on iron and chromium base with refractory borides, the possibilities of combining both structure research methods to reveal the crystallization mechanism of eutectic system alloys and predict their properties are demonstrated. From an analysis of the structures of cast alloys of the considered eutectic systems, it was found that the crystallization mechanism changes, depending on the cooling rate, from the cooperative growth of eutectic components to independent growth with the formation of a structure of a thin phase conglomerate. The real forms of eutectic boride crystals are given, their relationship to each other in the alloy with the formation of a supporting framework of boride phases in eutectic colonies, which allows us to consider such eutectics as composite materials, and in the future, to predict their behavior under real operating conditions. The work is of interest, both for developers of new alloy compositions, and for the theory of crystallization, as well as for use in the educational process in courses on materials science.

Keywords

• alloy structure
• scanning electronic microscope
• eutectic
• crystallization mechanism.