ON THE INTERACTION OF ALLOYING ELEMENTS WITH GRAIN BOUNDARIES OF HIGH-PURITY NICKEL AND IRON

Abstract

Purpose. Proof of the reality of the effect of displacement of some microadditives from the internal boundaries of the grains into their internal volumes for reasons of purely thermodynamic concepts.
 Research methods. The initial data were specially selected chemical compositions of model alloys based on high-purity nickel and iron, which are microalloyed with yttrium, lanthanum, zirconium and rhenium. The choice of nickel and iron as the basis for the alloys under study is due to the fact that they are the base for a large group of industrial alloys (heat-resistant nickel materials and a wide range of steels for various purposes).
 The lattice parameters of nickel and iron were determined using an improved DRON-1 type diffractometer in copper (nickel alloys) and iron (iron alloys) X-ray radiation with monochromatization of diffracted beams. The lattice parameters were determined, respectively, using the (420)a and (220)a lines, respectively, for nickel and iron alloys.
 Results. During recrystallization, migrating grain boundaries in nickel and iron retain impurity atoms and still partially “sweep” them out of the grain volume. The thickening of the boundary zones (that is, their "loosening") prevents the possibility of supersaturation of the interfaces with microalloying impurities.
 The effect of significant displacement of some microalloying elements (zirconium and rhenium) deep into the grains of the matrix phases (nickel and iron) has been established.
 It has been found that such microalloying elements as lanthanum (cerium) and yttrium have the most effective influence on the strength characteristics of the studied metallic materials.
 Scientific novelty. Graphs of changes in the chemical composition of microalloyed basic solutions (nickel and iron) are plotted while maintaining the fine structure of grain boundaries. If they are loosened, this crowding out effect disappears.
 Practical value. Since the effect of microalloying (as shown in the presented works) significantly affects the strength characteristics of materials, the results of the study showed which of the selected microalloying elements act most effectively in this direction.