Abstract
The paper discusses the researches that formed the basis of the study of the transition of “ordering-phase separation” and the reasons for such transition occurrence. Experimental results have presented what diffusion pairs are and how they occur in binary and multicomponent alloys. The paper illustrates that the chemical bonds between atoms are realized on the principle of pair interaction in both solid and liquid states of the alloy. The process of separating a multi-component ABC alloy into diffusion pairs A/B, A/C, and B/C occurs in a liquid solution, where the diffusion mobility of atoms is very high, and the resistance of the environment is relatively low. The driving force of such a process is the chemical attraction between like and unlike atoms, that is, the tendency to phase separation and the tendency to ordering. Quenching the liquid alloy into the water fixes a microstructure consisting of microscopic areas corresponding in composition to one or another diffusion pairs. The paper shows what exactly should be done so that such a branch of science as Materials Science could get rid of the empirical approach when creating new alloys.
Highlights
The contradictions discovered in the study of phase transformations in alloys were first seriously considered way back in the 1970s
The discussion held at that time on the initiative of Асta Metallurgica [1]-[6] did not lead to anything that could reasonably explain the appearance of particles of the second phase after quenching alloys from the solid solution range
If we look at the generally accepted phase diagrams of Co-Cr and Cr-Mo we can conclude that with approximately the same component ratios as in the corresponding diffusion pairs of the Co53Mo35Cr12 alloy under study, only a tendency to phase separation takes place between Co and Cr atoms, Cr and Mo atoms, in the entire range of heating temperatures
Summary
The contradictions discovered in the study of phase transformations in alloys were first seriously considered way back in the 1970s. The discussion held at that time on the initiative of Асta Metallurgica [1]-[6] did not lead to anything that could reasonably explain the appearance of particles of the second phase after quenching alloys from the solid solution range. Guinier [7] forewarned of these limitations Despite this warning, almost all phase diagram compilers utilized the X-ray phase analysis method without any doubt. TEM allows identifying such fine particles at a resolution where the X-ray phase analysis is powerless to compete
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