15: Critical evaluation of ternary alloys of iron and molybdenum with cobalt, chromium, manganese, and nickel

Abstract

Existing experimental information on the constitutions of the four ternary systems Co-Fe-Mo, Cr-Fe-Mo, Fe-Mn-Mo, and Fe-Mo-Ni has been critically assessed, and used to suggest probable constitutional features in each case. In all cases difficulties arise because much of the work on the ternary systems was carried out before a complete understanding of the Fe-Mo system had been arrived at. Consequently, interpretation of the results was frequently incomplete or erroneous. In particular the R-phase of the Fe-Mo system was rarely considered as a constituent In the proposed equilibria. In the case of the Co-Fe-Mo system, it is possible to present a probable surface of primary separation based on original work. Solid-state isothermals from 1300 to 800°C are described. The chief feature is complete solid-solution formation between Fe₇Mo₆ and Co₇Mo₆ to form the μ-phase, and the predominating equilibrium in Fe-rich alloys is a α + γ + μ. It is also possible to arrive at a probable liquidus surface for the Cr-Fe-Mo system, where an important feature is the existence of a ternary compound with the structure of αaMn, which was not recognized in early work. Solid-state isothermals from 1250 to 700°C are presented and illustrate that the o phase field is of considerable extent. Little work has been done on Fe-Mn-Mo alloys, but it is suggested that a reported ternary compound may be more probably“represented as a solid solution of Mn in the Fe-Mo R-phase. In the case of Fe-Mn-Ni alloys, the nature of the equilibria in the solid state at 1200–1100°C is discussed, and the system contains a ternary.,compound T₁ with an orthorhombic structure. In all the cases covered in this assessment, further experimental work is required for the clarification of details of the constitution.