Abstract
Phase transitions in the Co-rich part of the Co–Al–Nb–Mo phase diagram are studied by energy dispersive spectroscopy (EDS), X-ray analysis, transmission electron microscopy (TEM), and differential scanning calorimetry (DSC) measurements. The obtained results were compared with the results for alloys of the binary Co–Al and ternary Co–Al–Nb, and Co–Al–Mo systems. Formation of the intermetallic phase with the L12 structure was found in a range of alloys with 10 at.% Al, 2–9 at.% Nb, and 3–7 at.% Mo. Intermetallic compound Co2Nb, Laves phase with the different chemical composition and crystal structure (C14 and C36) was detected in the Co–Al–Nb and Co–Al–Nb–Mo samples after vacuum solution treating at 1250 °C for 30 h.
Highlights
Cobalt and nickel heat resistant alloys are widely used in industry
Ternary phase diagrams have tried to reduce to a pseudo-binary, while multicomponent ones are reduced to pseudo-ternary phase diagrams
In addition to the solid solution based on cobalt (γ–Co) in this alloy, the presence of six different intermetallic phases has been reported in different works (Table 2)
Summary
Cobalt and nickel heat resistant alloys are widely used in industry. The last ones are limited by the mechanical and physical properties of its heat-resistant parts. The development of new heat resistant alloys used for manufacturing such parts requires knowledge of the phase diagram of multicomponent systems. It was believed that carbides are the main hardening phases in cobalt-based alloys [1]. The discovery of an intermetallic phase with an ordered L12 structure in cobalt alloys of the Co–Al–W system initiated the study of new heat resistant cobalt-based intermetallic superalloys and of the possibility of the formation of an intermetallic phase with an L12 structure in other cobalt and nickel systems including multicomponent ones. Isothermal sections of the phase multicomponent diagram are usually divided into parts (slices) including the concentration region of interest of the phase diagram. It is not always possible to find phase diagrams of a multi-component system
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