Synthesis and Structure of Refractory Multicomponent Alloys

Many applications in industry require refractory alloys having high mechanical properties and heat resistance at high temperatures. One of the possible alternatives of the existing nowadays materials is the high entropy alloys based on refractory metals like niobium, tantalum, molybdenum and tungsten. So, in present work, the synthesis of four-component Nb25Ta25Mo25W25 and five-component Nb20Ta20Cr20Mo20W20 alloys in an arc furnace was performed and their structure was studied. Energy dispersive chemical analysis demonstrates that the chemical compositions of the alloy Nb25Ta25Mo25W25 corresponds to the nominal one, but Nb20Ta20Cr20Mo20W20 alloy has loss of chromium. It was found that alloys have structure of bcc solid solutions (SS). Both alloys have dendritic structure where the excess of tungsten is in dendrite arms, niobium and molybdenum excess is found in interdendrite regions, while tantalum is randomly distributed in the SS. Chromium in the composition of the system Nb–Ta–Mo–W lead to suppressing of oxides formation according to XRD and EDX data. Coefficients of thermal expansion (CTE) of the NbTaCrMoW and NbTaMoW alloys are smaller than of nickel-based superalloys in a wide temperature range (300–1270 K). Relatively small CTEs of investigated alloys are beneficial for materials used in high-temperature applications.