Derivation and application of concentration formula of alloy genes of DO₃-type in BCC alloy systems

Abstract

Taking Ta–W alloy system as an example, the concentration formulae of alloy genes of DO₃-type alloys in BCC structures were derived on the basis of the theory of alloy genes and the number of coordination atoms. The concentrations of alloy genes of DO₃-TaW₃ and DO₃-Ta₃W ordered alloys were calculated as functions of composition xW and ordering degree (s). When s=smax, the concentrations of alloy genes of stoichiometric DO₃-TaW₃ compound are equal to those of alloys, that is, x₈^Ta 0.25(at), x₄^W 0.5(at), x₈^W 0.25(at). The concentrations of alloy genes of stoichiometric DO₃-Ta₃W compound are also equal to those of alloys, that is, x₀^Ta 0.25(at), x₄^Ta 0.5(at), x₀^W 0.5(at). As ordering degree decreases, alloy genes of DO₃-TaW₃ and DO₃-Ta₃W ordered alloys will split. And the degree of splitting of alloy genes increases with the ordering degree decreasing. The atomic states and properties of DO₃-TaW₃ and DO₃-Ta₃W ordered alloys were calculated as a function of composition xW. The reason was pointed out that preparation of DO₃-TaW₃ and DO₃-Ta₃W intermetallic compounds is difficult due to small differences in their cohesive energies. It will provide theoretical guidance for the scientific designation to new candidate for ultrahigh- temperature materials in areo-engine applications.

Keywords

Ta–W alloy system / BCC structure / alloy gene

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