Diffusion in BCC multi-principal element alloys from experiment and ab initio: Impact of thermal vibrations and chemical complexity

Basic data for this project

Description

Diffusion in concentrated alloys, especially in so-called multi-principal element alloys (MPEAs), attracts increasing attention due to advanced technological applications. Such alloys exhibit unique features prominently sluggish diffusion that critically affect various materials properties, e.g., microstructure evolution, phase stability, creep behavior, radiation tolerance. The unique features of MPEAs generally originate from the significant chemical complexity which, at the same time, brings about tremendous challenges for both experimental and theoretical studies. Theoretically, the role of lattice thermal vibrations in combination with the strong heterogeneity of local environments and their impact on diffusion in MPEAs are far from being understood, impeding a quantitative, and sometimes even a qualitative, prediction of diffusivities. Based on a concerted effort of teams from Stuttgart (simulation) and Münster (experiment) both established leaders in their respective research fields and connected with each other through a long-standing collaboration—the present project aims at developing accurate and versatile approaches to investigate and fundamentally understand diffusion in complex MPEAs. Utilizing a combination of an advanced radiotracer technique together with several highly accurate ab initio-informed simulation techniques, we will focus in the present project on vacancy-mediated diffusion in BCC MPEAs of the MoNbTaVW system. Owing to the high melting points of the constituent elements, BCC MPEAs were reported to possess outstanding high-temperature strength that may surpass the conventional superalloys. Indeed, the MoNbTaVW system is considered as a next-generation structural and functional alloy with superior high-temperature performance. Through the joint, interactive analyses of accurately measured and simulated tracer diffusivities for a collection of BCC MPEAs featuring different chemical complexities, e.g., random solid solutions and alloys with short-/long-range order (B2), we will not only provide an extensive set of diffusion data with unprecedented accuracy but also a thorough physical understanding of the impact of thermal vibrations, chemical interactions, element substitutions, and chemical ordering as well as their interplay. A significant advance in the fundamental understanding of diffusion and related ordering/disordering tendencies in MPEAs is expected.