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Final Report Summary - ATMODALLOY (Atomic Scale Modeling of Concentrated Multi-Component Alloys)

The main goal of this project was to systematically develop atomic scale models of concentrated multi-component alloys. Specifically, we targeted W and Ti-based alloys -- systems that are of interest with respect to applications in fusion energy, air and spacecraft technology, as well as medicine and dentistry. The project entailed on two major components: (1) The systematic development of atomic scale models using methods that are specifically designed to describe concentrated multi-component systems. (2) The application and development of a suite of modeling techniques for studying phase diagrams, short and long-range order, precipitation and mechanical properties of alloy systems taking into account defects.

The project has progressed well and the research team has achieved most of the original objectives with relatively minor deviations. The major work performed includes:
(1) The development of the *atomicrex* code for the construction of interatomic potentials. The code is written in C++ and python, supports a wide array of potential schemes, is computationally very efficient, flexible, and fully documented. This code is currently being finalized for public release (in open source form).
(2) The development of the *icet* code for the construction of cluster expansions using a similar combination of C++ and python.
(3) The further development and application of techniques for studying alloy thermodynamics, in particular for interfaces and precipitates.
(4) The construction of extensive databases for refractory alloys containing W, Ti, Re, and V.
(5) The construction of atomic scale models for W, Ti and Re-based alloy systems.
(6) The analysis of defects in these systems with relevance to the nucleation of secondary phases.
(7) Extensive calculations pertaining to the thermodynamics of oxygen in Ti.

The most significant results achieved in the project are summarized below.
In terms of method development we have accomplished
(1) the description and detailed analysis of a size-dependent phase diagram for a nanoprecipitate using our large-scale massively parallel Monte Carlo algorithm based on the variance constrained semi-grandcanonical ensemble;
(2) modeling the interaction of dislocations with precipitates as a function of not only their size but also their structure and orientation;
(3) modeling and understanding of several W and Ti-based alloys with relevance for applications in fusion reactor environments; and
(4) the development of a highly efficient and flexible codes for constructing atomic scale models for multi-component systems.

In terms of further applications of these methods, we have
(1) analyzed the defect properties of various transition metals in W with respect to applications in fusion reactors;
(2) analyzed the properties of oxygen defects in Ti with respect to the formation of Ti-suboxides and constructed a phase-diagram for the Ti-rich end (up to 30% oxygen) of the composition range; and
(3) constructed models for e.g., the W-Re, W-Ti, and W-V systems.

The tools developed in this project are of general usage and were used for example to resolve chemical ordering in thermoelectric materials and its coupling to transport properties.

In this project we have established a strong basis for future work both in the focus area of the present project and beyond. Specifically, we developed a set of tools that will enable us to extend our scope in the future, both in terms of the alloy systems studied, their dimensionality, and their properties.

This project has furthermore provided the PI with the possibility and freedom to build up and strengthen a viable scientific network both within his new home institution (Chalmers) and Europe. This is evident from a number of joint publications that have resulted from these efforts and have thus been made possible by this grant.

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Life Sciences
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