A hierarchical computational thermodynamic and kinetic approach to discontinuous precipitation in the U-Nb system

• U-Nb alloys decompose via discontinuous precipitation (DP) over a broad range of aging conditions, adversely affecting their properties. The growth kinetics, lamellar spacing, and Nb partitioning have been measured, but the thermodynamic and kinetic factors underlying these specific transformation characteristics and reaction paths, vis-a-vis the monotectoid reaction, are not fully resolved. In this work, a hierarchical computational thermodynamic and kinetic approach was carried out to investigate DP. The hierarchical approach started with density-functional theory (DFT) investigations of ground-state formation energies of bcc-based U-Nb alloys. The estimated energetic data was then utilized as an imposed first-principles-based constraint to improve the consistency of the CALPHAD thermodynamic and, subsequently, kinetic assessments of U-Nb. Phasefield simulations were then carried out to study DP's microstructure evolution using the assessed CALPHAD thermodynamic and kinetic representations. Good agreement with experiments on different physical/length scales was achieved, which validates the present theoretical contributions to a better understanding of DP in U-Nb alloys.

Ämnesord

TEKNIK OCH TEKNOLOGIER  -- Materialteknik (hsv//swe)

ENGINEERING AND TECHNOLOGY  -- Materials Engineering (hsv//eng)

Nyckelord

CALPHAD

DFT

Discontinuous precipitation

PFM

Computation theory

Density functional theory

Ground state

Growth kinetics

Kinetics

Microstructure

Niobium alloys

Precipitation (chemical)

Reaction kinetics

Thermodynamics

Uranium alloys

Computational thermodynamics

Hierarchical approach

Lamellar spacing

Micro-structure evolutions

Monotectoid reactions

Phase-field simulation

Phase transitions

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