Exploring solute segregation and precipitation in W-X (X=Ti, Ag, Ta) binary alloys: experiments and atomistic modeling

This study examines the segregation and precipitation kinetics in W-X binary alloys (X= Ti, Ag, and Ta). Advanced transmission electron microscopy techniques and atomistic modeling are employed for this comprehensive study. Following the high temperature annealing of the samples, distinct behaviors are observed for each alloying element. In the W-Ti alloy, depleted/enriched GBs with solutes are present. Ti-rich clusters form at the GBs in the fcc phase, exhibiting varying cluster sizes. On the other hand, Ag-rich clusters form within the grain interior, which is particularly pronounced at GBs. Unlike Ti and Ag, no Ta clusters observed however, regions within the grain interior and GBs appear depleted in W, suggesting the presence of enriched Ta segregants. Additionally, the W-Ta alloy exhibits notably less grain growth compared to other W alloys. The Metropolis Monte Carlo (MMC) method and density function theory (DFT) simulations are employed to support and explain these findings. The MMC results indicate that different solutes have varying tendencies to segregate or precipitate at different symmetrical tilt GBs. The DFT studies confirm that the character of the GBs significantly influences both the solute-vacancy binding and solute migration barrier. Furthermore, the analysis of the Projected Density of States (PDOS) and charge transfer between initial and transition states in the bulk material and at GBs reveals a strong correlation between the activation energy, the amount of charge transfer, and the nature of bonding. Among the solutes investigated in this study, Ta shows promise as a dopant in W for nuclear applications.