Microstructural Evolution and Crystallization Behavior of Amorphous Medium-Entropy Ti-Nb-Zr-Ag Thin Films

TL;DR

This study investigates how adding silver to Ti-Nb-Zr medium-entropy alloy thin films affects their microstructure and crystallization behavior, revealing enhanced stability and potential for antibacterial biomedical coatings.

Contribution

It demonstrates that silver promotes early crystallization and stabilizes amorphous structures in Ti-Nb-Zr-based thin films, advancing multifunctional coating development.

Findings

Ag induces early-stage crystallization in amorphous films

Ag-containing films retain compact structure after annealing

Surface morphology is favorable for protein adhesion

Abstract

Improving the performance of metallic implants increasingly relies on the development of multifunctional surface modifications that combine structural stability, bioactivity, and prevention of bacterial colonization. Medium-entropy alloys (MEAs) represent a promising approach for such coatings, as their chemical complexity allows the formation of structurally stable matrices with tunable properties. In this study, Ti-Nb-Zr and Ti-Nb-Zr-Ag thin films were deposited by magnetron sputtering and subjected to annealing at temperatures of up to 1100 $^{\circ}$C to evaluate the influence of Ag, added for its antibacterial potential, on structural evolution. The as-deposited Ag-free film was fully amorphous, whereas the Ag-containing film exhibited a predominantly amorphous matrix with finely dispersed crystalline nanoparticles, indicating that Ag promoted early-stage crystallization. Both films displayed a fine columnar morphology (column diameter $\sim$15 nm) with dome-like protrusions, a hierarchical surface structure favorable for protein adhesion. Upon annealing, the Ag-free film recrystallized into a granular, loosely packed morphology, while the Ag-containing film retained a compact structure, demonstrating the stabilizing role of Ag. These findings underscore the potential of Ag-containing amorphous MEAs for forming multifunctional coatings with enhanced thermal stability, antibacterial functionality, and biointerface-relevant surface features for advanced biomedical applications.