Systematic Investigation of Cold Spray for the Manufacturing of Tantalum-Silver Composites

Abstract

This work investigates the fabrication and properties of tantalum-silver (Ta-Ag) composites produced using cold spray technology. Despite the inherent immiscibility of Ta and Ag, Ta-Ag composites were successfully fabricated via cold spraying. This study provides a detailed analysis of the deposition mechanisms, antibacterial efficacy, and corrosion resistance of the Ta-Ag composites. Furthermore, it explores the application potential of cold-sprayed Ta-Ag composites in protective coatings for magnesium alloys and evaluates their mechanical properties as load-bearing materials. It was confirmed that Ta-Ag composites can be effectively fabricated through cold spray technology, with mechanical interlocking as the primary bonding mechanism. An increase in the volume of soft Ag in pre-mixed powders resulted in larger Ag agglomerations, influencing the rebounding of Ta particles and the micro-forging effect. This led to varied microstructures and reduced Ta retention. A synergistic deposition behaviour was observed, affecting the dissolution of Ag and its antibacterial properties. The absence of effective passivation of Ag in chloride-containing environments allowed for Ag dissolution, while the well-passivated Ta protected the Ta matrix from corrosion. This dissolution of Ag significantly contributed to the antibacterial properties. The microstructure of Ag agglomerations, formed by the synergistic deposition process, greatly influenced the antibacterial effectiveness of the Ta-Ag composites. Composites with 5% volume of Ag (Ta-5Ag) displayed the best overall antibacterial activity and corrosion resistance. Following the investigation of the deposition mechanism, antibacterial, and corrosion properties, two potential application scenarios were evaluated. Firstly, Ta-Ag coatings were applied to AZ31 magnesium (Mg) alloys to assess their protective capabilities. The bonding between Ta-Ag coatings and Mg alloys was primarily due to mechanical interlocking, with minimal contribution from metallurgical bonding between Ag agglomerations and Mg alloys. The coatings exhibited good adhesion to the Mg alloy substrates, with failures predominantly occurring within the coating itself due to unbonded boundaries, rather than at the coating-substrate interface. The Ta-5Ag coating, which experienced the most severe peening effect during cold spraying, exhibited the highest adhesive strength. The coatings provided effective corrosion protection in chloride-containing environments but showed reduced corrosion resistance with higher Ag content. However, higher Ag volumes improved wear resistance and reduced delamination, suggesting potential applications in metallic biomedical devices. In addition to Mg alloy protection, the load-bearing application of Ta-5Ag composites was investigated. The cold-sprayed Ta-5Ag composites demonstrated comparable ultimate tensile strength (UTS) to mild steel and high-strength aluminum alloys, albeit with lower elongation. Mechanical properties were affected by deposition defects, such as pores and unbonded boundaries, but could be enhanced through annealing. Atom diffusion between Ta and Ag, facilitated by severe deformation and annealing, could further improve mechanical properties. The study suggests that increasing the annealing temperature or deformation extent could optimize the material's performance. This research provides valuable insights into the cold spray deposition of Ta-Ag composites, highlighting their potential for advanced biomedical and protective applications. The revealed mechanisms offer a reference for designing novel metal matrix composites using cold spray technology.