Surface alloying of Ti-20Nb-6Ta with Cu and Ag: The critical role of laser processing in microstructure and crack formation

Postoperative infections remain a major concern in implantology, often leading to severe complications such as osteomyelitis and implant failure. To address this issue, a surface modification strategy was developed to impart antibacterial properties to a Ti-20Nb-6Ta (wt%) alloy by incorporating Cu and Ag via laser surface alloying. Cu and Ag were first deposited onto the substrate using electrodeposition and galvanic replacement, respectively, followed by surface melting using a laser under varying power levels and scanning speeds. The effects of processing parameters on the layer composition, microstructure, and defect formation were evaluated. The modified layers primarily exhibited a β-Ti structure, with fine Ti₂(Cu,Ag) intermetallic precipitates forming in samples with higher Cu and Ag contents. Crack density decreased with increasing energy density and the application of multiple laser scans. This was attributed to a reduced thermal gradient and stress. Lower Cu and Ag concentrations were also associated with lower crack densities. A nearly crack-free sample was obtained with average Cu and Ag levels of 3.4 and 0.6 wt%, respectively. In this condition, thermodynamic calculations predicted – and experimental results confirmed – the formation of the antibacterial Ti₂Cu phase upon post-heat treatment. Additionally, the presence of Cu and Ag in solid solution within the β phase suggests potential antibacterial ion release. The results highlight the complex interplay of several processing parameters in tailoring Ti-based surfaces for biomedical applications through laser surface alloying.