Influence of processing-induced changes on the performance of Ti-based alloy in biological systems

This work explores the impact of high-pressure torsion (HPT) and laser surface modification on the microstructure, surface features, mechanical properties, corrosion resistance, and biological response of the Ti-45Nb (mass%) alloy, considering its potential for biomedical application. HPT processing resulted in significant grain refinement, producing an ultrafine-grained alloy. Microstructural characterization revealed two phases, β-Ti and Ti₄Nb, present in both the coarse- and ultrafine-grained alloy microstructures, consistent with theoretical investigations. Subsequently, laser scanning of the Ti-45Nb alloy in both microstructural states produced uniform linear surface micropatterns accompanied by changes in surface chemistry (increased oxygen content and oxide layer formation) and surface topography (increased surface roughness). Mechanical testing showed that the elastic modulus, hardness, and plasticity increased in both microstructural variants after laser surface modification, with higher values observed in the ultrafine-grained alloy. Additionally, theoretical investigations confirmed these findings and highlighted the impact of both structural and surface modifications on the alloy’s mechanical behavior. Furthermore, corrosion testing demonstrated that all alloy samples exhibited high corrosion resistance, which was attributed to the formation of a dual-layer oxide film. The ultrafine-grained alloy developed a thicker inner barrier layer, whereas the coarse-grained alloy exhibited a thicker outer porous layer. Specifically, the best corrosion resistance was observed in the coarse-grained alloy prior to laser modification and in the ultrafine-grained alloy following laser modification. Finally, biological tests confirmed excellent cytocompatibility of the alloy in both microstructural states, before and after surface modification. In vitro tests further showed that laser surface modification enhances the attachment, adhesion, and proliferation of fibroblast cells on all alloy sample surfaces, indicating excellent biocompatibility, especially pronounced in the ultrafine-grained alloy.