A comparative study of surface characterization and corrosion performance properties of laser surface modified biomedical grade nitinol

摘要

Laser melting and quick solidification of shape memory alloy surfaces promise to explore the multifunctional capabilities required for enhanced biocompatibility of different implantable medical devices. Before subsequent bio-trial, understanding of the effect of cooling rate vis-a-vis laser fluence on surface characteristics and corrosion protection performance is essential before designing a tailor-made biocompatible surface for various implantable devices. The current study systematically investigates the effect of laser fluence on physical, mechanical and chemical surface characteristics along with corrosion protection performance of the modified surface as compared to bare Nitinol surface. Various phases were prominent on the top surface, namely nickel and titanium-rich phase along with different nickel-titanium intermetallics and nano-structure of titanium oxide, based on varying melting pool recirculation time and cooling rate with laser fluence energy. At low laser fluence up to 4 J/mm(2), no significant melting pool were formed and only transformation to the martensitic phase of Nitinol took place on the top surface, which seemed to be highly too much corrosion-prone under simulated body fluid. M moderate laser fluence of 6-8 J/mm(2), mostly titanium-rich phases are prominent on the surfaces on account of optimum recirculation of melting pool and subsequent surfacing out of comparably light phase of titanium. Titanium-rich phases on top surface exhibit superior corrosion resistance as compared to all other samples including bare nitinol. However, titanium oxide nano-particles-reinforced martensitic structure is formed under high laser fluence due to over recirculation of molten pool. The modulus of elasticity also varied from 10 to 110 GPa based on top surface formation under different fluence levels, and thus this process can act as a tailor-made controllable pre-treatment process over the traditional coating processes.