Microstructure and mechanical properties of NiTi nanoporous structures fabricated with dealloying process

Dealloying is an emerging material processing technology to fabricate nanoporous functional surface. Systematic characterization of microstructure and mechanical properties for dealloyed surface is a basis for tailoring dealloying parameters. This paper aims to investigate the effect of dealloying treatment on the evolution of microstructures and mechanical properties of NiTi alloy. Firstly, nanoporous layer is fabricated with electrochemical dealloying method to dissolve nickel element selectively from NiTi alloy. Secondly, the microstructures of dealloyed layer are characterized and analyzed with microscopic test methods. The release characteristics of nickel ions from the sample surface before and after dealloying treatment were evaluated using SBF immersion tests. Thirdly, the mechanical properties of NiTi nanoporous structure are evaluated with nanoindentation and micro scratch tests. The results show that both elastic modulus and nanohardness of the NiTi nanoporous layer are over 80% lower than those of the matrix material. The super-elastic property of NiTi alloy is weakened. Meanwhile, the scratching force at the same scratching depth is reduced by over 30% after dealloying process. Instead of severe plastic deformation, irregular brittle fracture occurs along the scratched groove and it demonstrates the plasticity degradation of dealloyed surface. Finally, the weakening mechanism of nanoporous structures fabricated with dealloying treatment is discussed. • Microstructures of NiTi dealloyed nanoporous layer are characterized and analyzed. • Mechanical properties of NiTi dealloyed structures are systematically evaluated. • Super-elastic properties of NiTi alloy were weakened by dealloying treatment. • Superficial nanoporous structure reduces plastic deformation of NiTi alloy. • Weakening mechanism of dealloyed nanoporous structures is revealed.