Fabrication of TiO2-coated nanostructured Ni foams for improved mechanical properties

Abstract

We demonstrate a composite approach to improve the mechanical strength of nanostructured Ni foams by producing a conformal coating of TiO2 on the skeletons of the Ni foam. The nanostructured Ni foam is fabricated by a template approach in which colloidal crystals of polystyrene microspheres in 720 nm diameter are constructed by a vertical electrophoresis process, followed by electroplating of Ni to fill the interstitial voids among the closely-packed microspheres and removal of the colloidal template afterward. The formation of TiO2 overcoat is achieved by optimization of sol-gel synthesis to prepare desirable TiO2 sols and their subsequent electrophoresis toward the nanostructured Ni foam in a square wave pulsing mode. The thickness of the TiO2 deposit is proportional to the duration of pulsing electrophoresis. From nano-indentation, the TiO2-coated nanostructured Ni foams exhibit notable improvements in hardness (53–68%) and reduced elastic modulus (26–37%) over those of pristine nanostructured Ni foams. This strategy of implementing a thin ceramic overcoat provides an effective mean to improve the mechanical properties of nanostructured metals.