High strength Ni matrix TiO2 composites by supercritical CO2 assisted Co-electrodeposition with different sizes of TiO2 particle

High strength Ni matrix TiO₂ composites are prepared by co-electrodeposition with an electrolyte composed of Ni Watts bath, surfactants, CO₂ in the supercritical fluid state and various sizes of TiO₂ particles. The surfactants and supercritical CO₂ (SC-CO₂) are used to emulsify the aqueous Ni Watts bath to promote the incorporation of TiO₂ particles into the Ni matrix. TiO₂ particles with three different average sizes are used in the co-electrodeposition to evaluate the effect on properties of the Ni-TiO₂ composites. The grain sizes of the Ni matrix in the composites are compared from the X-ray diffraction results and the Scherrer eq. A refined average grain size in the Ni matrix is observed when using TiO₂ particles with a larger size. The TiO₂ is evaluated by energy-dispersive X-ray spectroscopy (EDX), and the TiO₂ distribution is quantified by the coefficient of variation (cov) of the local density of Ti from the EDX result. The TiO₂ content attained 4.5 wt% with the lowest cov value (which suggests the most uniform distribution) in the composite when the smallest (21 nm) TiO₂ particles are used. The TiO₂ content achieves 22.3 wt% with the highest cov value (which suggests the least uniform distribution) when the largest (5 μm) TiO₂ particles are used. Microhardness of the Ni-TiO₂ composites is found to be highly depended on the cov value. Hence, the Ni-TiO₂ composite prepared with the smallest TiO₂ particles shows the highest microhardness at 1274 HV.