Grain growth and thermal stability of nanocrystalline Ni–TiO₂ composites

The grain growth and thermal stability of nanocrystalline Ni–TiO₂ composites were systematically investigated. The nanocrystalline Ni–TiO₂ composites with different contents of TiO₂ were prepared via electroplating method with the variation of TiO₂ nano-particles concentration. The effect of TiO₂ content on the grain size, phase structure and microhardness was investigated in detail. The corresponding grain growth and diffusion mechanisms during the heating process were also discussed. The optimal microhardness of HV₅₀ 270 was achieved for the composite with addition of 20 g/L TiO₂ nano-particles after annealing at 400 °C for 90 min. The calculation of the activation energy indicated that lattice diffusion dominated at high temperatures for the nanocrystalline Ni–TiO₂ composites. It was indicated that the increase of TiO₂ nano-particles content took effect on restricting the grain growth at high temperatures by increasing the grain growth activation energy.