Thermal instability of Ni electrodeposits applied in replication of optical recording devices

Thermal evolution of the crystallographic texture and microstructure in Ni electrodeposits, with a specific application for replication of optical recording devices, was examined. As-deposited microstructure was comprised of bimodal grains with a size of 4 and 0.1 μ m and the 〈100〉 fibre texture with inhomogeneous strength across the deposit thickness. The 〈100〉 texture was unstable and transformed during annealing to the 〈211〉 fibre. The texture transformation was accompanied by grain growth and deposit softening and the temperature range for rapid changes of all parameters was between 623 and 673 K. A numerical analysis of texture data was conducted to identify the type of Ni grain boundaries, which control grain growth and texture transformation. The microstructural observations suggested that the growth of grains with new orientation starts in fine-grained regions and controls the thermal stability of the entire deposit. The results are discussed in terms of the mechanism of texture transformation during annealing.