Effects of annealing temperatures on the physicochemical properties of nickel–phosphorus deposits

The dependence of physicochemical properties, including microhardness, magnetism, morphology, crystalline information, roughness factor and hydrogen evolution ability, on the phosphorus content, varying from 0 to 28 atomic percentage (at.%), of Ni–P deposits with annealing in air at eight temperatures (i.e., 100, 200, 300, 400, 500, 600, 700 and 800 °C) were systematically compared. The microhardness reached a maximum at 400 °C due to the crystallization of Ni and Ni3P at 400 °C and the significant diffusion of Cu into the Ni–P deposit at temperatures ≥500 °C, confirmed by the depth profiles of Ni, P, Cu and O elements. The paramagnetism of Ni–P deposit was gradually transformed into ferromagnetism at 400 °C, attributable to the phase separation of Ni and Ni3P. The roughness factor, Ra, of the deposits with P contents ≤12 at.% were increased with increasing the annealing temperature at temperatures <400 °C but Ra of the deposits with 17–28 at.% of P is approximately independent of the annealing temperature. The rate of hydrogen evolution decreased with increasing the annealing temperature because the specific activity (i/Ra) of the Ni–P deposits was decreased with increasing the annealing temperature.