Structure and Mechanical Properties of Electrodeposited Nanocrystalline Ni-Fe Alloys

Nickel-iron alloy coatings were produced by electrodeposition from an additive free electrolyte, at room temperature and current density in the range of 1 to 5 A dm–2, with Fe content up to 75 wt.%. The structure and mechanical properties of the electrodeposited alloys are reported in the present work and analysed focusing on structure-property relationships. In particular, the influence of the hydrogen evolution reaction is highlighted as a process factor affecting alloy phase structure, notably the composition limit of the γ-phase field. The variations of the mechanical properties with alloy composition are analysed in the light of the concurrent modifications in phase structure and crystal size of the alloys. In particular, an assessment of the different factors influencing the hardness of γ phase alloys is proposed. Solid solution effects contribute significantly to the strength of γ phase alloys over a wide composition range, approximately from 5 to 25%, though a complex interplay between solid solution and Hall-Petch strengthening needs to be envisaged to account for the variations in hardness with composition over this range. Moreover, it is emphasized that with decreasing grain size, the increasing level of internal stresses and decreasing stiffness engender significant softening in nanocrystalline γ phase alloys with Fe content exceeding about 25%.