Effect of copper concentrations on microstructure, residual stress and corrosion behavior of Ni100−x-Cux alloy films processed by magnetron co-sputtering

Nickel based alloys have gained importance due to their very good mechanical properties as well as their electrochemical behavior in different environmental conditions. In this regard, thin films of nanocrystalline Ni-Cu alloys have been processed by RF / DC magnetron co-sputtering in Ar gas environment for different copper concentration (10 %, 21 %, 28 % and 39 %). Grain size determination, phase identification and residual stress measurement have been done using an X-ray diffraction technique. A compressive residual stress has been observed and the value of the compressive stress increases with an increase in the Cu concentration in the Ni100−x-Cux alloy films. The electrochemical behavior of thin films of the Ni100−x-Cux alloy has been investigated with the help of potentiodynamic polarization experiments which revealed susceptibility towards pitting corrosion. The rate of corrosion decreases from 0.92 ×10−2 to 0.26 ×10−2 mm / year with the increase in Cu concentration from 10 % to 39 %. The microstructure of thin films of the Ni100−x-Cux alloy has been investigated using a field emission scanning electron microscope (FESEM). The FESEM micrograph shows the formation of pits, and the size of pits decreases with increasing concentration of doped Cu. Experimental results also reveal that the increase in corrosion resistance can correlate with the developing residual stress in the films.