Abstract
Vickers hardness of Ni-Cu alloy films which have composition gradient along thickness direction was investigated. The composition-gradient Ni-Cu films were fabricated on copper substrate by the special electrodeposition technique where electrode potential changed continuously. The films were composed of alternate stack of layers having positive and negative gradients. Total thickness of all the films was 1.2μm. The gradient films differed in both composition gradient dc_<Ni>/dx and amplitude of Ni concentration Δc_<Ni>. The dc_<Ni>/dx and Δc_<Ni> values varied from 5×10^<-6> to 2×10^<-2>nm^<-1> and 0.006 to 0.6, respectively. The composition-gradient Ni-Cu films having high gradient or high Ni concentration amplitude showed higher Vickers hardness than the Ni-Cu multilayered film with defined Ni/Cu interfaces: the maximum hardness of the composition-gradient Ni-Cu films was amounted up to Hv250 while that of the multilayered film was Hv140. The hardness of the composition-gradient Ni-Cu films revealed good correlation with the gradient dc_<Ni>/dx, compared with the Ni concentration amplitude Δc_<Ni>. From this result, the high strength of the composition-gradient Ni-Cu films could be explained not by internal stress induced by lattice mismatch, but by high-density misfit dislocations caused by the composition gradient.
