Preparation, characterization and the study of the thermal strain in Ni–W gradient deposits with nanostructure

In this paper the Ni–W gradient deposit with nanostructure is prepared by controlling the bath temperature. The plating bath contained sodium tungsten, nickel sulfate and citrate, and the preparation was operated at various current densities. During the course of electrodepositing, the bath was heated gradually from 298 to 333 K, and the corresponding current density (DK) changed from 5 to 12 A/dm2. X-ray diffraction and energy dispersive X-ray Analysis indicate that crystallite size of the deposit decreases from 10.89 to 1.54 nm and lattice strain increases with the increase of W content in the direction of deposition. The structure of the deposit changes from crystalline to amorphous stepwise with associated increase in lattice strain. These show that the deposit is gradient with nanostructure. Furthermore, the strain distribution in the Ni–W gradient deposit studied by the digital-image correlation method can eliminate the mismatch of expansion coefficients at the interface, thus relaxing the thermal stresses of the materials.