Relationship between the crystallographic structure of electrodeposited Ni-W alloy film and its thermal equilibrium diagram

Electrodeposited Ni-W alloy films were obtained from Nickel Sulfate baths containing Na2WO4. The crystallographic structure and morphology of electrodeposited Ni-W films were studied by XRD, HRTEM, SEM and heat-treatment technique. The crystallographic structures of electrodeposited Ni-W alloy films were also compared with the Ni-W thermal equilibrium diagram. The X-ray diffraction patterns of Ni-W electrodeposited films with various W contents gradually changed from sharp peaks to broad peaks with increasing W contents in electrodeposited films. HRTEM observation revealed that the crystallographic structure of electrodeposited Ni-W film with 19.7 at% W content was crystalline and its crystal size was about 10 nm. Moreover, the crystalline structure was observed and the crystal size was about 5 nm in the electrodeposited Ni-W alloy film with 24.4 at%W content. However, when the film with 24.4 at%W content was heat treated, the crystalline phase did not grow and an unknown phase (Ni4W?) existed alone under 600 degreesC heat-treatment. From this result, it was clear that the crystallographic structure of Ni-W film with 24.4 at%W content was amorphous. Therefore, it can be concluded that the micro crystalline phase existed up to 22 at%W in electrodeposited Ni-W alloy film and the amorphous phase existed from 22 at% to 35 at%W.