Relationship between film composition and microhardness of electrodeposited Ni-W-B films prepared using a citrate-glycinate bath

In the present study, the authors fabricated the electrodeposited Ni-W-B films with various W and B contents and evaluated their composition, surface morphology, crystal structure and microhardness. The Ni-W-B films were deposited using a Ni-W plating bath containing dimethylamine borane as the boron source and citrate and glycine as complexing agents. It was possible to prepare Ni-W-B films with a wide range of W (0-19 at.%) and B (0-18 at.%) content by controlling the plating condition (tungstate concentration, glycine concentration and current density). The hardness of the Ni-W-B films with a nanocrystalline phase was proportional to the square root of the grain size, in accordance with the Hall-Petch relation. However, in the region of amorphous or nanocrystalline phase of 2-3 nm or less in grain size, hardness decreased. The maximum hardness of the Ni-W-B films was about 850 Hv, comparable to that of hard chromium plated films. It is very important to optimize the film composition in order to fabricate Ni-W-B films with high hardness.