Corrosion behaviors of nanocrystalline Ni-W alloys

Abstract

Owing to the substantially enhanced hardness of the nanocrystalline (nc) grain size, nc Ni-W alloys show great promise as coating materials. However, the limited knowledge on corrosion of these materials has hindered their utilization in a range of industries. Thus, this research employs a systematic investigation, which is designed to address various factors influencing corrosion, namely, grain size, W content, crystallographic texture, surface composition, grain boundary relaxation, grain growth and pH, in 3.5 wt.% NaCl solution at room temperature. This research is divided into three parts. In part I, electrodeposited nc Ni-W alloys with a range of grain size were investigated. It was found that W content and crystallographic texture are the factors governing corrosion in alkaline condition, while W content is the factor governing corrosion in acidic condition. In Part II, the annealed nc Ni-W specimens were investigated to single out the effects of grain boundary relaxation and grain growth on corrosion. Both effects were found to have insignificant effect on corrosion rate. In part III, electrochemical impedance spectroscopy was utilized to examine the electrochemical corrosion phenomena at the sample/electrolyte interface. Corrosion of nc Ni-W alloys was controlled by capacitance (C[subscript dl]) and charge transfer resistance (R[subscript ct]), which indicates corrosion resistance of nc Ni-W alloys. The results in Part III show the similar trends in corrosion resistance to those shown in Parts I and II.