Effects of 2-butyne-1,4-diol on structures and morphologies of electroplating Ni–W alloy

Effects of brightener 2-butyne-1,4-diol on plating process and structures of Ni–W electro-deposit were investigated by means of cyclic voltammetric measurement, SEM and atomic force microscopy (AFM). A full-bright and smooth Ni–W alloy can be electrodeposited as 2-butyne-1,4-diol is added in the plating bath, but 2-butyne-1,4-diol decreases W content gradually in the deposit and current efficiency rapidly with its concentration. 2-Butyne-1,4-diol in the solution is in favor of hydrogen evolution reaction to decrease current efficiency. Bright Ni–W deposit has much lower root mean square (RMS) surface roughness than corresponding dim one and the RMS difference reduces with W content of the deposit. However, when measured area is 0.1×0.1 μm2, RMS roughness of bright Ni–W alloy is higher than that of corresponding dim one. It may result from the more micro-defects in the bright deposit. Grain size of bright deposit is much smaller than corresponding dim one and the grain size difference decreases with increasing W content in the deposit. When W content is more than 42 wt.% (near to the eutectic point in Ni–W equilibrium diagraph), one could not observe grain with AFM.