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.