Nanostructuring of NiAl-Mo eutectic alloys by selective phase dissolution

A technique for the electrochemical structuring of directionally solidified NiAl–Mo eutectic by selective phase dissolution is presented. Local matrix dissolution at 200 mV SHE in 1 M HCl of pH 1 yielded the grid of Mo nanowires spanning along the central part of the sample. On the other hand, the dissolution of the fibrous minor phase while passivating the continuous NiAl matrix resulted in continuous nanopore arrays. Initially, mechanical polishing and electropolishing were employed to thin the samples. Etching time was optimized by plotting the etch time until hole formation as a function of initial sample thickness, along with plotting sample thickness versus etching time. As a next step, an investigation into the passivation behaviour of the NiAl was performed in order to determine the optimal potential for wire dissolution. A potential scan from 0 to 2500 mV SHE on a bulk sample of pure NiAl in an electrolyte of 0.1 M acetate buffer pH 6.0 indicated that a potential of 500 mV SHE, just below the breakdown potential would provide maximum driving force for wire dissolution process. Different parameters within the electrochemical system are varied in order to optimize the wire dissolution. The extent of wire dissolution is measured both quantitatively (total charge transfer) and qualitatively (optical and SEM imaging).