The high throughput electrochemical screening of the corrosion resistance of Ni–Cr thin film alloys

Abstract

The corrosion behaviour of a series of NiCr thin film alloys were characterised through the high-throughput electrochemical measurement of their polarisation resistance on a micro-fabricated array of electrodes. The linear polarisation resistance (LPR) method has been compared to the results from Tafel extrapolation, and the alloy compositional dependence of the polarisation resistance as a function of composition is consistent. There are, however, some systematic differences in the absolute values extracted using the two methodologies which are likely to be a result of the smaller current densities associated with the LPR method. In the case of the NiCr alloys deposited at 300K, the observed bulk phases closely agree with those expected from the literature. The polarisation resistance behaviour is shown to be directly related to the bulk alloy structures. Besides the b.c.c. α-Cr(Im3m) phase and its Ni solid solutions which exhibit the highest polarisation resistances, the σ-Cr3Ni2(P42/mnm) phase exhibits the next best polarisation resistance, and its co-existence with the σ-Cr7Ni3 (P42/mnm) phase at higher Cr content results in a lowering of that resistance.