ABSTRACT

Ni–Co alloy coatings exhibit excellent tribological properties. However, these coatings are vulnerable to corrosion due to the lower corrosion potential of Co when compared to Ni. The decrease in the corrosion resistance of Ni–Co alloy with increasing Co content is not monotonous. At an optimum Co content, very high corrosion resistance behaviour is observed. This anomaly is investigated here. Ni–Co coatings (Ni, Ni–9 wt% Co and Ni–20 wt% Co) were electrodeposited over mild steel. Potentiodynamic polarisation illustrated Ni coatings highest corrosion resistance, whereas, between the Ni–Co coatings, Ni–20 wt% Co coating exhibited higher corrosion resistance in 3.5 wt% NaCl medium. Higher corrosion resistance in Ni–20 wt% Co coating was primarily due to uniform distribution of low energy grain boundaries like Σ3 coincidence site lattices (CSLs) in the coating. Higher corrosion rate for Ni–9 wt% Co coatings was due to strained grains and non-uniform distribution of low energy grain boundaries.

摘要

Ni-Co 合金涂层表现出优异的摩擦学性能。然而，由于与 Ni 相比，Co 的腐蚀电位较低，因此这些涂层容易受到腐蚀。Ni-Co 合金的耐蚀性随着 Co 含量的增加而降低并不是单调的。在最佳 Co 含量下，观察到非常高的耐腐蚀性能。此处调查此异常。Ni-Co 涂层（Ni、Ni-9 wt% Co 和 Ni-20 wt% Co）在低碳钢上电沉积。动电位极化表明 Ni 涂层具有最高的耐腐蚀性，而在 Ni-Co 涂层之间，Ni-20 wt% Co 涂层在 3.5 wt% NaCl 介质中表现出更高的耐腐蚀性。Ni–20 wt% Co 涂层具有更高的耐腐蚀性，这主要是由于涂层中低能量晶界（如 Σ3 重合位点晶格 (CSL)）的均匀分布。Ni–9 wt% Co 涂层的较高腐蚀速率是由于应变晶粒和低能晶界分布不均匀所致。