ABSTRACT

The corrosion rates of Ni-W, Co-W, Ni-Mo, and Co-Mo electrodeposited coatings after two-hour immersion tests in HNO₃, H₂SO₄ and HCl environments were studied by the weight loss method. The best corrosion resistance was revealed for Ni-W alloy, and the worst for Co-Mo. For all tested samples (36 in total), the maximal corrosion rate was observed in nitric acid, and the minimal one, with an exception of Ni-W, in hydrochloric acid. It was found that for the W-containing coatings corrosion evenly affected each individual crystallite of the alloy structure changing its shape and volume, and the corrosion of Mo alloy-based coatings showed mixed character. According to the Pourbaix diagram, for Mo alloys (Ni-Mo and Co-Mo) the lower corrosion resistance compared to the coatings containing W can be explained by a narrower region of MoO₃ formation, as well as by their higher solubility in comparison with WO₃.

摘要

在HNO ₃，H ₂ SO _4中浸泡2小时后，Ni-W，Co-W，Ni-Mo和Co-Mo电沉积涂层的腐蚀速率用失重法研究了HCl和HCl的环境。Ni-W合金显示出最佳的耐腐蚀性，而Co-Mo显示出最差的耐腐蚀性。对于所有测试样品（总共36个），在硝酸中观察到最大腐蚀速率，而在Ni-W中，在盐酸中观察到最小的腐蚀速率。结果发现，对于含W的涂层，腐蚀均匀地影响合金结构的每个微晶，从而改变其形状和体积，而Mo合金基涂层的腐蚀表现出混合特性。根据Pourbaix图，对于Mo合金（Ni-Mo和Co-Mo），与含W的涂层相比，较低的耐蚀性可以通过形成MoO _3的区域更窄以及与Al相比具有更高的溶解度来解释。WO ₃。