ABSTRACT

SnCu coatings (Cu between 0–33.0 at.%) were electrodeposited over mild steel. Corrosion analysis was performed over mirror polished SnCu coatings to remove surface morphology effect. Highest corrosion resistance was observed for the SnCu coating with ∼21.2 at.% Cu and lowest corrosion resistance was observed for the SnCu coating with ∼9.9 at.% Cu. Sn-rich phase and Cu₆Sn₅ intermetallic were present in all the coatings. For lower Cu content (∼6.0 at.% Cu), a significant fraction of Cu was found to be incorporated into the Sn rich solid solution phase, thus increasing strain within the grains. As the Cu content increased, the Cu₆Sn₅ phase formed predominantly at the Sn-rich phase grain boundaries. For the Sn rich phase, a preferred crystallographic orientation along the (001) was observed in SnCu coating with lower Cu content (Cu < 10 at.%). On the other hand, at high Cu content (Cu > 20 at.%), the low surface energy (100) texture was dominant. Addition of Cu decreased the Sn-rich phase grain size. The SnCu coating with ∼21.2 at.% Cu exhibited highest fraction of low angle grain boundaries (LAGBs) and low energy $\left(031\right)\left[0\overline{1}3\right]$ twin boundaries. It was established that the presence of low surface free energy (100) atomic planes exposed to corrosive medium, a high fraction of LAGBs, and low energy $\left(031\right)\left[0\overline{1}3\right]$ twin boundaries yields high corrosion resistance for SnCu coating with 21.2 at.% Cu, while a strong (001) texture and high strain within the grains, increased the corrosion susceptibility of the SnCu coating with ∼9.9 at.% Cu.

摘要

SnCu 涂层（Cu 在 0-33.0 at.% 之间）被电沉积在低碳钢上。在镜面抛光的 SnCu 涂层上进行腐蚀分析，以消除表面形态效应。观察到含有~21.2 at.% Cu 的 SnCu 涂层的耐腐蚀性最高，观察到含有~9.9 at.% Cu 的 SnCu 涂层的耐腐蚀性能最低。富锡相和Cu ₆ Sn ₅金属间化合物存在于所有涂层中。对于较低的 Cu 含量（~6.0 at.% Cu），发现很大一部分 Cu 被结合到富锡固溶体相中，从而增加了晶粒内的应变。随着 Cu 含量的增加，Cu ₆ Sn ₅相主要在富锡相晶界处形成。对于富锡相，在具有较低 Cu 含量（Cu < 10 at.%）的 SnCu 涂层中观察到沿 (001) 的优选晶体取向。另一方面，在高 Cu 含量（Cu > 20 at.%）下，低表面能 (100) 织构占主导地位。Cu的添加降低了富Sn相的晶粒尺寸。含~21.2 at.% Cu 的 SnCu 涂层表现出最高比例的低角度晶界 (LAGB) 和低能量$\left(031\right)\left[0\overline{1}3\right]$双边界。已确定存在暴露于腐蚀性介质的低表面自由能 (100) 原子平面、高比例的 LAGB 和低能量$\left(031\right)\left[0\overline{1}3\right]$ 双晶界为含 21.2 at.% Cu 的 SnCu 涂层提供了高耐腐蚀性，而晶粒内的强（001）织构和高应变增加了含 9.9 at.% Cu 的 SnCu 涂层的腐蚀敏感性。