Fe-20Cr纳米涂层的电化学行为

ELECTROCHEMICAL BEHAVIOR OF Fe-20Cr NANOCRYSTALLINE COATINGS

利用磁控溅射技术在玻璃基体上制备了Fe-20Cr纳米晶涂层.分别测试了Fe-20Cr铸态和纳米晶涂层在含氯离子溶液(0.005 mol/L H2SO4+0.5 mol/L NaCl)与不含氯离子的溶液(0.005 mol/L H2SO4+0.25 mol/LNa2SO4)中的动电位极化曲线.结果表明,纳米化使材料的溶解速度增大,纳米晶涂层在两种溶液体系中均容易钝化;与铸态合金相比,纳米涂层的维钝电流增大两个数量级.在含氯离子溶液中,纳米晶涂层的维钝区间是铸态合金的两倍,耐局部腐蚀性能得到很大提高.利用电容测试技术和Mott-Schottky关系研究了Fe-20Cr铸态合金与纳米晶涂层分别在两种溶液中所形成钝化膜的半导体性能.结果表明铸态合金在不含氯离子的溶液中低电位下所形成的钝化膜为p型半导体,高电位下形成n型半导体,在含氯离子溶液中形成的钝化膜为p型半导体;而纳米晶涂层在两种溶液体系中形成的钝化膜均为n型半导体.钝化膜的结构类型的不同是导致Fe-20Cr纳米晶涂层与铸态合金具有不同电化学行为的主要原因.

Fe-20Cr nanocrystallized coatings （NC） were prepared by magnetron sputtering on a glass substrate. The potentiodynamic polarization of Fe- 20Cr cast alloy and NC were measured respectively in 0.05 mol/L H2SO4 ＋ 0.25 mol/L Na2SO4 and 0.05 mol/L H2SO4 ＋ 0.5 mol/L NaCl solutions. The results showed that NC has greater trend to be auto - passivated in both solutions and the passive current density increased about 2 order magnitude compared with cast alloy. In solution containing Cl^-, the passivity region of NC is 2 times than that of cast alloy. It indicated that the pitting resistance of NC was greatly improved. The semiconducting properties of the passive films formed on NC and cast alloy in both solutions were investigated by capacitance measurements. The results showed that Fe - 20Cr cast alloy has poor resistance to pitting corrosion in chloride acidic solution due to its p- type semiconducting passive film. However, the passive film on Fe-20Cr NC was a n - type semi- conductor which had a higher transpassivation potential and therefore higher resistance to pitting corrosion. The passive current density of NC was higher because of the higher donor/acceptor density in the passive film. The investigations showed that the type of passive films is responsible for the electrochemical behavior difference between NC and cast alloy.