Evaluation of Pinhole Defects and Corrosion Resistance of TiN-coated Stainless Steels

TiN薄膜作为代表性的干式涂层非常硬，因此它们具有高度的耐磨性和耐腐蚀性，并且它们的外观具有诱人的金色。然而，由于存在微缺陷，它们通常不适合耐腐蚀应用。特别是所谓的穿孔针孔缺陷损害了TiN膜的环境屏蔽效果，并且存在与提高基底的耐腐蚀性有关的许多问题。为了使TiN薄膜中的针孔缺陷密度最小化，必须对工艺参数进行适当的控制，为此，必须发展一种快速、定量的针孔缺陷评价方法。因此，在这项研究中，临界钝化电流密度（CPCD）的方法被用来评估针孔缺陷定量的缺陷面积比的TiN涂层不锈钢制备的射频反应溅射。所得的主要结果可归纳如下 关于我们 当N_2流量与总流量之比F_2/F_2大于0.4时，沉积的~ 0.5 μ m厚的TiN薄膜<N2><total>具有特征的类金颜色。随着<220><111>F_ /F_的增加，其择优取向由向<N2>转变<total>。在此，针孔缺陷的电化学评价集中在F_<N2>/F_<total>为0.4的TiN薄膜上。TiN涂层不锈钢的临界钝化电流密度i<crit>随着膜厚的增加而显著降低，TiN涂层显著提高了不锈钢的耐蚀性。然而，在厚度大于1.5 μ m时，i有增加的趋势，<crit>并伴有开裂和/或剥落。针孔缺陷的面积比通过<crit>涂覆的和未涂覆的试样的i的比率来评估，即，通过CPCD方法。该结果与阳极极化前后光学显微照片上的真实缺陷面积比吻合较好。因此，这种电化学测量作为耐腐蚀涂层针孔缺陷的评价方法是优越的上级。少

TiN films as a representative dry coating are very hard, so they are highly resistant against wear and corrosion, and furthermore their appearance is attractive gold-like color. Due to the presence of micro-defects, however, they are usually unsuited for corrosion-resistible applications. In particular, the so-called perforating pinhole defect impairs the environment shielding effect of TiN film, and there are many problems remaining in connection with improving the corrosion resistance of the substrat. In orter to minimize pinhole defect density in a TiN film, the process parameters must be adequately controlled, for this to happen, a quick and quantitative evaluation method of pinhole defect must be developed. In this study, therefore, the critical passivation current density (CPCD) method was used to evaluate pinhole defects quantitatively as the defect area ratio for the TiN-coated stainless steels prepared by the r.f.reactive sputtering. The main results obtained can be summarized … More as follows :The -0.5mum thick TiN-films deposited at the N_2 flow-to-total flow ratio F_<N2>/F_<total> of 0.4 and above were with the characteristic gold-like color. They exhibited the columnar structure, of which the preferential orientation changed from<220>to<111>direction with an increasing F_<N2>/F_<total>. Here, the electrochemical evaluation of pinhole defects is focused on the TiN films deposited at F_<N2>/F_<total> of 0.4. The critical passivation current density i_<crit> in the TiN-Coated stainless steels decreased considerably with an increasing film thickness, and the resulting corrosion resistance was improved remarkably by TiN-coating. Above 1.5mum in thickness, however, there was an increasing tendency in i_<crit> with cracking and/or peeling. The area ratio of pinhole defects was evaluated by the ratio of i_<crit> of a coated and a non-coated specimen, i.e., by the CPCD method. The result coincided well with the true defect area ratio based on the optical micrographs before and after polarized anodically. Consequently, such electrochemical measurement is superior as an evaluation method for the pinhole defects of corrosion-resistible coating. Less