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

TiN薄膜作为干法涂层的代表，硬度高，耐磨性强，耐腐蚀性强，外观呈金黄色，具有很好的耐磨性。然而，由于微缺陷的存在，它们通常不适合用于耐腐蚀应用。特别是，所谓的穿孔针孔缺陷损害了TiN薄膜的环境屏蔽作用，在提高衬底耐蚀性方面还存在许多问题。为了使TiN薄膜中的针孔缺陷密度最小，必须充分控制工艺参数，为此，必须发展一种快速、定量的针孔缺陷评估方法。因此，本研究采用临界钝化电流密度(CPCD)方法对射频反应溅射TiN涂层不锈钢的针孔缺陷进行了定量评价。所获得的主要结果可以概括为…当N_2流量与总流量之比F_2为0.4以上时，沉积的-0.5微米厚的TiN薄膜具有金黄色特征。它们呈柱状结构，择优取向由&lt；220&gt；向&lt；111&gt；方向转变，F_&lt；n2&gt；/F_&lt；总&gt；增加。在这里，针孔缺陷的电化学评价主要集中在F_&lt；N_2&gt；/F_&lt；Total&gt；为0.4的TiN薄膜上。TiN涂层不锈钢的临界钝化电流密度随涂层厚度的增加而显著降低，涂层的耐蚀性显著提高。当厚度大于1.5um时，裂纹和/或剥落有增加的趋势。针孔缺陷的面积比是通过涂层和非涂层试件的I_lt；Crit&Gt；比率来评估的，即通过CPCD方法。这一结果与阳极极化前后光学显微镜下的真实缺陷面积比吻合得很好。因此，这种电化学测试方法作为评价耐腐蚀涂层针孔缺陷的一种方法是一种优越的方法。较少

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