Preparation of highly corrosion-resistant compositionally graded coatings using multi-ion vapor deposition system

利用多离子气相沉积系统，采用动态离子束混合(DM)方法制备了具有低针孔缺陷密度的薄膜。在304不锈钢(304SS)衬底上溅射沉积了CrTa二元合金和成分梯度(CrTa型304不锈钢)合金薄膜。得出以下结论：(1)针孔缺陷密度(R)在很大程度上取决于衬底的表面光洁度。(2)铬-钽涂层304SS的R值随薄膜厚度的增加而减小。厚度为5μm的薄膜的R值最低，为5×10~(-5)~(-5)%，比TiN涂层304SS的R值低一个数量级。(3)弗里曼型离子源加速电压增加到30kV时，R值降低。因此，DM是一种非常有效的提高薄膜涂层耐蚀性的方法。(4)透射电子显微镜观察发现，DM制备的铬-钽合金薄膜是由体心立方微晶Ta在非晶态基质中混合而成，而X射线衍射仪认为它们是无定形的单相。此外，在薄膜和与薄膜接触的衬底表面观察到气泡状颗粒。(5)成分梯度(CrTa-304SS)薄膜涂层的R值高于CrTa-Ta二元合金涂层。这可能是由于在沉积过程中生长了304SS层而导致表面粗糙度显著增加的原因。

An attempt was made to tailor thin film coatings with a low pinhole defect density by dynamic ion beam mixing (DM) method using multi-ion vapor deposition system. The Cr-Ta binary alloy and the compositionally graded (CrTa-type 304 stainless steel) alloy thin films were sputter-deposited on a type 304 stainless steel (304SS) substrate. The following conclusions were drawn ;(1) The pinhole defect density (R) depends largely on the surface finishing of the substrate.(2) R value for the Cr-Ta coated 304SS decreases with an increase in the film thickness. The lowest R value was obtained for the film of 5 μm in thickness, and is 5x10^<-5>%, Which is about one order of magnitude lower than that for TiN coated 304SS.(3) An increase in acceleration voltage of Freeman Type argon ion source up to 30 kV leads to decrease in R value. Accordingly, DM is quite effective method in enhancing the corrosion resistance of thin film coatings.(4) TEM observation revealed that the Cr-Ta alloy thin films prepared by DM consist of a mixture of bcc microcrystalline Ta in the amorphous matrix, although they are considered to be amorphous single phase by XRD. Furthermore, bubble-shaped particles were observed in the films and in substrate surface in contact with the film. The diameter of the particle is in the range of 2-10 nm.(5) The compositionally graded (CrTa-304SS) thin film coatings shows higher R value compared with the Cr-Ta binary alloy coatings. This may be responsible for significant increase in surface roughness by crystal growth of 304SS layer during deposition.