Overview of accelerated corrosion tests on thin film magnetic media

In this study, the characteristics of two relatively fast pore decoration techniques used for studying corrosion susceptibility of thin film disks with the structure CoCrTa/Cr/NiP-plated AlMg substrate are discussed. The first technique employs HCl vapor. Since the HCl vapor reacts with both the cobalt alloy and the NiP layers, it has the capability of revealing pores in the sputtered layers with different sizes and depths that have openings at the disk surface. The other technique uses concentrated nitric acid solution. Because concentrated nitric acid reacts only extensively with the NiP layer, it is used to reveal the deeper pores in the sputtered layers with depth reaching the NiP layer. These two accelerated tests are used to study the coverage effect of sputter film in terms of pinhole density. The pinhole densities are found to decrease with better film coverage by reducing substrate roughness and increasing Cr thickness and substrate bias. Texture line affects grain nucleation and growth of Cr layer and in turn influences the corrosion resistance. Ion bombardment on the growing film associated with substrate bias densifies the film structure and reduces corrosion susceptibility. The porosity results obtained are compared with conventional environmental chamber test. Good correlation among these tests has been established.