| Тойм: | Components used in magnetic storage systems (hard discs, tape heads and drums) are often very small and lightweight, and operate under very low loads (of the order of a few microgrames to a few milligrams). As a result, friction and wear processes occur on a nanometre scale and conventional tribological test methods and assessment tools are usually not appropriate. Furthermore, the assessment of the mechanical properties of the coatings or surface treatments used to protect these components from wear is complicated by the low thickness of the layers generally used. This paper details the problems associated with the assessment of the mechanical properties of thin diamond-like carbon coatings used to protect hard discs, tape heads and air bearings. Whereas thick coatings (> 1 μm) are relatively easy to assess, even if the substrate has a low hardness and offers little support to the coating, there are many more problems when it comes to measuring the properties of the 5-10 nm layer on a hard disc. In many cases there is no plastic deformation of the coating which merely flexes and bends into the hole produced by plastic deformation of the substrate. Deformation of the coating is then limited to localised plasticity at the indenter edges, and/or fracture along the same edges and at the edge of the contact. The limits for use of Nanoindentation to assess the plasticity of the coating are discussed for such cases.
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