The nano-scratch tester (NST) as a new tool for assessing the strength of ultrathin hard coatings and the mar resistance of polymer films

At present, functional coatings are used in increasingly demanding applications that require good adhesion and specific resistance to damage. This has prompted a rising interest in improving the mechanical properties of polymer coatings, especially their scratch and mar resistance, as well as ultra-thin hard coatings as used for protective overcoats in the magnetic storage industry. The nano-scratch tester (NST) is a new instrument overcoming the limitations of both the classical stylus scratch test (normal force range) and the atomic force microscope technique (short sliding distances), allowing scratch lengths of up to 10 mm. Tangential force and penetration depth are simultaneously measured during the scratching process, both in a multipass contact fatigue mode. For high resolution inspection of the deformed or damaged area, a scanning force microscope (SFM) is integrated into the system. Experimental results are presented for two very different types of material; polymeric clear-coat samples which give a range of mar resistance and DLC ultra-thin films used as protective overcoats for hard disks. The results indicate very good reproducibility and confirm the application of this new instrument for the accurate characterization of elasticity, hardness, adhesion and mechanical integrity in coated systems where the film thickness is less than 1 mu m.