HARD COATINGS ON LIGHT-METAL COMPONENTS UNDER MECHANICAL SURFACE LOADING

In this work the behaviour of hard coated light-metal components was i nvestigated when they are mechanically loaded. Three light-metal alloy s, Ti-6Al-4V, Al1Si7Mg and AlMgSi0.5 and 100Cr6 steel (as a reference material) were coated by two different physical vapour deposition proc esses: radio frequency magnetron sputtering and electron beam evaporat ion. The coating materials utilised were CrN and TIN. Standard test me thods with different loading conditions were used to evaluate the subs trate/coating-combinations: the hardness test (applying a static norma l load), the scratch test (applying a combination of a static normal a nd a static tangential force) and the impact test (applying a dynamic normal load). It was observed that the load support of coated material s depends on the loading conditions. The coated aluminium alloys showe d poor load support under all loading test conditions but produced a h igher surface hardness than uncoated steel. Coated Ti-6Al-4V showed ve ry good load support properties, similar to coated steel. All coated l ight-metal substrates demonstrated significant improvement in load sup port behaviour with an increase in coating thickness. The results of t he scratch test, which is commonly used to assess adhesion properties of thin coatings, showed an immediate indenter-breakthrough on the alu minium alloy substrates, but causing no coating delamination. Due to t his behaviour, the scratch test is not suitable to evaluate adhesion p roperties on coated soft light-metals. Yet the impact test allowed ass essment of coating delamination on the aluminium alloys, proving its u sefulness for adhesion measurement even on soft substrates. The study indicates that substitution of steel with coated light-metal alloys is a viable proposition for certain applications.