MECHANICAL-BEHAVIOR OF NITROGEN-IMPLANTED ALUMINUM-ALLOYS

The effect of nitrogen implantation into pure aluminium has been exten sively explored, taking into account the variation of several physical and technological properties of the implanted layer. In particular, t he formation of aluminium nitride, which occurs under specific choices of the implantation parameters, is associated with an increase in har dness. In this work, we consider two Al alloys (Al-7075 and Al-2011), frequently employed in the mechanical industry, with properties strong ly dependent on the thermomechanical treatment. Molecular nitrogen bom bardment at 150 keV (75 keV N+) was employed, up to a total dose of 3 x 10(17) N cm(-2), varying the substrate temperature from 373 to 473 K . The samples were then characterized with respect to composition, str ucture, morphology, microhardness, scratch resistance (also performing multi-pass testing) and friction coefficient. The results were interp reted within the framework of micromechanical models describing the ha rdness of thin coatings deposited onto soft substrates; the microhardn ess of the implanted layer increased by a factor of five. It appears t hat nitrogen-implanted aluminium alloy layers, in spite of their shall ow thickness, behave better than hard TiN-coated surfaces. Care must b e taken to implant bath alloys at the lowest possible temperature to a void degradation of the substrate properties.