The generating of a functional film by multiply nitriding of aluminum using the In situ reduction reaction.

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An Aluminum (Al) has been interested as a material for lightning such as automotive or machine parts. However, it is not applicable in sliding parts since the hardness and wear resistance of Al are respectively inferior to steel. In previous study, an aluminum nitride (AlN) layer was formed in nitrogen atmosphere using the commercial glade pure Al (JIS-A1050) below the melting point of Al in barrel which was loosely filled with average diameter 0.1 mm alumina powder and average diameter 0.2 mm aluminum-magnesium alloy powder for activating the Al substrate surface chemically and/or physically. In this study, the mechanism of formation of AlN layer in barrel was examined and the hardness of modified layer was controlled using ion nitriding with barrel nitriding.Before the Al is nitrided, the incubation period exists. In this period, at the cross section near the surface the white region is observed by the optical micro scope and also the existence of magnesium (Mg) is observed by Electr … More on Probe Micro Analyzer (EPMA). It seems that Mg is infiltrated and diffused from the filled Al-Mg alloy powder in barrel. After this step, the AlN is partially generated at the surface of Al substrate, it grows even with substrate surface. The AlN layer thickness increases proportionally to the root of nitriding time in barrel. After the barrel nitriding, the ion nitriding was combined for some specimens. In the combined processes, the thickness of the modified layer is less than that obtained by barrel nitriding alone. By choosing the ratio of the barrel nitriding period and the ion nitriding period, the hardness of the modified layer can be controlled in respect.In order to identify the diffusion species in the nitride layer, φ0.8 mm zirconia (ZrO_2) wire was used as a marker. The wire was squeezed into the surface of Al substrate with a hand press. There are three possible wire positions after nitriding. First, (a) if the nitrogen diffuses to the nitride layer, the marker wire will stay on nitride surface, second, (b) if the Al diffuses to the nitride layer, it will wander between the nitride layer and the substrate, third, (c) both nitrogen and Al diffuse then the marker will reside in the nitride layer. By the cross sectional optical micrographs of the substrate before and after nitriding, the marker is stay on the surface of nitride layer, therefore we can see that the nitride layer grows by nitrogen diffusion into the nitride layer. Less