Structure of the Al-Ni intermetallic layers produced on nickel alloy by duplex treatment

摘要

Hard and wear and corrosion resistant Al-Ni type intermetallic layers, with an external Al_2O_3 zone, were successfully produced on Inconel 600 using a duplex method. The duplex method combines glow discharge assisted oxidizing with pre-coating the Inconel substrate with aluminum by magnetron sputtering. The oxidizing process carried out at 560 deg C for 4 h leads to a diffusion-induced transformation of the aluminum coating and adjacent Inconel into a 15 mu m thick composite layer of Al_2O_3 +AlNi + AlCr_2 +AlNi_3 + Cr(Fe_2Ni) + Ni(Cr,Fe Al) The structure of the layer was examined in cross-section by transmission electron microscopy (TEM). The surface zone of the layer is constituted by nanocrystalline Al_2O_3 covering the main zone of the AlNi layer. In this zone, near its border with the oxide zone, are small agglomerates of nanocrystalline Al_2O_3. The upper and thicker part of the AlNi zone also contains precipitates of the AlCr_2 phase. The AlNi zone is separated from Inconel by a diffusion zone of Ni(Cr,Fe,Al). In this region grains of AlNi_3 are found with groups of Cr(FeNi) phase grains. As a consequence, the region is locally strongly enriched with chromium. This suggests that the formation of AlNi induces an uphill diffusion of chromium into the Inconel substrate.