The Effect of Cr Implantation on the Isothermal-Oxidation Behavior of a Ni3Al PM Alloy

The isothermal-oxidation behavior ofnonimplanted and Cr-implanted Ni3Al obtainedby powder metallurgy (PM) was investigated at 585, 635,and 900°C for exposures up to 200 hr. For thenonimplanted material, the mass gain at 900°C was lower than thatfound at 635°C, whereas for the implanted materialthe oxidation rate increased with temperature, asexpected. Furthermore, Cr implantation significantlyreduced the oxidation rate with respect to thenonimplanted material, particularly at the lowertemperatures. Cross-sectional examination of theimplanted alloy revealed a heterogeneous attackcharacterized by a thin Al-rich oxide layer, occasionallydisrupted by isolated zones with a thicker three-layerscale, the morphology of which was similar to that ofthe nonimplanted alloy. The density of these zonesdecreased with increasing temperature. The beneficialeffect of Cr is associated with the rapid establishmentof a protective Al-rich oxide layer.