The effect of Cr implantation on the isothermal-oxidation behavior of a Ni3Al PM alloy

The isothermal-oxidation behavior of nonimplanted and Cr-implanted Ni3Al ob tained by powder metallurgy (PM) was investigated at 585, 635, and 900 degr ees C for exposures up to 200 hr. For the nonimplanted material, the mass g ain at 900 degrees C was lower than that found at 635 degrees C, whereas fo r the implanted material the oxidation rate increased with temperature, as expected. Furthermore, Cr implantation significantly reduced the oxidation rate with respect to the nonimplanted material, particularly at the lower t emperatures. Cross-sectional examination of the implanted alloy revealed a heterogeneous attack characterized by a thin Al-rich oxide layer, occasiona lly disrupted by isolated zones with a thicker three-layer scale, the morph ology of which was similar to that of the nonimplanted alloy. The density o f these zones decreased with increasing temperarure. The beneficial effect of Cr is associated with the rapid establishment of a protective Al-rich ox ide layer.