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 obtained by powder metallurgy (PM) was investigated at 585, 635, and 900 degrees C for exposures up to 200 hr. For the nonimplanted material, the mass gain at 900 degrees C was lower than that found at 635 degrees C, whereas for 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 temperatures. Cross-sectional examination of the implanted alloy revealed a heterogeneous attack characterized by a thin Al-rich oxide layer, occasionally disrupted by isolated zones with a thicker three-layer scale, the morphology of which was similar to that of the nonimplanted alloy. The density of these zones decreased with increasing temperarure. The beneficial effect of Cr is associated with the rapid establishment of a protective Al-rich oxide layer.