The surface morphologies and microstructures as well as phase compositions of scale on the
alloy Ni20Cr and the alloy implanted
by Y+ (with the dose of 1×1O15,2×1016 and 1×1017 Y/ cm2 respectively) oxidized in air at 1000℃ have been investigated by means of SEM / EDS, XRD and TEM / EDS. It was found that all the scale of
alloy Ni20Cr with and without yttrium implantation were composed of larger grained NiO, NiCr2O4 and finer grained Cr2O3, and among of which small pores were created at the triangular junctions of grain boundaries of NiO. The implanted yttrium ions over 2×1016/cm2 increased the volume fraction of Cr-containing oxide, in which yttrium, most of which formed small Y-containing oxide particles, was detected. According to the experimental results, it was believed that in the initial oxidation stage yttrium oxidized in preference to alloy elements and formed fine oxide particles (10-20nm), and sequentially the particles may not only promote the nucleation and growth for Cr2O3 also produce Y ions segregated to its grain boundaries due to the partial dissolution of the particles itselves, the latter was beneficial to decrease the scale growth rate as well as improve its mechanical properties for the reason that segragated Y ions may inhibit the Cr3+ out-diffusion along "short-circuit' and enhance the cohesion between oxide grains.