INFLUENCE OF YTTRIUM ON TRANSPORT-PROPERTIES OF ALPHA-ALUMINA SCALES DEVELOPED ON YTTRIUM IMPLANTED BETA-NIAL

The influence of yttrium doping on the ionic and electronic conductivi ties of or alumina developed on a beta NiAl alloy by oxidation at 1100 degrees C was investigated by electrochemical measurements, in order to point out the possible effect of this element on the transport prop erties of alumina scales. It appears that the yttrium influence is sma ll. It slightly reduces the ionic transport number at low oxygen press ure and increases it at high pO(2): the alumina scale behaves as an io nic conductor near the substrate-oxide interface and progressively bec omes a mixed conductor or an electronic conductor near the outer oxide -gas interface. The ionic-electronic transition is sharper for undoped scales.