Correlation of alloy microstructure with oxidation behavior in chromia-forming intermetallic-reinforced Cr alloys

The oxidation behavior of the Cr(X) solid solution and intermetallic Cr2X L aves phases (X = Nh, Ta) was studied individually and in combination at 1,1 00 degrees C in humid air. The two-phase Cr(Ta) + Cr2Ta alloys exhibited su perior oxidation resistance to either the single-phase Cr(Ta) or the single -phase Cr2Ta alloys. However, the two-phase Cr(Nb) + Cr2Nb alloys exhibited lower oxidation resistance than either the single-phase Cr(Nb) or Cr2Nb al loys. The two-phase Cr(Ta)+ Cr2Ta alloys were also found to exhibit superio r oxidation resistance to the two-phase Cr(Nb) + Cr2Nb alloys. This was hyp othesized to be related to the lower amount of the Cr2X phase in the Cr(Ta) -Cr2Ta eutectic and to the lower solubility of Ta in the Cr(X) phase, relat ive to the Cr-Nb system. Both of these factors resulted in significantly le ss oxidation and nitridation in the Cr(Ta) + Cr2Ta alloys.