Cyclic oxidation evaluation - Approaching application conditions.
Review of 1000 to 1200 C cyclic oxidation testing conducted on potential aircraft gas turbine Ni-, Co-, and Fe-base alloys. Furnace and burner rig testing are discussed, and the results are compared for selected alloys. The alloys fall into two groups, depending on their Cr and Al contents. One group forms mainly Cr2O3/chromite spinel scale(s), while the other forms alpha Al2O3/aluminate spinel scale(s). Spalling on thermal cycling leading to increased metal consumption is associated with the appearance of a chromite spinel. In the case of high-velocity burner rig tests this chromite forming tendency is reinforced by Cr2O3 vaporization depleting Cr in the alloy. In both types of tests, specific weight change is used as an indirect indicator of metal attack, since direct metal loss measurements require destructive analysis. An alternative nondestructive metal loss estimating parameter, based on a tentative mass balance gravimetric approach, shows some potential.