Oxidation properties for 2nd-5th generation Ni-base single-crystal superalloys at 1023, 1173 and 1373 K

The oxidation properties of the 2(nd)-5(th) generation Ni-base superalloys were investigated. Isothermal oxidation examination was performed at 1023, 1173 and 1373 K in air for up to 3.6 x 10(6) s and the oxides were identified by using XRD analysis and SEM cross section observation. The 3(rd), 4(th) generation superalloys and 5(th) generation superalloy TMS-173 formed thick NiO layers at the surface caused by the outward diffusion of Ni at 1023 K. These alloys showed poor oxidation resistance at 1173 and 1373 K due to the spinel formation, except for the oxidation resistances of the 3rd generation superalloys at 1373 K which were slightly improved by forming Al2O3 layers under the spinel layers. The 2(nd) generation superalloy and 5(th) generation superalloy TMS-196 show excellent oxidation resistance at all temperatures examined in this study, forming Al2O3 protective layers. These favorable results were caused by their high Cr content.