Effects of cyclic stress and temperature on oxidation damage of a nickel-based superalloy

Abstract

Citation: KARABELA, A. ... et al., 2011 AbstractOxidation damage, combined with fatigue, is a concern for nickel-based superalloys utilised as disc rotors in high pressure compressor and turbine of aero-engines. A study has been carried out for a nickel-based alloy RR1000, which includes cyclic experiments at selected temperatures (700°C~800°C) and microscopy examination using Focused Ion Beam (FIB). The results suggest that the major mechanism of oxidation damage consists of the formation of surface oxide scales and internal micro-voids and oxide particles beneath the oxide scales, which become more severe with the increase of temperature. Applying a cyclic stress does not change the nature of oxidation damage but tends to enhance the extent of oxidation damage for temperatures at 750°C and 800°C. The influence of cyclic stress on oxidation damage appears to be insignificant at 700°C, indicating a combined effect of cyclic stress and temperature. Further energy dispersive x-ray (EDX) analyses show the enrichment of Cr and Ti, together with lower Ni and Co levels, in the surface oxide scales, suggesting the formation of brittle Cr 2 O 3 , TiO 2 , NiO and Co 3 O 4 oxides on the specimen surface.Penetration of oxygen into the material and associated internal oxidation, which leads to further 2 material embrittlement and associated failure, are evidenced from both secondary ion imaging and EDX analyses.

Influence of orientation-dependent grain boundary oxidation on fatigue cracking behaviour in an advanced Ni-based superalloy

“…According to studies conducted on RR1000 by Foss et al [28] and Karabela et al [20], the applied load does not influence the oxidation products, but enhances the oxidation processes.…”

“…thermodynamic unstable oxides such as CoO and NiO at the surface and thermodynamic stable oxides such as Cr 2 O 3 , TiO 2 and Al 2 O 3 at the subsurface. Such layered oxides are usually observed in stressed and unstressed disc alloys RR1000 and ME3 [12,18,20,28], so may also form in the LSHR alloy due to the similarity in alloying composition and the comparable/equivalent test conditions. At the beginning of the fatigue loading process at elevated temperature, non-selective oxidation can occur at the specimen surface, and thereby Ni and Co oxidise rapidly and form a continuous single-phase solid solution scale due to their abundance in the alloy and the same crystal structure of NiO and CoO [18,30].…”

“…Extensive studies on SAGBO have shown that the most common oxides observed in the disc alloys are oxides of Ni, Cr, Nb, Ti and Al [3,16,17,[19][20][21], as well as Co-rich oxides in those superalloys with relatively high Co content such as RR1000 [18]. These oxide complexes usually possess a layered structure which consists of a thermodynamically unstable central layer of NiO [3,16,18].…”

Oxidation of a Commercial Nickel-Based Superalloy under Static Loading

“…The difference in oxide morphologies comes as a surprise given that most of the current literature only reports expedited kinetics. [27][28][29][30][31][32] The isotopic tracer experiments indicated that shot-peening and applied stresses have very little influence on the inward oxygen diffusion, thus eliminating enhancement due to a greater contribution from inward anionic growth. This suggests that the shot-peening and mechanical loads applied to polished samples act to influence the diffusivity of the oxidized solute species (i.e., chromium and titanium) in the parent and recrystallized alloy, [33][34][35] and this is proposed to result from defects induced from creep deformation.…”

“…The premise of this argument states that the hydrostatic stress increases the oxygen diffusivity. For example, modeling conducted by Karabela et al 27,28 described accelerated internal oxidation kinetics by first computing the hydrostatic stress gradient through crystal plasticity modeling and then the oxygen diffusion. The authors successfully rationalized the amplified oxygen penetration depths through this method; however, this analysis did not account for flux of the metallic species and the oxidation processes themselves, which inherently modify the media in which the oxygen diffuses through.…”