On the Oxidation Resistance of Nickel-Based Superalloys

Abstract

Abstract. In this paper, the factors influencing the oxidation resistance of superalloys are studied. A model is proposed by which the Al 2 O 3 -forming properties of a given composition can be estimated, based upon the thermodynamic and kinetic factors influencing scale growth. The numerical modelling is tested by experimental work on a number of compositional variants of the newly-developed SCA425+ superalloy, which contains appreciable quantities of Cr. The modelling is shown to be in broad agreement with experiment. The effects of Al, Cr and Si on the oxidation resistance of this class of alloy have been rationalised.

On Localized Deformation and Recrystallization as Damage Mechanisms during Thermomechanical Fatigue of Single Crystal Nickel-Based Superalloys

“…Some of the alloys have also been investigated in different heat treatment conditions, as indicated in Table 1. For further details regarding the alloys see references [2][3][4][5][6]. [4] SCA425+ HT A -Primary γ' size: 0.65µm [5], [6] HT B -Primary γ' size: 0.35µm [5], [6] HT C -Bi-modal [5], [6] Out of phase (OP) thermomechanical fatigue tests were conducted under mechanical strain control in the 100-950ºC or 100-1000ºC temperature range with a strain ratio of R = ε min /ε max = -∞.…”

“…For further details regarding the alloys see references [2][3][4][5][6]. [5], [6] HT B -Primary γ' size: 0.35µm [5], [6] HT C -Bi-modal [5], [6] Out of phase (OP) thermomechanical fatigue tests were conducted under mechanical strain control in the 100-950ºC or 100-1000ºC temperature range with a strain ratio of R = ε min /ε max = -∞. An MTS 810 servo-hydraulic thermomechanical fatigue machine with the MTS model 793 software was used for this purpose.…”

“…Effect of γ γ γ γ' size and morphology. Siemens Industrial Turbomachinery have recently initiated a project to find an alloy suitable for industrial gas turbines which exhibits combined high oxidation resistance and high corrosion resistance, see reference [5,6]. As part of this project a modified version of SCA425Hf has been studied which has a higher Al-content; this is currently referred to as SCA425+.…”

The effect of systematic variation of Ni:Co ratio on the oxidation behaviour of γ-γ′ Ni-Co-Al-Ti-Cr alloys

“…Alumina formed as discrete internal oxides below the Cr2O3 scale, although Astroloy, following isothermal oxidation at 1000°C, developed a semi-continuous internal Al2O3 layer, reportedly due to its relatively high Al content. An alumina layer is also known to form during high-temperature oxidation of single-crystal Ni-based superalloys [4,5]. To elucidate the mechanism of scale formation in Ni-based superalloys, Bensch et al [5] modelled the high-temperature oxide growth and substrate response in the single-crystal strong Al2O3forming René N5 and weak Al2O3-forming SCA425+ and showed a high degree of correlation with experimental data for oxidation at 900°C.…”

Crack growth in single crystal gas turbine blade alloys under service-like conditions

“…At higher temperatures, the crack growth may be influenced by creep, oxidation and microstructural degradation. TMF crack growth testing, resembling service conditions, is generally required to accurately characterize the material behaviour [13][14][15][16] . TMF of nickel base superalloys has been studied previously, but the majority of the work has been concerning the cyclic deformation behaviour and crack initiation life [17][18][19][20][21][22][23][24][25][26][27][28][29][30] .…”