Modelling compositional changes in nickel base alloy 602 CA during high temperature oxidation

Abstract

The high chromium nickel base alloy 602 CA is used as construction material for high temperature components in aggressive environments such as gas burners or heat exchangers. The high temperature oxidation behaviour of this alloy is characterised by the formation of an external Cr 2 O 3 scale and internal precipitation of alumina. The main goal of the present investigation was to elucidate the effect of aluminum on the subscale chromium depletion phenomena. The chromium concentration profiles were found to be flat and sometimes even increasing towards the oxide-alloy interface. The experimental observations were interpreted in terms of alloy thermodynamics, i.e. effect of oxidation induced compositional changes on chemical potentials of the alloy constituents. The concentration profiles in alloy 602 CA observed during high temperature exposure were modelled using the CALPHAD approach for thermodynamic and kinetic calculations. Thermodynamic calculations revealed that the Al depletion in the alloy subsurface due to internal alumina precipitation leads to enhanced Cr diffusion towards the alloy surface.

Modes of Deposit-Induced Accelerated Attack of MCrAlY Systems at 1100 °C

“…In general, these alloys grow external Al 2 O 3 at low temperatures and internal Al 2 O 3 plus external Cr 2 O 3 at higher temperatures. Recently published studies of alloy 602 CA [39,40], for example, illustrate these similarities. Although the present NiC-oCrAlY alloys had higher Al and Cr concentrations, the resemblance with 602 CA reflects the effect of the deposits on the oxide map (Fig.…”

Effect of gas flow rate on oxidation behaviour of alloy 625 in wet air in the temperature range 900–1000 °C

“…The formation of the chromia‐based surface oxide scale results in a progressive depletion of the selectively oxidising element chromium from the alloy, which leads to compositional and microstructural changes in the alloy beneath the oxide scale . These changes may obviously affect the mechanical properties of the material, e.g.…”

Partitioning of Ti and Kinetic Growth Predictions on the Thermally Grown Chromia Scale of a Polycrystalline Nickel-Based Superalloy

“…The scale growth itself was not included in the calculations nor was the effect of multi-component diffusion-this is a challenging problem in itself and it is beyond the scope of this paper. Note however, that literature on oxidation modeling is largely focused on oxygen ingress [29] and subsurface elemental depletion, [29,30] but not outward diffusion of alloying elements. [29] Additionally, existing models only consider the effective diffusion of a single element, usually oxygen.…”

“…Note however, that literature on oxidation modeling is largely focused on oxygen ingress [29] and subsurface elemental depletion, [29,30] but not outward diffusion of alloying elements. [29] Additionally, existing models only consider the effective diffusion of a single element, usually oxygen. [29,30] Since the scale growth rate is related to the effective diffusivity of the elements contributing to its formation, [29] the present calculations give a semi-quantitative estimate of the thickening rate as a function of grain boundary diffusion.…”