Some aspects on modelling of the β-phase depletion behaviour under different oxide growth kinetics in HVOF CoNiCrAlY coatings

Abstract

In this paper, β-phase depletion behaviour of free-standing high velocity oxy-fuel (HVOF) thermally sprayed CoNiCrAlY coatings was studied. Microstructural analysis showed a twophase microstructure of γ-Ni matrix and β-NiAl secondary phase after heat treatment. Fine grains were found around the sprayed particle boundaries and coarse grains were retained as the original particle structure, with grain sizes varying from 2 to 0.5 µm or even less for both phases. The β-phase depletion behaviour was investigated during isothermal oxidation and was also modelled through diffusion calculations. A previously developed β-phase depletion model was utilised to study the evolution of β-phase depletion under different oxide growth kinetics. Three oxide growth models were tried: 1) Meier model, 2) thermogravimetric analysis (TGA) model, and 3) experimentally fitted oxide growth model. The oxide growth kinetics were converted to Al flux functions which were used as the boundary conditions in the DICTRA modelling. It is shown that the results obtained from the three models exhibit good agreements between the measured and predicted results for times up to 100 h at 1100 C, but discrepancies were noted at longer oxidation times. Further improvements on closely 2 modelling the oxidation kinetics and the effective diffusion behaviour are needed to minimise the discrepancies at longer oxidation times.

Effects of temperature on the β-phase depletion in MCrAlYs: A modelling and experimental study towards designing new bond coat alloys

“…But since Eq. ( 1) has been previously demonstrated to be suitable for the MCrAlYs used in this work and reasonable agreements have been achieved between model predictions and experimental measurements for the HVOF sprayed MCrAlYs in previous studies [39,48], the oxidation model in Eq. ( 1) is thus assumed here to approximate the oxide growth.…”

“…(1) has shown the capability of modelling MCrAlYs at different Al-contents. Furthermore, the effects of different oxide growth models on the subsequent β-phase depletion have been investigated in one of our previous studies [48]. No significant difference in the calculated β-phase depletion was reported when using Eq.…”

Coated single crystal superalloys: processing, characterization, and modeling of protective coatings

“…The major concern, similar to TGO growth analysis, is to obtain a realistic value of the diffusion coefficients. Most advanced models for the estimation of diffusion coefficients are based on CALPHAD, considering multi-component alloys and mobility database to modify the diffusion coefficient as a function of local composition [214,33,135] where phase field models are straightforward to model diffusion coefficient [216].…”

Some considerations in using the small punch testing for thermally sprayed CoNiCrAlY coatings

“…pores, oxide inclusions and un-melted particles [39,40]. This means the coatings generally exhibit quite different structures and properties than the cast alloys of the same chemistry [41,42]. The defects embedded in the coatings can have a significant influence on their mechanical response during the SPT.…”