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An analytical approach to the β-phase coarsening behaviour in a thermally sprayed CoNiCrAlY bond coat alloy

Chen, H.; Si, Y.Q.; McCartney, D.G.

Authors

H. Chen Hao.Chen@nottingham.edu.cn

Y.Q. Si

D.G. McCartney graham.mccartney@nottingham.ac.uk



Abstract

This paper investigates the β-phase coarsening behaviour during isothermal heat treatment of free-standing CoNiCrAlY (Co-31.7%Ni-20.8%Cr-8.1%Al-0.5%Y, all in wt%) coatings prepared by high velocity oxy-fuel (HVOF) thermal spraying. The microstructure of the coatings was characterised using scanning electron microscopy with energy dispersive X-ray (EDX) analysis and electron backscatter diffraction (EBSD). It comprises a two phase structure of fcc γ-Ni matrix and bcc β-NiAl precipitates. The volume fraction of the γ-Ni and the β-NiAl phases were measured to be around 70% and 30% respectively, with grain sizes varying largely from 0.5 to 2 μm for both phases. Isothermal heat treatments of the free-standing coatings were carried out at 1100 C for times up to 250 h. The β-phase coarsening behaviour during isothermal heat treatments was analysed by quantitative metallography. It is shown that the coarsening behaviour of β phase in the CoNiCrAlY alloy followed the classical Lifshitz-Slyozov-Wagner (LSW) theory of Ostwald ripening. By incorporating a dimensionless factor which correlates with volume fraction of the β phase, a modified LSW model coupled with formulaic interfacial energy and effective diffusion coefficient of the CoNiCrAlY alloy was utilised to interpret the coarsening behaviour of the β phase. The coarsening rate coefficient obtained from the modified LSW model shows good agreement with the corresponding experimental result.

Journal Article Type Article
Journal Journal of Alloys and Compounds
Print ISSN 0925-8388
Electronic ISSN 1873-4669
Publisher Elsevier
Peer Reviewed Peer Reviewed
APA6 Citation Chen, H., Si, Y., & McCartney, D. (in press). An analytical approach to the β-phase coarsening behaviour in a thermally sprayed CoNiCrAlY bond coat alloy. Journal of Alloys and Compounds, doi:10.1016/j.jallcom.2017.02.002
DOI https://doi.org/10.1016/j.jallcom.2017.02.002
Keywords HVOF spraying; MCrAlY; β-phase; Coarsening; Heat treatment; Diffusion
Publisher URL http://www.sciencedirect.com/science/article/pii/S0925838817304176
Copyright Statement Copyright information regarding this work can be found at the following address: http://creativecommons.org/licenses/by-nc-nd/4.0

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Copyright Statement
Copyright information regarding this work can be found at the following address: http://creativecommons.org/licenses/by-nc-nd/4.0





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