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

作者：Chen, H.^*; Si, Y. Q.; McCartney, D. G.

来源：Journal of Alloys and Compounds, 2017, 704: 359-365.

DOI：10.1016/j.jallcom.2017.02.002

• HVOF spraying
• MCrAlY
• beta-phase
• Coarsening
• Heat treatment
• Diffusion

This paper investigates the beta-phase coarsening behaviour during isothermal heat treatment of freestanding 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 gamma-Ni matrix and bcc beta-NiAl precipitates. The volume fraction of the gamma-Ni and the beta-NiAl phases were measured to be around 70% and 30% respectively, with grain sizes varying largely from 0.5 to 2 mu m for both phases. Isothermal heat treatments of the freestanding coatings were carried out at 1100 degrees C for times up to 250 h. The beta-phase coarsening behaviour during isothermal heat treatments was analysed by quantitative metallography. It is shown that the coarsening behaviour of beta 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 beta 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 beta phase. The coarsening rate coefficient obtained from the modified LSW model shows good agreement with the corresponding experimental result.

• 出版日期2017-5-15
• 单位宁波诺丁汉大学