INTERDIFFUSION AND STRUCTURAL CHANGES IN THE Cr₂O₂–Al₂O₃(ZrO₂) DIFFUSION COUPLE UNDER MICROWAVE HEATING

Abstract

The kinetics of interdiffusion and accompanying microstructure evolution in diffusion couples Cr₂O₂–Al₂O₃ (5 vol.% ZrO₂) were studied in temperature range 1600–1800ºC under microwave heating (MWH) of 24GHz and, for comparison, under traditional heating (TH) by the methods of MRSA and microscopic analysis of microstructure. It was found the different character of concentration distributions for Cr ions in Al₂O₃ in diffusion zones formed at MWH and TH, what was attributed to increase the contribution of grain boundary diffusion into effective diffusion flux at MWH. This result is found to be in agreement with smaller grain sizes in diffusion zone under MWH comparing to ones under TH. The microstructure evolution during TH consists in the grain growth by recrystallization process, whereas two processes, the recrystallization and polygonization, are superimposed during MWH. The polygonization process during MWH is caused by dislocation generation under thermal stresses, originated from non-uniform temperature distribution in diffusion zones with variable component concentrations. From analysis of measured concentration distributions with accounting for superposition of diffusion fluxes along GBs and inside the grain bulk the GB and bulk diffusion coefficients were calculated using appropriate diffusion equations. Obtained diffusion coefficients can be useful for prognosis the kinetics of the various diffusional mass transfer processes in oxide systems of Al₂O₃, Zr₂O₃ and their mixtures.