Electron spectroscopic imaging and fine probe EDX analysis of liquid phasesintered ceramics

This paper is focussed on high resolution imaging and microanalysis of two classes of liquid phase sintered ceramic materials, alpha and duplex alpha/ beta sialons and alpha-SiC ceramics. The microstructures there characterize d in a FEGTEM equipped with surrounding interactive instrumentation for EDX and EELS analysis and electron energy filtering, and special attention was pain to the intergranular microstructure and the variation in local chemic al composition. The alpha and duplex alpha/beta sialon ceramics had been fa bricated from balanced starting powder mixtures corresponding to the a-sial on composition R0.4Si10.2Al1.8O0.6N15.4 (R = Sm, Dy or Yb) and the beta-sia lon composition Si5.4Al0.6O0.6N7.4. The alpha-SiC ceramics had been pressur eless sintered or hot isostatically pressed with smaller additions of Al2O3 and Y2O3. Combined high resolution analytical and spatial information was obtained front electron spectroscopic images recorded around the C K, N K, O K, Al L-2,L-3 and rare earth element N-4,N-5 edges in the electron energy loss spectrum. Residual glassy grain boundary films rich in O and cations originating from the metal oxide/nitride additives were present at all char acterized grain boundaries. High resolution imaging and elemental maps comp uted from the electron energy filtered images showed intergranular film thi cknesses in the range 1.5 to 2.3 nm. The results imply that the intergranul ar film thickness in the sialon microstructures is dependent upon the parti cular grain boundary and the local chemistry as well as the alpha' stabiliz ing cation. Elemental concentration profiles obtained by stepwise fine prob e EDX analysis across alpha'/alpha', alpha'/beta' and beta'/beta' sialon gr ain boundaries revealed significant variations in the local alpha' and beta ' substitution levels, both within and between analysed grains. Concentrati on gradients within the sialon and alpha-SiC grains, associated with the di fferent grain boundaries, were not detected. (C) 1998 Elsevier Science Limi ted. All rights reserved.