Energy dispersive spectroscopy analysis of aluminium segregation in silicon carbide grain boundaries

Abstract

SummaryThe aluminium distribution in polycrystalline SiC hot-pressed with aluminium, boron and carbon additives was studied using X-ray energy-dispersive spectroscopy (EDS) and transmission electron microscopy (TEM). The Al excess in homophase SiC grain boundary films was determined, taking into account dissolved Al in the SiC lattice. In the spot-EDS analysis, an electron beam probe with a calibrated diameter was formed, and the total beam-specimen interaction volume was defined, taking the beam spreading through crystalline TEM foil into consideration. EDS spectra were collected from regions containing intergranular films and adjacent matrix grains, respectively. A theoretical treatment was presented and experimental errors were estimated, with a further discussion about the effects of foil thickness. Experimental examples are given, followed by statistical EDS analyses for grain boundary films in SiC samples hot-pressed with increased amounts of Al additions. The results demonstrated a substantial Al segregation in the nanometer-wide intergranular films in all samples. Al additions higher than 3 wt% saturated the Al concentrations in SiC grains and in grain boundary films. The effect of foil thickness, and the parameters for determining the optimum incident beam diameter in the EDS analysis are discussed.

Aluminum-containing intergranular phases in hot-pressed silicon carbide

“…Here N Al GB follows from the determination of the total Al excess per unit area of the IGF, Γ Al , so that N Al GB = Γ Al /w, where w denotes the IFG width which can be measured in high-resolution TEM images. The EDS determination of Γ Al requires knowledge of the foil thickness and the electron beam probe diameter [32]. The fairly large standard deviation implied that the Al content in grain boundary films was influenced by other constituents.…”

“…Detailed description and discussion for the quantitative EDS analysis method has been published elsewhere [32].…”

Microstructure and Properties of in Situ Toughened Silicon Carbide

“…A spatial-difference methodology was developed to determine the concentration of the impurities in the SiC grain boundaries using a nanoprobe with a diameter varied between 3 and 20 nm [8,9]. Indentation hardness, four-point bending strength, creep resistance, abrasive wear properties, Rcurve fracture toughness, and cyclic fatigue-crack growth behavior at ambient and elevated temperatures were all evaluated for ABC-SiC.…”

Microstructure development in hot-pressed silicon carbide: effects of aluminum, boron, and carbon additives

“…The Al concentration in the IGFs was analyzed by energy-dispersive X-ray spectroscopy (EDS), with a 10 nm diameter electron beam probe. The detailed methodology and experimental parameters for chemical analysis have been reported previously [32]. The polished SiC pieces were plasma-etched in CF 4 containing 4% O 2 , for scanning electron microscopy (SEM) examination.…”

“…Cao et al hot-pressed SiC in the presence of aluminum, boron, and carbon, (ABC-SiC), demonstrating excellent flexural strength, high fracture toughness, fatigue resistance, improved creep resistance, and enhanced wear resistance at ambient and elevated temperatures [18,[27][28][29][30][31]. Detailed transmission electron microscopy (TEM) study confirmed the existence of about 1 nm wide amorphous intergranular films (IGFs) [25], of which the Al-rich composition was quantitatively determined by nanoprobe electron-beam analysis [32]. Prolonged heating above 1000 o C crystallized the amorphous IGFs [25].…”