Abstract. 2014 Spatially resolved chemical composition and spectroscopic line profiles have been gathered from the space charge region across a spinel/sapphire interface using a dedicated scanning transmission electron microscope. The electron energy-loss spectra reveal an excess of Mg (relative to stoichiometric spinel) along with Cr segregated to the interfacial zone. A quantitative least squares decomposition of a spectrum-line profile of the Al L2, 3 absorption edge fine structures into two standard components clearly highlights the transition from sapphire into spinel; further analysis indicates that the degree of site inversion, which is the fractional occupancy of tetrahedral sites by trivalent Al, increases within 5 nm of the boundary. The overall charge neutrality at the interface is maintained by the increased concentration of negative charge, probably interstitial O anions which are also present in excess quantity relative to stoichiometric spinel and sapphire.

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SUMMARY Applications of scanning ion imaging with high lateral resolution in the microchemical investigation of metal – and ceramic‐matrix composites are described. The technique, which combines a scanning ion microprobe with secondary ion mass spectrometry (SIMS), is ideally suited to the study of complex, multicomponent composite structures. Most elements can be detected with good sensitivity, enabling the determination of spatial distributions for major and minor elements. Analytical images obtained with this technique reveal unprecedented chemical information about interfacial segregation and interdiffusion phenomena. As examples, the characterization of both ceramic–matrix (Al borate–SiC) and metal–matrix (Ni alloy–Al2O3) composite materials is described.

SUMMARY The chemical microstructure of Ni‐base superalloy/Al2O3 metal‐matrix composites (MMCs) has been studied by scanning ion microprobe microanalysis, using the secondary ion mass spectrometry (SIMS) technique. The MMCs were fabricated using the transient‐liquid‐phase bonding (TLP) process, with B‐doped superalloy powder as an interlayer. Boron was found to diffuse rapidly throughout the matrix to form boride phases, mostly at the grain boundaries in the matrix. These borides contain excess Cr (also Mo, Si, W) in comparison with the Ni alloy‐matrix, but are depleted in Ni (also in Al and Co). Carbides form at the grain boundaries as thin platelets and inside the grains as fine particles. Chemical reaction occurs between the sapphire fibre and the matrix; formation of NiAl2O4 spinel at the interface is suggested. This interface reaction layer is friable and parts of it peel off during consolidation to become inclusions in the matrix near the fibre/matrix interface.