Papers by Keyword: Chemical Potential Diagram

Abstract: The microstructure of the solid-state diffusion bonded interfaces of silicon carbide (SiC) and titanium aluminide (TiAl) were investigated. A 100-µm-thick Ti-48at%Al foil was inserted between two SiC specimens and then heat-treated in vacuum. The interfacial microstructure has been analyzed by scanning electron microscopy, electron probe microanalysis and X-ray diffractometry. Four layers of reaction products are formed at the interface by diffusion bonding: a layer of TiC adjacent to SiC followed by a diphase layer of TiC+Ti2AlC, a layer of Ti5Si3CX containing Ti2AlC particles and a layer of TiAl2. However, the TiAl2 layer is formed during cooling. The actual phase sequence at the bonding temperatures of 1573 K and 1673 K are described as SiC/TiC/(TiC+ Ti2AlC)/(Ti5Si3CX+Ti2AlC)/Ti1-XAl1+X/TiAl and SiC/TiC/(TiC+Ti2AlC)/(Ti5Si3CX+Ti2AlC)/Ti5Al11 /Ti1-XAl1+X/TiAl, respectively. The phase sequences are successfully expressed on the basis of the Ti-Al-Si-C quaternary chemical potential diagram.

Abstract: Utilization of chemical potential diagrams is powerful in predicting the chemical stability of dissimilar materials and analyzing the diffusion path when reactions are proceeded. Since practical materials consist of many components so that construction of chemical potential diagrams for the multi-component systems becomes crucial. There is one powerful way of treating phase equilibria for such complicated systems in chemical potential diagrams; that is, a construction of three dimensional diagrams, although all phase relations are not visible in such a diagram. To make phase relations visible, there are several ways; one is to make selected phase transparent. This makes it possible to examine the detailed relations between selected materials. Second one is to make dissections at selected values for the chemical potential of selected chemical species. By swinging the dissected value, the change in phase relations can be examined as a function of given chemical potential. Some examples will be given for the formation of oxide scale on ferritic alloys.