Evaluation of interface stability and melt-processing techniques of Ni 3Al/SiC particulate composites

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Nickel aluminides, in particular Ni 3Al, are potential matrix materials for high temperature composites. Several powder metallurgy and melt-processing routes to fabricate such composites have been investigated to date. A major concern has been the excessive interfacial reaction between the matrix and the reinforcement. This paper addresses issues related to the selection of the proper processing technique and to the development of diffusion barriers on the reinforcement to minimize such reactions. Melt-processing techniques such as liquid metal infiltration and mechanical mixing for fabrication of Ni 3Al/SiC particulate composites are evaluated. The effectiveness of surface oxidation of SiC to minimize the extent of interfacial reaction is also investigated. Sessile drop experiments indicate an increment in contact angle due to surface oxidation of SiC. Further, differential thermal analysis results suggest the formation of reaction products for untreated SiC as compared with surface-oxidized SiC. Electron probe microanalysis has identified nickel as the major diffusing element in the case of untreated SiC. The diffusion of nickel is significantly reduced when an oxide layer exists on the SiC. Finally, it is concluded that, depending on the reaction kinetics, it is not only necessary to provide a diffusion barrier but is equally important to employ a processing technique that minimizes the contact time between molten Ni 3Al and the SiC reinforcement. It was indeed found that, while complete dissolution of SiC particles occurs during liquid mixing, Ni 3Al/SiC composites can be produced through liquid infiltration.