Alloy compositions, nickel aluminides

The large difference in stability between NiO and A1203 makes nearly all Al-Ni alloy compositions in equilibrium with A1203, as shown by the wide A1203 stability region in Fig. 10, even though numerous very stable nickel aluminides can form. Once again, a balance between the alloy liquidus surface composition, matrix formation rate, and the diffusion of transition metal away from the reaction front must be maintained. Typically the presence of a reducible compound in the preform, especially if it is the sole constituent, results in a further refinement of the composite microstructure. 

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