Abstract
The effect of dispersed oxide particles on the mechanical and high-temperature properties of a composite is closely related to their cohesion with the matrix and to their stability at elevated temperatures. Both these properties are affected by solutes in the matrix and the effect can be positive or negative in either case. The stability of the dispersion is reflected by its resistance to coarsening by Ostwald ripening. The coarsening rate is governed by several factors, most of which are affected by alloying additives in the matrix. The nature of this influence is discussed on the basis of results obtained on composites of alumina in matrices of nickel, iron, and iron–40% nickel with various minor alloying additions. Particle/matrix bonding is largely dependent on the magnitude of the interfacial energy between the oxide and the metal, which in turn is dependent on matrix alloying. The work of adhesion between matrix and particles has been determined by measuring contact angles at strain-induced and annealed cavities using high-voltage transmission microscopy. The results are correlated with the fracture strain of the composite. It is shown that alloying can improve both the stability and the bonding of the phases in a composite.
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