Toughening Al 2 O 3 with NiAl and NiAl(Fe) particles

Abstract

Aluminia composites of Al₂O₃–NiAl and NiAl(Fe) were prepared by hot pressing mixtures of Al₂O₃with NiAl and NiAl(Fe) powders respectively to a density >98·5%theoretical for evaluation of toughness as a function of intermetallic content and comparison with hot pressed Al₂O₃, NiAl and NiAl(Fe). The intermetallic grain size, in both cases, was found to be smaller than the as received powder particle size in alumina rich composites because of the pinning effect of alumina particles on grain boundaries, but increased with increase in intermetallic content due to grain growth as the pinning effect decreased at lower alumina contents. The toughness of hot pressed NiAl(Fe) was ∼50% greater than for NiAl. Both intermetallic compositions showed a steady increase in the toughness of the composites with increase in intermetallic content, with NiAl(Fe) composites being somewhat tougher at higher intermetallic contents. The Fe content in NiAl(Fe) appears to increase the interfacial strength in the composites with the result that, although Al₂O₃–NiAl(Fe) composites are the tougher of the two systems, the toughness enhancement over rule of mixtures values is less in the NiAl(Fe) system. Toughness enhancement in the Al₂O₃–NiAl system is attributed to a combination of crack deflection and crack bridging but in the Al₂O₃–NiAl(Fe) system it is mainly attributed to crack bridging.