Abstract
The strength degradation of alumina/alumina:calcium‐hexaluminate/alumina trilayers, after damage from Hertzian contacts, is evaluated. Relative to the monolithic alumina and alumina:calcium‐hexaluminate constituent layer materials, the trilayers show markedly improved strength retention in the damaged state at high contact loads. The outer, fine‐grained alumina layers are classically brittle, characterized by cone cracking, whereas the inner alumina:calcium hexaluminate layer is essentially quasi‐plastic, with a well‐defined “yield” zone that consists of distributed microdamage. The improved strength behavior of the trilayer composite is rationalized in terms of a synergistic interaction between the contact‐induced deformation modes in the two layers, with each mode partially ne‐gating the effectiveness of the other as a source of failure. This result offers the prospect of hybrid structures with hard outer layers, to provide wear resistance, and soft, tough underlayers, to inhibit brittle fracture.
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