The effect of interfacial free energies on the stability of microlaminates

Laminated composites with polycrystalline layers typically break down at high temperatures through grain boundary grooving and the pinch-off of individual layers. Such materials, when exposed to high temperatures, develop grooves where grain boundaries meet the interfaces between layers. The depths of the grooves are controlled by the ratios of grain boundary and interfacial free energies, γ_gb/γ_int. Depending on the dimensions of the grains, these grooves can extend through the entire layer, causing pinch-off at the grain boundary. This pinch-off destroys the layering and eventually leads to a gross coarsening of the microstructure. Because microstructural stability is critical to performance for most applications, the ability to understand and predict the stability of microlaminates is a necessary tool. An existing model of this capillarity-driven breakdown requires the interfacial free energies, γ_gb and γ_int, as input parameters. Both biaxial and uniaxial zero creep tests have been used in conjunction with transmission electron microscopy to measure these interfacial energies in Ag/Ni and Nb/Nb₅Si₃ microlaminates.