Interface adhesion: effects of plasticity and segregation

The adhesion at interfaces between dissimilar materials is strongly affected by both segregation and the extent of plasticity in the adjoining material, particularly when one of these is a metal (or thermoplastic). It will be shown that these interfaces when clean, are generally strong and tough, such that failure occurs in one of the adjoining materials, rather than at the interface. However, segregrants and contaminants often embrittle and weaken the interface, especially in combination with ambient moisture. The embrittlement is obviated either by alloying with elements that “getter” the contaminants or by using an “adhesion layer” that has essentially the same effect: Cr and Ti are particularly effective gettering elements. Models that relate these effects to fundamental material parameters through non-dimensional indices are described. They comprise linkages between atomistic and continuum, enabled by implementation of a plasticity length scale, within the context of a crack growth simulation routine. Comparison with the experimental results is conducted, leading to suggestions for development of a predictive scheme.