How interfaces limit nanoscale stress concentrations and prevent catastrophic failure in single-asperity contacts.

Contact between materials occurs through microscale asperities, where stress evolves under highly localized, multiaxial deformation. Despite the significant importance to numerous scientific fields, to date, direct experimental quantification of these stress fields across the materials in contact has remained elusive. Here, we combine in situ scanning synchrotron X-ray nanodiffraction with 80 nm spatial resolution and a custom indentation setup to resolve nanoscale stress fields developing at the contact between a diamond indenter and both single-layer ZrN and multilayered ZrN-ZrCu thin films. We introduce a nanomechanical probe comprising a single-crystalline diamond wedge coated with nanocrystalline diamond to simultaneously probe stress accumulation within the indenter. X-ray scattering and scanning electron microscopy, micromechanical testing, analytical and elastic-plastic finite element modeling corroborate the nanoscale stress maps obtained for both sides of the tip-surface contact region. The individual interfaces along the projected load paths diffuse stresses in both the tip and the multilayer, thereby controlling the overall mechanical response at the asperity. Consequently, the stored elastic energy is reduced by 30% in the multi-layered film in comparison with the monolithic ZrN. Finally, the measured nanoscale stress distributions elucidate the fundamental mechanisms by which artificial multi-layered materials effectively dissipate energy and prevent catastrophic failure.