Surface stress release in AlCrN coatings determined by synchrotron radiation multi-reflection grazing-incidence X-ray diffraction

Abstract

In this work, the residual stress distribution of c. 3.8 μm arc-evaporated AlCrN coatings was investigated by the synchrotron radiation multi-reflection grazing-incidence X-ray diffraction method. Ar ion bombardment post-treatment was also used to tune the stresses in the AlCrN coating to elucidate the evolution of stress therein. The result showed that the as-deposited AlCrN coating showed large surface stress of −1500 MPa, this sharply decreased in magnitude to −800 MPa in the internal coating. Ar ion bombardment (post-treatment) could significantly reduce the surface stresses by around −1000 MPa and the interior stresses by around −400 MPa for an AlCrN coating, the “shot peening” effect arising therefrom could promote migration and diffusion of the adatoms, which contributed to the reduction of the micro-strain and interior stress. Furthermore, Ar ion bombardment also promoted the growth of surface grains, which also contributed to the stress reduction in the near-surface region of the AlCrN coating. In addition, Ar ion bombardment could increase the substrate stresses from −32 MPa to −210 MPa. The results suggested that internal stress reduction could be achieved by promoting the migration and diffusion of adatoms.