Under tensile stresses, this channeling process does not arrest until it encounters another channel or an edge, creating a connected channel network . Sources of channel networks at higher stresses are surface cracks starting from a flaw even at lower stresses, based on fracture mechanics based cracking models.
HR-TEM images of 50 nm thin TiN thin films on PU: (a) Cross-section image with arrows indicating the intercolumnar areas. (b) Small angle electron diffraction pattern. (c) Top-view image with indicated intercolumnar crack.
Typical failure modes of hard coatings on polymer substrates in scratch testing with progressive loads in the mN range and very sharp indenter (3 µm tip radius), shown for a 100 nm a-C:H film on PC. (a) Start of plastic deformation of the PC substrate and cohesive film fracture in the scratch track close to the edge (Lc1). (b) Start of cohesive film fracture by transverse semi-circular cracks in the scratch track. (c) Start of adhesive fracture (chipping at edge of scratch track) between film and substrate (Lc2). 1e1e36bf2d