Fracture mode transitions during indentation of columnar TiN coatings on metal

Deformation and failure of a film/substrate system subjected to spherical indentation: Part I. Experimental validation of stresses and strains derived using Hankel transform technique in an elastic film/substrate system

“…1,2 Depending on the combination of the parameters, films may display a mechanism of strain accommodation that is non-catastrophic and insensitive to load, or, alternatively, crack at very low loads in a manner that is likely to lead to spalling. 3 Because these different domains of behavior have important implications for coating design, it is of interest to see whether such transitions in behavior can be predicted by an analysis of the driving forces for different accommodation mechanisms, One of the key driving forces for failure turns out to be the strain induced in a predominantly elastic film by a plastically deforming substrate. While analytical treatments exist for the solution of contact loading of a layered half-space, a full elastic-plastic solution is not available in closed form.…”

Fracture Behaviors of TiN and TiN/Ti Multilayer Coatings on Ti Substrate during Nanoindentation

“…It is interesting to see that the circumferential crack at the right-hand edge evolves to an inclined crack when it penetrates to a certail thickness in the coating film. There are two possible reasons: kind of the columnar grains [14] and shear stress. The increase of the latter will change the direction of the prinicpal stress and in turn the direction of the crack propogation.…”

“…This indicates that the inter-columnar shear is not the major fracture mechanism in the studied TiN film. Bhowmick et al's study demonstrated that the fracture mode in the TiN film strongly depends on the film thickness and substrate hardness [14]. Hard substrates and thin films promote the inter-columnar shear crack, while thick films on soft substrates exhibit the bending crack, inclined crack and lateral crack.…”

“…It has been known that TiNbased coating by PVD has a columnar grain structure [10][11][12], which exhibits anisotropy in elastic and damage behaviours. The shear cracking along columnar grain boundaries often occurs during indentation or scratch on the surface of the coating [10,[13][14][15][16][17][18]. The deformation processes also induces the inclined, lateral, edge and bending cracks.…”

“…Cairney et al studied the degradation of TiN coatings under cyclic contact loading up to 400 mN [20]. Bhowmick et al examined the influence of the substrate hardness and coating thickness on the type and extent of fracture during indentation [14]. It has been concluded that hard substrates and thin films promote inter-columnar sliding, while thick films on soft substrates exhibit severe damage.…”