M. Larsson et al., Mechanisms of coating failure as demonstrated by scratch and indentation testing of tin coated HSS, SURF ENG, 16(5), 2000, pp. 436-444
In situ monitoring of acoustic emission during scratching and indentation i
n combination with post-test light optical and scanning electron microscopy
were used in order to evaluate the dominant coating failure mechanisms TiN
coated high speed steel. During scratching, six different coating failure
mechanisms could be distinguished, i.e. cracks parallel with the scratch ch
annel, semicircular cracks within the scratch channel, external transverse
cracks, cohesive chipping, adhesive spalling, and complete breakthrough of
the coating within the scratch channel resulting ill substrate ate exposure
. During indentation, four different types of coating failure could be dist
inguished, i.e. circular cracks within the indentation, radial clacks outsi
de the indentation, cohesive chipping, and adhesive spalling. The influence
of coating thickness, substrate hardness, and substrate sur-face topograph
y on the coating failure mechanisms is very complex and depends on the type
of contact, i.e. static or dynamic, contact load, etc. However; the result
s show that indentation testing enables a more appropriate method for the e
valuation of the intrinsic fracture resistance of the coating material and
coating/substrate adhesion as compared with scratch testing. In contrast, s
cratch testing, simulating the contact condition between all asperity slidi
ng on a flat, is preferably used for evaluating the load carrying capacity
of a coating/substrate composite. It call also be used in order to find the
optimum substrate surface roughness for coated components used in various
sliding applications.