Load-bearing capacity of coating–substrate systems obtained from spherical indentation tests

Despite the numerous applications of tribological coatings, a methodology that estimates the load-bearing capacity of coating–substrate systems has not yet been developed. In this paper, the allowable loads for coated surfaces were determined using spherical indentation tests with a 20–500 μm range of indenter tip radius. Titanium nitride (TiN) coatings, 0.7–2.4 μm thick, deposited on steel substrates by the pulsed laser deposition (PLD) technique were tested. Indentation results allow to draw the map of deformation of this coating–substrate system and estimate the allowable loads, into avoid the destruction of the system by the substrate yield and coating fracture. Tribological studies, carried out in the ball-on-disc contact, showed a completely different character of wear of the systems for loads below and above the permissible level. The wear process was analyzed by transmission electron microscopy (TEM) on thin films prepared from wear tracks by the focus ion beam technique (FIB).