The repeated spherical indentation test: an efficient way to evaluate the adhesion of hard coatings

Abstract

Fatigue failure of hard coatings usually occurs at much lower loads than failure under static loading. Hence one way to evaluate coating adhesion should be cyclic loading close to service conditions. In this study, a new method of adhesion measurement for hard coatings is introduced based on interfacial fatigue under repeated indentation. Mono-and multi-layered coatings with different interfacial states are evaluated by a repeated-indentation test. Detachment of the coatings occurs initially at the rim of the indenter imprint, apparently as a result of adhesive failure. In contrast to monolayer coatings, peeling of multilayer coatings depends on the lowest strength of the interfaces. This study also demonstrates that the adhesion determined by the repeatedindentation test is sensitive to the interfacial state, allowing an optimised or weakened interface to be clearly revealed.

Micro-impact testing of AlTiN and TiAlCrN coatings

“…Torres and co-workers have noted that, by switching from sharp to blunter spherical indenters, there is an intrinsic suitability for examining damage evolution in bulk materials as a function of number of cycles [40] and it is possible to assess fatigue sensitivity. Qiu and coworkers have argued that very large radius probes are less suited for coating systems as the peak stresses are well into the substrate [41][42]. They, therefore, developed a repeated indentation test using a 200-micron radius probe and applied loads in the range 90-300 N.…”

“…Although the test was not fully instrumented, so that it was necessary to stop it to observe deformation, they were able to show enhanced sensitivity to differences in adhesion strength due to changing interlayers [41][42].…”

Influence of ALD-Al2O3 film on anti-scratch and anti-tarnish of silver

“…As can be seen in Figure 5, the ALD film has higher hardness as compared to Al 2 O 3 films prepared by electron-beam evaporation (EBE) and reactive magnetron sputtering (RMS) [18, 19]. In addition, the deposition temperature affects the mechanical properties of ALD Al 2 O 3 film [20]. Indeed, the films deposited at 177 and 200°C had good mechanical properties, and their hardness was close to γ-Al 2 O 3 [19], indicating that atoms in the films were closely arranged.…”

Tribological behaviour of a self-lubricated GO/WC–12Co thermal spray coating

“…Figure 6 shows the evolution of the friction coefficient recorded during the wear test as a function of the sliding time for Coatings A (no GO) and B (add GO) under a normal load of 50 N. As shown in this figure, the friction coefficients of both coatings rapidly increased during the initial running-in phase, which is believed to be the result of a transition in the contact conditions from two-body abrasion to interfacial sliding [18]. A significant difference can be observed: Coating A (no GO) showed a broader and more pronounced running-in phase that lasted for 300 s, after which a steady-state friction coefficient of μ A ≈ 0.63 was obtained, whereas the transition from the running-in phase to the steady-state phase for Coating B (add GO) was not obvious, and the running-in phase lasted only approximately 100 s before a steady-state friction coefficient of μ B ≈ 0.5 was obtained.…”