Some of the Young's modulus and the fracture toughness values measured before and after the wear tests carried out for all materials, presented change statistically significantly, however these may not be relevant to their tribological performance.
The tribological analysis carried out to both Al2O3coatings has evidenced the development of different wear mechanisms as a function of the test temperature. In both samples evaluated at 25 °C (Fig. 1a), were identified friction marks produced by plastic flow of the asperities in their surface due to sliding contact with the alumina ball. While in those tested at 500 °C and 750 °C (Fig. 1b) high levels of particle detachments produced by the propagation of cracks in the coatings, were observed, as well as fine and rounded particles which join forming small as island-shaped layers, that in some cases plug the wear tracks produced by the detachment. On the other hand, in the both coatings tested at 1000 °C (Fig. 1c) a continuous layer was formed on the wear track, consisting of fine particles, on which was observed a plastic flow.
Fig. 1. Characteristics identified on the surface of polished Al2O3coatings tribologically tested at: a) 25 °C, b) 500 and 750 °C et c) 1000 °C.
Concerning the wear track of the electro-melted Al2O3 refractory used as reference, it was detected the same change aforementioned from ductile to fragile for returning to ductile deformation again when the temperature increased (Fig. 2). A bigger quantity of debris was detected despite the fact that the tests conditions applied were the same than those for the coatings.
Fig. 2. Characteristics identified on the surface of electromelted refractory tribologically tested at: a) 25 °C, b) 500 and 750 °C et c) 1000 °C.
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