High Temperature Tribological Study of Cobalt-based Coatings Reinforced with Different Percentages of Alumina.

Contact surfaces, subjected to high pressure coupled with low-amplitude oscillation, are used to a great extent in aerospace engine components to reduce vibrations. Relative displacement of contact surfaces coupled with friction force dissipates energy and damps the vibrations. Fretting wear is harmful on interference-fit contacts because the loss of material reduces the normal load and hence, reduces their effectiveness in damping vibrations. Coating is an important means to control friction and wear of contact surfaces. To address this issue an experimental layout was designed, and fretting wear tests were performed at high temperature (1000 °C). A representative sphere-flat contact was investigated in laboratory environment. Two types of metal-ceramic coatings, made of the same metal but with a different alumina percentage, were tested. Results were reported in terms of volume loss against number of wear cycles. It was found that increasing the alumina percentage was detrimental because the volume loss increased dramatically with high number of wear cycles. It was shown that wear results were strongly related to material properties, such as modulus of elasticity, while no correlation was found with contact parameters, friction coefficient and contact stiffness.