T800 coatings are commonly applied on damping surfaces of turbine blades to mitigate wear. If severe wear occurs, the effectiveness of the damping effect could decrease. Therefore, vibrations increase and the life of blade could be endanger. These mating surfaces are usually stressed with reciprocating relative displacement in dry condition with low amplitude. In other word, the damping surfaces are usually fretted. This study investigates the wear mechanism at the contact damping interfaces coated by Tribaloy® T-800.

The methodology was based on an experimental tests campaign performed with point contact test rig. A peculiarity of this rig is that relative displacement measurements are not affected by the test rig compliance affects. This is not common in fretting test rig. The reason is that there are test rig components with a compliance between the contact surfaces and displacements measurement points. In other words, there is no difference between the amplitude imposed in the measurement point of relative displacement and effective amplitude of the contact surfaces. Nine sets of experimental parameters was analyzed at three temperatures (room temperature, 600 and 800°C), two normal loads (12 and 32 N), three strokes (30, 60, 150 micrometers) and test durations of 3, 5, 10, 15 M-cycles. Friction coefficient was computed using the hysteresis loops measured during the fretting tests. The worn surfaces were measured by optical instrument based on focus variation. Wear volumes were accurately computed with a procedure that takes into account the roughness of contact surfaces. The wear groove was observed by scanning electron microscopy (SEM) at end of the test.

At room temperature the friction coefficient was substantially independent from the normal load. The wear rates at the room temperature ware higher than at high temperature (600, 800 °C). The scanning electron microscopy (SEM) observation of the worn surfaces reveals a morphology of the wear scar that was completely covered with brittle cracks in each sample. The damage mechanism change from brittle (at room temperature) to ductile (at high temperature). In contrast with relation between wear volume and number of wear cycles, the relation between wear volume and energy dissipated was independent from normal load.


Fretting Wear of T800 Coating in Aero-Engine Applications

Division / Sponsor:
International Gas Turbine Institute (IGTI)

Paper Proceedings: https://asmedigitalcollection.asme.org/GT/GT2020/volume/84058

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