Wear Behavior of Cobalt-Based Alloy Brush Bristles and Chromium Carbide Coating under High Line Speed

Due to the superior sealing performance of brush seal, the application of brush seal became an important way to reduce the leakage and power loss of turbomachinery, such as aircraft engines, steam turbines, ground and marine gas turbines. However, the wear between brush bristles and rotor weakens the sealing performance of brush seal and many researchers have paid attention to the wear behavior of brush seal. In this study, wear tests for brush seal were completed on an ultra-high line speed wear test rig, and the friction pair consisted of bristle pack made by the GH5605 and superalloy specimen sprayed with chromium carbide wear-resistant coating. Different sliding velocities and interferences were set during the tests and the maximum velocity reached 400 m/s. The wear morphologies and material compositions were investigated by using scanning electron microscope (SEM). It was found that some materials peeled off from the chromium carbide coatings and some brush materials were attached to the coatings after the tests. The main wear characteristics at the tips of brush bristles were furrows and smearing. In addition, there were adhesion and severe oxidation at the tips of bristles after the 400 m/s friction linear speed test. By analyzing wear morphologies and the material transfer behaviors, it was considered that the main wear mechanism of the brush bristle tips was two-body abrasive wear, and the peeling off of the wear-resistant coating aggravated the abrasive wear. In order to further study the material transfer mechanism, a comparative wear test between brush bristles and sandpaper was conducted. The attachment of brush material was also found on the sand particles of the sandpaper, which showed that material transfer may also occur in the abrasive wear. Therefore, it is speculated that the brush materials were separated from the bristles mainly by abrasive wear and adhered to the coated rotor surface after separation. The hardness measurement showed that the Vickers hardness HV_0.5 value of chromium carbide coating on the rotor surface was 804, and the Vickers hardness HV_0.5 value of the GH5605 sample was 490, the hardness difference of the rubbing surfaces also supported the conclusion of abrasive wear. In addition, wear depth was measured using a confocal microscope and the depth of wear scar on the coated specimen reached 0.3 mm after the 400 m/s wear test, which significantly exceeded the initial interference of 0.1 mm. The simulation results showed that there was a centrifugal growth of about 0.26 mm on the rotor radius under the linear speed of 400 m/s. Therefore, the interference between the bristle pack and the coated specimen was significantly increased by the centrifugal expansion under the ultra-high line speed, which aggravated the wear of the friction pair. Inspired by the above results, the peeling resistance of wear-resistant coating should be concerned and improved to reduce abrasive wear of brush seal, and the initial interference between the bristle pack and rotor should be chosen properly to avoid severe wear, especially the expansion deformation of the rotor should be fully considered under a high line speed.