Tribological Performance of Al2O3/YAG Amorphous Ceramic Coating Fabricated by Atmospheric Plasma Spraying

Abstract

In this study, the spray-dried Al2O3/Y2O3 composite powder was prepared using commercially available nanosized Al2O3 and Y2O3 feedstock. The mass ratio of Al2O3 to Y2O3 was 2:1. Atmospheric plasma spraying possesses high thermal enthalpy, large temperature gradient and rapid cooling rate. The microstructure and wear resistant performance of plasma-sprayed Al2O3.Y3Al5O12 (YAG) coating were investigated. As-sprayed Al2O3.YAG coating was chiefly composed of amorphous phase, which may reveal superplastic feature in supercooled liquid region (from 503.0°C to 906.5°C). The as-sprayed Al2O3.YAG coating exhibits fine plasticity and toughness. Friction and wear tests of the coatings were executed on a MMU-5GL tribological tester using a ring-on-disk arrangement. The coatings were deposited on end flat surfaces of the wear rings. The graphite disks were prepared. The wear tests were conducted at following conditions: relatively high load of 2000N; a rotational speed of 500rpm (equivalent to a sliding velocity of 0.68m/s). Friction coefficients could be obtained real-timely. The thermocouple was applied to measure the worn surface temperatures. The Al2O3/YAG amorphous coating/graphite pair possessed lower friction coefficient and worn surface temperature, compared with Al2O3 coating/graphite and Al2O3-Cr2O3 coating/graphite pairs. After wear tests, many network cracks visible to naked eye appeared the surfaces of Al2O3 and Al2O3-Cr2O3 coatings. However, no cracks were observed on the worn surface of the Al2O3/YAG amorphous coating. Therefore, plasma-sprayed Al2O3.YAG coating possesses excellent wear resistance under severe conditions with high pv values (p: contact pressure; v: friction velocity).