Sliding and abrasive wear of composite sol-gel alumina coated Al alloys

Alumina coatings, 60-mum thick (HV10g 647 +/- 144 kg mm(-2)), were deposite d using a novel sol-gel technique on 6061 Al. The samples were subjected to dry sliding wear tests against hard bearing steel balls (SAE 52100 steel) and softer mild steel pins (AISI 1018 steel) at different sliding speeds an d contact loads. Wear at low contact loads and sliding speeds was character ized by steel oxide (Fe2O3) transfer to the coating. Coating rupture arose at a critical transition boundary of sliding contact loads and speeds which were approximately twice as high for mild steel as against the harder bear ing steel. The coated alloy was also subjected to abrasive wear against SiC abrasives of increasing coarseness. Coating wear rates approached those of the substrate alloy as the indentation depth increased. A similar reductio n in coating hardness was observed for Vickers diamond pyramid indentations at greater depths. When abrasion indentation depths were greater than simi lar to 20% of the coating thickness, a rapid degradation in wear resistance arose and the same effect was seen for scratch test indentation depths. Th e use of normalizing parameters for sliding wear, hardness, abrasive wear a nd indentation depth were found to be useful in interpreting coating wear p erformance. (C) 2000 Elsevier Science B.V. All rights reserved.