Scale effects in abrasive wear of composite sol-gel alumina coated light alloys

Chemically-bonded composite sol-gel (CB-CSG) coatings have been developed t hat incorporate calcined ceramic powder particles (filler) dispersed in a s ol-gel (SG) matrix (binder). As a result, they have significantly reduced d ensification strains compared to conventional SG coatings. The CB-CSG coati ngs, which are several orders of magnitude thicker than typical micron-thic k SG films, can be produced easily by spray depositing onto Al and Mg alloy s, followed by a short low temperature (300 degreesC) heat treatment. The abrasive wear performance was determined for Al2O3(binder)/Al2O3(filler ) Al2O3(binder)/Al2O3-SiC(fillers) and a hybrid Al2O3(binder)/Al2O3(filler) + Al-(40 mum particle filler) coatings on commercial Al and Mg alloys. In two-body abrasion tests, the coated alloys were abraded by bonded SiC abras ives of increasing coarseness with comparative experiments also being perfo rmed on the uncoated substrate alloys. Coating wear rates exhibited an orde r of magnitude increase when the scale of indentation increased above a cri tical depth, whereupon wear rates approached those of the substrate alloy. Similar observations were made in three-body microabrasion experiments usin g a ball-cratering technique to abrade the coatings with very fine and coar se alumina slurries. The modes and mechanisms of coating damage were charac terized by SEM and optical surface profilometry techniques. Normalized para meters for hardness, abrasive wear and indentation depth, were used in inte rpreting and comparing coating tribological performance. (C) 2001 Elsevier Science B.V. All rights reserved.