Fabrication and evaluation of plasma sprayed nanostructured alumina-titania coatings with superior properties

Reconstituted nanostructured powders were plasma sprayed using various processing conditions to produce nanostructured alumina-titania coatings. Properties of the nanostructured coatings were related to processing conditions through a critical plasma spray parameter (CPSP) that in turn, can be related to the amount of unmelted powder incorporated into the final coating. Those coatings that retain a significant amount of unmelted powder show optimum microstructure and properties. Selected physical and mechanical properties were evaluated by X-ray diffraction (XRD), optical and electron microscopy. quantitative image analysis and mechanical testing. Constituent phases and the microstructure of the reconstituted particles and plasma sprayed coatings were examined with the aid of quantitative image analysis as a function of processing conditions. Mechanical properties including hardness, indentation crack growth resistance, adhesion strength, spallation resistance during bend- and cup-tests, abrasive wear resistance and sliding wear resistance were also evaluated. These properties were compared with a commercial plasma sprayed alumina-titania coating with similar composition. Superior properties were demonstrated for nanostructured alumina-titania coatings plasma sprayed at optimum processing conditions. (C) 2001 Elsevier Science B.V. All rights reserved.