Correlations between microstructural parameters, micromechanical properties and wear resistance of plasma sprayed ceramic coatings

The micromechanical integrity of a ceramic plasma sprayed (PS) coating is d etermined by the size and distribution of the defects found in the coating, such as porosity, the inter-lamellar microcrack density, the intra-lamella r microcrack density as well as the lamellar, or splat, dimensions. In this work, several micromechanical tests were used to advance our understanding of the relationships between the different microstructural parameters foun d in PS ceramic coatings. The tests included depth sensing indentation, mic ro and macrohardness testing, and controlled scratch testing. Abrasive and erosive wear tests were performed on the same set of coatings, including pl asma sprayed alumina and chromia, as well as sintered alumina as a referenc e material. The best correlations were found between the material hardness (H), the level of porosity (P) and the abrasive wear volume (W). Knoop hard ness measurements provided the best correlation with wear data, followed by scratch hardness and Vickers hardness. An exponential function of the type W = k/H-n was found, where k and n are constants. A similar function descr ibes the correlation of wear volume with the elastic modulus of the coating . Fracture toughness could only be correlated with wear volume when combine d with hardness in a function of the type W = k/(HKc0.5)-K-0.5 C. The incor poration into this function of a "microstructural factor" M = P-n improves the correlation. (C) 2001 Elsevier Science B.V. All rights reserved.