Wear 250 (2001) 569–575 Correlations between microstructural parameters, micromechanical properties and wear resistance of plasma sprayed ceramic coatings L.C. Erickson a,∗ , H.M. Hawthorne b , T. Troczynski a a Metals and Materials Engineering, University of British Columbia, Vancouver, BC, Canada V6T Z4 b National Research Council Canada, Vancouver, BC, Canada V6T W5 Abstract The micromechanical integrity of a ceramic plasma sprayed (PS) coating is determined by the size and distribution of the defects found in the coating, such as porosity, the inter-lamellar microcrack density, the intra-lamellar 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 found in PS ceramic coatings. The tests included depth sensing indentation, micro and macrohardness testing, and controlled scratch testing. Abrasive and erosive wear tests were performed on the same set of coatings, including plasma sprayed alumina and chromia, as well as sintered alumina as a reference material. The best correlations were found between the material hardness (H), the level of porosity (P) and the abrasive wear volume (W). Knoop hardness 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 describes the correlation of wear volume with the elastic modulus of the coating. Fracture toughness could only be correlated with wear volume when combined with hardness in a function of the type W = k/H 0.5 K 0.5 c . The incorporation into this function of a “microstructural factor” M = P n improves the correlation. © 2001 Elsevier Science B.V. All rights reserved. Keywords: Wear; Microstructure; Indentation; Plasma spray coatings 1. Introduction The micromechanical integrity of a plasma sprayed (PS) ceramic coating is determined by the size and distribution of the microstructural features, in particular the defects, found in the coating. These can be divided into two size ranges, those at the inter- and intra-lamellar scales. The microstruc- tural features that affect the micromechanical integrity in- clude the overall porosity, the inter-lamellar (horizontal) microcrack density, the intra-lamellar (vertical) microcrack density as well as the lamellar, or splat, dimensions [1]. In order to advance understanding of the relationships between the different microstructural parameters found in PS ceramic coatings, several micromechanical and wear test methods involving damage by hard particles were used. These included indentation techniques, including depth sensing indentation (DSI), micro and macrohardness testing, and controlled scratch testing (representing ideal single point abrasion) as well as two-body abrasion and erosion by hard particles. This work presents some of the ∗ Corresponding author. Present address: Ballard Power Systems, Burn- aby, BC, Canada V5J 5J9. Tel.: +1-604-412-3175; fax: +1-604-412-4700. E-mail address: lyneri@ballard.com (L.C. Erickson). experimental methods used, along with the results of these tests, for evaluating the responses of a variety of coating mi- crostructures compared to those of a bulk sintered alumina (SA). More complete evaluations of the microstructural integrity of PS ceramic coatings using these methods can be found elsewhere [1–4]. This paper reports, and seeks to rationalize, the correlations found between the wear results of various PS coatings and their microstructural parameters and micromechanical properties. 2. Experimental details 2.1. Materials Alumina, chromia and alumina–titania PS coatings, rang- ing in thickness from 200 to 370 m were deposited on grit blasted mild carbon steel. All coatings, with one excep- tion were sprayed using a commercial axial injection plasma spray system. 1 For the alumina coatings, four different pow- ders with nominal particle sizes of 5, 10, 18 and 30 m were 1 Northwest Mettech Axial III TM plasma spray torch system. 0043-1648/01/$ – see front matter © 2001 Elsevier Science B.V. All rights reserved. PII:S0043-1648(01)00608-1