Contents lists available at ScienceDirect Ceramics International journal homepage: www.elsevier.com/locate/ceramint Effect of microstructure and mechanical properties on wear behavior of plasma-sprayed Cr 2 O 3 -YSZ-SiC coatings S.M. Hashemi a , N. Parvin a, ⁎ , Z. Valefi b a Department of Mining and Metallurgical Engineering, Amirkabir University of Technology, PO Box 15875-4413, Tehran, Iran b Materials Engineering Research Center, Malek Ashtar University of Technology, PO Box 15875-1774, Tehran, Iran ARTICLE INFO Keywords: Ball-on-disk wear Cr 2 O 3 -YSZ-SiC Plasma spray coating Ceramic matrix composite Multimodal/nano Mechanical properties ABSTRACT In this study, the microstructure and mechanical properties of the atmospheric plasma-sprayed Cr 2 O 3 (C), Cr 2 O 3 - 20YSZ (CZ), and Cr 2 O 3 -20YSZ-10SiC (CZS) coatings were evaluated and also compared with each other, so as to explain the coatings wear behavior. Microstructural evaluations included X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM) equipped with energy dispersive X-ray spectroscopy (EDX) and porosity measurements. Mechanical tests including bonding strength, fracture toughness, and micro-hardness tests were used to advance our understanding of the correlation between the coatings properties and their wear behavior. The sliding wear test was conducted using a ball-on-disk configuration against an alumina counterpart at room temperature. Addition of multimodal YSZ and subsequent SiC reinforcements to the Cr 2 O 3 matrix resulted in an increase in the fracture toughness and Vickers micro-hardness, respectively. It was found that the composite coatings had comparable coefficients of friction with pure Cr 2 O 3 coatings. When compared with the C coating, the CZ and CZS composite coatings with higher fracture toughness exhibited superior wear resistance. Observation of the wear tracks of the coatings indicated that the lower wear rates of the CZ and CZS coatings were due to the higher plastic deformation of the detached materials. In fact, improvement in the wear resistance of the composite coatings was attributed to a phase transformation toughening mechanism associated with tetragonal zirconia which created more ductile tribofilms during the wear test participated in filling the pores of coatings. 1. Introduction Ceramics are among the best candidates as corrosion and wear re- sistant materials due to their high hardness, strength, chemical stabi- lity, and resistance against oxidation at elevated temperatures. High production costs and low fracture toughness of bulk ceramics are the most challenging issues in development of these materials. Therefore, producing ceramic coatings on metallic substrates has already been extended. Owing to generating high temperatures and high deposition rates, the Atmospheric Plasma Spray (APS) process has been considered as a proper alternative for producing high-quality ceramic coatings [1–4]. Numerous efforts have been devoted to modify the microstructure and enhance the mechanical properties and wear/corrosion perfor- mance of Cr 2 O 3 coatings due to their inherent hardness and chemical stability in most environments [5,6]. The main drawback of nanostructured oxide ceramics in tribological applications is their low fracture toughness at ambient temperature and under compressive stress [7]. In this regard, many efforts have been formerly done to use the initially nano-agglomerated powders for producing nanostructured chromium oxide coating to improve its me- chanical properties including toughness and wear performance [8–11]. According to the previous studies, the wear resistance of ceramics increases with hardness, toughness, and toughness-to-hardness ratio; so that the toughness compared to the hardness has a greater effect on increasing the wear resistance [12,13]. Moreover, some reports in- dicated that wear resistance of the coatings can be directly proportional to their “hardness+toughness” values [14]. Recent studies on plasma sprayed brittle coatings indicated that decreasing hardness-to-tough- ness ratio, commonly known as brittleness index, enhance the coating wear resistance [15]. Previous researchers added various reinforcements including Al 2 O 3 [16] and TiO 2 [17] particles to the Cr 2 O 3 matrix so as to produce composites with denser microstructures, higher hardness along with higher fracture toughness and therefore enhanced wear behavior [9,18]. Zirconia (zirconium oxide, ZrO 2 ), formerly added to many https://doi.org/10.1016/j.ceramint.2018.11.226 Received 13 November 2018; Received in revised form 27 November 2018; Accepted 28 November 2018 ⁎ Corresponding author. E-mail address: nparvin@aut.ac.ir (N. Parvin). Ceramics International 45 (2019) 5284–5296 Available online 29 November 2018 0272-8842/ © 2018 Elsevier Ltd and Techna Group S.r.l. All rights reserved. T