CERAMICS INTERNATIONAL Available online at www.sciencedirect.com Ceramics International 38 (2012) 6705–6712 Comparison of thermal shock resistances of plasma-sprayed nanostructured and conventional yttria stabilized zirconia thermal barrier coatings Hossein Jamali n , Reza Mozafarinia, Reza Shoja Razavi, Raheleh Ahmadi-Pidani Malek-Ashtar University of Technology, Department of Materials Engineering, Shahinshahr, Isfahan, Iran Received 7 May 2012; received in revised form 20 May 2012; accepted 20 May 2012 Available online 25 May 2012 Abstract The main goal of the current study is evaluation and comparison of thermal shock behavior of plasma-sprayed nanostructured and conventional yttria stabilized zirconia (YSZ) thermal barrier coatings (TBCs). To this end, the nanostructured and conventional YSZ coatings were deposited by atmospheric plasma spraying (APS) on NiCoCrAlY-coated Inconel 738LC substrates. The thermal shock test was administered by quenching the samples in cold water of temperature 20–25 1C from 950 1C. In order to characterize elastic modulus of plasma-sprayed coatings, the Knoop indentation method was employed. Microstructural evaluation, elemental analysis, and phase analysis were performed using scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), and X-ray diffractometry (XRD) respectively. The results revealed that failures of both nanostructured and conventional TBCs were due to the spallation of ceramic top coat. Thermal stresses caused by mismatch of thermal expansion coefficients between the ceramic top coat and the underlying metallic components were recognized as the major factor of TBC failure. However, the nanostructured TBC, due to bimodal unique microstructure, presented an average thermal cycling lifetime that was approximately 1.5 times higher than that of the conventional TBC. & 2012 Elsevier Ltd and Techna Group S.r.l. All rights reserved. Keywords: Nanostructured thermal barrier coating; Yttria stabilized zirconia; Thermal shock; Atmospheric plasma spraying 1. Introduction Increased operating temperatures and hence, improved performance of gas turbines or diesel engines can be realized by using thermal barrier coatings (TBCs) [1–6]. A typical TBC system consists of a metallic bond coat and a ceramic top coat. The bond coat (PtAl or MCrAlY, M=Ni and Co) protects the substrates from oxidation and improves the adhesion of the ceramic top coat to the metallic substrate. The ceramic top coat has a significantly low thermal conductivity and reduces the temperature of the underlying superalloy in relation to the gas path temperature [7–11]. Yttria stabilized zirconia (YSZ) is the current industrial standard material of TBCs, owing to its low thermal conductivity, phase stability at relatively high temperatures, a relatively high coefficient of thermal expansion (CTE), and chemical inertness in combustion atmospheres as compared to other ceramics [12–15]. Nowadays, TBCs are usually produced by either atmo- spheric plasma spraying (APS) or electron beam-physical vapor deposition (EB-PVD) [16–18]. However, due to the comparatively cost-effective deposition conditions and high deposition efficiency, plasma spraying technology has enjoyed widespread acceptance up to now [3,19]. Due to a high demand for high-temperature operation of gas turbines, an advanced TBC is essential to improve the performance of gas turbines. Creation of nano-struc- tures is a promising approach to fabricate novel TBCs. In recent years, the nanostructured zirconia based TBCs deposited by atmospheric plasma spraying have been the focus of attention. It was reported that nanostructured thermal barrier coatings had high bonding strength [20], low thermal conductivity [20–24], and prolonged thermal www.elsevier.com/locate/ceramint 0272-8842/$36.00 & 2012 Elsevier Ltd and Techna Group S.r.l. All rights reserved. http://dx.doi.org/10.1016/j.ceramint.2012.05.060 n Corresponding author. Tel.: þ 98 312 5232090; fax: þ 98 312 5228530. E-mail address: h.jamali@mut-es.ac.ir (H. Jamali).