Materials Science and Engineering A366 (2004) 175–182 Mechanical and elastic properties of modified thick thermal barrier coatings S. Ahmaniemi ∗ , P. Vuoristo, T. Mäntylä Institute of Materials Science, Tampere University of Technology, P.O. Box 589, 33101 Tampere, Finland Received 16 May 2003; received in revised form 9 September 2003 Abstract Mechanical and elastic properties of the phosphate sealed and laser-glazed 8Y 2 O 3 –ZrO 2 and 22MgO–ZrO 2 thick thermal barrier coatings (TBCs) were studied. Mechanical properties were determined by erosion and abrasion experiments and the elastic properties were evaluated by four-point bending (4PB) tests. Phosphate based sealing treatments improved significantly the erosion and abrasion resistance of the coatings and also increased the coating microhardness, bending strength and stiffness. The improvements of mechanical properties in the phosphate sealed coatings were caused by the lamellae bonding, due to the sealant. The effect of laser-glazing on the mechanical and elastic properties varied between the studied materials. The melted surface layer of the laser-glazed 8Y 2 O 3 –ZrO 2 coating was very hard and dense and had excellent resistance against mechanical wear. At the same time the vertical segmentation crack network in the coating structure lowered the bending strength and stiffness. In laser-glazed 22MgO–ZrO 2 coating the melted layer was also very hard, but most of the segmentation cracks were curved and branched and under mechanical loads they had tendency to coalesce. For this reason the laser-glazed 22MgO–ZrO 2 coating had poor mechanical properties. © 2003 Elsevier B.V. All rights reserved. Keywords: Thermal barrier coating; Elastic modulus; Erosion resistance; Sealing; Laser-glazing 1. Introduction The main function of thermal barrier coatings (TBCs) is the protection of metallic component surfaces at high temperatures (900–1250 ◦ C) in gas turbines. With TBCs it is possible to lower the surface temperature of metal by 100–300 ◦ C depending on the coating thickness and ther- mal properties. This temperature drop is significant if con- sidering the mechanical strength or oxidation rate of the metallic superalloy component at high temperatures. TBCs should keep their protective properties over the whole main- tenance interval and resist, in addition to high temperatures, several loads such as particle erosion, hot corrosion and thermo-mechanical fatigue. The microstructure of plasma sprayed TBC is normally designed for optimal strain toler- ance and for as low thermal conductivity as possible with other properties compromised. Even if the pores and cracks ∗ Corresponding author. Present address: Metso Paper Inc., Global Service Operations, P.O. Box 587, 40101 Jyväskylä, Finland. Tel.: +358-20-482-6837; fax: +358-20-482-5993. E-mail address: samppa.ahmaniemi@metso.com (S. Ahmaniemi). in the coating structure are beneficial for the low thermal conductivity and high strain tolerance, they deteriorate ero- sion and hot corrosion resistance. Mechanical and elastic properties of thermal barrier coat- ings has been studied extensively in near past. A lot of effort is put on understanding the relationships of elastic modulus (E) and strain tolerance of TBCs. Elastic modulus studies have been used, for example, in developing new TBC struc- tures [1–3], in spray parameter optimisation [4–6] and in es- timating the increased stiffness of high temperature exposed TBCs [6–10]. Erosion studies for TBCs has been carried out in order to understand the erosion wear mechanism in plasma sprayed TBCs [11,12]. Microhardness (HV 0.3 ) mea- surement has been used in many cases as a basic quality control technique and in many cases it can give rough es- timation of the wear resistance and elastic modulus of the coating. The elastic modulus can be estimated for example from the Knoop indentation test by measuring the relaxation of the minor diagonal [13]. There have been several approaches to determine elas- tic modulus of plasma sprayed thermal barrier coatings. Most of them have been based on bending techniques or on 0921-5093/$ – see front matter © 2003 Elsevier B.V. All rights reserved. doi:10.1016/j.msea.2003.09.061