PEER REVIEWED Development and Optimization of Tailored Composite TBC Design Architectures for Improved Erosion Durability Michael P. Schmitt 1,2 • Jeremy M. Schreiber 2,3 • Amarendra K. Rai 4 • Timothy J. Eden 3 • Douglas E. Wolfe 1,2,3 Submitted: 5 January 2017 / in revised form: 27 March 2017 Ó ASM International 2017 Abstract Rare-earth pyrochlores, RE 2 Zr 2 O 7 , have been identified as potential thermal barrier coating (TBC) materials due to their attractive thermal properties and CMAS resistance. However, they possess a low fracture toughness which results in poor erosion durability/foreign object damage resistance. This research focuses on the development of tailored composite air plasma spray (APS) TBC design architectures utilizing a t 0 Low-k secondary toughening phase (ZrO 2 -2Y 2 O 3 -1Gd 2 O 3 -1Yb 2 O 3 ; mol.%) to enhance the erosion durability of a hyper-stoichiometric pyrochlore, NZO (ZrO 2 -25Nd 2 O 3 -5Y 2 O 3 -5Yb 2 O 3 ; mol.%). In this study, composite coatings have been deposited with 30, 50, and 70% (wt.%) t 0 Low-k toughening phase in a horizontally aligned lamellar morphology which enhances the toughening response of the coating. The coatings were characterized via SEM and XRD and were tested for ero- sion durability before and after isothermal heat treatment at 1100 °C. Analysis with mixing laws indicated improved erosion performance; however, a lack of long-term thermal stability was shown via isothermal heat treatments at 1316 °C. An impact stress analysis was performed using finite element analysis of a coating cross section, repre- senting the first microstructurally realistic study of mechanical properties of TBCs with the results correlating well with observed behavior. Keywords composite  design architecture  durability  erosion  pyrochlore  thermal barrier coatings (TBCs) Introduction There is a desire to develop new thermal barrier coatings (TBCs) capable of elevated temperature operation; how- ever, materials which exhibit the requisite thermal stability and low thermal conductivity do not possess the required durability. The most well-known candidate for replacement of the current benchmark TBC, 6-8 wt.% yttria-stabilized zirconia (7YSZ), is gadolinium zirconate (Gd 2 Zr 2 O 7 -GZO) (Ref 1). This material exhibits a low thermal conductivity of *1.5 W/m K in bulk (Ref 2), phase stability up to 1550 °C with melting at *2400 °C (Ref 3), and a resis- tance to CMAS degradation (Ref 4-7). Unfortunately, GZO also exhibits a low fracture toughness of 1 MPaHm (Ref 8) which results in very low durability. Additionally, this material reacts with the Al 2 O 3 thermally grown oxide (TGO) layer to form a gadolinium aluminate perovskite (Ref 3) and so must be protected by incorporating an initial layer of YSZ. A variety of concepts have been explored to improve the durability of GZO-based materials and coatings. By applying an initial layer of YSZ, the GZO-Al 2 O 3 reaction can be prevented and the thermal cyclic life can be improved due to the higher toughness YSZ material at the interface (Ref 9). Additionally, several authors have investigated modification of the pyrochlore zirconate & Douglas E. Wolfe dew125@psu.edu 1 Department of Materials Science and Engineering, Pennsylvania State University, University Park, PA 16802, USA 2 The Applied Research Laboratory, Pennsylvania State University, University Park, PA 16802, USA 3 Department of Engineering Science and Mechanics, Pennsylvania State University, University Park, PA 16802, USA 4 UES Inc., 4401 Dayton Xenia Road, Dayton, OH 45432, USA 123 J Therm Spray Tech DOI 10.1007/s11666-017-0561-6