Exceptionally high fracture toughness of carbon nanotube reinforced plasma sprayed lanthanum zirconate coatings

Lanthanum zirconate (La2Zr2O7), an emerging candidate for TBC system, faces stringent concern owing to poor fracture toughness. We report an exceptionally high fracture toughness (5.3 +/- 0.4 MPa m(0.5)) value for a La2Zr2O7 coating prepared by atmospheric plasma spray technique reinforced by carbon nanotubes (2 wt %); the enhancement in fracture toughness was noted to be more than 300% compared to all previous works. Several factors, viz. increased density, uniform distribution of CNTs in La2Zr2O7 matrix, stabilization of pyrochlore La2Zr2O7 phase and various associated toughening mechanism offered by CNTs (e.g., CNT pull out, CNT bridging and crack arresting etc.) was attributed for this surprising enhancement. In addition, splat sandwiching and nanomechanical interlocking between CNT and La2Zr2O7 was found to be unique toughening mechanism. Apart from it, thermal shock resistance of LZC-SD coating performed at 1300 degrees C, showed the 145 numbers of cycle before the partial delamination of the coating. While, it was only 87 numbers of cycle for LZ-SD coating. The density, hardness, elastic modulus values also depicted a suitable increase. The introduction of CNTs in the La2Zr2O7 matrix did not alter/ affect any of the physical properties (phase purity, compositional integrity etc.) of the pristine La2Zr2O7 system. (C) 2018 Elsevier B.V. All rights reserved.