This paper studies how the nano-mecha nical properties of thermal barrier coatings (TBCs) vary during thermal cy- cling, as a way to shed new light on their failure mechanisms. In particular, high-throughput nanoindentation re- vealed the evolution of hardness and elastic modulus distributions of plasma-sprayed yttria-stabilized zirconia (YSZ) top layers. The evolution of fracture toughness of the YSZ layers and the thermally grown oxide (TGO) formed onto the vacuum plasma-sprayed NiCoCrAlY bond coat were investigated by nanoindentation micro-pillar splitting. The TGO fracture toughness increases up to≈2.5–3.5 MPa√m at the early stages of thermal cycling, followed by a rapiddecrease to ≈2.0 MPa√m after a critical TGO thickness of ≈5μm isreached. Consequently, interface damage is initially limited to short cracks within the YSZ material. As TGO thickness exceeds the critical threshold, multiple cracks originate within the TGO and join through the YSZ to form long delamination cracks. Joining is favoured by a simultaneous loss in YSZ strength, testified by a decrease in the nanomechanical properties (hardness, elastic modulus) of both high- and low-porosity top coats. This is due to microstructural changes occurringbecause of the continuous interplay between sintering and thermal shock cracking in the YSZ layers. © 2019 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license ( http://creativecommons.org/licenses/by-nc-nd/4.0/).
Bolelli, G., Righi, M.G., Mughal, M.Z., Moscatelli, R., Ligabue, O., Antolotti, N., et al. (2019). Damage progression in thermal barrier coating systems during thermal cycling: A nano-mechanical assessment. MATERIALS & DESIGN, 166, 107615 [10.1016/j.matdes.2019.107615].
Damage progression in thermal barrier coating systems during thermal cycling: A nano-mechanical assessment
Mughal, Muhammad ZeeshanWriting – Original Draft Preparation
;Moscatelli, RiccardoWriting – Original Draft Preparation
;Sebastiani, MarcoWriting – Review & Editing
;Bemporad, EdoardoSupervision
2019-01-01
Abstract
This paper studies how the nano-mecha nical properties of thermal barrier coatings (TBCs) vary during thermal cy- cling, as a way to shed new light on their failure mechanisms. In particular, high-throughput nanoindentation re- vealed the evolution of hardness and elastic modulus distributions of plasma-sprayed yttria-stabilized zirconia (YSZ) top layers. The evolution of fracture toughness of the YSZ layers and the thermally grown oxide (TGO) formed onto the vacuum plasma-sprayed NiCoCrAlY bond coat were investigated by nanoindentation micro-pillar splitting. The TGO fracture toughness increases up to≈2.5–3.5 MPa√m at the early stages of thermal cycling, followed by a rapiddecrease to ≈2.0 MPa√m after a critical TGO thickness of ≈5μm isreached. Consequently, interface damage is initially limited to short cracks within the YSZ material. As TGO thickness exceeds the critical threshold, multiple cracks originate within the TGO and join through the YSZ to form long delamination cracks. Joining is favoured by a simultaneous loss in YSZ strength, testified by a decrease in the nanomechanical properties (hardness, elastic modulus) of both high- and low-porosity top coats. This is due to microstructural changes occurringbecause of the continuous interplay between sintering and thermal shock cracking in the YSZ layers. © 2019 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license ( http://creativecommons.org/licenses/by-nc-nd/4.0/).I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
