Measurements of the interfacial fracture energy of thermal barrier coatings (original) (raw)
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The primary intention of this work is to investigate the thermo-mechanical buckling delamination failure characteristic of air plasma sprayed thermal barrier coatings (TBCs) under compression tests at high temperature. The TBCs samples with a pre-delamination were firstly designed and they had been successfully prepared by air plasma sprayed technique. The main novelty of this paper is that the first work to validate and obtain three kinds of the interface failure forms in TBCs system during compression tests, i.e. buckling delamination, edge delamination and global buckling failure. The effects of the initial delamination length, temperature gradient and applied mechanical load on the delamination resistance of the TBCs system were discussed in detail. It is difficult to observe buckling delamination or edge delamination failure phenomena until the initial delamination length in TBCs reaches or exceeds 4 mm or more. For edge delamination failure, the interface fracture toughness (Γ iII), energy release rate (Gssedge) and stress intensity factor (KII) between the TBC/TGO interface were 35 J m− 2, 38.8 J m− 2 and 0.97 MPa pffiffiffiffim at high temperature gradient, respectively. Using scanning electron microscopy (SEM) and energy dispersive X-ray (EDX), it was inferred that the delamination fracture located within the ceramic coating close to the TBC/TGO interface. The results agree well with other experimental and theoretical results
Coatings
Beneficial properties achieved by nanostructuring effects in materials have generated tremendous interests in applications in surface engineering, especially in thermal barrier coatings (TBC). Limitations in conventional TBC processing for gas turbines and aero-propulsion systems have been exposed during past decades when rapid progress was made in nano-structuring coating research and developments. The present work is a comprehensive review of the current state of progress in nanostructured TBC (Ntbc) in reference to its microstructure, damage progression, failure mechanisms and a wide range of properties. The review aims to address the comparative performance analysis between the nanostructured and conventional (microstructured) 6–8 wt.% yttrium stabilized zirconia (YSZ) TBC systems. Oxidation resistance and sintering behavior in two TBCs are considered as the central focus of discussion. A few schematics are used to represent major microstructural features and failure progression...
Progress update on failure mechanisms of advanced thermal barrier coatings: A review
Thermal barrier coatings (TBCs) have proved to be a key technology in thermal stability and their use to achieve surface temperature reduction of the underlying super alloys surpass all other achievements in the field of material technologies that have taken place in last three decades. The technological advances in TBCs also make them suitable for wider engineering and defense applications. The performance of these multi-layered and multi-material systems, tailored for high temperature applications is closely linked to their microstructure evolution. The article presents a comprehensive review of various degradation mechanisms to which the TBC system is subjected during service life viz. hot corrosion, CMAS attack, oxidation, erosion, foreign object damage, sintering and phase transformations. Strategies to mitigate the adverse impact of the degradation mechanisms and the recent advances toward reduction in the thermal conductivity of TBCs have also been discussed. The emphasis of this review is on the relationship between the properties and the microstructure of TBCs for better understanding of their life limiting mechanisms to assist developments in advanced and novel TBCs for engineering applications.
Corrosion Science, 2019
Using experimentally measured temperature-process-dependent model parameters, the failure analysis and life evaluation were conducted for electron beam-physical vapor deposition thermal barrier coatings (EB-PVD TBCs) with Pt-modified β-NiAl bond coats deposited on Ni-base single crystal superalloys. The failure analysis and life model were applied to two failure modes of A and B identified experimentally subjected to thermal cyclic process. The rumpling effect and the associated roughness of the constituent coating layers were shown to play a key role in evaluating the coating's failure and life. The experimentally determined temperature-dependent thickness of thermally grown oxide (TGO), interfacial roughness, elastic moduli of the constituent coatings and their coefficients of thermal expansion were incorporated into the life prediction model. The maximum average rumpling amplitude of the bond coat/TGO interface associated with bond coat rumpling was used in failure analysis and life evaluation for the failure mode A. The global wavelength related to the interface rumpling and its radius curvature were identified as essential parameters in life evaluation, and the predicted life results for failure mode A were verified by existing furnace cyclic test data. For the failure mode B, the crack growth rate along the TGO/top coat interface was calculated using the crack length dependent fracture toughness.
LASER SURFACE SEALING PROCESSING For.pdf
The main objective of this book is to investigate the effect of laser surface sealing processing of thermal barrier coatings produced by plasma spraying technique. The thermal barrier coatings produced by this technique suffer from many defects like porosity, voids, and high surface roughness. With these defects the performance of thermal barrier coating layers is degraded, therefore laser surface sealing processing must be introduced to enhance their properties and increase their resistance to the external effects. The previously published literatures are very little about the laser surface sealing processing of thermal barrier coatings using solid lasers. Detailed study has been carried out on the feasibility of using high power density laser beam in order to optimize the properties of plasma – sprayed thermal barrier coatings by decreasing the porosity and improving the surface finish, mechanical, thermal insulation properties, oxidation, hot corrosion and thermal shock resistance.
Principle and Practice to Achieve Improvements in TBC Thermal Cycle Lifetime
Thermal Spray 2021: Proceedings from the International Thermal Spray Conference
As a critical technology, thermal barrier coatings (TBC) have been used in both aero engines and industrial gas turbines for a few decades, however, the most commonly used MCrAlY bond coats which control air plasma sprayed (APS) TBC lifetime are still deposited by the powders developed in 1980s. This motivates a reconsideration of development of MCrAlY at a fundamental level to understand why the huge efforts in the past three decades has so little impact on industrial application of MCrAlY alloys. Detailed examination of crack trajectories of thermally cycled samples and statistic image analyses of fracture surface of APS TBCs confirmed that APS TBCs predominately fails in top coat. Cracks initiate and propagate along splat boundaries next to interface area. TBC lifetime can be increased by either increasing top coat fracture strength (strain tolerance) or reducing the tensile stress in top coat or both. By focusing on the reduction of tensile stress in top coats, three new bond co...