Abstract An approach to make air plasma sprayed ( APS ) thermal barrier coatings ( TBC s) with the enhanced strain and damage tolerance was reported, using a novel hollow spheres produced by electro‐spraying ( ESP ) technique. Compared with agglomerated & sintered (A&S) and hollow spherical ( HOSP ) yttria‐stabilized zirconia ( YSZ ) powders, the ESP powder showed a unique network microstructure and the TBC s exhibited a 2‐3 times longer thermal cycling lifetime. The splat morphology and the top coats microstructure were investigated. Some semi‐melted ESP particles were observed in the as‐sprayed top coat. The indentation coupled with the Raman mapping technique was employed to evaluate the strain and damage tolerance of the TBC s. The coatings deposited by the ESP powder show a lower in‐plane stiffness determined by three‐point bending tests. It is proposed that the superior performance is attributed to the lower amount of the short microcracks (0.5‐4 μm) with low angle (<45°) and the semi‐melted ESP particles remained in the YSZ top coat.
Mechanically strong but highly porous structured ceramics are desirable for a range of applications like water purification and energy conversion. Yttria-stabilized zirconia membranes, possessing a hierarchical arrangement of voids from hundreds of micrometers to nanometers, were prepared by a non-solvent induced phase separation technique. Effects of the multi-scale voids on stress distributions and related mechanical properties were experimentally studied and simulated. The gradually varying diameter of the finger-like voids led to a loading direction dependent fracture strength. Meanwhile, no strength degradation was found when penetration depths of these macro-voids increased from 70% to 80% of the membrane thickness, because the void tails caused no interference to the bending stress. The sponge-like structure surrounding the finger-like voids absorbed strains, and the resultant stress concentration determined the fracture strength.
Abstract Weak interface bonding is a critical factor that compromises the long‐term durability of the thermal barrier coatings. To mitigate this, we introduce an innovative interface‐strengthening approach by integrating four types of 3D patterns at the top coat/bond coat interface using the laser cladding technique. Tensile tests demonstrate a significant enhancement in interfacial bonding strength, increasing by over 139.2% from 21.6 ± 1.7 MPa for conventional thermal barrier coatings without patterns to 51.67 MPa for the patterned coatings. Moreover, the thermal cycling lifetime has been extended by 41%, from 1026 ± 25 cycles for the conventional coating to 1936 ± 164 cycles for the patterned coating. This enhancement in interfacial toughness and thermal cycling lifetime is primarily because of the blocking and deflection effects of 3D patterns on interfacial crack propagation. Besides, the geometric parameters of the patterns play a crucial role in determining the failure behavior of the thermal barrier coatings. This strategy presents a practical solution for the development of durable thermal barrier coatings and provides the valuable insights for the optimization of other heterogeneous interfaces.
Developing high thrust-weight ratio of aero-engine poses great challenges to current top coat of thermal barrier coatings (TBCs) and environmental barrier coatings (EBCs) in service. Medium/high-entropy ceramics are highly promising candidate materials for advanced T/EBCs owing to their low thermal conductivity, high melting point, high-temperature stability and CMAS resistance. Most of feedstock powders used for medium/high-entropy T/EBCs are prepared by using traditional spray drying, which cannot give full play to the advantages of the multi-component ceramics. The density, sphericity, inner structure and flowability of feedstock powders affect its melting state during thermal spraying process, which strongly determine microstructure and properties of deposited coatings. Therefore, the deposited coatings show phase segregation, amorphous phases, and microstructure defects, owing to unpredictable variation of feedstock powders with random morphology and structure. Here, the structure and properties of feedstock powders prepared by the by the state-of-the-art granulation technologies, and their influences on the deposited coatings were systematically investigated, which can provide guidance for configuration optimization of feedstock powders and the manufacturing accuracy of the deposited coating. This review is aim to bridge the gap between cutting-edge ceramics and advanced engineering technologies, thus providing concrete background knowledge and crucial guidelines for designing and developing T/EBCs.
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