Mechanical Properties Of Thermal Barrier Coatings Research Articles

Investigations on the water-jet guided laser scribing of thermal barrier coated IC21 nickel-based superalloy

Ceramic thermal barrier coatings (TBCs) are widely recognized as state-of-the-art for ensuring the stability and reliability of turbine blades operating in extreme conditions. However, the significant disparities between the thermal and mechanical properties of TBCs, bonding layers (BCs), and nickel-based superalloy substrates pose considerable challenges for machining film cooling structures on turbine blades while minimizing coating delamination, heat-affected zones (HAZs), and other potential defects. The utilization of Water-Jet Guided Laser (WJGL) has gained significant attention as a promising approach for the machining of advanced materials, including ceramics and multi-layer composites. In this study, a theoretical model is proposed to describe the transient interaction between WJGL and TBC IC21 nickel-based superalloy. A numerical simulation using the deformation geometry method is employed to investigate the evolution of ablation morphology, which is further validated by experimental data. Specifically, the formation mechanism of the shoulder structure at the material interface is explained. Furthermore, orthogonal experiments are conducted to establish the fundamental influence rule and significance level of machining parameters on the microscopic groove morphology. Based on these findings, multi-row cutting experiments are performed to identify the optimized scanning trajectory for achieving the high-quality thorough cutting of the substrate with a thickness of 2.7 mm, while minimizing oxidation, residue deposition, and delamination. The outcomes of this study contribute to the knowledge of WJGL machining, and could potentially improve the efficiency and accuracy of advanced material processing techniques.

Study on thermal resistance performance of 8YSZ thermal barrier coatings

The application of ceramic thermal barrier coatings (TBCs) can significantly increase gas turbine performance. The microstructure of TBCs fabricated by APS and EB-PVD is remarkably different. The thermal and mechanical properties of TBCs with the same material are determined by its microstructures. In order to establish structure-property relationships of TBCs with complex inhomogeneous geometry, in this work, various 3D-microstructures of TBCs were reconstructed using the geometric reconstruction software developed by our team. A three-dimensional model based on Lattice Bolzmann method (LBM) was developed to investigate the heat transfer behaviors in TBCs. The effect of microstructure parameters such as porosity, pore size and pore shape on the effective thermal conductivity of TBCs was studied in detail. The relationship between microstructures and effective thermal conductivity of TBCs was obtained. The calculated values of the effective thermal conductivity of 3D-TBCs agree well with the experimental values, and all relative errors are less than 4%. It can be found that the layered coatings should have larger size pores, and the columnar coatings should have smaller size pores. This can make the internal temperature distribution of TBCs more uniform. The effect of pores size on the thermal conductivity of two types of TBCs is different, but their thermal conductivity increase with the increase of porosity. The effective thermal conductivity of the columnar TBCs with the same porosity decreases with the decrease of pores size, but that of the layered TBCs increases with the decrease of pores size. The pores shape has a great influence on the effective thermal conductivity of the coating, especially for high porosity columnar coating. The effective thermal conductivity of the columnar coatings logarithmically increases with the length of the elongated pores, and it is increased by 21.6% when the porosity is 20%. However, the effective thermal conductivity of the layered structure coatings logarithmically decreases with the length of the elongated pores. The results will provide us a theoretical guide to design TBCs with a high thermal insulation property.

Quantitative assessment of the surface crack density in thermal barrier coatings

In this paper, a modified shear-lag model is developed to calculate the surface crack density in thermal barrier coatings (TBCs). The mechanical properties of TBCs are also measured to quantitatively assess their surface crack density. Acoustic emission (AE) and digital image correlation methods are applied to monitor the surface cracking in TBCs under tensile loading. The results show that the calculated surface crack density from the modified model is in agreement with that obtained from experiments. The surface cracking process of TBCs can be discriminated by their AE characteristics and strain evolution. Based on the correlation of energy released from cracking and its corresponding AE signals, a linear relationship is built up between the surface crack density and AE parameters, with the slope being dependent on the mechanical properties of TBCs.

THERMAL AND MECHANICAL PROPERTIES OF PARTIALLY STABILIZED ZIRCONIA MANUFACTURED BY HYBRID PLASMA SPRAY PROCESS

Thermal barrier coatings (TBCs) constituted by Yttria Partially Stabilized Zirconia (i.e., Y-PSZ, ZrO2 + 7wt% Y2O3) and a metallic bond layer (i.e., MCrAlY where M represents a combination of Ni and Co) are extensively used to improve the performance of hot-section components of gas turbines. Air plasma spray and in situ laser irradiation by diode laser processes are combined to modify thermal and mechanical properties of TBCs. Two types of experiment were conducted to estimate the coating elastic response: Berkovich nano-indentation to evaluate the Young's modulus of the bulk material, and Knoop micro-indentation to evaluate the effective Young's modulus of the coating and its cohesion.