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È presentato l’effetto che particelle riparatrici hanno sulle proprietà termofisiche di rivestimenti con funzione di barriera termica.
Yttria-stabilised zirconia (YSZ) is a good thermal insulator that provides thermal protection of workingcomponents in high temperature applications, such as gas turbines and hot sections of aircraft engine turbineblades. However, the thermal mismatch in the thermal barrier coating (TBC), leads to generation of cracks,delamination of the coating and, ultimately, to failure of the TBC system.
To prolong the lifetime of TBCs a new method of crack healing has been developed, which relies on embedding molybdenum disilicide (MoSi2) healing particles within the TBC matrix. Upon high temperature oxidation, MoSi2 decomposes and amorphous silica (SiO2) is formed as a reaction product. SiO2 fills and seals the cracks created during thermal cycling thus providing a self-repairing mechanism to prolong the lifetime of the TBC.
MoSi2 has relatively high thermal conductivity (30 W/mK at 1400 oC). Therefore, embedding a good thermal conductor into a thermally insulating matrix (thermal conductivity of dense YSZ is about 2.3 W/mK at 1000 oC) could have an unfavourable impact on thermal conductivity of the TBCs.In this work the thermal conductivity of YSZ embedded with various volumetric percentages of MoSi2 healing particles prepared by spark plasma sintering (SPS) was investigated using the laser flash method. Measurements were performed on free- standing composite material at the temperature range 100-1000 oC.
The measurements were compared with results from microstructure-based finite element (FE) models and analytic models (asymmetric Bruggeman model) to address how the addition of MoSi2 particles has affected the apparent thermal conductivity. Microstructural analysis was carried out by SEM combined with image analysis to determine the size, distribution and area fraction of healing particles. X-ray diffraction (XRD) analysis was carried out to evaluate the chemical structure and composition of the composite materials.
The results presented here show an increase in the thermal conductivity of the composite material with the ratio of MoSi 2 particles.
31 Dicembre 2016
Self-Healing Thermal Barrier Coatings (SAMBA)