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Proparation and Properties of Zirconia Based Thermal Barrier Coatings Codoped with Two Rare Earth Oxides

Author: LiuHuaiFei
Tutor: HuangBoYun；LiSongLin；LiQiLian
School: Central South University
Course: Materials Science
Keywords: Thermal Barrier Coating Plasma spraying Sc2O3-Y2O3-ZrO2 Phase stability Thermal conductivity
CLC: TG174.4
Type: PhD thesis
Year: 2011
Downloads: 349
Quote: 0
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Abstract

Traditional 6 to 8 wt.% Y203-of Zr02 (YSZ) thermal barrier coating phase transition and sintering (gt; 1200 ℃), limiting its use in higher temperature. Therefore, to meet the performance requirements of high thrust-to-weight ratio of aero-engine thermal barrier coating material, developed with relative stability above 1200 ℃ sintering resistance and low thermal conductivity of the new thermal barrier coating material has an extremely important significance. By chemical coprecipitation - the calcination prepared (La2O3, Y2O3)-ZrO2 (LaYSZ), (Yb2O3, Y2O3)-ZrO2 (YbYSZ), (Sc2O3, Y2O3)-ZrO2 (ScYSZ) three systems of rare earth oxide composite stable oxidation zirconium ceramic material, and its high-temperature phase stability and thermophysical properties of the study, analysis and discussion of the possibility of three systems as a high-temperature thermal barrier coating material applied; reveals binary rare earth oxide stabilized zirconia crystals school characteristics, stabilizer content on the phase stability of the law as well as multi-system phase-change mechanism; plasma spraying (APS) was prepared ScYSZ system thermal barrier coatings, and analysis of the relative stability of the coating, the phase transformation kinetics characteristics as well as dopant atoms characteristics (valence, atomic weight, ionic radius) mechanism of the thermal conductivity in the organizational structure of high-temperature oxidation, corrosion, thermal shock environment evolution and failure mechanisms and coating research for new thermal barrier coating the development and application of the layer of material to provide a theoretical basis. More systematic study of the relative stability of LaYSZ, YbYSZ, ScYSZ system of ceramic powder and thermophysical properties. Compared with YSZ ceramic material, 1.OLaYSZ 1400 ℃ has good phase stability, and La2O3 join ceramics preform can effectively inhibit sintering. 3.5YbYSZ, (5.3 to 7.1) ScYSZ at 1400 ° C, 1500 ° C has good phase stability, anti-sintering properties and lower thermal conductivity, wherein ScYSZ system nonequilibrium tetragonal phase (t ') of the stability region The larger and Sc2O3 added to inhibit sintering and reduce the effect of thermal conductivity is most significant. Accordingly, the three systems, ScYSZ system for TBCs material best choice. Crystallography three polyhydric system ceramic powder, characterized in that the stabilizer content and the heat treatment temperature is decided to t 'phase stability of the important factors. Establish a quantitative relationship between the content of the multi-system Quartet degree (c / (?) A) with the stabilizer, the three systems Quartet with stabilizer content increases and decreases linearly. The high stabilizer region easy to t 'phase and the cubic phase (c) stable, while the low-stabilizer area formed easily balanced tetragonal (t) and the monoclinic phase (m). The powder phase transformation kinetics characteristics of ScYSZ system that t 'opposite of t relative and c phase transition is closely related to the temperature and time of diffusion type phase change its phase-change rate is determined by the rate of diffusion of the dopant atoms. Stabilizer by diffusion of the doping atoms of the uneven distribution leads to t 'to reduce the direct cause of phase stability in the high-temperature heat treatment process. Avrami equation established ScYSZ ceramic powder and the coating phase variable in relation to time. The higher the heat treatment temperature, the phase change of the coating to the incubation period of the smaller; For the same component materials, in the same heat treatment conditions, the phase of the coating becomes significantly greater than the incubation period of the phase change of the powder incubation period, indicating that the microstructure of the coating structure, stress, defects, lattice distortion has an important effect on the phase transition. 6.4Sc0.5YSZ, and 7.1Sc0.53YSZ coatings respectively phase transition did not occur in 1400 ℃ heat treatment 550h and 1500 ° C heat treatment 300h. 6.4Sc0.5YSZ, and 7.1Sc0.53YSZ has excellent high temperature phase stability. According to the phonon thermal conductivity mechanisms and defect chemical principles, doped atomic characteristics and doped amount of thermal conductivity mechanism. Cheap cation-doped stabilized zirconia system, oxygen vacancies and replacement atomic defects may enhance the phonon scattering, to reduce the phonon mean free path, thereby reducing the thermal conductivity. The larger the atomic weight of Sc and Zr and ionic radius difference ScYSZ system to reduce the thermal conductivity contribution; increase the content of the increased number of oxygen vacancies can also be effective to reduce the thermal conductivity of the of ScYSZ system Sc2O3. Coating phase composition, grain boundaries, cracks and pores have an important impact on thermal conductivity. Compared to the 8YSZ coatings, ScYSZ coating the Takaso stability and resistance to sintering is an important reason for having a low thermal conductivity. The failure mechanism of ScYSZ (TC) / NiCoCrAlTaY (BC) double-layer structure of thermal barrier coatings in high temperature oxidation, corrosion and thermal cycling load conditions. The high-temperature oxidation test results show that the oxidation of the BC layer result in a TC / BC interface to form a thermally grown oxide layer (TGO) on TGO layer growth stress and TGO TC, BC thermal expansion coefficient does not match the thermal stress generated to cause the coating oxidation failure the main reason. TGO layer growth stress primarily by the large volume of oxide (Cr, Al) 2O3 (Co, Ni) (Cr, Al) 2O4 of NiO (CSN), the formation and growth generated; continuous TGO layer interface when the TC / BC generation time, TGO the onset of action of the thermal stress generated by thermal mismatch with TC, BC. TC / TGO / BC coating and interface thermal stress distribution simulation results show that the thermal mismatch cause TGO layer have a greater radial compressive stress, which destruction caused by compression of the coating using ANSYS software. TC / TGO interface compressive stress maximum value and the white center of the sample to edge gradually reduce. With the increase of the oxidation time, the coating failure, ultimately manner the TC layer center muster and peeling peeling surface for the TC / TGO interface. Coating high-temperature corrosion and thermal shock test results showed that, compared with traditional YSZ coating, ScYSZ coating having better anti-V and S corrosion resistance and thermal shock resistance, but in the etchant effect, the adhesive layer of oxidation The rate is greatly improved;, TC / BC interface a larger thickness TGO layer generated in the long-term thermal cycle load conditions, the oxidation of the adhesive layer is the main reason for the failure of the coating thermal shock. Therefore, the preferred coating is to meet the thermal shock conditions, should try to improve the density and the thickness of the coating. The thermal barrier coatings ScYSZ system with the organizational structure of the stable phase at 1400 ℃ and 1500 ℃, compared with YSZ has superior anti-sintering resistance, thermal shock resistance, resistance to the molten salt corrosion, and lower thermal conductivity, as an ultra-high temperature (≥ 1400 ℃) thermal protective coating has great application prospects.

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CLC: > Industrial Technology > Metallurgy and Metal Craft > Metallurgy and Heat Treatment > Metal corrosion protection,metal surface treatment > Corrosion control and protection > Metal surface protection technology
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