Comparative Study Of Microstructure And Measure Of Thermal Conductivity Of8YSZ Coatings Deposited By APS And VLPPS

8YSZ thermal barrier coating is widely used in aviation and aerospace turbine engines to improve their working temperature. Plasma spray, with a high-velocity and high-temperature plasma jet, can be adopted to prepare excellent8YSZ coating economically and quickly. Recently, it has become a reality to manufacture new special coatings different from traditional lamellar structure after the very low pressure plasma spray appeared which has broad application prospect.On the other hand, the thermal conductivity and phase evolution of8YSZ coatings has attract more and more attention. But there is little about the relationship of the phase composition between8YSZ powder and coating. It is also significant to develop simple methods to measure the thermal conductivity of coating.In this thesis, a comparative study of the phase composition and microstructure of8YSZ coatings manufactured by atmospheric plasma spray (APS) and very low pressure plasma spray (VLLPS) from two different phase powder was carried out. Meanwhile, a new easy method was developed to measure the thermal conductivity of coatings at different temperatures. The phase composition of8YSZ coatings were investigated quantitatively by X-Ray diffraction (XRD) and the microstructure were observed by optical microscope (OM) and scanning electron microscope (SEM). Furthermore, the thermal conductivity of coatings was measured at different temperatures by self-developed method. The results indicate that:1. Regardless of the original phase composition of powder, the8YSZ coating fabricated by APS or VLPPS is mainly composed of t’phase, while m and c phase in the coatings decreases compared with the original powder. The heating process during spray is beneficial for the growth of grain.2. For VLPPS,8YSZ vapor had been detected inside the plasma jet by the optical spectra during the spray process, but no evident vapor-condensed structure inside coatings are observed. 3. The coatings prepared by VLPPS obtain denser structure and higher micro hardness than those prepared by APS. The8YSZ powder with loose internal structure can get a good melting state easily during heated inside the plasma jet, of which coating is denser.4. The thermal conductivity of8YSZ coatings prepared by APS decreases with the increasing temperature. The phase composition and porosity can influence the thermal conductivity of8YSZ coatings.