The Study Of La₂(Zr_0.7Ce_0.3)₂O₇Thermal Barrier Coating By EB-PVD

The hot end protection of Aircraft engine parts has become an effective way forenhancing the inlet temperature of aero-engine. Thermal barrier coating technology wasconsiderated as one of the three key technologies besides high temperature structuralmaterials and efficient blade cooling technology. This reflects the importance of thermalbarrier coating technology. Nowadays,6-8wt%Y2O3doped ZrO2(YSZ) thermal coatingwere generally prepared by using EB-PVD technology for the hot end protection ofAircraft engine parts. However, YSZ thermal coatings were usually used at lowertemperature than1200oC, which can’t meet with the demand of aero-engine with higherthrust-weight ratio and higher efficiency and higher stability. Because of its relatively lowthermal conductivity, high sintering resistance, high thermal expansion coefficient, novelLa2(Zr0.7Ce0.3)2O7material has become a research focus. Few work have reported about thethermal barrier coating of La2(Zr0.7Ce0.3)2O7prepared by EB-PVD technology. And further,The structures and thermal properties of La2(Zr0.7Ce0.3)2O7coating prepared by EB-PVDtechnology with different process parameters, such as temperature and rotate speed, havenever been reported until now.In this thesis, the structure and the thermal conductivity of La2(Zr0.7Ce0.3)2O7coatingprepared with different temperature and rotating speed were investigated. At the same time,the thermal cycles life of La2(Zr0.7Ce0.3)2O7coating were evaluated under certainconditions. The temperatures for deposition were respectively set at760-780℃,860-880℃and920-950℃and the rotating speed were respectively set at5rmin-1,15rmin-1and25rmin-1. The microstructures of La2(Zr0.7Ce0.3)2O7coating were investigated by scanningelectron microscope (SEM). The phase structures and textures of La2(Zr0.7Ce0.3)2O7coatingwere tested by X-ray diffraction technology (XRD) and the thermal conductivity wereresearched by laser-flash apparatus (LFA).The surface top of La2(Zr0.7Ce0.3)2O7coatings, which were deposited with rotatingspeed of5rmin-1and15rmin-1at760-780℃, with rotating speed of15rmin-1and25rmin-1 at860-880℃and920-950℃, formed columnar grain with a Pyramid or like-Pyramid top.The columnar grain with four (222) crystal plane growths along <001> direction which isperpendicular to (400) crystal plane. The coatings diposited on stationary substrate showed(440) texture at all experimental temperature.The coatings diposited on stationary substrate lead to a coarse-grain microstructure at760-780℃and a certain welding of grain had happened when the coatings were dipositedat860-880℃and920-950℃. The results of scanning electron microscope suggested thatthe columnar grain appeared a typical ‘C’ type structure when the coatings diposited onrotary substrate.The lower rotary speed of the substrate leads to the more prominent ‘C’type structure which are benefit to reduce the thermal conductivity of the coating.Thethermal conductivity of the coating is not only relative to ‘C’ type column structure, butalso relative to the diameter of columnar grain and the size of branch grain of columnargrain.The results of thermal cycles suggested the spallation of the coating occurred ininterior of ceramic near the interface between the ceramic layer and the bonding layer. Athin ceramic layer still remaind on the bonding layer after the spallation of the coating.The thermal cycling life of the coating deposited at high temperature is obviously longerthan that deposited at low temperature. The lowest life of the coating reach to364h at920-950℃. The life of the coating deposited at low rotary speed were longer than thatdeposited at high rotary speed and at the higher temperature zone(860-880℃,920-950℃).After the spalling of coating, the microstructures of remainder of coating deposited at thehigher temperature zone(860-880℃,920-950℃) were similar as that deposited at lowtemperature zone(760-780℃) with higher rotary speed (25r/min), which showed a lot ofsmall planar structures.