| Thermal Barrier Coatings(TBCs)are ceramic coatings that have a good thermal insulation effect deposited on the surface of a metal substrate.TBCs use the low thermal conductivity of ceramics to reduce the temperature of parts working in high temperature environments to the normal operating temperature range and protect hot end parts from high temperature oxidation,hot corrosion or mechanical wear.The thermal barrier coating system,which combines the excellent thermal insulation properties of porcelain coating materials with the high toughness and high strength of metal materials,has been widely used in aviation,aerospace and thermal power generation.However,in the long-term work in high temperature environment,the spalling failure of the ceramic layer seriously hinders the development and application of the thermal barrier coating.In order to continuously increase the use temperature of the thermal barrier coating and prolong its service life,people have adjusted the coating structure of the thermal barrier coating,selected new ceramic layer materials and metal bonding layer materials,and analyzed the failure mechanism of the coating.In-depth research.These studies have profound implications for the development of thermal barrier coatings.In this paper,yttria-stabilized zirconia(YSZ)and lanthanum zirconate(LZO)powders were selected.A single-layer YSZ coating and YSZ+LZO composite coating were prepared on a nickel-base superalloy substrate by atmospheric plasma spraying equipment.After the coating was prepared,the coating was subjected to thermal shock test and high temperature oxidation test at 1200°C using a high temperature heat treatment furnace to detect the thermal shock resistance and high temperature oxidation resistance of the coating,and by scanning electron microscopy(SEM),X-ray diffractometer(XRD)and energy dispersive spectroscopy(EDS)analyzed the causes of the failure of the thermal barrier coating and the composition of the thermally grown oxide(TGO).The friction and abrasion tester and Vickers hardness tester were used to test the mechanical properties of the coating.Under the same thermal shock test conditions,the single-layer YSZ thermal barrier coating and the LZO + YSZ composite thermal barrier coating experienced 93 and 102 thermal shock test failures respectively.The composite LZO structure made the life of the thermal barrier coating 9 times of improvement.The main cause of coating peeling failure is due to the inconsistent thermal expansion coefficient between the coating and the base material,which causes thermal stress inside the coating during the high and low temperature cycle and eventually causes the coating to fall off and fail.In the high-temperature oxidation test,the coating enters the interior of the coating due to oxygen through the pores and micro-cracks on the coating surface in a long-term high-temperature environment.Oxygen entering the interior of the coating chemically reacts with metal elements in the bonding layer.A TGO layer is formed at the interface between the adhesive layer and the ceramic layer,and the irregular growth of TGO eventually causes the coating to fall off with the high temperature oxidation test.In the early stage of the reaction,due to the relatively high reactivity of the Al element,it is first reacted with the O element to generate Al2O3.As the content of the Al element continues to decrease,the O element and Ni,Cr elements in the bonding layer form spinels such as Ni O.Stone phase oxides.The mechanical property test shows that the friction coefficient of YSZ + LZO composite coating is higher than that of single-layer YSZ coating,indicating that its surface is rougher.Compared with YSZ + LZO composite coating,the single-layer YSZ coating has a higher microhardness value under the same load test conditions,that is,it has better resistance to compressive deformation. |
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