| Forsterite?Mg2SiO4?has the advantages of high temperature phase stability,low sintering rate,low thermal conductivity and good mechanical properties,and is expected to be a new material for thermal barrier coating?TBC?.In this paper,Mg2SiO4 was investigated systematically for thermal barrier coating applications by XRD,TG-DSC,EDS and other methods.The Mg2SiO4-TBCs was prepared by APS technology and the thermal cycling performance was also studied.The Mg2SiO4 ceramic powder was synthesized by high temperature solid-state reaction at 1873 K.Results show that Mg2SiO4 has high phase stability up to 1573 K,low thermal conductivity?1.8 W/m·K,1273 K?and presented moderate thermal expansion coefficient,which increases from 8.6×10-6 K-1 to 11.3×10-6 K-1?4731623 K?.In addition,the hardness and fracture toughness of Mg2SiO4 are10GPa and 2.8 MPa·m1/2,respectively.The sintering results indicated a promising low-sintering activity of Mg2SiO4,which is superior to that of advanced thermal barrier coating materials such as 8YSZ,La2Zr2O7 and SrCeO3.The Mg2SiO4samples were subjected to water quenching test at 1573 K and showed a superior thermal shock resistance compared to 8YSZ.Mg2SiO4 coating with stoichiometric composition was produced by atmospheric plasma spraying.The thermal cycling test result showed that Mg2SiO4coating had a lifetime of more than 830 cycles at 1273 K.The main reasons of longer thermal cycle life of Mg2SiO4 coating are good fracture toughness,sintering resistance and special microstructure evolution of Mg2SiO4 coating under high temperature exposure.The main causes of failure are recrystallization,thermal expansion mismatch and TGO.In addition,formation and thickening of the chemical reaction layer also an important reason.Novel thermal barrier coatings based on Mg2SiO4/8YSZ double-ceramic-layer?DCL?were also prepared by APS.The results show that the service life of DCL coating is longer than that of single-layer Mg2SiO4 coating,and even comparable to that of single-layer 8YSZ coating,which due to the fact that the DCL Mg2SiO4/8YSZ TBCs further enhance the thermal insulation effect,improve the sintering resistance ability and relieve the thermal mismatch between the ceramic layer and the bond coat.The top layer of Mg2SiO4 ceramic layer has good sintering ability and lower thermal conductivity.The bottom layer YSZ ceramic layer has a good stress buffering effect,which is very helpful for improving the thermal cycle life of the coating.The failure mode of the coating is mainly the initiation and expansion of cracks,the abnormal oxidation of the bonding layer and the recrystallization of the coating.The Mg2SiO4 is subjected to hot corrosion by V2O5?Tm=690°C?at 700-1050°C range.Two corrosion products formed such as Mg2V2O7?rod shaped?,and SiO2?granular shaped?,the types of corrosion products being temperature independent.Two different cross-sectional morphologies were distinguished that correspond to a thin outermost layer?PRZ?,and an inner porous layer?MIRZ?.Note that V2O5 penetrated the specimen preferentially at grain boundaries and dissolved the Mg2SiO4 ceramic to form low-melting grain boundary pocket?Mg2V2O7?.A hot corrosion study of calcium magnesium aluminosilicate?CMAS?glass on Mg2SiO4 ceramics was carried out at 1250°C.The results show that CMAS can dissolve Mg2SiO4 ceramic rapidly,precipitate diopside phase CaMgSi2O6,and form continuous and dense corrosion layer.As the corrosion time increases,the thickness of the corrosion layer does not increase significantly because the glassy component of CMAS is converted from the original"hard crystal"to a crystallizable compound after the corrosion reaction.Al and Ca are enriched in the reaction layer and forming a closed layer to prevent the porous ceramic from open characteristics of the melt penetration,thereby inhibiting further penetration of the CMAS. |
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