Study On Preparetion And Properties Of Thermal Barrier Coating Ba(B'_1/3Ta_2/3)O₃

With the rapid development of aviation industry,the gas turbines is required to increase higher inlet temperature and thrust-weight ratio then before.The most popular material identified for the function of heat insulation is 7-8wt.%yttria stabilized zirconia(YSZ).But subsequent research found that Long-term exposure beyond high temperature leads to sintering and catastrophic phase transformation of the YSZ coating,which has been difficult to meet the work requirements of aircraft engine.This leads to a widespread search of new TBC materials with higher thermal stability.This paper used the first-principles density-functional theory(DFT)combine with experiment to design and analyze the new ceramic material Ba(B'_1/3Ta_2/3)O₃(B'=Zn?Ni).The first-principles density-functional theory(DFT)was applied to optimization the crystal structure,the electronic structure and the ion population among BMT,BZT and BNT.Ba(B'_1/3Ta_2/3)O₃(B'=Zn?Ni)powders were prepared by high temperature solid-phase synthesis method.The Ba(B'_1/3Ta_2/3)O₃(B'=Zn?Ni)thermal barrier coatings were prepared by air plasma spraying.Phase structure,thermal and physical properties of the bulks were investigated.Mechanical property,thermal stability,thermal conductivity and sintering resistance of the coatings was also investigated.And evolution of the coating structure as well as the failure mechanism under thermal shock was investigated.The calculation of the first-principles showed that due to the absence of d-orbital in Mg,there is no obvious covalent interaction between Mg and other irons in BMT.However,the interaction among B',O and Ta are distinctly shown in BZTand BNT,especially in Ni and O.Hence,the crystal structure of BNT is the most stable under the ground state.The studies on crystal characteristion of the powders reveal that the powders were ordered hexagonal phase.There is small error in lattice parameter between the result of calculation and experiment.Compare with BZT,the coefficient of thermal expansion of BNT is lower during indoor temperature to 1400?.And because the bond energy of Zn-O is lower than Ni-O,the thermal conductivity of BZT is lower than BNT.There were no second-phase in coatings of BZT and BNT,and the coatings have great bonding strength.Compare with BZT,the occur of second-phase of the BNT coating is later.This result showed that thermal stability of BNT coating is better than the BZT coating.Moreover,the sintering resistance and thermal conductivity of the BNT coating were all better than the BZT coating.During the thermal shock process,the thermal shock lifetime of the BZT coating is 16,and the BNT coating is 21.This is due to the high temperature stability of BZT is poorer,prone to"loss of zinc"phenomenon produced more,lead to crack extension,TGO layer growth,eventually result in the crack of the coating.And the BNT coating has good high temperature stability,produce only a small amount of tantalum acid barium.The thermal stress caused by the mismatch between the thermal expansion coefficient of the ceramic layer and the adhesive layer is the reason for the crack in the inner porosity of the coating,which causes the coating to gradually peel off and eventually fail.