Fabrication Of Lanthanum Strontium Manganite/YSZ Composite Coating And Its Mechanical Properties

Aiming at the absorbing application demand of coating in broad band,in the radar absorbing coating strcture with resistive electromagnetic periodic pattern（RPP）,the improvement of the electromagnetic wave loss of ceramic coating based on has become an important technical approach to enhance the absorbing property.However,the addition of electrical loss ceramic material not only changes the thermal physical properties of the original ceramic coating,but also causes the change of microstructure due to the difference of intrinsic properties such as density and thermal conductivity of the two materials,which will affect the service reliability of the coating at high temperature.In order to solve the problem of poor thermal shock resistance of composite coatings and the difficult process regulation,the influences on the phase structure,microstructure and mechanical properties of the La_0.2Sr_0.8Mn O₃（LSM）/YSZ composite coating were investigated and the mechanism was discussed.The relationship between the mechanism and thermal shock resistance properties of coating was constructed,and the mechanism of the thermal shock failure were analyzed.The main research contents are as follow:La_0.8Sr_0.2MnO₃nanopowders were synthesized by sol-gel method,and the effects of organic additions（ethanol and acetic acid）on the crystal growth behavior were studied.In contrast,the effect of acetic acid on crystal growth behavior was more obvious than that of ethanol.When the volume of water solvent and acetic acid were300ml and 0.06ml resepectively,the monoclinic La_0.8Sr_0.2Mn O₃nanopowders could be obtained after La_0.8Sr_0.2Mn O₃dry gel powders were heat treated at 1200℃ for 2 h.With the La_0.8Sr_0.2Mn O₃nanopowders the raw material,the LSM/YSZ composite powders with excellent technical properties were prepared by ball milling-atomization drying process and 1100℃-10 h heat treatment process.With 20wt%LSM/YSZ composite powders heat treated at 1100℃ for 10 h as raw material,20wt%LSM/YSZ composite coating was prepared,and the effect of critical plasma spray parameters（CPSP）on the microstructure,micro-mechanical properties and thermal shock resistance of the coating was studied,so as to optimize the CPSP process parameters.The results showed that with CPSP increasing from 0.83 to 1.17,the porosity of the coating was decreased from（19.22±0.72）%to（11.95±0.32）%.The reduction of porosity decreased the strain tolerance of the coating,resulting in the increase of compressive residual stress.When the bonding strength of the coating was similar,the residual stress of the coating fabricated with CPSP of 1.06（-（87.04±1.91）MPa）was much lower than that with CPSP of 1.17（-（128.69±2.02）MPa）,while the corresponding fracture toughness was slightly increased.Meanwhile,the thermal cycling lifes of the coating prepared with CPSP of1.06 are（165±30）times and（227±22）times,respectively.Therefore,the composite coating prepared with CPSP of 1.06 had better comprehensive properties.Combined with the optimal CPSP,the effects of LSM content on the microstructure,mechanical properties and thermal shock resistance of the LSM/YSZ composite coating was investigated.The results indicated that the addition of LSM could improve the melting state of the composite powders,which is conducive to the reduction of the porosity of the coating,so as to affect its mechanical and thermal shock resistance.With the increase of LSM content from 1wt%to 50wt%,the residual stress was increased from-（53.76±1.00）MPa to-（137.12±1.15）MPa.The thermal cycling life of the coating was degraded from（323±16）times to（118±10）times with the rise of LSM content,which is mainly affected by the increase of the compressive residual stress.