Study On Plasma Sprayed Alumina-based Eutectic Ceramic Coating

Plasma sprayed Al₂O₃ coating has high hardness,good high temperature stability and chemical stability,but its low bonding strength,poor toughness and thermal shock resistance limit its wider application.In this paper,the Al₂O₃-ZrO₂ and Al₂O₃-Y₂O₃ eutectic ceramic composite coatings were prepared based on the composition of Al₂O₃ based binary eutectic ceramics.The microstructure and properties of plasma sprayed Al₂O₃-ZrO₂ and Al₂O₃-Y₂O₃ eutectic ceramic coatings were studied.The effects of additives?Y₂O₃,CeO₂,TiO₂?on the microstructure and properties of Al₂O₃-ZrO₂ and Al₂O₃-Y₂O₃ eutectic ceramic coatings were also studied.At the same time,the evolution of microstructure and properties of Al₂O₃-ZrO₂ and Al₂O₃-Y₂O₃ coatings at high temperature was studied.It was found that plasma sprayed Al₂O₃-ZrO₂ coating consists of t-ZrO₂??-Al₂O₃ and?-Al₂O₃ phases.The Al₂O₃-Y₂O₃ coating consists of?-Al₂O₃?c-Y₂O₃?Y₃Al₅O₁₂?YAG?and Y₄Al₂O₉?YAM?phases.Both the plasma sprayed Al₂O₃-ZrO₂ system coatings and the Al₂O₃-Y₂O₃ system coatings have a large amount of amorphous phase,which is determined by the characteristics of the plasma spraying process and the eutectic composition of the coatings.Al₂O₃ exists as?-Al₂O₃ phase in the Al₂O₃-Y₂O₃ system coatings,instead of.?-Al₂O₃ phase in the Al₂O₃-ZrO₂ system coatings.Under the experimental conditions of this paper,by comparing plasma sprayed Al₂O₃-ZrO₂ coating and that with different content of Y₂O₃,CeO₂ and TiO₂,it was found that the Al₂O₃-ZrO₂ coatings with 3 wt.%Y₂O₃,4 wt.%CeO₂ and 10 wt.%TiO₂ have lower porosity,the coating structures become more uniform and denser.The Al₂O₃-ZrO₂ system coatings have lamellar structure and obvious river pattern.By comparing plasma sprayed Al₂O₃-ZrO₂ coating and that with different content of TiO₂,it was found that the size and number of the pores in Al₂O₃-Y₂O₃ coating decrease obviously,and the distribution of the microstructure is more uniformThe mechanical properties of the coatings show that adding 3 wt.%Y₂O₃,4 wt.%CeO₂and 10 wt.%TiO₂ could improve the hardness,toughness,bonding strength,friction and wear properties of Al₂O₃-ZrO₂ coating.Adding 2 wt.%TiO₂ is beneficial to improve the hardness,toughness,bonding strength,friction and wear properties of Al₂O₃-Y₂O₃ coating.The thermal shock resistance of Al₂O₃-ZrO₂ and Al₂O₃-Y₂O₃ coatings at 850°C was investigated.Compared with the Q235 steel,the two system coatings have better thermal shock resistance when using TC4 titanium alloy as substrate.In particular,using TC4titanium alloy as substrate and spraying NiCrAlY as bond coating can effectively alleviate the mismatch of the thermal expansion coefficient between the Al₂O₃-ZrO₂?Al₂O₃-Y₂O₃system coatings and the metal substrate,and improve the thermal cycle times of the coatings.At the same time,it was found that adding additives?Y₂O₃,CeO₂ and TiO₂?is beneficial to improve the thermal shock resistance of Al₂O₃-ZrO₂ and Al₂O₃-Y₂O₃ system coatings.The heat treatment of Al₂O₃-ZrO₂ and Al₂O₃-Y₂O₃ system coatings at different temperatures?800°C,1000°C,1200°C?for 2 h showed that the microstructure and properties of both systems are stable at 800°C.With the increase of temperature,the Al₂O₃-ZrO₂ system coatings have a phase transition at high temperature.At 1000°C,the amorphous phase crystallizes,and?-Al₂O₃ transforms into?-Al₂O₃.At 1200°C,the amorphous phase completely crystallizes,?-Al₂O₃ completely transforms into?-Al₂O₃.With the increase of temperature,the phase transition of Al₂O₃-Y₂O₃ coating also occurred.Amorphous phase crystallizes at 1000°C,and Y₂O₃ completely reacts with Al₂O₃ to form YAG phase and YAM phase.At 1200°C,the amorphous phase completely crystallizes.After high temperature treatment,the porosity of Al₂O₃-ZrO₂ and Al₂O₃-Y₂O₃ system coatings decreases and the hardness increases.