Preparation And High Temperature Oxidation Behavior Of Ceramic Coating Contained ZrO₂ Prepared By Micro-arc Oxidation On TiAl Alloy

TiAl-based alloys exhibit low density,high melting point,high specific strength and high creep resistance.However,the oxidation resistance of TiAl-based alloys quickly decreases at high temperatures up to 850 °C.Surface engineering is a common approach to protect TiAl-based alloys against high temperature environment.Ceramic coatings contained ZrO2 were prepared by micro-arc oxidation on TiAl alloy in this thesis.The effects of micro-arc oxidation voltage,time and zirconate concentration on microstructure and phase composition of MAO coating were studied by SEM,XRD and EDS.The cyclic oxidation tests of coated samples were carried out at 900 °C.Thermal shock behavior of the composite ceramic coatings was investigated.The results show that coatings prepared in this thesis mainly consisted of t-ZrO2,m-ZrO2,Al2O3,TiO2 and the main phase crystals was t-ZrO2.Voltage and zirconate concentration had a little effect on phase composition of MAO coatings.ZrTiO4 and Al2TiO5 appeared after TiAl sample treated 60 min by micro-arc oxidation.With higher voltage and longer time,micro-hole size and thickness of MAO coatings became larger.The difference was that the surface porosity of MAO coating decreased with longer time and increased with higher voltage.Voltage had a significant impact on the thickness of coating while coating stopped growing after certain time.Zirconate concentration had a little effect on phase composition and microstructure of the coating.The 100 hour oxidation kinetic curve of MAO coating samples obeyed parabola law at 900 °C.Compared with TiAl sample,mass gain of MAO coating sample decreased 70 %—90 %.Phase composition,surface micro-morphology and micro-morphology of the section did not change significantly.It indicated that MAO coatings were steady at 900 °C.Oxidation resistance of the TiAl alloy was improved due to MAO coating.MAO voltage and time had a comprehensive impact on the oxidation resistance of TiAl alloy.A multilayer structure of TiO2 +Al2O3 composite layer/ rich Al2O3 layer/ Ti3 Al layer formed between MAO coating and TiAl substrate from outside to inside after 100 h oxidation at 900 °C.The thermal shock resistance of MAO coating was insufficient at high temperatures up to 700 °C.The thermal shock resistance of MAO coating was good at 600 °C.Phase composition and microstructure of the coating had no obvious change after subjected to thermal shocking with temperature difference 580 °C for 10 cycles.