Phase Equilibria In ZrO₂-RETaO₄ Systems And Their Mechanical Properties And Their Interaction With Ca–Mg–Al–Silicate Melts

Thermal barrier coatings are widely used as thermal protection materials for high temperature components of aero-engines.However,as the operating temperature of aero-engines is getting higher and higher,the current 7YSZ thermal barrier coating materials have been difficult to meet due to challenges such as high-temperature sintering,phase change,and CMAS corrosion.The use of high-performance engines requires the search for new thermal barrier coating materials that are resistant to high temperature and corrosion.In the ZrO₂-RETaO₄ system,oxides doped with equimolar REO_1.5 and TaO_2.5have the potential to become the next generation of thermal barrier coating materials.In this paper,the ZrO₂-RETaO₄ system ceramic powder was prepared by the chemical co-precipitation method,the influence factors of the formation of tetragonal zirconia in the ZrO₂-RETaO₄ system were studied,and the mechanical properties and CMAS corrosion mechanism were explored.The main conclusions are as follows:(1)The phase stability sequence of ZrO₂-RETaO₄ system and the formation law of tetragonal zirconia were studied through microstructure characterization.The results show that the phase stability sequence of the ZrO₂-RETaO₄ system gradually transitions from tetragonal zirconia to monoclinic zirconia with the increase of the radius of rare earth ions,and this transition occurs between Gd³⁺and Nd³⁺rare earth ions;the tetragonal phase of t-ZrO₂ the forming ability gradually increases with the decrease of the rare earth ion radius.Smaller rare earth ion doping will make t-ZrO₂ stable at a higher doping concentration,and a larger range of stable composition can be obtained,while a larger range of stable composition can be obtained.Rare earth ion doping will reduce the stable composition range of t-ZrO₂ and even inhibit the formation of tetragonal zirconia.(2)The mechanical properties such as hardness and toughness of ZrO₂-RETaO₄system were studied by Vickers indentation method.The results show that the hardness and toughness of the tetragonal phase t-ZrO₂ increase with the increase of the doped rare earth ion radius;the hardness of the t-ZrO₂+Yb TaO₄ two-phase structure area first increases and then gradually decreases with the increase of the Yb TaO₄ phase content.The toughness decrease first and then increase;the hardness and toughness of the t-ZrO₂+Dy TaO₄ two-phase structure area increase with the increase of the Dy TaO₄ phase content;the hardness of the t-ZrO₂+Gd TaO₄ two-phase structure area first decreases with the increase of the Gd TaO₄ phase content increase,the toughness gradually decreases.(3)The CMAS corrosion resistance and corrosion mechanism of ZrO₂-RETaO₄system materials were studied through CMAS corrosion penetration experiment and phase equilibrium reaction experiment.The results show that co-doped t-ZrO₂ is not resistant to CMAS corrosion,and its reaction with CMAS will cause Ta⁵⁺,RE³⁺and Zr⁴⁺to be solid-dissolved into CMAS,thereby inducing t-ZrO₂?m-ZrO₂ phase transition,which produces greater strain energy,making the corroded tissue loose and porous.When the t-ZrO₂+Yb TaO₄ structure reacts with CMAS,t-ZrO₂ is the main part of the reaction,while Yb TaO₄ is relatively inert.The reaction product is c-ZrO₂,which is loose and porous and does not have the characteristics of resistance to CMAS corrosion.The corrosion structure of t-ZrO₂+Gd TaO₄ and t-ZrO₂+Dy TaO₄ two-phase structure is basically the same.In the CMAS corrosion process,RETaO₄mainly participates in the reaction,and the reaction product is pyrochlore Ca RETa₂O₇.The corrosion reaction layer is continuous and dense to hinder the role of CMAS corrosion.