25. Відділ фізико-хімії і технології тугоплавких оксидів
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Документ THE ROLE OF HAFNIUM IN MODERN THERMAL BARRIER COATINGS(Springer Science+Business Media, LLC, 2021) S.M. Lakiza; M.I. Hrechanyuk; V.P. Red’ko; O.K. Ruban; Ja.S. Tyshchenko; A.O. Makudera; O.V. DudnikThe world’s experience in using hafnium in two important parts of high-temperature thermal barrier coatings, such as the top thermal barrier layer and bond coat layer, was analyzed. In the top thermal barrier layer, hafnium is present as HfO2 completely or partially stabilized by yttria (or other rare- earth oxides). Another approach is to use hafnium dioxide as an addition to conventional coatings based on ZrO2 stabilized completely or partially. Electron-beam physical vapor deposition (EB- PVD) and air plasma spray process (APS) are most common techniques for applying thermal barrier coatings containing hafnium dioxide. Magnetron sputtering turned out to be successful as well. Compared to the 8YSZ coating, the 7.5YSH coating showed reduced Young’s modulus, 30% lower thermal conductivity (decreased to 0.5–1.1 W/(m · K)) at high temperatures for HfO2 stabilized with 27 wt.% Y2O3, and higher sintering resistance and heat resistance. Doping of ZrO2 and HfO2 by several stabilizers proved to be promising: specifically, doping by a mixture of one trivalent ion larger than Y3+ and another trivalent ion smaller than Y3+, preserving the metastable structure of the t phase. The importance of phase diagrams for a correct choice of the top coat composition and doping elements for the bond coat is shown. Doping the bond coat with a small amount (up to 1 wt.%) of hafnium improved its cyclic oxidation resistance and increased the adhesion of the thermally grown oxide layer to the bond coat and strength of the latter.Документ THERMAL BARRIER COATINGS BASED ON ZrO2 SOLID SOLUTIONS(Springer Science and Business Media LLC, 2020) E.V. Dudnik; S.N. Lakiza; I.N. Hrechanyuk; A.K. Ruban; V.P. Redko; I.O. Marek; V.B. Shmibelsky; A.A. Makudera; N.I. HrechanyukThe standard material of the ceramic layer in thermal barrier coatings (TBCs)—a solid solution of ZrO2 stabilized with (6–8 wt.%) Y2O3 (YSZ)—approaches the temperature limit of its application (<1200°C) because the ZrO2 t phase sinters and undergoes t-ZrO2 T-ZrO2 + F-ZrO2 phase transformations to form M-ZrO2 at elevated temperatures. Ceramic materials for a new generation of TBCs need to be developed to increase the operating temperature (up to 1600°C), efficiency, and productivity of gas-turbine engines. The overview paper analyzes research efforts focusing on the development of TBCs using solid solutions of ZrO2 with rare-earth metal and titanium oxides. When Y2O3 in YSZ is partially substituted by CeO2, TiO2, La2O3, Sc2O3, Gd2O3, Nd2O3, Yb2O3, Er2O3, and Ta2O5, ceramics with high phase stability (ZrO2 t phase being retained in the coating) up to 1500°C, lower thermal conductivity, and required fracture toughness and sintering resistance but shorter thermal fatigue life than that of standard YSZ are produced. The concepts of greater tetragonality of the ZrO2 t phase (ceramics in the ZrO2–CeO2–TiO2 system) and a 'multicomponent defective cluster' (ceramics in the ZrO2–Y2O3–Nd2O3 (Gd2O3, Sm2O3)–Yb2O3 (Sc2O3) system) explain how the operating temperature of the TBC ceramic layer increases to 1350oC and 1600oC, respectively. The thermal conductivity of TBC ceramics in the binary ZrO2–CeO2, ZrO2–Er2O3, ZrO2–Sm2O3, ZrO2–Nd2O3, ZrO2–Gd2O3, ZrO2–Dy2O3, and ZrO2–Yb2O3 systems is lower than that of YSZ. Ceramics with high phase stability and low thermal conductivity have been produced in the ternary ZrO2–Sc2O3–Gd2O3, ZrO2–CeO2–Gd2O3, ZrO2–YbO1.5–TaO2.5, and ZrO2–Yb2O3–TiO2 systems. An integrated approach is needed to choose the composition of the ceramic layer based on the ZrO2 solid solution, select the coating technique, and improve the coating architecture to design effective TBCs with balanced properties.