Interaction of multicomponent disilicate (Yb0.2Y0.2Lu0.2Sc0.2Gd0.2)2Si2O7 with molten calcia-magnesia-aluminosilicate

Environmental barrier coating (EBC) materials that are resistant against molten calcia-magnesia-aluminosilicate (CMAS) corrosion are urgently required. Herein, multicomponent rare-earth (RE) disilicate ((Yb0.2Y0.2Lu0.2Sc0.2Gd0.2)2Si2O7, (5RE)2Si2O7) was investigated with regard to its CMAS interaction behavior at 1400 °C. Compared with the individual RE disilicates, the (5RE)2Si2O7 material exhibited improved resistance against CMAS attack. The dominant process involved in the interaction of (5RE)2Si2O7 with CMAS was reaction-recrystallization. A dense and continuous reaction layer protected the substrate from rapid corrosion at high temperatures. The results demonstrated that multicomponent strategy of RE species in disilicate can provide a new perspective in the development of promising EBC materials with improved corrosion resistance.

Water vapor and CMAS corrosion tests of Si/Y2SiO5 Thermal and Environmental Barrier Coating

Thermal and environmental barrier coating (TEBC), the up-to-date concept, is introduced to protect silicon-based ceramics matrix composites (CMC) from not only high temperature water vapor but also the alkali salt from volcanic ash and dust suspending in atmosphere. Because both of high temperature steam and CMAS will make Si-based CMC deteriorate rapidly. By executing the corrosion test against high temperature water vapor, we find that Si/Y2SiO5 double-layer TEBC can effectively protect SiCf/SiC CMC from water vapor at 1300 ℃ for over 205 hours. Almost all Y2SiO5 transform into Y4.67(SiO4)3O after corrosion test. It is also found that in CMAS corrosion test, the reaction zone formed between CMAS and Y2SiO5 layer prevents the mutual diffusion of elements in CMAS and Y2SiO5 layer. The apparent activation energy of reaction between CMAS and Y2SiO5 in 1200~1300℃ temperature ranges is calculated to be 713.749kJ/mol. These findings provide a reference to select appropriate materials for TEBC.

Rear Earth Oxide Multilayer Deposited by Plasma Spray-Physical Vapor Deposition for Envisaged Application as Thermal/Environmental Barrier Coating

SiC fiber-reinforced SiC ceramic matrix composites (SiCf/SiC CMCs) are being increasingly used in the hot sections of gas turbines because of their light weight and mechanical properties at high temperatures. The objective of this investigation was the development of a thermal/environmental barrier coating (T/EBC) composite coating system consisting of an environmental barrier coating (EBC) to protect the ceramic matrix composites from chemical attack and a thermal barrier coating (TBC) that insulates and reduces the ceramic matrix composites substrate temperature for increased lifetime. In this paper, a plasma spray-physical vapor deposition (PS-PVD) method was used to prepare multilayer Si–HfO2/Yb2Si2O7/Yb2SiO5/Gd2Zr2O7 composite coatings on the surface of SiCf/SiC ceramic matrix composites. The purpose of this study is to develop a coating with resistance to high temperatures and chemical attack. Different process parameters are adopted, and their influence on the microstructure characteristics of the coating is discussed. The water quenching thermal cycle of the coating at high temperatures was tested. The results show that the structure of the thermal/environmental barrier composite coating changes after water quenching because point defects and dislocations appear in the Gd2Zr2O7 and Yb2SiO5 coatings. A phase transition was found to occur in the Yb2SiO5 and Yb2Si2O7 coatings. The failure mechanism of the T/EBC composite coating is mainly spalling when the top layer penetrates cracks and cracking occurs in the interface of the Si–HfO2/Yb2Si2O7 coating.

Deposição de recobrimentos de proteção térmica e ambiental por plasma spray utilizando precursor híbrido de SiO2+ZrO2/ Plasma spray deposition of thermal and environmental protection coatings using SiO2+ZrO2 hybrid precursor

Compósitos reforçados com fibra de carbono (C/C) são materiais amplamente utilizados em componentes estruturais, especialmente quando expostos as intensas cargas aerotermodinâmicas. Sua alta resistência e excepcional tenacidade à fratura, combinados com suas propriedades refratárias, resistência à erosão, corrosão e desgaste tornam este material ideal para aplicações em componentes estruturais, submetidos a altas temperaturas, tais como turbinas e veículos de reentrada atmosférica. Quando utilizados em atmosferas inertes ou em vácuo, os compósitos C/C mantêm suas propriedades a temperaturas superiores a 2000°C. Porém, nas condições de ambientes oxidantes e de elevadas temperaturas, os compósitos a base de fibras de carbono sofrem intensa degradação devido à elevada catalicidade de reações entre o carbono e o oxigênio, dificultando e, muitas vezes, impossibilitando seu uso em dispositivos aeroespaciais. Neste contexto, o objetivo deste trabalho é a deposição de recobrimentos de barreira ambiental (Environmental Barrier Coating, EBC), utilizando precursores híbridos de ZrO2+SiO2 visando proteção contra oxidação dos compósitos estruturais de C/C. Os recobrimentos serão depositados por meio do processo de spray a plasma de alta velocidade (High Velocity Plasma Spray, HVPS).