Pressure infiltration of molten aluminum for densification of environmental barrier coatings

Abstract

Environmental barrier coatings (EBCs) effectively protect the ceramic matrix composites (CMCs) from harsh engine environments, especially steam and molten salts. However, open pores inevitably formed during the deposition process provide the transport channels for oxidants and corrosives, and lead to premature failure of EBCs. This research work proposed a method of pressure infiltration densification which blocked these open pores in the coatings. These results showed that it was difficult for aluminum to infiltrate spontaneously, but with the increase of external gas pressure and internal vacuum simultaneously, the molten aluminum obviously moved forward, and finally stopped infiltrating at a depth of a specific geometry. Based on the wrinkled zigzag pore model, a mathematical relationship between the critical pressure with the infiltration depth and the pore intrinsic geometry was established. The infiltration results confirmed this relationship, indicating that for a given coating, a dense thick film can be obtained by adjusting the internal and external gas pressures to drive a melt infiltration.

Influence of average radii of RE3+ions on phase structures and thermal expansion coefficients of high-entropy pyrosilicates

“…Rare earth silicates (RE2SiO5 and RE2Si2O7) are known as the preferred environmental barrier coating materials [9,10]. The thermal expansion coefficient (CTE) of β-type and γ-type pyrosilicate is about 4.0-5.4 × 10 -6 k -1 [11], which is very close to that of CMCs and Si bond layers, whose damage tolerance is excellent [12].…”

“…The enthalpy (𝛥𝛥𝐻𝐻 𝑚𝑚 ) required for the γ-phase transition is greater than that for the β-phase transition. As shown in formula (10), high mixing entropy (𝛥𝛥𝑆𝑆 𝑚𝑚𝑖𝑖𝑥𝑥 ) can provide a driving force for the high-temperature phase to move toward the low temperature (when the 𝛥𝛥𝐺𝐺 𝑚𝑚𝑖𝑖𝑥𝑥 is less than zero), so the high-temperature phase can exist stably at a low temperature [30].…”

Unveiling surface stability and oxygen vacancy segregation of Yb2SiO5 and Lu2SiO5 by first‐principles calculations

“…[7][8][9][10][11] To avoid oxidation or corrosion on the CMCs components, therefore, there is an urgency to develop the environmental barrier coating (EBC). [12][13][14][15][16] Much attention and academic investigations have gone to the surface and related defects of EBC materials as they are believed to play a crucial role in various physical and chemical properties when applied in the engineering sector. For instance, the study of the interaction between oxygen atoms and MoSi 2 surfaces can provide measures for enhancing the oxidation resistance of MoSi 2 .…”

Origins of high fracture toughness and glass‐like thermal conductivity in Zr–Ta–O composites

“…Furthermore, Y 2 O 3 is corroded by CaO–MgO–Al 2 O 3 –SiO 2 (CMAS) silicates, which causes a property recession 21 . Y 2 SiO 5 , Y 2 Si 2 O 7 , and Y 3 Al 5 O 12 are studied as EBCs for Al 2 O 3f /Al 2 O 3 CMCs 20–26 . Y 2 SiO 5 (6.9 × 10 −6 K −1 ) and Y 2 Si 2 O 7 (4.6 × 10 −6 K −1 ) have lower TECs than Al 2 O 3f /Al 2 O 3 CMCs.…”