The influence of calcium–magnesium–aluminosilicate deposits on internal stresses in Yb2Si2O7 multilayer environmental barrier coatings

Abstract

The interaction of calcium-magnesium-aluminosilicates (CMAS) with Yb 2 Si 2 O 7-based multilayer environmental barrier coatings was studied using a combination of high-energy synchrotron X-ray techniques. Changes in the phase-specific stresses and lattice spacings as a function of temperature were investigated with wide-angle X-ray scattering. Small-angle X-ray scattering was used to study the interaction of CMAS with nanoporosity, while X-ray computed tomography was used to study the formation of cracks in the coating. It was found that CMAS interacts strongly with the Yb 2 Si 2 O 7 topcoat, leading to changes in lattice spacing, alterations of the ambient temperature stresses, and large cracks in the CMAS that extend through the topcoat.

Reactions of molten silicate deposits with yttrium monosilicate

“…Reactions of molten silicate deposits with RE monosilicates and disilicates exhibit significant similarities and differences. Disilicates frequently react with the deposits to form apatite, nominally of composition Ca 2 RE 8 (SiO 4 ) 6 O 2 .…”

Yb2Si2O7 Environmental barrier coatings with reduced bond coat oxidation rates via chemical modifications for long life

“…Most of the current EBCs are variants of the second‐generation EBCs. Various aspects of current EBCs, including processing, volatility in water vapor, silica activity in Y 2 O 3 ‐SiO 2 and Yb 2 O 3 ‐SiO 2 systems, interactions with CMAS, stress analysis, fracture mechanism, impact damage, and oxidation, have been reported.…”

“…Using a current state‐of‐the‐art EBC (Si/Yb 2 Si 2 O 7 ) as the baseline, the Yb 2 Si 2 O 7 layer was modified by adding Al 2 O 3 or Al 2 O 3 ‐containing oxide compounds, such as mullite and YAG (Y 3 Al 5 O 12 ), and TiO 2 . Si/mullite/Yb 2 Si 2 O 7 is another baseline investigated in the literature . Si/Yb 2 Si 2 O 7 was selected as the baseline over Si/mullite/Yb 2 Si 2 O 7 mainly to avoid the phase transformation‐induced cracking of conventionally plasma‐sprayed mullite .…”

The role of ceramic and glass science research in meeting societal challenges: Report from an NSF‐sponsored workshop

“…In situ measurements of material characteristics and operando monitoring of materials evolution are critically needed to enable a quantitative understanding of the composition‐structure‐property relations in a complex environment. Using X‐rays as probes, especially in combination with μ‐CT, one should be able to assess the synergistic effects of temperature, environment, and stress on the mechanical properties and the mechanisms of failure, phase stability, oxidation, oxidation‐induced stresses, and effects of high‐temperature corrosion by CMAS and gradients in internal strain …”

“…In situ measurements of material characteristics and operando monitoring of materials evolution are critically needed to enable a quantitative understanding of the F I G U R E 5 High-temperature and high-pressure techniques applicable to extreme environmental research; clockwise from upper left: high-resolution microcomputed tomography (l-CT) of SiC-SiC composites 219 (reprinted with permission, Nature Publishing Group); arc jet test 151 (Source: NASA Ames Research Center); diamond anvil cell for extreme pressures; ultra high-temperature (UHT) calorimetry 208 ; and a time sequence of surface melting of silicate deposits from a high heat flux laser gradient test 209 composition-structure-property relations in a complex environment. Using X-rays as probes, especially in combination with l-CT, one should be able to assess the synergistic effects of temperature, environment, and stress on the mechanical properties and the mechanisms of failure, 219,220,234 phase stability, oxidation, oxidation-induced stresses, 235 and effects of high-temperature corrosion by CMAS 236,237 and gradients in internal strain. 238…”