The interaction of calcium–magnesium–aluminosilicate with ytterbium silicate environmental barrier materials

• Reactivity of Yb2SiO5 and Yb2Si2O7 with CMAS was explored at 1300 °C.
• Amorphous/crystal phase fractions quantified by reference intensity ratio method.
• Silicate oxyapatite, Ca2Yb8(SiO4)6O2, readily forms by reaction of Yb2SiO5 with CMAS.
• Yb2Si2O7 reveals limited dissolution and no Ca2Yb8(SiO4)6O2 formation after 96 h.

The interactions of two potential topcoat materials for environmental barrier coatings, Yb2SiO5 and Yb2Si2O7, with calcium-magnesium-aluminosilicate (CMAS) engine deposits were studied. X-ray diffraction, scanning electron microscopy, energy-dispersive X-ray spectroscopy, and electron diffraction were used to investigate the phase transformation associated with the exposure of Yb2SiO5 and Yb2Si2O7 to CMAS at 1300 °C. It was found that Yb2SiO5 strongly reacts with CMAS to completely dissolve the Yb2SiO5 and form hexagonal Ca2Yb8(SiO4)6O2 deposits. In contrast, no discernable reaction between CMAS and Yb2Si2O7, was observed over the 96-h exposure.