Thermochemical degradation of HfSiO4 by molten CMAS

The thermochemical degradation of hafnium silicate (HfSiO 4 ) was investigated with a molten calcium-magnesium-aluminosilicate (CMAS) glass relevant to gas turbine engine applications. Sintered HfSiO 4 coupons were fabricated, within which wells were drilled and filled with CMAS glass powder at a loading of ∼35 mg/cm 2 . Samples were heat treated at 1200 °C, 1300 °C, 1400 °C, and 1500 °C for 1 h, 10 h, and 50 h. At 1200 °C and 1300 °C, slow formation of a Ca 2 HfSi 4 O 12 cyclosilicate phase was observed at the HfSiO 4 -CMAS interface. At 1300 °C and higher, rapid infiltration of CMAS into the material along the grain boundaries was observed. Initial conjecture into CMAS degradation mechanisms of HfSiO 4 are presented herein.