Thermochemical degradation of HfSiO4 by molten CMAS

The thermochemical degradation of hafnium silicate (HfSiO4) was investigated with a molten calcium-magnesium-aluminosilicate (CMAS) glass relevant to gas turbine engine applications. Sintered HfSiO4 coupons were fabricated, within which wells drilled and filled CMAS powder at loading ∼35 mg/cm2. Samples heat treated 1200°C, 1300°C, 1400°C, 1500°C for 1 h, 10 50 h. At 1200°C slow formation Ca2HfSi4O12 cyclosilicate phase observed the HfSiO4-CMAS interface. 1300°C higher, rapid infiltration into material along grain boundaries observed. Initial conjecture mechanisms are presented herein.