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 were drilled and filled with CMAS glass powder at a loading of ~35 mg/cm2. Samples were heat treated at1200°C, 1300°C, 1400°C, and 1500°C for 1 hour, 10 hours, and 50 hours. At 1200°C and1300°C, slow formation of a Ca2HfSi4O12 cyclosilicate phase was observed at the HfSiO4-CMASinterface. 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 HfSiO4 are presented herein.