The effect of TiO2 additions on CaO-MgO-Al2O3-SiO2 (CMAS) crystallization behavior from the melt

Titania (TiO2) was introduced into a model calcium-magnesium aluminosilicate (CMAS) glass in additions of 5-20wt%. The crystallization behavior of the mixtures was characterized over a series of temperature profiles and compared to that of CMAS alone. X-ray diffraction, differential scanning calorimetry, light and scanning electron microscopy, and energy dispersive spectroscopy were used to characterize glass and crystalline products. Titania additions in the amount of approximately 12.5-20wt% aided in the formation of CaTiO3 from melts equilibrated at either 1300 or 1500 degrees C and cooled at 10 degrees C/min. Holding CMAS + TiO2 (TiO2 10wt%) at 900 degrees C after cooling from 1300/1500 degrees C resulted in the formation of additional crystalline phases including melilite, paqueite, and diopside. Implications for CMAS interactions with thermal and environmental barrier coatings are discussed.