Combined Effects of CMAS and FOD in Ceramic Matrix Composites

The combined effects of CMAS (calcium magnesium aluminosilicate) and FOD (foreign object damage) were determined in three different ceramic matrix composites (CMCs), two melt-infiltrated (MI) SiC/SiCs and one oxide/oxide. Foreign object damage was introduced at ambient temperature in CMC test targets using 1.6 mm steel ball projectiles at an impact velocity of 340 m/s utilizing a ballistic impact gun. One type of target support, partial support, was used. The impact-damaged test coupons were then CMAS-exposed at 1200°C for 10 hrs in air. Additional tests were also performed by exposing impact-damaged test coupons to a mixture of CMAS and salt (sodium sulfate) at 1200°C for 10 hrs in air. The combined effects of FOD and CMAS or CMAS/salt were quantified by determining the residual strengths of test coupons after exposures. Also, six different sands ingested into aeroengines were analyzed in their chemical compositions. The melt CMAS solid, melted at 1300°C and solidified, was assessed in its mechanical properties of microhardness and fracture toughness.