THE DUCTILE-BRITTLE SIZE TRANSITION OF IRON ALUMINIDE LIGAMENTS IN ANFEAL TIC COMPOSITE/

The fracture surfaces of FeAl/TiC composites containing 70 vol.% TiC w ere investigated. Since thin iron aluminide ligaments in the composite s fractured in a ductile manner, whereas thicker ones fractured by cle avage, a systematic correlation of the fracture mode to the ligament t hickness was performed. The results clearly show that FeAl ligaments t hicker than about 1-2 mu m fracture by cleavage and those smaller in s ize fracture predominantly in a ductile manner. The ductile failure mo de is attributed to the limited dislocation pile-up distance available for very thin ligaments, which prevents high stresses from building u p and eliminates cleavage fracture. It is also shown that the ductile- brittle transition size is controlled by alloying and/or heal treatmen t. No significant dependence of the fracture toughness on the fracture mode could be found. (C) 1998 Acta Metallurgica Inc. Published bl; El sevier Science Ltd. Ali rights reserved.