Interpenetrating microstructure and fracture mechanism of NiAl/TiC composites by pressureless melt infiltration

NiAl/TiC composites with TiC content of 86-92 vol.% were prepared by pressureless melt infiltration. The high content of TiC and consequent TiC particles joining were obtained by pre-sintering of the as-pressed TiC preform before infiltration. Mechanical properties including bending strength, Vickers hardness, fracture toughness and Young's modulus were measured. The microstructure of the composites is characterized by the three-dimensional interpenetration of TiC and NiAl phases. Four-point bending strength and Vickers indentation hardness of NiAl/86 vol.%TiC composite are as high as 670 +/- 80 MPa and 14.0 GPa, respectively. This has been attributed to the characters of the microstructure such as the two interpenetrating phases, a high densification degree and freedom of defects as well. The fracture surface observed by SEM shows a dominant brittle fracture with somehow a ductile deformation in some thin NiAl ligaments. The thin NiAl ligament in the composites acts as crack bridge during fracture evidenced by indentation test. (C) 2004 Elsevier B.V. All rights reserved.