Microstructure, fracture toughness and compressive property of as-cast and directionally solidified NiAl-based eutectic composite

Microstructure and room temperature mechanical property of as-cast and directionally solidified NiAl-Cr(Mo) eutectic composite were investigated by SEM, EDS, three point bending test and compression test. The microstructure of as-cast alloy consists of Cr(Mo) primary dendrites and equiaxed eutectic cells. For the directional solidification of liquid metal cooling technique (LMC), only the small quantity of Cr(Mo) primary dendrites appear in the beginning of solidification, and the fully and well-aligned lamellar structure parallel to the growth direction is obtained in the steady-state zone. However, the Cr(Mo) primary phase is always observed in the whole directional solidification of zone melted liquid metal cooling technique (ZMLMC), and the eutectic lamellas are disordered and not parallel to the growth direction in the steady-state zone. Compared to the ZMLMC alloys, the LMC alloy has the better room temperature fracture toughness and compressive property due to the well-aligned lamellar structure. Crack propagation and fracture surface are also observed to understand the fracture behavior.