Strength improvement and fracture mechanism in Fe40Al/TiC composites with high content of TiC

TiC preforms with high degrees of densification (80 and 88%) were prepared by pre-sintering (1500 °C×1 h and 1500 °C×4 h). Fe40Al melt (1450 °C) infiltrated the preforms in an indirect upward infiltration method to produce Fe40Al/TiC composites with TiC volume fraction ranging of 74-88%. Bending strength, hardness, fracture toughness and Young's modulus were measured. The highest values of four-point bending strength and indentation Vickers hardness reach 1400 MPa and 14.4 GPa, respectively. The strength is significantly improved compared to the values previously reported in the literature. This is attributed to the processing technique optimisation including powder de-agglomerating, preform pre-sintering and indirect upward infiltration, all leading to fully dense and nearly defect free composites. Microstructural characteristics and fracture mechanism of the composites were investigated with SEM and TEM. The results show that TiC and Fe0.6Al0.4 are the only two phases in the composites. Fe40Al ligaments exhibit ductile behaviour and act as bridges during the fracture process. The effect of the surface roughness of the test samples on the bending strength was also investigated.