Microstructure and mechanical properties of Fe–Cr–C eutectic composites

In the present investigation, an Fe–Cr–C eutectic alloy was prepared from industry-grade materials and subjected to unidirectional solidification (UDS), through which new types of fibre reinforced composites, eutectic composites, were generated. The composites obtained were examined using X-ray diffraction (XRD), electron microprobe and field emission scanning electron microscopy (FESEM). According to XRD, the composites consist of three phases, i.e. γ, M7C3 and trace amounts of M23C6. While the compositions of γ and M7C3 were determined by electron microprobe analysis, M23C6 was not detected due to the limited amount present. Fibre morphology was studied as a function of solidification rate (R) using FESEM. Fibre diameter, spacing and regularity decreased with increasing solidification rate; however, the volume fraction of fibres remained essentially constant at around 32%. Mechanical testing was carried out on both eutectic composites and as cast alloys. The tensile strength of Fe–Cr–C eutectic composites varied parabolically with solidification rate. When R was 58 mm h−1, a maximum strength of 2300 MPa was reached, which is about seven times as strong as that of conventional high chromium cast iron of similar composition. Two other alloys with hyper- and hypo-eutectic compositions were included in the present investigation for comparison purposes. It was found that the presence of primary phases significantly diminished fibre regularity and, therefore, the material strength.