Effect of chromium content on microstructure and mechanical properties of large dimensional bulk nanocrystalline based Fe–Al–Cr alloys prepared by aluminothermic reaction

Highlights: ► We prepared large dimensional bulk nanocrystalline alloy, ∅ 200 mm × 10 mm. ► Grain size varied in range of 15–18 nm with Cr content. ► Cr7C3 phase appears in nanocrystalline matrix and varied with Cr content. ► Compressive strength was 1.2 GPa, much higher than those of small dimensional alloys. - Abstract: Large dimensional bulk nanocrystalline based Fe–Al–Cr alloys with 5, 10 and 15 wt.% Cr which were about 200 mm in diameter and 10 mm in thickness was prepared by an aluminothermic reaction casting method. Microstructures of the alloys were investigated by scanning electron microscope (SEM) attached with energy dispersive spectrometer (EDS) and electron backscattered diffraction (EBSD), X-ray diffraction (XRD) and transmission electron microscope (TEM). Compressive properties of the alloys were tested. The results show that the alloys were consisted of a Fe–Al–Cr nanocrystalline matrix with the grain size in a range of 15–18 nm and a precipitated Cr7C3 phase which dispersed homogeneously in the matrix. The content of Cr dissolved in the nanocrystalline matrix, volume fraction and morphology of the Cr7C3 phase varied with the increasing of Cr element added in the alloys. Compressive strength of the alloys was in a range of 1100–1200 MPa. The alloy with 10 wt.% Cr had the highest yield strength of about 1048 MPa, while the alloy with 15 wt.% Cr had the lowest yield strength of about 911 MPa. The alloys showed considerable ductility and best plastic deformation capability for that of 15 wt.% Cr