Local structural evolution of Fe54C18Cr16Mo12 bulk metallic glass during tensile deformation and a temperature elevation process: a molecular dynamics study

Abstract

The mechanical and thermal properties of Fe₅₄C₁₈Cr₁₆Mo₁₂ bulk metallic glasses (BMGs) were investigated by a molecular dynamics simulation with the 2NN modified embedded-atom method (MEAM) potential. The fitting process of the cross-element parameters of 2NN MEAM (Fe–C, Fe–Cr, Fe–Mo, C–Cr, C–Mo, and Cr–Mo) was carried out first by the force matching method (FMM) on the basis of the reference data from density functional theory (DFT) calculations. With these fitted parameters, the structure of Fe₅₄C₁₈Cr₁₆Mo₁₂ BMG was constructed by the simulated-annealing basin-hopping (SABH) method, and the angle distribution range of the X-ray diffraction profile of the predicted Fe₅₄C₁₈Cr₁₆Mo₁₂ BMG closely matches that of the experiment profile, indicating the fitted 2NN MEAM parameters can accurately reflect the interatomic interactions of Fe₅₄C₁₈Cr₁₆Mo₁₂ BMG. The Honeycutt–Andersen (HA) index analysis results show a significant percentage of icosahedral-like structures within Fe₅₄C₁₈Cr₁₆Mo₁₂ BMG, which suggests an amorphous state. According to the tensile test results, the estimated Young's modulus of Fe₅₄Cr₁₆Mo₁₂C₁₈ bulk metallic glass is about 139 GPa and the large plastic region of the stress–strain curve shows that the Fe₅₄C₁₈Cr₁₆Mo₁₂ BMG possesses good ductility. Local strain distribution was used to analyze the deformation mechanism, and the results show that a shear band develops homogeneously with the tensile fracture angle (θ_T) at about 50 degrees, in agreement with experimental results 45° < θ_T < 90°. For the temperature elevation results, the discontinuity of the enthalpy–temperature profile indicates the melting point of Fe₅₄Cr₁₆Mo₁₂C₁₈ BMG is about 1310 K. The diffusion coefficients near the melting point were derived by the Einstein equation from the mean-square-displacement (MSD) profiles between 800–1400 K. On the basis of diffusion coefficients at different temperatures, the diffusion barriers of Fe₅₄Cr₁₆Mo₁₂C₁₈ can be determined by the Arrhenius equation. The diffusion barriers of total for Fe, Cr, Mo, C are 31.88, 24.68, 35.26, 22.50 and 31.79 kJ mol⁻¹, respectively. The diffusion barriers of Fe and Cr atoms are relatively lower, indicating Fe and Cr atoms more easily diffuse with the increasing temperature.