Effects of pressure on microstructure evolution of liquid Fe-S-Bi alloy during rapid solidification: A molecular dynamics study.

To understand the effects of pressure on microstructural evolution, a molecular dynamics simulation study has been performed under pressures of 0-20 GPa for liquid Fe-S-Bi alloy during the solidification process. The variations in the radial distribution function, average atomic energy, and H-A bond index of the cooling system are analyzed. The rapid solidification process of liquid Fe-S-Bi alloy into crystalline and amorphous alloys is investigated from different perspective. The results show that the glass transition temperature Tg, the sizes of the MnS atomic groups, and major bond-types increase almost linearly with increasing pressure. In addition, the recovery rate of Bi increased first and then decreased with increasing pressure, reaching a peak of 68.97% under 5 GPa. The manganese sulfide compound is embedded in the alloy with a spindle-shape under 20 GPa, which is a better clusters structure.

Effects of MnS inclusions on mechanical behavior and damage mechanism of free-cutting steel: A molecular dynamics study.

In order to research the effect pattern of MnS inclusions on free-cutting steel, we study the microstructure evolution, the damage mechanism and the mechanical properties in free-cutting steel in the presence of MnS inclusions. Spindle shaped MnS is added as inclusions within the free-cutting steel. The mechanical properties were found to change when inclusions were present. The gained results show that the formation of voids causing fracture starts from the interface inside the matrix close to the MnS. From the point of view of nanocomposite strength, the main effect of MnS inclusions is related to stress concentration, leading to the effect of increased stresses near the interface between the interior of the matrix and the inclusions. The inclusions have lower Young's modulus and lower dislocation activity, resulting in smaller deformation of the alloy system, larger interfacial stress concentrations and earlier hole formation. The maximum strain and stress regions of the alloy also appear near the MnS inclusions, which leads to the formation of defects near the MnS inclusions and then fracture of the alloy. MnS inclusions adversely affect the tensile properties of the alloy, such as Young's modulus, yield stress and yield strain. By comparing the stress-strain curves of single crystal iron and alloy containing MnS inclusions, it is indicated that the yield strength of the latter decreases. Slip bands and dislocation lines are first generated around the MnS inclusion, and the phase transition is induced from the original single BCC structure to FCC, HCP and amorphous structures, and the atoms of FCC, HCP and amorphous structures increase with increasing strain, while those of BCC structure decrease, especially after yield strain. This study is significant for understanding the effect of inclusions on the mechanical laws and fracture mechanisms of the alloy.