Effect Of Pressure During Solidification Process On The Structure And Mechanical Properties Of Amorphous Alloys

Amorphous alloys have excellent properties such as high hardness,high elastic limit and good soft magnetic properties,and are widely used in many fields.These excellent properties are due to their unique internal structure.The external factors during the rapid solidification process,such as temperature,pressure,and cooling rate,will affect the structure of the amorphous alloys and further their performance.Among these factors,the mechanism of pressure effect has not been extensively studied due to the limitation of experimental technology.However,as the high pressure die-casting is one of the main methods for preparing amorphous alloys in industry,the pressure effect during solidification process cannot be ignored.In this study,Zr₄₆Cu₄₆Al₈ alloy was taken as the model system and the effect of hydrostatic pressure on the structure of amorphous alloys during rapid solidification was studied by applying molecular dynamics simulation,and then the uniaxial tensile simulation was performed to investigate the plastic deformation of amorphous alloy samples obtained under different pressure.The rapid solidification results indicated that the average volume decreases,the potential energy increases and the glass transition temperature increases with the increase of pressure during the solidification process for the Zr₄₆Cu₄₆Al₈ amorphous alloys obtained under different pressure.The results of the pair distribution function indicated that with the increase of pressure during solidification,the first peaks of Cu-Zr,Cu-Cu,and Cu-Al all shift to the right,indicating that the bonding between Cu and other atoms weakens as the pressure increases.The Voronoi polyhedron analysis reveals that the Voronoi volumes of Zr and Al atoms decrease with increasing pressure,while the Voronoi volumes of Cu atoms show an increasing trend.This abnormal increase of Voronoi volume for Cu atoms was further verified mainly existing in the minority polyhedra(content<2%).The uniaxial tensile results indicated that,as the pressure increases during solidification,the yield strength of the amorphous alloy decreases,the degree of strain localization decreases,and the shear transition zone(STZ)distribution is more uniform and extensive.Structural analysis shows that during the formation of the shear band,the content and Voronoi volume of Cu centered icosahedrons gradually decreases,while the content and Voronoi volume of the fragmental Cu centered polyhedrons increase.These fragmental polyhedrons are widely distributed and loosely packed,acting as flow units in the tensile process and can dissipate a lot of strain energy.Furthermore,as the pressure increases during the solidification process,the increase of the Voronoi volume of fragmental polyhedrons is more steeper,and shows larger range of increase,resulting in broadening of the shear band formation,which contributes to the improvement of the plasticity for the Zr₄₆Cu₄₆Al₈ amorphous alloy.This study has important scientific significance for understanding the formation mechanism under pressure and the structure-performance relationship for amorphous alloys.It can also provide important guidance for large-scale die-casting of amorphous alloys,optimizing their performance,and expanding their application range.