Simulation Study Of Microstructure Evolution During Solidification Of Liquid Ag-Ni Allo

This paper briefly describes the theory of rapid solidification,the theory of phase transition,the structural characteristics of metallic glasses and the basic principles of molecular dynamics.The rapid solidification of AgNi liquid alloy was simulated by molecular dynamics and EAM potential,detailed analysis of energy,volume,and structural changes during solidification using methods such as average atomic energy,pair distribution function（PDF）,maximum standard cluster analysis（La SCA）,and coordination number.The theoretical research in this paper has certain guiding significance for improving the processing technology and properties of AgNi alloys.This paper shows that the solidification process of AgNi alloy is a seemingly crystalline amorphization process,which includes a liquid-liquid and a liquid-solid transition（LLT and LST）.In the LLT stage among 9 primary short-range order（SRO）structures,only three TCP CNSs（S444,S666,and S555）increases in number,indicating both BCC-crystallization and vitrification are possible,but only glass MRO structures are formed,so that vitrification has been on the way in LLT;whereas the topological LRO（TLRO）structures do not increase distinctly until the commence of the liquid-solid transition（LST）.At T<T_g the LRO parameter S_max based on ICO structures fluctuates violently,while that based on TCP structures is quite stable,representing the essential metastable characteristic of amorphous solids.The atoms in the Ag₅₀Ni₅₀ alloy system are divided into two categories according to the properties of element,coordination number,atomic potential energy and icosahedron,the corresponding partial pair distribution function（p PDF）curve has a large deviation from the total PDF curve,but the peak positions of the p PDF curve based on TCP atomic classification are in good agreement,indicating that the TCP structure has a strong correlation with the splitting of the main peak of the PDF curve.At 200 K,the Ni-centered TCP La SC is about twice as Ag-centered.The two TCP clusters in the alloy are mainly connected in three ways:point-shared,face-shared and volume-shared.The average distance from each part of the atoms to the central atom of the two TCP La SCs in the computational system is consistent with the positions of the PDF peaks,indicating that TCP La SC is the structural origin of the splitting of the PDF main peak.The microstructure evolution of Ag_100-xNi_x（x=10,20,30,40,50,60,70,80,90）alloys with 9 compositions during rapid solidification at 10¹¹ K/s.When x≤70,the solidification of AgNi alloy is a seemingly crystalline amorphization process,which includes a LLT and LST.With the increase of x,T_ls and T_g increase accordingly,the content of TCP atoms in the alloy increases,the heritability increases,and the correlation of TCP La SC increases,which makes the structure of the system more stable and the alloy GFA better.When x>70,Ni-rich local FCC crystallization occurs in the system,and with the increase of x,the number of crystal atoms increases,the rest of the structure is dominated by the TCP structure mixed with Ag and Ni atoms.