Study On Glass Formation And Atomic Structure In Cu-Zr-Ag Alloys

More attention has been paid in the Cu-Zr glasses not only because of its scientific research value but also extensive application prospects in the field of amorphous alloys due to its lower cost and better mechanical property compared to other systems. The glass-forming ability （GFA） of Cu-Zr system are improved notably after the addition of Ag. In the paper, MD simulation are performed based on the EAM potential on Cu-Zr binary alloys and Cu-Zr-Ag ternary alloys to explore the dependence of glass-forming ability （GFA） and atomic structure on the changes of compositions.In Cu100-xZrx （x=8-83） system, optimum glasses formation actually occur at near-eutectic compositions rather than off-eutectic compositions. In near-eutectic compositions, the stronger interaction in elements Cu and Zr promotes the formation of icosahedra clusters with Cu atom acting as the center atoms. The icosahedra form short-range order clusters and medium-range order clusters, which restricts the mobility of atoms, resulting in better GFA.In （CuZr）_100-xAg_x （x=0,10,20,30） system, with Ag content increasing, the GFA rise first and then decline, reaching maximum in Cu₄0Zr₄0Ag₂0 alloy. Compared to the Cu50Zr50 alloy, Cu₄0Zr₄0Ag₂0 alloy shows higher main peaks in three pair correlation functions gCuCuO（r）, gCuZr（r） and gzrzr（r）, lower values in chemical short-range order parameters aCuZr and αZrCu and stronger interactions in particles, all of these are in favor of the formation of icosahedra. In Cu₄0Zr₄0Ag₂0 alloy, the total coordination number is closer to ideal icosahedra formation value （12）, and the icosahedral order parameter W6 is closer to the theoretical value （0.169754）. Larger numbers of icosahedra are linked together by sharing atom along point, line, plane and body linking, forming medium-range icosahedra cluster, which promotes glass formation. Among all partial structure factors, the highest main peak happens in ScuZr（Q）,then SzrAg（Q） shows the second highest main peak, demonstrating strong interaction in heterogeneous atoms. The enthalpy of mixing in Cu atom and Zr atom is -23kJ/mol, less than that in Zr atom and Ag atom （-20kJ/mol）. The small peaks with negative amplitude ahead of the main peak in SCuZr（Q）,SzrAg（Q） and SAgAg（Q） suggest preference of Cu-Zr, Zr-Ag and Ag-Ag pairs. The prepeaks in SCcuCu（Q）, SCuAg（Q） and SZrZr（Q） represent the avoidance of atom neighbours.In CuxZr80-xAg20 （x=10,15,20,25,30） system, Cu₄0Zr₄0Ag₂0 alloy shows highest GFA. Compared with Cu₃0Zr₅0Ag₂0 alloy, Cu₄0Zr₄0Ag₂0 shows higher GFA reflected by the structure parameters, such as interatomic distance Rmin, chemical short-range order parameters αCuZr,total coordination number, number of icosahedra, and density of short ranged and medium ranged icosahedra clusters. Interestingly, highest main peak occurring in gAgAg（r） among all partial pair correlation functions, short-range order parameters αCuZr showing negative value and the obvious negative amplitude ahead of the main peak in SAgAg（Q） denote the Ag-Ag neighbors. The atomic structure in alloys shows too many Ag atoms gathered together and linked, without Cu atoms and Zr atoms acting as neighbors, because of the positive enthalpy of mixing in Cu-Ag, resulting in the avoidance of atom neighbours in Cu and Ag.