Cluster Formulas And Composition Design Of Cu-Zr-based Bulk Metallic Glasses

Metallic glasses have obtained more and more interests due to its unique properties compared with crystalline materials and it is always a hot topic for researchers to find out bulk metallic glasses (BMG). In this paper, we optimize the Cu-based Cu-Zr-Al system and Zr-Al-Ni-Cu system based on criteria of cluster line and cluster-plus-glue-atom model. A series of new bulk amorphous alloys are successfully found. The minor alloying of Nb is also found to increase the glass forming ability (GFA) in (Zr7Cu6) Al1 amorphous alloys.Cluster line and cluster-plus-glue-atom model were used to analysis the GFA in Cu-based Cu-Zr-Al bulk metallic glasses. In order to compare with the classic composition based on the cluster Cu8Zr5, new alloy compositions that can be described by the compostion formular of:Cu8Zr5-Alx, Cu7.1Zr5-Alx, Cu8.9Zr5-Alx and Cu11.26Zr5-Alx, are studied. Thermal analyses and XRD results show that the composition formulated by [Cu8Zr5]Al1 has the highest thermal stability and the largest glass forming ability. It is notable that such composition locates at the equilibrium state of the electrochemical potentions. By comparing the variations of the thermal parameters with respect to composition deviations from the ideal [Cu8Zr5]Al1, it is found that there is another group of bulk metallic glasses lying in the third composition line, in which Cu60.2Zr33.8Al6 also has the highest thermodynamic parameters in its group.The classic Al7.5Cu17.5Ni10Zr65 can be interpreted as the composition formular of [(Cu2.45Ni1.4)Zr9.1]Al1.05. Such formular indicates that the quaternary Zr-Al-Ni-Cu BMGs can be understood as a mixture of the Cu4Zr9 and Ni4Zr9 clusters plus the glue atom Al. However, the calculations of the electrical chemical potentials suggested that the value of glue atoms is close to 1 (6.5 to 8.5 at.%Al). Therefore, we design four series of components in the form of [(Cu,Ni)Zr9]Alx where x=0.9～1.2 (6.5 to 8.5 at.% Al) are designed to optimize the amorphous composition Al7.5Cu17.5Ni10Zr65 according to the Ni, Cu ratio of 3/1,2/2,1.5/2.5, 1/3, respectively. This results in the successful finding of the composition with the largest GFA in this local domain. According to the variations of the thermal parameters with respect to composition deviations, we found that No.10 (Al8.5Cu14.1Ni14.1Zr63.4) and No.15 (Al8.5Cu17.6Ni10.6Zr63.4) have the largest GFA and the highest thermal stability which the diameter is up toΦ10mm in each domainAs the glass-forming ability of (Zr7Cu6)Al1 is less thanΦ5mm by copper suction casting, we use the method of minor alloying to increase the GFA through adding the minor element Nb into (Zr7Cu6)Al1 alloys. Further studies will focus on the effects of the minor alloying of Nb on the thermal stability and mechanical properties. We designed a series of components described as:[(Zr7Cu6) Al1]100-xNbx (x=0,1,2,3,5 at.%), and found that the glass-forming ability of (Zr7Cu6)Al1 metallic alloy can be dramatically enhanced with the addition of 2 at% Nb, while the mechanical properties of (Zr7Cu6)Al1 metallic alloy enhanced a little when 5 at% Nb is added.