Influence Factors On Structural And Mechanical Properties Of CuZrAl Bulk Metallic Glasses

To date, Cu-based bulk metallic glasses (BMGs) have attracted great attention. It was reported that BMGs were quite sensitive to the oxygen content. In this work, properties and inner structures with different oxygen content of Cu-based BMGs were systematically studied. Although with low cost and high strength, it was still a difficult problem to enhance the plastic properties of Cu-based BMGs. Hence, in this work, plastic properties were enhanced due to the phase separation by Fe addition replacing of Cu in CuZrAl BMGs. The influence of Y and Nb addition on properties, and mechanical properties under different cooling rate by unidirectional solidification in CuZrAl BMGs were also discussed. The studies and conclusions are as follows:First of all, the crystallization and thermal analysis of Cu45Z48Al7 BMGs were studied. the glass formation ability (GFA) was significantly increased by micro-addition of Y in CuZrAl BMGs, while the fracture strength decreased. Based on the Cu46Zr42Al7Y5 BMGs, Zr was partly replaced by Nb and Cu46Zr42-xAl7Y5Nbx(x=0,1,2,3,4,8)alloys were prepared. The GFA and fracture strength were enlarged with a small amount of Nb addition, but when the addition was above a certain value, not only can no whole amorphous alloys be obtained, the fracture strength was markedly deducted. When 1 at.% Fe was added replacing of Cu, the GFA of Cu45Zr48Al7 BMGs was increased, and plastic deformation was also significantly improved as a result of phase separation.In the next place, we invented a new method that prepared bulk metallic glasses of low oxygen content. We firstly used high-purity hydrogen to remove oxygen at the melting point of the parent alloys, also bulk metallic glasses had a certain hydrogen-storage capacity. When bulk metallic glasses were formed, we used the reductive crucible such as graphite crucible. Therefore, the parent alloy could remelted at a reductive atmosphere, we could obtained a low cost bulk metallic glasses of a low oxygen. Two kinds of Cu45Zr48Al7 BMGs with different oxygen content were prepared. The lower the oxygen content was, the better plastic properties and greater fracture strength could be obtained. The vein pattern amount of fracture surface in Cu45Zr48Al7 BMGs with low oxygen content was more than that with high oxygen content, and the former pattern was evenly distributed. The microstructure short-range order (SRO) was also affected by oxygen content.Lastly, Cu45Zr48Al7 BMGs was prepared by unidirectional solidification under the condition of 4 different cooling rates. All BMGs under different cooling rates possessed good hardness. The variations of Microscopic Vickers hardness (HV) in both center and boundary of the BMGs were little. With the decrease of cooling rate, the HV values of BMGs were reduced and the diamond indentations were increasingly enlarged.