The Fabrication And Study Of CuZr-Based Bulk Metallic Glasses

In this paper, a series of CuZr-based bulk metallic glasses (BMGs) are fabricated by the Cu mold casting method. The glass-forming ability (GFA), mechanical properties, and liquid behavior of the alloys are investigated.The Cu50Zr50, (Cu50Zr50) 100-xAlx (x=4~10) ,and (Cu50Zr50) 93-xAl7Gdx(x=1~7) BMGs with different critical dimension are fabricated by casting method. The critical dimension of Cu50Zr50 is up to at least 2mm, and it is one of the binary alloys with best GFA. When the Al composition at 4~8at.%, the ternary alloys have a critical dimension at least 5mm and have the best GFA in CuZrAl (rich Cu) systems. The critical dimension of quaternary (Cu50Zr50) 92Al7Gd1 reach to about 1cm.The CuZr-based alloys have an excellent GFA. The GFA of CuZr-based system is increased from binary, ternary to quaternary alloy. The additions of the third, fourth element are the key factor to increase the GFA of CuZr-based glasses.The CuZr-based BMGs have wonderful fracture properties of compression. The fracture strength of (Cu50Zr50)95Al5 sample is up to 2265MPa with 18% plastic deformation. Only appropriate additions can improve the mechanical properties of the CuZr-based glasses. The additions of rare earth element Gd make the glasses more "brittle" than the ternary alloy.The elastic constants are derived from the acoustic and density measurement. The CuZr-based BMGs have higher bulk modulus K, Young's modulus E, shear modulus G and K/G compared to oxide glasses. The elastic constants of the BMGs are changed by Al and Gd additions. Because the elastic constants are very sensitive to the microstructure of the alloy, the changes of elastic constants reflect the microstructure transformation of alloy with addition.The relation between liquid behavior and addition of the BMGs is studied by DSC measurement and VFT method. The best fits results show the trend that m decreases with more element additions. The proper minor addition induces a strong tendency of short-range ordering which leads to an extra decrease of configuration entropy, and makes the liquid stronger and more viscous, and thus slows down the crystallization kinetics. The results confirm that the GFA and fragility of an alloy correlate with high degree of short and medium range order in BMG-forming systems.