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Li-Fang Wang,Xiao Cui,Qi-Dong Zhang,Fang-Qiu Zu 대한금속·재료학회 2014 METALS AND MATERIALS International Vol.20 No.4
The thermal stability and crystallization kinetics of the CuxZr84-xAl8Ag8 (x = 42, 40, 38, and 36) bulk metallicglasses (BMGs) were studied by measurement of isothermal electrical-resistance. As the composition becomesricher in Zr, the longer incubation time at the same relative annealing temperature, and the larger local activationenergy needed to achieve the same crystallized volume-fraction, indicate improved thermal stability,which resists crystallization. The improved thermal stability is attributed to a denser atomic random-stackingstructure and larger negative heat-of-mixing. During isothermal annealing processes, the four BMGs exhibitedthe same nucleation mechanism, which is a decreasing rate of nucleation over time. However, the crystal growthmechanisms of the four BMGs are different. The crystallization of the Cu36Zr48Al8Ag8 and Cu38Zr46Al8Ag8BMGs is interface-controlled growth, contrasting with diffusion-controlled growth for the Cu40Zr44Al8Ag8 andCu42Zr42Al8Ag8 alloys. The different growth modes may be caused by fluctuations in composition due tochanges in the quantity and distribution of Cu-rich and Ag-rich regions.
Xiao Cui,Jing Guo,Qi‑dong Zhang,Xiao‑jun Meng,Bing‑chuan Bian,Ren‑gao Zhao,Yu‑bai Ma,Fang‑qiu Zu 대한금속·재료학회 2020 METALS AND MATERIALS International Vol.26 No.10
The slow β relaxation which occurring at temperatures far below glass transition temperature, typically playing importantroles in the plastic deformation behavior of metallic glasses. Compared with polymer glasses, most of the metallic glasses donot exhibit obvious β relaxation based on dynamic mechanical analysis. In the current work, prominent β relaxation behaviorsof a series (LaxCe100−x) Al10Co25(x = 50, 60, 70, 80) bulk metallic glasses (BMGs) at low temperature are observed usingdynamic mechanical analysis. Compared with other BMGs, the LaCe based BMGs show a pronounced β relaxation peak andrelative low peak temperature, the activation energy of the β relaxation based on Arrhenius equation are calculated around79.3 kJ/mol to 86.4 kJ/mol, which obey an empirical rule that Eβ ≈ (26 ± 4) RTg, with the coefficient of 23. Experimentalresults from room temperature compression tests for the LaCe based BMGs indicate that low temperature activated β relaxationbehaviors facilitate the good plasticity of the LaCe based BMGs.
Xiao‑Bo Mei,Bao‑Chuan Liu,Wei Jiang,Quan Xu,Qi‑Dong Zhang,Yu‑Bai Ma,Fang‑Qiu Zu 대한금속·재료학회 2020 METALS AND MATERIALS International Vol.26 No.9
The influence of cooling rates on the mechanical properties of a Zr-based bulk metallic glass prepared with high rheologicalrate forming (HRRF) was investigated and compared with traditional suction cast methods. Amorphous samples of Zr57Cu-20Ni8Al10Ag5 were prepared in copper molds with different sizes in order to obtain different cooling rates for both HRRFand traditional cast methods. These specimens were subjected to compression experiments, including microhardness testing,X-ray diffraction testing and differential scanning calorimetry analysis. The results indicate that the plasticity of the samplesformed by HRRF are higher than that of the as-cast ones at the same cooling rates, while the microhardness manifests theopposite principle. As the cooling rate increases further, the difference in plasticity further increases between two methods,indicating that the plasticity of metallic glasses is more sensitive to cooling rates during the HRRF process. At the core ofthis phenomenon is the fact that HRRF methods can introduce more free volume into glasses than traditional cast methodswith an elevated cooling rate are able to.