Tension and stress relaxation behavior of a La-based bulk metallic glass
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K. Jiang, X.P. Nie, and L.Y. Chen International Center for New-Structured Materials (ICNSM) and Laboratory of New-Structured Materials, Department of Materials Science and Engineering, Zhejiang University, Hangzhou 310027, People’s Republic of China
L.N. Wang and M. Shao Key Laboratory of Advanced Textile Materials and Manufacturing Technology (Zhejiang Sci-Tech University), Ministry of Education, Hangzhou 310018, People’s Republic of China
X.D. Wang International Center for New-Structured Materials (ICNSM) and Laboratory of New-Structured Materials, Department of Materials Science and Engineering, Zhejiang University, Hangzhou 310027, People’s Republic of China
Y.G. Liu and H.S. Xie Institute of Geochemistry, Chinese Academy of Sciences, Guiyang 550002, People’s Republic of China
C.L. Qin Japan Science and Technology Agency, Institute for Materials Research, Tohoku University, 2-1-1 Katahira, Aoba-ku, Sendai, Japan
A. Inoue Institute for Materials Research, Tohoku University, Sendai 980-8577, Japan
Y.W. Wang and J.Z. Jianga) International Center for New-Structured Materials (ICNSM) and Laboratory of New-Structured Materials, Department of Materials Science and Engineering, Zhejiang University, Hangzhou 310027, People’s Republic of China (Received 26 January 2007; accepted 20 March 2007)
Tension and stress-relaxation behaviors of a La62Al14Cu11.7Ag2.3Ni5Co5 bulk metallic glass (BMG) as a function of isothermal annealing time have been investigated. It is found that annealing at 373 K below the glass-transition temperature (423 K) of the BMG alloy causes an increase of special heat difference at the glass transition and density of the alloy, indicating a reduction of free volume in the BMG alloy with annealing time. Compared with the as-cast sample, the fracture strength, Vickers hardness, viscosity, Young’s modulus, and stress-relaxation stability of the annealed BMGs increase with annealing time, which is caused by the reduction of free volume in the annealed samples. Furthermore, a change of fracture morphology from a mixture of smooth and furrow zones in the as-cast sample to a mainly furrow zone in the sample annealed for 8 h was also observed. All samples exhibit brittle behavior during tension tests. I. INTRODUCTION
More and more multicomponent bulk metallic glass (BMG) systems with a critical size larger than 10 mm, such as Zr-,1–4 Pd-,5,6 Mg-,7 Cu-,8,9 Fe-,10–12 Ca-,13 Y-,14 a)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2007.0425 J. Mater. Res., Vol. 22, No. 12, Dec 2007
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and rare-earth-based15–17 BMGs, have been discovered using conventional copper mold casting. Very recently, a 20-mm-diameter La62Al14Cu11.7Ag2.3Ni5Co5 BMG rod was synthesized by copper mold casting.18 La-based BMGs with lower glass-transition temperature (Tg) values and a broader supercooled liquid region could be easily machined into shaped parts. Knowledge of tensile fracture and stress-relaxation behavior is commonly required for a
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