The effect of primary crystallizing phases on mechanical properties of Cu 46 Zr 47 Al 7 bulk metallic glass composites
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hang and Z.F. Zhang Shenyang National Laboratory for Materials Science, Institute of Metal Research, Chinese Academy of Sciences, Shenyang 110016, People’s Republic of China (Received 22 March 2006; accepted 12 July 2006)
Cu46Zr47Al7 bulk metallic glass (BMG) and its composites in plate with different thicknesses up to 6 mm were prepared by copper mold casting. Primary crystallizing phases with different microstructures and volume fractions could be obtained under different cooling rates, forming some composites with different mechanical properties. Under compression tests, the 2-mm-thick monolithic BMG has a yield strength of 1894 MPa and a high fracture strength of up to 2250 MPa at plastic strain up to 6%, exhibiting apparent “work-hardening” behavior. The 4-mm-thick Cu46Zr47Al7 BMG composite containing martensite phase yields at 1733 MPa and finally fails at 1964 MPa with a plastic strain of 3.7%. I. INTRODUCTION
Recently, there has been considerable scientific and industrial interest in a variety of bulk metallic glass (BMG) composites as an effective way of further improving mechanical properties compared with monolithic BMGs.1–9 In these composites, the second phase hinders single shear band to extend critically through the whole sample at the onset of plastic deformation and seeds the initiation of multiple shear bands. Therefore, plasticity is distributed more homogeneously in the shear band patterns, which results in local high strains to failure of the composites. The elements with high melting points, such as Ta, Nb, or Mo, are often added to ZrCu- and Ti-based BMGs by in situ precipitation of ductile micrometersized particles,3,4 body-centered cubic- (bcc-) dendrites,5,6 or nanostructure dendrites7,8 upon cooling from the melting to improve the ductility of the composites. On one hand, the suitable composition design is important to ensure to high glass-forming ability (GFA) necessary for the formation of bulk amorphous matrix and to introduce an appropriate primary crystallizing phase. On the other hand, the size, geometry, and volume fraction of the primary crystallizing phase are also crucial for efficiently controlling of the shear band propagation and improving the ductility. Many efforts have been made to investigate the effect of alloy element addition on the microstructure and volume fraction of primary
crystallizing phase. 7–9 However, there is little research10,11 that deals with the microstructure and volume fraction of primary crystallizing phases under different cooling rates upon solidification. Recently, it was reported that Cu47.5Zr47.5Al5 BMG rod of 2 mm in diameter exhibited high compressive strength of up to 2265 MPa together with extensive ‘‘work hardening’’ and large plastic strain of 18%.12 In addition, plasticity-improved Zr-Cu-Al BMG matrix composites were also prepared by in situ precipitation of CuZr martensite phase.13 Compared with the former ZrCu- and Ti-based BMG composites,1–9 Zr-Cu-Al (or Cu-Zr-Al) ternary alloys have a better combination of strength, ductility, and l
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