Synthesis of Ni-based bulk metallic glass matrix composites containing ductile brass phase by warm extrusion of gas atom
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D.J. Sordelet Ames Laboratory, Iowa State University, Ames, Iowa 50014 (Received 26 March 2003; accepted 9 June 2003)
To prevent catastrophic failure by propagating highly localized shear bands and to overcome the limited dimension of metallic glass, centimeter-scale Ni59Zr20Ti16Si2Sn3 bulk metallic glass matrix composites were fabricated by warm extrusion of a mixture of gas-atomized fully amorphous powders and ductile brass powders. After consolidation, the composite retained the fully amorphous matrix found in the gas-atomized powder combined with the brass second phase. The glass-transition and crystallization temperatures of the extruded material were the same as those of the starting powders. The confined ductile brass phase enabled the bulk metallic glass matrix composites to deform plastically under uniaxial compression at room temperature. The combination of strength and ductility in the inherently brittle Ni-based monolithic materials could be obtained by introducing a ductile phase in the bulk metallic glass matrix. However, control of the volume fraction and distribution of the ductile brass phase was important for the proper combination of the strength and plasticity.
I. INTRODUCTION
Bulk metallic glasses (BMGs) are known to have unique mechanical properties, including high strength, relatively low Young’s modulus, and perfect elastic behavior.1 However, they show little overall room temperature plasticity, but rather deform by highly localized shear banding, resulting in catastrophic failure.2 Recent attempts to improve the ductility of the BMGs have focused on the preparation of composite materials exhibiting a microstructure consisting of crystalline phases such as particles,3 fibers,4 or in situ formed precipitates5 dispersed in the metallic glass matrix. The metallic glass matrix composites have been found to exhibit enhanced plasticity not generally observed in monolithic bulk metallic glasses.6 This deformation behavior stems possibly from the formation of multiple shear bands initiated at the interface between the reinforcing agent and the metallic glass matrix, and their confinement in metallic glass matrix composites.7 The improved ductility may
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Address all correspondence to this author. e-mail: [email protected] J. Mater. Res., Vol. 18, No. 9, Sep 2003
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open the possibility of overcoming the limited applications of monolithic bulk metallic glasses that fail catastrophically with little plastic elongation in an apparently brittle manner, although the bulk metallic glasses usually have high strength, high hardness, and excellent corrosion resistance. However, only a few alloy systems with high glass-forming ability—for example, Zr- and Tibased metallic glasses8,9—so far can be obtained as bulk metallic glass matrix composites. Recently, it has been shown that the production of BMGs by consolidation of amorphous powders has promising and important practical applications in the near-net-shape fabrication of components with novel p
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