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Composites with a bulk metallic glass matrix were synthesized and characterized. This was made possible by the recent development of bulk metallic glasses that exhibit high resistance to crystallization in the undercooled liquid state. In this letter, experimental methods for processing metallic glass composites are introduced. Three different bulk metallic glass forming alloys were used as the matrix materials. Both ceramics and metals were introduced as reinforcement into the metallic glass. The metallic glass matrix remained amorphous after adding up to a 30 vol% fraction of particles or short wires. X-ray diffraction patterns of the composites show only peaks from the second phase particles superimposed on the broad diffuse maxima from the amorphous phase. Optical micrographs reveal uniformly distributed particles in the matrix. The glass transition of the amorphous matrix and the crystallization behavior of the composites were studied by calorimetric methods. © 1997 American Institute of Physics. ͓S0003-6951͑97͒02852-0͔Recently there has been considerable scientific and industrial interest in a variety of metal matrix composites as a way to improve mechanical properties compared to unreinforced alloys.1-3 Those materials are made by reinforcing alloys with long or short fibers, whiskers, or particles. Continuously reinforced composites provide maximum strength and stiffness in one direction but are anisotropic.4 Discontinuously reinforced metal matrix composites have been demonstrated to offer essentially isotropic properties with substantial improvements in strength and stiffness relative to those available with unreinforced materials. 5,6 Particulate composites have the further advantages of being machinable and workable using many conventional processing techniques. Many metals and ceramics have been considered as possible matrix materials. The most studied metal matrix for application at temperatures below 450°C is aluminum.7 Titanium has been extensively studied from the perspective of higher-temperature applications. 8 In this work, bulk metallic glasses were used as matrices reinforced with refractory ceramics, ductile metal particles, or short wires. This was made possible by the use of recently reported multicomponent alloys that exhibit an extremely high glass forming ability, e.g., La-Al-Ni, 9 Zr-Al-Cu-Ni, 10 and Zr-Ti-Cu-Ni-Be. 11In the work described here, Zr-Ti-Cu-Ni ͑Ref. 12͒ and Zr-Ti͑Nb͒-Al-Cu-Ni ͑Ref. 13͒ alloys, which show extraordinary glass forming ability, were used as the matrix. These bulk metallic glasses have promising properties such as high yield strength and a high elastic strain limit combined with relatively high fracture toughness, fatigue, and corrosion resistance. 14-17 However, they have little ductility in tension. This lack of tensile ductility could be an important drawback in many applications. Thus, one of the motivations for adding second phase particles to the metallic glass was to hinder propagation of shear bands and encourage the formation of multiple shear bands...

Composites of the Cu 47 Ti 34 Zr 11 Ni 8 bulk metallic glass, reinforced with up to 30 vol % SiC particles are synthesized and characterized. Results based on x-ray diffraction, optical microscopy, scanning Auger microscopy, and differential scanning calorimetry ͑DSC͒ are presented. During processing of the composites, a TiC layer forms around the SiC particles and Si diffuses into the Cu 47 Ti 34 Zr 11 Ni 8 matrix stabilizing the supercooled liquid against crystallization. The small Si addition between 0.5 and 1 at. % increases the attainable maximum thickness of glassy ingots from 4 mm for Cu-TiZr-Ni alloys to 7 mm for Cu-Ti-Zr-Ni-Si alloys. DSC analyses show that neither the thermodynamics nor the kinetics of the alloy are affected significantly by the Si addition. This suggests that Si enhances the glass forming ability by chemically passivating impurities such as oxygen and carbon that cause heterogeneous nucleation in the melt.

To increase the toughness of a metallic glass with the nominal composition Zr 57 Nb 5 Al 10 Cu 15.4 Ni 12.6 , it was used as the matrix in particulate composites reinforced with W, WC, Ta, and SiC. The composites were tested in compression and tension experiments. Compressive strain to failure increased by more than 300% compared with the unreinforced Zr 57 Nb 5 Al 10 Cu 15.4 Ni 12.6 , and energy to break of the tensile samples increased by more than 50%. The increase in toughness came from the particles restricting shear band propagation, promoting the generation of multiple shear bands and additional fracture surface area. There was direct evidence of viscous flow of the metallic glass matrix within the confines of the shear bands.

Refractory Ni-based bulk metallic glasses are formed in the three-component Ni–Nb–Sn system near a ternary eutectic composition located within the three-phase field bounded by the three intermetallics Ni3Nb, Ni6Nb7 (μ-phase), and Ni2NbSn (BiF3-type). Bulk amorphous alloys of composition Ni60Nb40−xSnx with 3<x<9 were prepared by injection-casting the molten alloys into copper models. X-ray diffraction and differential scanning calorimetry studies show the cast strips to be fully amorphous up to thicknesses from 0.5 to 3 mm as x is varied. Maximum glass-forming ability (GFA) observed when x is between 6 and 7. These refractory bulk amorphous alloys exhibit high glass transition temperatures 881<Tg<895 K, a large, stable, undercooled liquid region with ΔT=Tx−Tg, at ∼40–60 K, very high Vickers hardness (VH∼1000–1280 Kg/mm2), and estimated yield strengths in the range of 3 to 3.8 GPa. The effects of small quaternary additions of B and Fe on the GFA of the ternary alloys are also reported.