Papers by Keyword: Bulk Metallic Glass Composites

Abstract: The mechanical behavior of CuZr-based bulk metallic glass composites with different B2-CuZr phase transformation ability was investigated. The B2 phase transformation is conducive to enhance the mechanical properties of CuZr-based bulk metallic glass composites. The mechanical properties of the austenitic B2 phase specimens were also studied to understand the mechanism of phase transformation effect. It was found that the B2 phase with martensitic transformation exhibits lower yield strength and stronger work-hardening capability than the B2 phase without martensitic transformation. Thus, the phase transformation effect of B2-CuZr phase, accompanying with its lower yield strength and stronger work-hardening capability, is the main reason for the CuZr-based bulk metallic glass composites possess outstanding mechanical properties.

Abstract: Bulk metallic glasses (BMGs) are amorphous alloys that exhibit unique mechanical properties such as high strength due to their liquid-like structure in the vitreous solid state. While they usually exhibit low ductility, they can be toughened by incorporating secondary phase particles within the amorphous matrix via composite fabrication to generate amorphous metal matrix composites (MMCs). Traditional MMCs are fabricated at high temperature in the liquid state with tedious blending processes. This high temperature processing route often leads to unwanted reactions at the reinforcement/matrix interface, creating brittle intermetallic by-products and damaging the reinforcement. In the present work, novel bulk metallic glass composites (BMGCs) were fabricated at low processing temperatures via thermoplastic forming (TPF) above the glass transition temperature of the amorphous matrix. Here, the unique thermophysical features of the matrix material allow for TPF of composites in non-sacrificial moulds incorporating various types of reinforcement, via processing in the solid state at low temperatures (less than 200 °C), within a short timeframe (less than 10 minutes); this avoids the formation of brittle phases at the reinforcement/matrix interface leading to efficient bonding between particles and matrix, thereby creating a tough, low density composite material.

Abstract: The work hardening ability under room temperature compression of ductile Cu47.5Zr47.5Al5 and Cu47Ti33Zr11Ni8Si1 bulk metallic glass-forming alloys has been studied and compared. Both alloys exhibit high fracture strength, distinct work hardening and large plastic strain. Systematic investigations on the microstructural evolution reveal the occurrence of nano-scale heterogeneities, of both structural and chemical nature, which enables multiplication, branching, and restriction of the shear bands, thus controlling the plastic instability of metallic glasses. Phase separation in the liquid state leading to chemical inhomogeneities has been revealed for as-cast Cu47.5Zr47.5Al5 samples. In the case of Cu47Ti33Zr11Ni8Si1, a composite-type microstructure with in-situ formed nano-scale precipitates embedded in a glassy matrix is responsible for the distinct work hardening recorded on the stress-strain curves. The present results support the important role of nano-scale heterogeneities for promoting efficient work hardening in Cu-based metallic glass composites.

Abstract: In the present study, Ti50Cu28Ni15Sn7 metallic glass and its composite powders reinforced with 4~12 vol% of SiC additions were successfully prepared by mechanical alloying. The as-milled Ti50Cu28Ni15Sn7 and composite powders were then consolidated by vacuum hot pressing into disc compacts with a 10 mm diameter and thickness of 2 mm. The structure of the as-milled powders and consolidated compacts was characterized by X-ray diffraction. While the thermal stability was examined by differential scanning calorimeter. In addition, the mechanical property of the consolidated bulk metallic glass and its composite was evaluated by Vickers microhardness tests. In the ball-milled composites, initial SiC particles were homogeneously dispersed in the Ti-based alloy glassy matrix. The presence of SiC particles did not dramatically change the thermal stability of Ti50Cu28Ni15Sn7 glassy powders. BMG composite with submicron SiC particles homogeneously embedded in a highly dense nanocrystalline/amorphous matrix was successfully prepared. A significant hardness increase with SiC additions was noticed for consolidated composite compacts.

Abstract: The compressive deformation behavior of as-cast Zr55.9Cu18.6Ta8Al7.5Ni10 Bulk Metallic Glass (BMG) composite with micro-scale particles of Ta-rich solid solution embedded in an amorphous matrix was investigated in the supercooled liquid region. It was found that the apparent viscosity of the BMG is dependent on temperature and strain rate. A deviation from a Newtonian behavior was observed at high strain rate and low temperature. The experimental results can be described by a master curve based on a stretched exponential function and the free volume theory. The structural state and the thermal ability of the BMG composite after deformation are also discussed in the paper.

Abstract: The preparation of Ti50Cu28Ni15Sn7 metallic glass composite powders was accomplished by the mechanical alloying of a pure Ti, Cu, Ni, Sn and carbon nanotube (CNT) powder mixture after 8 h milling. In the ball-milled composites, the initial CNT particles were dissolved in the Ti-based alloy glassy matrix. The thermal stability of the amorphous matrix is affected by the presence of the CNT particles. Changes in Tg and Tx suggest deviations in the chemical composition of the glassy matrix due to a partial dissolution of the CNT species in the amorphous phase. The bulk metallic glass composite was successfully prepared by vacuum hot pressing the as-milled CNT/ Ti50Cu28Ni15Sn7 metallic glass composite powders. A significant hardness increase with the CNT additions was observed for the consolidated composite compacts.

Abstract: In the present study, WC/Cu60Zr30Ti10 metallic glass composite powders were prepared by mechanical alloying of pure Cu, Zr, Ti, and WC powder mixtures. Cu60Zr30Ti10 metallic glass composite powders were obtained after 5 h of milling as confirmed by X-ray diffraction and differential scanning calorimetry. The metallic glass composites powders were found to exhibit a supercooled liquid region before crystallization. Bulk metallic glass (BMG) composites were synthesized by vacuum hot pressing the as-milled Cu60Zr30Ti10 metallic glass composite powders at 723 K in the pressure range of 0.72-1.20 GPa. BMG composite with submicron WC particles homogeneously embedded in a highly dense anocrystalline/amorphous matrix was successfully prepared under applied pressure of 1.20 GPa. It was found that the pressure could enhance the thermal stability and promotes nocrystallization of WC/Cu60Zr30Ti10 BMG composites.