Zr-based Bulk Metallic Glass Matrix Research Articles

Strain rate response of mechanical behaviors for a Zr-based bulk metallic glass matrix composite

The strain rate response of compressive mechanical behaviors for a Zr 60.0Ti 14.7Nb 5.3Cu 5.6Ni 4.4Be 10.0 bulk metallic glass matrix composite with the tensile fracture strain of 2.9%, was investigated. The dislocation-related deformation mode was employed to interpret the failure of the composite containing continuous network dendrites with high-volume fraction. Under the quasi-static compression, a positive dependence of the plasticity on the increasing strain rate was obtained. However, upon the dynamic loading, the composite exhibited premature fracture and the very limited plasticity accompanied, which suggested the strain was not kinetically accommodated during the prompt deformation.

Synthesis of plastic Zr-based bulk metallic glass matrix composites by the copper-mould suction casting and the Bridgman solidification

Zr-based bulk metallic glass matrix composites with the composition of Zr 56.2Ti 13.8Nb 5.0Cu 6.9Ni 5.6Be 12.5 were synthesized by the copper-mould suction casting and the Bridgman solidification. The composite, containing a well-developed flowery β-Zr dendritic phase, was obtained by the Bridgman solidification with the withdrawal velocity of 0.8 mm/s and the temperature gradient of 45 K/mm, and the ultimate strength of 2050 MPa and fracture plastic strain of 14.6% of the composite were achieved, which was mainly interpreted by the homogeneous dispersion of bcc β-Zr phase in the glass matrix.

Change in free volume during the homogeneous flow of Zr-based bulk metallic glass matrix composite

The influence of plastic deformation on the structure of a Zr55.9Cu18.6Ta8Al7.5Ni10 bulk metallic glass composite (BMGC) with a Ta solid solution as the second phase was investigated during a compression test in the supercooled liquid region, as a function of strain rate and the amount of strain. The structure of the BMGC after deformation was characterized by means of X-ray diffraction (XRD), differential scanning calorimetry (DSC) and transmission electron microscopy (TEM). It was found that an increase in excess free volume took place during plastic deformation. High strain rate can promote the generation of more free volume, which eventually leads to a reduction of the glass transition temperature and even splitting of the crystallization process. Microhardness measurement indicated that deformation induced softening of the BMG composite, probably due to the formation of nanovoids resulting from the increase of free volume.

Temperature, strain rate and reinforcement volume fraction dependence of plastic deformation in metallic glass matrix composites

A systematic study of mechanical properties is presented for Zr-based bulk metallic glass matrix composites, spanning a wide range of strain rates and temperatures, as well as various levels of reinforcement volume fraction. All of the experimental materials exhibit mechanical properties dominated by deformation of the amorphous matrix phase, including inhomogeneous flow and fracture at low temperatures, as well as homogeneous flow of both Newtonian and non-Newtonian character at high temperatures. In the homogeneous flow regime, the composites exhibit clear strengthening as the volume fraction of reinforcement increases. This strengthening effect is quantitatively explained in both the Newtonian and non-Newtonian regimes, and is found to arise from two contributions: (i) load transfer from the amorphous matrix to the reinforcements; and (ii) a shift in the glass structure and properties upon precipitation of the reinforcements. An additional source of apparent strengthening – in situ precipitation of reinforcement during deformation – is also discussed.

Observation of shear bands formation on tungsten fiber-reinforced Zr-based bulk metallic glass matrix composite

A Zr-based metallic glass matrix composite with 40 vol% tungsten fiber reinforcement was loaded step by step. After each loading step, shear-band patterns and fracture surface were observed. The results show that shear bands, cracks, and voids form during plastic deformation, and they exhibit different feature characteristics at various loading stages. As reinforcement, the tungsten fiber substantially affects the deformation and fracture processes of the composite.

Mechanical properties of metallic glass matrix composites: Effects of reinforcement character and connectivity

We present a systematic study of the room-temperature mechanical behavior of in situ Zr-based bulk metallic glass matrix composites over the full range of reinforcement volume fractions (f = 0–100%). In line with prior work, our data show a transition where the deformation behavior is governed by the properties of the glassy matrix at low f and by those of the reinforcement phase at high f. However, unlike the situation in ductile-phase reinforced glasses, where percolation of the second phase is apparently beneficial, we show that a high volume fraction of brittle reinforcement is undesirable.

The effect of the addition of Ta on the structure, crystallization and mechanical properties of Zr–Cu–Ni–Al–Ta bulk metallic glasses

Zr-based bulk metallic glasses (BMGs) or bulk metallic glass matrix composites (BMGCs) have been prepared by using a copper-mold casting in the Zr 65− x Ta x Cu 17.5Al 7.5Ni 10 (where x = 1–10 at%) alloy system while varying the Ta content. A monolithic amorphous phase of BMG was achieved when Ta was less than 2 at%, while amorphous matrix composites reinforced by Ta-solid solutions were obtained when Ta is 5 at% or higher. The addition of Ta also affected significantly the crystallization of the amorphous phase. A multi-step process of crystallization with a preferential formation of quasicrystals occurred in the alloys containing 2–5 at% Ta, while a single-step pathway of crystallization with the formation of stable Zr–Cu intermetallic compounds took place when Ta was beyond this range. In addition, a quasi-static compression test revealed that both fracture strength and plasticity of the base BMG were remarkably enhanced as Ta content increased. The effect of the addition of Ta on the structure; crystallization process; and deformation behavior of the Zr-based alloys is discussed.

Negative strain rate sensitivity in bulk metallic glass and its similarities with the dynamic strain aging effect during deformation

Detailed investigations were carried out on the deformation behavior of Zr-based monolithic bulk metallic glass and bulk metallic glass matrix composites. The latter, due to splitting and multiplication of shear bands, exhibits larger compressive strains than the former, without significant loss of strength. Serrated flow in conjunction with a negative strain rate sensitivity was observed in both materials. This observation, together with an increase in stress drops with increasing strain and their decrease with increasing strain rate, indicates phenomenologically close similarities with the dynamic strain aging deformation mechanism known for crystalline solids. The micromechanical mechanism of a shear event is discussed in light of these results.

Enhanced Plasticity of Zr-based Bulk Metallic Glass Matrix Composite with Ductile Reinforcement

A composite material containing uniformly distributed micrometer-sized Nb particles in a Zr-based amorphous matrix was prepared by suction cast. The resulting material exhibits high fractured strength over 1550 MPa and enhanced plastic strain of about 29.7% before failure in uniaxial compression test at room temperature. Studies of the serrations on the stress–strain curves and the shear bands on the fractured samples reveal that the amplitude of the stress drop of each serration step corresponds to the extent of the propagation of a single shear band through the materials. The composite exhibits more serration steps and smaller amplitude of stress drop due to the pinning of shear band propagation by ductile Nb particles.

Brittleness of Zr-based bulk metallic glass matrix composites containing ductile dendritic phase

Zr 63Al 10Ni 10Cu 14Nb 3 monolithic bulk metallic glass (BMG) and Zr 55Al 8.5Ni 8.5Cu 13Nb 15 BMG matrix composite containing densely distributed bcc dendritic phase were prepared by copper mould casting. The ductility of the dendritic phase was verified by nanoindentation tests. However, the composite samples exhibit relatively lower yield strength and no plastic strain under room temperature compression test. Microstructural characterization and fractography studies reveal that the simultaneous formation of quasicrystalline phase on the outermost region of the composite results in the brittleness of the composites.