Zr-based Metallic Glass Composites Research Articles

A novel Zr-based metallic glass composite and its plasticizing mechanism

A novel Zr-based metallic glass composite was prepared utilizing a die casting process in this study. This composite utilizes high-porosity open-pored foam metal as the second phase and takes advantage of the unique distribution characteristics of this phase to achieve structural characteristics resembling hard regions surrounded by soft regions. This facilitates the formation and interleaving of numerous shear bands during the deformation process of the composite, resulting in work-hardening capability and favorable compressive plasticity. The results indicate that the compressive strength of the metallic glass composites containing 2.72 % foamed Ni and 3.71 % foamed Cu respectively does not decrease significantly compared to single-phase metallic glass, while their compressive plasticity increases from 1.60 ± 0.46 % to 12.21 ± 1.04 % and 13.01 ± 1.15 %, respectively. This study not only uncovers the preparation method and plasticizing mechanism of a novel metallic glass composite, but also offers a fresh perspective for the design of high-plasticity metallic glass composites.

Enhancing strength-ductility synergy in an ex situ Zr-based metallic glass composite via nanocrystal formation within high-entropy alloy particles

In this work, we prepared equiatomic AlCoCrFeNi high-entropy alloy (HEA)-particle-toughened, Zr-based metallic glass composites by spark plasma sintering. By adding HEA particles as the second phase, the strength and plasticity of the Zr-based metallic glass composites improved concomitantly. After fracture, high-density dislocations and nanocrystals were formed in the HEA particles due to local severe plastic deformation, which consumed massive strain energy to enable the resistance to crack formation. Substantial lattice distortion imparted a remarkable work-hardening capacity to the HEAs and enhanced crack-tip dislocation trapping, and thus led to an extreme refinement of the grain size. Finite-element analyses indicated that the strain hardening behavior of HEA particles reduced the magnitude of strain localization, promoted generation of multiple shear bands, and stabilized shear band propagation. We attribute the enhanced strength-ductility synergy in the current composites to high-density dislocations and nanocrystal formation in the HEA particles, and stable propagation of multiple shear bands.

Structural changes and kinetics of shear banding in metallic glass composites

In this work we studied the mechanical behavior, structural changes and kinetics of shear banding during compression tests of Cu–Zr-based metallic glass composites using molecular dynamics simulations. Starting from a Cu45Zr45Al10 metallic glass model, two composite models were generated by adding 2% in volume of CuZr (B2 structure) nanocrystals of 4 and 17 nm in diameter, respectively. The three models were then deformed in compression using embedded-atom method (EAM) interatomic potentials. Local shear strain analyses showed that the kinetics of shear banding could be modeled as a two-stage process: 1) shear band formation due to the coalescence of shear transformation zones, and 2) shear band coarsening/thickening. The growth rate of the first stage (coalescence of shear transformation zones) varied upon the addition of CuZr nanocrystals, while the growth rate of the second stage remained unchanged. The addition of CuZr nanocrystals did not induce significant changes in the radial distribution function and distribution of Voronoi polyhedra of the glassy matrix, independently of the nanocrystal size. However, the addition of CuZr nanocrystals induced changes in the rate at which the local density of Cu-centered ⟨0,0,12,0,0⟩ icosahedra decreased with strain (“kinetics of icosahedra destruction”). These changes in local density were also modeled as a two-stage process with corresponding growth rates very similar to those obtained for the kinetics of shear banding, thus indicating a close relationship between the kinetics of icosahedra destruction and the kinetics of shear banding.

A novel core-shell structure reinforced Zr-based metallic glass composite with combined high strength and good tensile ductility

Using the ZrO2 particles as precursor, a novel α-Zr/β-Zr core-shell structure reinforced Zr-based metallic glass (Zr-BMG) composite was fabricated. The oxygen is mainly concentrated in the α-Zr core, resulting in the very high hardness of α-Zr core. The β-Zr shell contained the relatively moderate amount of oxygen still has good ductility and work hardenability. The α-Zr/β-Zr core-shell structure reinforced Zr-BMG composite combined the advantages of the soft ductile and hard brittle phase reinforced BMG composites, and thereby exhibits the high strength and good tensile ductility. These findings give a new perspective to adjust the mechanical properties of the BMG composites.

Enhanced mechanical properties of 3D printed Zr-based BMG composite reinforced with Ta precipitates

3D printing technique based on selective laser melting (SLM) provides a new approach to fabricate complex bulk metallic glass (BMG) components. However, the structural relaxation and partial crystallization of the pre-formed amorphous phase in heat affect zones (HAZs) caused by repeated laser scanning deteriorate the mechanical properties, i.e., reducing plasticity and fracture toughness. Here, we attempted the preparation of Zr-based metallic glass composites reinforced with precipitation of Ta particles by SLM technique. The results show that, in a wide range of energy densities, the 3D printed BMG composites exhibit high amorphous fraction (>90%) and good mechanical properties with fracture strength of 1.9 GPa, plastic strain of around 2.15% and fracture toughness (Kq) of 60 MPa m1/2, and the plastic strain is the highest values achieved in 3D printed BMGs so far. The suppression of crystallization of amorphous phase in HAZs and the precipitation of Ta particles in amorphous matrix can account for the enhancement of plasticity and fracture toughness while maintaining high strength. This work provides a hint for the preparation of toughening BMG composites by using 3D printing technique.

Hydrogen effects on mechanical property and microstructure of a Zr-based metallic glass composite

Effects of hydrogen on the mechanical property and microstructure evolution are investigated on a Zr-based metallic glass composite contains both metallic glass matrix and body centered cubic (bcc) dendrite crystal. The compressive strength to failure descreased from 2.2 GPa to1.9 GPa; the fracture strain decreased from 39% to 26%. The composite retains a moderate compressive strength and strain after hydrogenation. The composite shows certain resistance of hydrogen embrittlement. Neither nanocrystallization in amorphous matrix nor amorphization in bcc dendrite crystal is detected. But there are so many stacking faults in the bcc dendrite crystal after hydrogen charging. Hydrogen lowers the value of stacking fault energy and promotes planar slip of the dendrite crystal. Planar slip and slip localization accelerate the deformation of the dendrite crystal and lead to premature fracture of the composite. The experimental results are consistent with the hydrogen enhanced local plasticity mechanism of hydrogen embrittlement.

Electrochemical and Friction Characteristics of Metallic Glass Composites at the Microstructural Length-scales

Metallic glass composites represent a unique alloy design strategy comprising of in situ crystalline dendrites in an amorphous matrix to achieve damage tolerance unseen in conventional structural materials. They are promising for a range of advanced applications including spacecraft gears, high-performance sporting goods and bio-implants, all of which demand high surface degradation resistance. Here, we evaluated the phase-specific electrochemical and friction characteristics of a Zr-based metallic glass composite, Zr56.2Ti13.8Nb5.0Cu6.9Ni5.6Be12.5, which comprised roughly of 40% by volume crystalline dendrites in an amorphous matrix. The amorphous matrix showed higher hardness and friction coefficient compared to the crystalline dendrites. But sliding reciprocating tests for the composite revealed inter-phase delamination rather than preferred wearing of one phase. Pitting during potentiodynamic polarization in NaCl solution was prevalent at the inter-phase boundary, confirming that galvanic coupling was the predominant corrosion mechanism. Scanning vibration electrode technique demonstrated that the amorphous matrix corroded much faster than the crystalline dendrites due to its unfavorable chemistry. Relative work function values measured using scanning kelvin probe showed the amorphous matrix to be more electropositive, which explain its preferred corrosion over the crystalline dendrites as well as its characteristic friction behavior. This study paves the way for careful partitioning of elements between the two phases in a metallic glass composite to tune its surface degradation behavior for a range of advanced applications.

Enhancement of tensile properties by the solid solution strengthening of nitrogen in Zr-based metallic glass composites

The effects of nitrogen on both the glass forming ability (GFA) and mechanical properties of Zr-based bulk metallic glasses were studied experimentally. The results show that the doping of nitrogen could induce the precipitation of N-rich Zr3Ni-type crystals, and the precipitated crystals don’t trigger heterogeneous nucleation. Therefore, the remainder molten metal contains very lower nitrogen content and keeps good glass formation ability. Based on this, using the precipitated β-Zr(Ti, Nb) acted as a solid solvent for absorbed nitrogen, the optimum mechanical properties of bulk metallic glass composites can be obtained by doping an appreciate amount of nitrogen. This finding not only gives us a clue to avoid the detriment of light interstitial impurity to glass formation, but also opens a window to adjust the mechanical properties of the composites.

Anisotropic compressive deformation behaviors of tungsten fiber reinforced Zr-based metallic glass composites

The compressive deformation behaviors of Zr-based metallic glass composites containing different tungsten fiber orientations were investigated. The angles (θf) between tungsten fiber orientation and loading axial direction are 0°, 15°, 30°, 45°, 60°, 75° and 90°, respectively. The results show that the strength, plasticity and the failure modes vary with θf. At θf =0°, the composite possesses the highest strength and the largest plasticity. When θf are 45° and 90°, the composites show relatively low compressive strength and plasticity. At θf≥15°, the composites fail in different shear modes. The composites fail by in-plane sliding at 0°<θf≤45°, while the composites fail by out-of-plane sliding at 45°<θf≤90°.

Microstructural and mechanical behavior of Zr-based metallic glasses with the addition of Nb

The effect of Nb content on the microstructure and mechanical properties of Zr-based bulk metallic glass (BMG) were investigated. The addition of Nb led to the formation of the Zr-based metallic glass composites with a ductile dentritic phase by in situ precipitation. The presence of the in situ precipitated phase enhanced significantly the plasticity of the composite under uniaxial compressive test. The interactions between the precipitated phase and the shear band affect the deformation mechanism and fracture mode of the BMG by enhancing the affecting level of the normal stress on the shear surface, and the constant α in the Mohr–Coulomb criterion can reflect the extent of the interactions among particles and the amorphous matrix.

Compressive deformation behaviors of tungsten fiber reinforced Zr-based metallic glass composites

Subjected to a wide range of strain rates, the compressive deformation and fracture behavior at different temperatures of tungsten fiber reinforced Zr-based metallic glass composites (BMGC) were investigated. Upon increasing temperature, the compressive strength decreases, accompanied with reduced elasticity and enhanced plasticity. In combination with fracture analysis, the effects of temperature, applied strain rate, and the reinforcement of tungsten fiber were explicitly described.

Fracture and fatigue behavior of a Zr–Ti–Nb ductile phase reinforced bulk metallic glass matrix composite

The fracture and fatigue behavior of a Zr-based metallic glass composite are presented. The fracture resistance and fatigue endurance limit was significantly higher than that of the matrix material. Results are rationalized in terms of the effects of the second phase on shear band formation and distribution.

Formation of High-Strength Zr-Nb-Cu-Ni-Al Alloys by Warm Extrusion of Gas Atomized Powders

ABSTRACTRecently developed Zr-based metallic glass composites containing a ductile phase demonstrate improved mechanical properties such as high strength combined with good ductility compared to the glass monoliths. Zr-Nb-Cu-Ni-Al amorphous powders with bcc phase precipitates were obtained by high pressure gas atomization. Formation of the bcc phase in the amorphous matrix strongly depends on the material composition and cooling rates during solidification. Melt spinning using various wheel speeds selected to simulate the cooling rates during gas atomization was used to define a specific composition for gas atomization. Gas atomized powders were consolidated by warm extrusion. Various processing conditions including starting powder particle size, extrusion temperature and extrusion ratio were examined to obtain materials having various microstructural features. Structure and thermal stability of consolidated bulk metallic glass composites as well as selected mechanical properties will be discussed.