Nanoindentation and Simulation Analysis of Deformation Behavior in Bulk Metallic Glass Alloy

The correlation among apparent global plasticity, Poisson’s ratio, and fragility in monolithic bulk metallic glass (BMG) alloys has been investigated in the present study. The shear and bulk moduli in monolithic Cu-based BMG alloys have been measured by resonant ultrasound spectroscopy (RUS) and ultrasonic technique. The Cu43Zr43Al7Ag7 BMG alloy showing a large apparent global plasticity (∼8%) exhibits a high Poisson’s ratio when compared with that of Cu43Zr43Al7Be7 BMG alloy. In addition, the fragility of Cu-based BMG alloys can be obtained by differential scanning calorimetry (DSC). The fragility index m of Cu43Zr43Al7Ag7 BMG alloy is slightly larger than that of Cu43Zr43Al7Be7 BMG alloy. The correlation between Poisson’s ratio and fragility in BMG alloys can be presented by a simple relation of m − 17 = 14 (B∞/G∞ − 1). Poisson’s ratio and fragility might be regarded as an important parameter that controls global plasticity of glass-forming alloys.

Preparation and properties of a bulk metallic glass and high-entropy alloy composite

Mechanical property and fracture behavior of strip cast Zr-base BMG alloy containing crystalline phase

Mechanical property and fracture behavior of strip cast Zr-base BMG alloy containing crystalline phase

Effect of (Mo, W) substitution for Nb on glass forming ability and magnetic properties of Fe–Co-based bulk amorphous alloys fabricated by centrifugal casting

Stable shear of Cu 46Zr 47Al 7 bulk metallic glass alloy by controlling temperature rise

We started investigation of new Ti-based bulk metallic glass (BMG) alloys with higher glass forming ability (GFA) for dental implants for medical market. These Ti-based BMG alloys do not contain Ni, Al and Be elements which are well known to be harmful for human body. In particular, cylindrical rod specimens of newly designed Ti-based BMG alloys with produced by copper mold casting exhibit compressive strength of above 1800 MPa. Ti-based BMG alloys also have high corrosion resistance that is passivated at the lower passive current densities of approximately 10-2Am-2 in 1 mass% lactic acid, 10-2~10-3Am-2 in PBS (-) at 310K which are lower than those of pure Titanium and Ti-6Al-4V alloy. These BMG alloys have high potentials to be applied as biomaterials in various forms, such as melt spun ribbons and cylindrical rods.

Zr 41.2 Ti 13.8 Cu 12.5 Ni 10 Be 22.5 bulk metallic glass (BMG) alloy obeys different yield criterions under different stress states. In order to accurately describe yield behavior of BMG alloy and clarify the effect of middle principal stress on material yield and fracture, Unified Strength Theory is introduced to study plastic yield behavior of BMG alloy. The unified expression of yield function and its corresponding yield locus on π plane of Zr 41.2 Ti 13.8 Cu 12.5 Ni 10 Be 22.5 BMG alloy are obtained.

ABSTRACTClassical heterogeneous nucleation theory coupled with DTA data has been used to closely estimate the crystallization behavior of continuously cooled bulk metallic glass (BMG) alloys. Continuous cooling transformation and time temperature transformation diagrams of three BMG alloys, Zr41.2Ti13.8Cu12.5Ni10Be22.5, Cu47Ti33Zr11Ni6Si1Sn2and Mg65Cu25Y10alloys, have been calculated. The critical cooling ratesRcof three alloys were calculated to be 1.7 K/s, 242 K/s and 36 K/s for Zr41.2Ti13.8Cu12.5Ni10Be22.5, Cu47Ti33Zr11Ni6Si1Sn2and of Mg65Cu25Y10alloys, respectively, which match well with the experimental values. We conclude that heterogeneous nucleation is more favorable than homogeneous nucleation for the formation of crystals during cooling of BMG alloy liquids. Our approach can be applied to the analyses of crystallization kinetics of BMG alloys with a wide range of critical cooling rates during continuous cooling as well as isothermal annealing.

In this research, Zr55Cu30Al10Ni5 bulk metallic glass (BMG) alloy is used as the base material to form tungsten fiber reinforced BMG composites. The composites are synthetized using melt infiltration casting method and their microstructure and compressive properties are investigated. Two different infiltration times of 10 min and 15 min are used to produce the composites. The microstructural evaluation of the interface between tungsten fiber and BMG matrix reveals that a narrow reaction band emerges between the tungsten wires and BMG alloy. Some portions of this layer are broken into the fine Zr/W-rich particles and eventually are dispersed in the BMG matrix, when the infiltration time is 15 min. The results also showed that increasing the infiltration time from 10 min to 15 min improves the compression strength of the composite from 1333 MPa to 1396 MPa and also increases the compression strain of the composite from 0.11 to 0.13. This is attributed to the lack of porosities and better metallurgical bonding between tungsten fibers and BMG matrix.

Adhesion of metallic glass and epoxy in composite-metal bonding

The crystallisation behaviour of Zr41.2Ti13.8Cu12.5Ni10.0Be22.5 bulk metallic glass (BMG) alloy during heating from the amorphous state has been investigated. Upon heating, the nucleation process was not consistent with classical nucleation theory. This problem can be overcome by substituting the nucleation density with the number density of nuclei, N, for growth of the crystalline phase, which is estimated from the length scale of the microstructure. The growth of crystalline phase is the governing process for crystallisation of the Zr41.2Ti13.8Cu12.5Ni10Be22.5 alloy upon heating. The growth process is more important than the nucleation process for analysing the crystallisation mechanisms of the amorphous state. Non-isothermal heating DSC data have been analysed with a modified crystallisation kinetics model based on the non-isothermal transformation theory. Using this model, the onset crystallisation temperatures at various heating rates have been calculated. The calculated critical heating rate to avoid crystallisation is 190 K s−1, which matches well with the experimental value. The onset crystallisation times for isothermal annealing conditions have also been calculated and compared with the isothermal DSC data. Time temperature transformation (TTT) and continuous heating transformation (CHT) diagrams have been constructed quantitatively. The crystallisation kinetics of BMG alloys can be more reliably analysed with our modified crystallisation kinetics model than with several nucleation models.

Microfracture mechanisms of Zr-based bulk metallic glass (BMG) alloy containing ductile crystalline particles were investigated by directly observing microfracture processes using an in situ loading stage. Strength of the BMG alloy containing crystalline particles was lower than that of the monolithic BMG alloy, while ductility was higher. According to the direct microfracture observation, crystalline particles initiated shear bands, acted as blocking sites of shear band or crack propagation, and provided the stable crack growth which could be confirmed by the R-curve analysis, although they negatively affected apparent fracture toughness. This increase in fracture resistance with increasing crack length improved overall fracture properties of the alloy containing crystalline particles, and could be explained by mechanisms of blocking of crack or shear band propagation, formation of multiple shear bands, crack blunting, and shear band branching.

Thermal stability and magnetocaloric properties of GdDyAlCo bulk metallic glasses

In this study, the effects of Cu, Zr, Ti, Y, Pt substitution for Nb additions on the stability and magnetic properties of Fe-Ni-based bulk metallic glass (BMG) alloys fabricated by the suction casting method are investigated. The saturation magnetization (J s) and coercivity (H c) for as-cast Fe36Ni36B19.2Si4.8Nb4−x M x (M=Cu, Ti) BMG alloys were in the range of 0.51 T–0.55 T and 76–779 A/m, respectively. Differential scanning calorimetry curves show that the Fe36Ni36B19.2Si4.8Nb4−x M x (M=Cu, Ti) bulk metallic glasses have a supercooled liquid region for Cu at 44 K and for Ti at 39 K.