Poor Glass-forming Ability Research Articles

First-principles prediction of the glass-forming ability in Zr–Ni binary metallic glasses

In the present study, the atomistic approach, developed previously by hybridizing both internal energies and atomic-scale defect structures, is extended to predict the trend of glass forming ability (GFA) from the Zr–Cu binary alloy system with good GFA to the Zr–Ni binary system with relatively poor GFA. The predicted composition dependence of the GFA in the Zr–Ni alloy system is consistent with those obtained from experimental results, indicating the validity of the proposed atomistic approach in both of the alloy systems. The different GFAs in the Zr–Cu and Zr–Ni systems have been puzzled by the metallic glass community for quite a long time, and our study provides the physical reasons for the different glass forming behaviors of the two alloy systems in terms of both atomic configurations and relative stability of their intermetallic phases.

The influence of clusters in the melt of Fe80Si10B10 alloy on the subsequent glass-formation

The structure of Fe80Si10B10 alloy melt was investigated by ab initio molecular dynamic simulation from the local atomic environments. It presents that Fe80Si10B10 alloy can be considered as the combination of B-centered prism-like clusters and bcc-like Fe-Si solid solution. The poor glass-forming ability of the alloy has been investigated and can be attributed to the bcc-like environment around Si atoms and the relative high content of pure Fe clusters.

Structural evolution of Ti50Cu50 on rapid cooling by molecular dynamics simulation

The structural evolution and atomic structure of the Ti50Cu50 compound have been investigated by means of molecular dynamics simulation using the generalized embedded-atom model (GEAM) potential. Gibbs free energy calculation manifests the large driving force of undercooled Ti50Cu50 for crystallization and thus the poor glass-forming ability. Radial distribution functions (RDFs) within the temperature range from 2000 K to 300 K are analyzed and reveal the increasing degree of short-range order and reducing periodic length between peaks on cooling. Atomic arrangement is characterized by the Voronoi tessellation method, showing that the frequency of icosahedral configurations is most sensitive to temperature and grows upon quenching while that of the others remains relatively stable. The thermal behavior of the structure factors follows the Debye model up to the supercooled liquid temperature. The structural investigation of amorphous Ti50Cu50 demonstrates that there exist a variety of polyhedral configurations in Ti50Cu50 amorphous alloy, where icosahedral and bcc clusters are the major types. Due to the existence of bcc clusters and the other distorted polyhedra other than full icosahedra, the structural analysis reconfirms the inference from the Gibbs free energy calculation.

Structural origin underlying poor glass forming ability of Al metallic glass

We performed molecular dynamics simulations to study the glass formation and local atomic structure of rapidly quenched Al. Both potential energy and structural parameters indicate that the glass transition temperature of amorphous Al is as low as 300 K, which may lead to the poor thermal stability of the amorphous Al as it is prone to crystallize even at room temperature. Voronoi polyhedra analysis reveals that the most popular polyhedron is the deformed body-centered cubic (bcc) cluster characterized by the index < 0, 3, 6, 4 > in the amorphous Al, while the icosahedron with the index < 0, 0, 12, 0 > is always predominant in bulk metallic glass formers with excellent glass forming ability (GFA). Moreover, these deformed-bcc short-range orders can make up medium-range orders via the linkage of vertex-, edge-, face-, intercrossed-shared atoms, which are believed to more easily transform into face-centered cubic (fcc) Al nanocrystal compared with the icosahedral clusters in terms of the symmetrical similarity between bcc and fcc structures. This finding could unveil the structural origin of poor GFA of Al-based alloys.

Consolidation of [(Fe<SUB>0.5</SUB>Co<SUB>0.5</SUB>)<SUB>0.75</SUB>Si<SUB>0.05</SUB>B<SUB>0.2</SUB>]<SUB>96</SUB>Nb<SUB>4</SUB> Metallic Glassy Powder by SPS Method

Metallic glasses have been reported to exhibit excellent properties, such as high strength, high corrosion resistance, high wear resistance, which result from their amorphous structure. Because of a drastic reduction in their viscosities in supercooled liquid region, metallic glasses have an excellent workability through viscous deformation for the production of various industrial parts. Recently, much attention has been paid to Fe-based metallic glasses because of their rich resources in addition to their excellent mechanical and magnetic properties. However, due to their poor glass-forming ability, the size of the Fe-based bulk metallic glass by conventional casting techniques is limited. In the present investigation, nearly fully densified disk-shaped compacts of [(Fe0:5Co0:5)0:75Si0:05B0:2]96Nb4 metallic glass were produced from a gas-atomized amorphous powder by spark plasma sintering (SPS). The processing temperature and the time that assure the supercooled liquid state of the compacts were determined from the Time-Temperature-Transformation (TTT) diagram that was constructed by isothermal differential scanning calorimetry. The mechanical properties of the consolidated samples were evaluated by compression test. Comparatively low values of the fracture stress, Young’s modulus and yielding stress of SPSed sample compared to the casted samples were observed, which is discussed on the basis of the integrity of the interparticle bonding. [doi:10.2320/matertrans.M2009093]

Electronic, magnetic, superconducting and amorphous-forming properties versus stability of the Ti-Fe, Zr-Ru and Hf-Os ordered alloys

The electronic, magnetic and superconducting properties of the Ti-Fe, Zr-Ru and Hf-Os ordered alloys of the B2-type and MgZn 2-type structures are described using original low temperature specific heat and susceptibilty results and known magnetization data. The stability of the B2-type ordered alloys, including that of TiFe, ZrRu and HfOs is discussed. The high stability of the B2-type ordered alloys having an average number of d electrons, N ̄ d , equal or nearly equal to five (which corresponds to a Fermi level lying in a deep valley of the band structure) is accompanied by a low electronic specific heat coefficient γ, no magnetic order, no superconductivity and poor glass-forming ability. However, deviations from N ̄ d = 5 produce a decrease in the stability, high γ values, appearance of magnetic order and martensitic transformations leading to superconductivity and good glass-forming ability.

Electron spin resonance study of copper(II) complexes with square pyramidal and compressed trigonal bipyramidal symmetries in different solvents at 295 K and 77 K

An electron spin resonance (ESR) study has been carried out on six copper(II) complexes. Two of these, Cu(den)(SCN) 2 and [Cu(den)(SCN)](ClO 4), have a square pyramidal CuN 4S coordination in the solid state while the remaining four complexes, Cu(pib)tu, Cu(bipy)tu, Cu(bipy) and Cu(bipyam), have compressed trigonal bipyramidal Cu(N 2S)N 2 Cu(N 2S)N 2, Cu(N 2Cl)N 2 and Cu(N 2I)N 2, respectively, type of coordination in the solid state. Excepting Cu(pib)tu, all complexes show characteristic isotropic fourline hyperfine structure in water, methanol, ethanol and dimethylformamide at 295 K. At 77 K, owing to the poor glass-forming ability of water, the spectral features are not properly resolved and are also not consistent with the lineshape requirements. Therefore, evaluation of spin Hamiltonian parameters is made from the frozen dimethylformamide spectra. Some interesting observations have been made. In highly viscous 2-methyl-benzoxazole, the spectral lineshape is considerably modified. Quantitative evaluation has been made of metal-ligand bonding and various contributions to linewidths.