X. J. Gu

Critical Poisson’s ratio for plasticity in Fe–Mo–C–B–Ln bulk amorphous steel

Fracture in compression has been investigated in Fe65Mo14C15B6 bulk amorphous steel doped with lanthanides to provide systematic variations of the elastic moduli. An onset of plasticity is observed as Poisson’s ratio approaches 0.32 from below. Combining with previous analysis reported by Lewandowski et al. [Philos. Mag. Lett. 85, 77 (2005)] using single-composition results from different sources, the findings are in support of universal critical Poisson’s ratio for plasticity in metallic glasses. The compositional dependences of elastic moduli are found to be anomalous considering the elastic moduli of the alloying elements. The role of interatomic interactions in designing ductile metallic glasses is suggested.

Tough Fe-based bulk metallic glasses

The toughness of Fe-based bulk metallic glasses (BMGs) has been significantly improved via systematic changes in chemistry. Chemistry changes were selected based on their likely effects on critical elastic constants shown to affect plasticity/toughness in various BMGs, in addition to their recently discovered effects on chemical bonding in these Fe-based systems. The fracture energy obtained on notched toughness samples tested in mode I was correlated with chemistry-induced changes to Poisson’s ratio ν and the ratio of the elastic shear modulus μ to the bulk modulus B, as was the strain energy at fracture for smooth cylindrical compression samples that failed under mode II conditions. Fractographic observations correlate well with the observed increases in toughness.

Mg–Ca–Zn Bulk Metallic Glasses with High Strength and Significant Ductility

The development of Mg–Ca–Zn metallic glasses with improved bulk glass forming ability, high strength, and significant ductility is reported. A typical size of at least 3–4 mm amorphous samples can be prepared using conventional casting techniques. By varying the composition, the mass density of these light metal based bulk amorphous alloys ranges from 2.0 to 3.0 g/cm 3 . The typical measured microhardness is 2.16 GPa, corresponding to a fracture strength of about 700 MPa and specific strength of around 250–300 MPa cm 3 /g. Unlike other Mg- or Ca-based metallic glasses, the present Mg–Ca–Zn amorphous alloys show significant ductility.

Mechanical properties, glass transition temperature, and bond enthalpy trends of high metalloid Fe-based bulk metallic glasses

Mechanical properties and glass transition temperatures (Tg) of Fe–Cr–Mo–P–C–B bulk metallic glasses containing up to 27at.% metalloids have been studied. The shear modulus (G) is found to decrease with increasing metalloid content and a maximum plastic strain of ∼3% is obtained, despite the increase in the number of strong metal-metalloid bonds. Also, Tg increases with the decrease in G, in contrast to usual behavior. By employing first-principles calculations, the results are discussed in light of atomic bonding and connectivity in the amorphous network. The findings are relevant to understanding ductility and glass transition of metallic glasses.

Influence of erbium on the electronic structure of Fe(65−x)Mo14C15B6Erx (x=0,1,2) bulk metallic glasses

Fe(65−x)Mo14C15B6Erx bulk metallic glasses have been investigated by means of photoelectron spectroscopy. In order to obtain a clean surface the samples were fractured and analyzed in vacuum. The impact of the incorporation of Er on the local atomic structure, the bonding, and the valence band density of states was examined. Our results show that Er addition modifies the B–C bonding environment, which is expressed in the appearance of an additional peak in the C 1s core level. It also affects the Fe 3s multiplet splitting, indicating changes in the valence band electronic configuration. The change in the electronic structure is corroborated by examination of x-ray photoelectron spectroscopy (XPS) valence band spectra.