Abstract:In situ high-temperature X-ray diffraction experiments using high-energy photons and ab initio molecular dynamics simulations are performed to probe the temperature-induced changes in the topological short-range order in magnetron sputtered Co 67 B 33 metallic glass thin films. Based on this correlative experimental and theoretical study, the presence of B-Co-B rigid second-order structures at room temperature and the temperature-induced decrease in the population of these strongly bonded building blocks are i… Show more
“…For identifying the origin of ultrahigh stiffness in metallic glasses, we have studied the effect of an order of magnitude increase of the B to Y ratio in Co-Fe-Y-B thin film and melt spun metallic glasses on the elastic behavior, both theoretically and experimentally. It is observed that with increasing B to Y ratio from 1.8 to 10.2 the bulk modulus increases, which is consistent with previous reports on Co-B based metallic glasses [6,7,30,[37][38][39]. Using high energy x-ray diffraction experiments combined with DFT based molecular dynamics simulations, it is shown that the B induced increase in stiffness is dominated by the increase in metal to metalloid bond density and the concomitant increase in molar density.…”
Section: Discussionsupporting
confidence: 89%
“…3 B 20.9 metallic glass, which is consistent with the reduced pair distribution function analysis of figure 3(a). In literature strong metal to metalloid hybridization, associated with an increase in bond energy is proposed as the cause for the increase in stiffness observed for Co-B based glasses with increasing B content [6,7,30,[37][38][39]. From figure 3 we learn that the experimentally obtained short range order data from high energy x-ray diffraction and the predicted data are consistent.…”
Section: Comparison Of Stiffness and Short Range Order Between Simula...supporting
confidence: 68%
“…For the high energy x-ray diffraction experiments thin film powders were synthesized by employing polycrystalline sodium chloride substrates. The sodium chloride was later removed by rinsing with demineralized water, acetone and methanol [30].…”
The elastic properties of crystalline metals scale with their valence electron density. Similar observations have been made for metallic glasses. However, for metallic glasses where covalent bonding predominates, such as metalloid metallic glasses, this relationship appears to break down. At present, the reasons for this are not understood. Using high energy x-ray diffraction analysis of melt spun and thin film metallic glasses combined with density functional theory based molecular dynamics simulations, we show that the physical origin of the ultrahigh stiffness in both metalloid and non-metalloid metallic glasses is best understood in terms of the bond energy density. Using the bond energy density as novel materials design criterion for ultra-stiff metallic glasses, we are able to predict a CoTaB short range ordered material by density functional theory based molecular dynamics simulations with a high bond energy density of 0.94 eV Å and a bulk modulus of 263 GPa, which is 17% greater than the stiffest Co-B based metallic glasses reported in literature.
“…For identifying the origin of ultrahigh stiffness in metallic glasses, we have studied the effect of an order of magnitude increase of the B to Y ratio in Co-Fe-Y-B thin film and melt spun metallic glasses on the elastic behavior, both theoretically and experimentally. It is observed that with increasing B to Y ratio from 1.8 to 10.2 the bulk modulus increases, which is consistent with previous reports on Co-B based metallic glasses [6,7,30,[37][38][39]. Using high energy x-ray diffraction experiments combined with DFT based molecular dynamics simulations, it is shown that the B induced increase in stiffness is dominated by the increase in metal to metalloid bond density and the concomitant increase in molar density.…”
Section: Discussionsupporting
confidence: 89%
“…3 B 20.9 metallic glass, which is consistent with the reduced pair distribution function analysis of figure 3(a). In literature strong metal to metalloid hybridization, associated with an increase in bond energy is proposed as the cause for the increase in stiffness observed for Co-B based glasses with increasing B content [6,7,30,[37][38][39]. From figure 3 we learn that the experimentally obtained short range order data from high energy x-ray diffraction and the predicted data are consistent.…”
Section: Comparison Of Stiffness and Short Range Order Between Simula...supporting
confidence: 68%
“…For the high energy x-ray diffraction experiments thin film powders were synthesized by employing polycrystalline sodium chloride substrates. The sodium chloride was later removed by rinsing with demineralized water, acetone and methanol [30].…”
The elastic properties of crystalline metals scale with their valence electron density. Similar observations have been made for metallic glasses. However, for metallic glasses where covalent bonding predominates, such as metalloid metallic glasses, this relationship appears to break down. At present, the reasons for this are not understood. Using high energy x-ray diffraction analysis of melt spun and thin film metallic glasses combined with density functional theory based molecular dynamics simulations, we show that the physical origin of the ultrahigh stiffness in both metalloid and non-metalloid metallic glasses is best understood in terms of the bond energy density. Using the bond energy density as novel materials design criterion for ultra-stiff metallic glasses, we are able to predict a CoTaB short range ordered material by density functional theory based molecular dynamics simulations with a high bond energy density of 0.94 eV Å and a bulk modulus of 263 GPa, which is 17% greater than the stiffest Co-B based metallic glasses reported in literature.
“…Pd 57.0 Al 23.9 Cu 11.4 Y 7.7 , Co 42.0 Fe 13.2 Zr 10.7 Ta 6.6 B 27.5 , Co 58.4 Fe 7.0 B 34.6 , Cu 67.8 Zr 32.2 and Co 68.3 Zr 31.7 metallic glass thin films were synthesised by physical vapour deposition59 by employing magnetron sputtering from 50 mm targets with a diameter of 50 mm using a ultrahigh-vacuum system59. Within this work, we report the synthesis and properties of the Pd 57.0 Al 23.9 Cu 11.4 Y 7.7 metallic glass thin film for the first time.…”
A paramount challenge in materials science is to design damage-tolerant glasses. Poisson’s ratio is commonly used as a criterion to gauge the brittle-ductile transition in glasses. However, our data, as well as results in the literature, are in conflict with the concept of Poisson’s ratio serving as a universal parameter for fracture energy. Here, we identify the electronic structure fingerprint associated with damage tolerance in thin film metallic glasses. Our correlative theoretical and experimental data reveal that the fraction of bonds stemming from hybridised states compared to the overall bonding can be associated with damage tolerance in thin film metallic glasses.
The atomic distribution in amorphous FeZr alloys is found to be close to random, nevertheless, the composition can not be viewed as being homogenous at the nm-scale. The spatial variation of the local composition is identified as the root of the unusual magnetic properties in amorphous Fe 1−x Zr x alloys. The findings are discussed and generalised with respect to the physical properties of amorphous and crystalline materials. The physical properties of amorphous materials are only partially understood and the relation between local atomic arrangements and emergent physical properties are not fully explored. Crystalline materials are readily characterised with respect to structure and chemical composition using standard scattering techniques, while amorphous materials being disordered, do not offer that possibility. Since the pioneering work on the amorphization of metals 1 and alloys 2 , the field has developed substantially and a large variety of methods are now available for the fabrication of amorphous alloys 3. While the end products are not always identical with respect to physical and chemical properties, it is challenging to identify the underlying reason for the observed differences. The atomic arrangements in amorphous alloys are not well-defined, exhibiting close resemblance to liquid like structures 4 , rendering the task of linking their structure to the observed physical properties challenging. Amorphous materials are known to exhibit extraordinary mechanical properties 5-9 and some of the observations can be rationalised using computational methods, e.g. linking shear-resistant structural 10 to the presence of short-range order 11. High-density icosahedral packing of atoms, with a Voronoi coordination polyhedron with index 0,0,12,0 , i.e. all nearest-neighbor pairs are five-fold bonds, exhibit the highest resistance to shear transformations, while the less-ordered and less-densely packed regions are easier to shear 10. These results have e.g. been used to explain the temperature dependence of the elastic limit of CoB metallic glasses 12. Amorphous metals do not only exhibit extraordinary mechanical properties, their magnetic properties are equally unique. For example, metallic glasses can be extremely soft magnetically, exhibit gigantic magnetic proximity effects 13 and have even been shown to violate Hund's third rule 14. The spatial variations in concentration and coordination number can be assumed to play a similar role for the magnetic and mechanical properties as e.g. discussed in the analysis of the density, elastic and magnetic properties of CoFeTaB and CoFeTaSi alloys using ab initio theory 15,16. This point is also immediately at hand when discussing the proposed magnetic states in amorphous Fe, which depends strongly on the distribution in the alloying element-induced atomic distances in Fe 17-19. While the spatial variation in atomic density and coordination number are used for rationalising the mechanical and magnetic properties of amorphous materials, the experimental determination of t...
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