Effects of minor alloying on the mechanical properties of Al based metallic glasses (original) (raw)
Related papers
2016
Metallic glasses (MGs) exhibit both high yield stresses and elastic strain limits owing to their metallic bonding character and lack of long-range order. Yet the structural state (i.e. local atomic packing), and the corresponding elastic and plastic mechanical response, of MGs is nuanced and dependent on processing history. Moreover, the interplay between small length scales and glass processing routes have produced seemingly conflicting results. Here, the influence of processing on MG mechanical behavior at sub-micron length scales is explored, revealing extreme sensitivity to ion irradiation, enhanced control over the mechanical response, and an underpinning of yield strength in thermodynamic properties. Using in situ testing methods, the deformation response of individual thermoplastically molded MG nanowires is studied. In contrast with previous literature reports the nanowire behavior is observed to be consistent with bulk deformation, exhibiting brittle fracture and shear band...
Mechanical Properties of Metallic Glasses
Metals, 2013
Metallic glasses are known for their outstanding mechanical strength. However, the microscopic mechanism of failure in metallic glasses is not well-understood. In this article we discuss elastic, anelastic and plastic behaviors of metallic glasses from the atomistic point of view, based upon recent results by simulations and experiments. Strong structural disorder affects all properties of metallic glasses, but the effects are more profound and intricate for the mechanical properties. In particular we suggest that mechanical failure is an intrinsic behavior of metallic glasses, a consequence of stress-induced glass transition, unlike crystalline solids which fail through the motion of extrinsic lattice defects such as dislocations.
Crystallisation behaviours of Al-based metallic glasses: Compositional and topological aspects
Journal of Alloys and Compounds, 2009
The different types of thermal crystallisation behaviours observed during continuous heating of Al-based metallic glasses have been successfully associated with the topological instability criterion, which is simply calculated from the alloy composition and metallic radii of the alloying elements and aluminium. In the present work, we report on new results evidencing the correlation between the values of and the crystallisation behaviours in Al-based alloys of the Al-Ni-Ce system and we compare the glass-forming abilities of alloys designed with compositions corresponding to the same topological instability condition. The results are discussed in terms of compositional and topological aspects emphasizing the relevance of the different types of clusters in the amorphous phase in defining the stability of the glass and the types of thermal crystallisation.
Intrinsic plasticity or brittleness of metallic glasses
Philosophical Magazine Letters, 2005
The intrinsic plasticity or brittleness of crystalline metals correlates with the ratio of the elastic shear modulus to the bulk modulus B; when the ratio /B exceeds a critical value, the metal is brittle. Sufficient data on elastic moduli and toughness are now available to permit an assessment for metallic glasses. We find a similar correlation, with the critical value of /B for metallic glasses (0.41-0.43) more sharply defined than for crystalline metals. This critical value applies also for annealing-induced embrittlement of metallic glasses. The clear correlation between mechanical behaviour (plasticity or brittleness) and /B assists in understanding flow and fracture mechanisms, and in guiding alloy design to alleviate brittleness of metallic glasses.
Journal of Applied Physics, 2014
To clarify the correlation of medium-range order (MRO) structure with glass forming ability (GFA) of Al-based metallic glasses, Al 86 Ni 14-a Y a (a ΒΌ 2$9 at. %) metallic glasses were analyzed by x-ray diffraction in detail and further verified by synchrotron high-energy x-ray diffraction. The prepeak that reflects the MRO structural evolution was found to be much sensitive to alloy composition. We have proposed an icosahedral supercluster MRO structure model in Al-TM (transition metal)-RE (rare earth metal) system, which consists of 12 RE(TM)-centered clusters on the vertex of icosahedral supercluster, one RE(TM)-centered clusters in the center, and TM(RE) atoms located at RE(TM)-centered cluster tetrahedral interstices in the icosahedral supercluster. It was indicated that the MRO structural stability mainly depends on the interaction of efficient dense packing and electrochemical potential equalization principle. The Al 86 Ni 9 Y(La) 5 alloys present good GFA due to the combination of the two structural factors. V
Al-rich bulk metallic glasses with plasticity and ultrahigh specific strength
Scripta Materialia, 2009
Aluminum-based amorphous metals are interesting lightweight alloys with superior mechanical and corrosion properties, but have never been achieved in bulk form. Here we report the first success of obtaining Al-rich (86 at.% Al) bulk metallic glasses (BMGs), based on an alloy composition designed from the preferable internal glass structure. The Al BMGs discovered exhibit ultrahigh specific strength, as well as obvious plasticity.
Chemical bonding effects on the brittle-to-ductile transition in metallic glasses
Acta Materialia, 2020
The influence of composition and temperature on the tensile deformation behavior of amorphous PdSi metal-metalloid alloys is investigated using large-scale molecular dynamics simulations. A correlation between highly directional Si-Si bonds and the deformation mechanisms is revealed by a Crystal Orbital Hamilton Population analysis based on electronic structure calculations from density functional theory. A transition from cracking perpendicular to the loading direction to shear banding can be achieved by increasing the temperature or decreasing the amount of silicon. Sampling of the saddle points on the potential energy surface reveals that a high fraction of rigid covalent Si-Si bonds increases the energy barriers for atomic rearrangements. These thermally-activated atomic relaxation events change the stress and strain state in the elastic regime and are precursor of local plasticity. High activation energies impede both the stress and the strain redistribution and cause cleavage-like cracking due to a delay of the onset of plasticity.
Mechanical responses of Mg-based bulk metallic glasses
Intermetallics, 2010
In this study, the mechanical responses of the bonded interface method derived Mg 58 Cu 28.5 Gd 11 Ag 2.5 bulk metallic glasses (BMG) under the micro-/nano-indentation are investigated. A modified expanding cavity model is developed to analyze the morphological observations of shear band by Vickers indentation. Results indicate that the radius ratio of any two adjacent shear band circles is approximately constant. The ratio of the shear band deformation zone to the contact radius induced by indentation is also a constant, which depends on the constraint factor (the ratio of hardness to yield strength) of the material. The features predicted by the present model are consistent with the results obtained from the indentation experiments, indicating the validity of the expanding cavity model for describing the mechanical behaviors of the BMG materials. The cross-sectional transmission electron microscopy (XTEM) observations reveal that the terraced shear bands are formed on the interface of the bonded Mg-based BMG. The microstructures for the Vickers indentation-induced terraced shear bands are also discussed.
Nature communications, 2018
The mechanical properties of crystalline materials can be quantitatively described by crystal defects of solute atoms, dislocations, twins, and grain boundaries with the models of solid solution strengthening, Taylor strain hardening and Hall-Petch grain boundary strengthening. However, for metallic glasses, a well-defined structure feature which dominates the mechanical properties of the disordered materials is still missing. Here, we report that nanoscale spatial heterogeneity is the inherent structural feature of metallic glasses. It has an intrinsic correlation with the strength and deformation behavior. The strength and Young's modulus of metallic glasses can be defined by the function of the square root reciprocal of the characteristic length of the spatial heterogeneity. Moreover, the stretching exponent of time-dependent strain relaxation can be quantitatively described by the characteristic length. Our study provides compelling evidence that the spatial heterogeneity is...
Advances in Materials Science and Engineering
The present study reveals the role of Nb and Ni minor addition on the nanomechanical properties and nanostructure of ZrCuAl bulk metallic glass (BMG). For this purpose, atomic force microscopy (AFM) was used to evaluate the viscoelastic response of the BMG surface at the nanoscale, while the nanoindentation technique was applied to show the mechanism of plastic deformation. The results indicated that minor Nb addition decreased the relaxation of enthalpy accompanied by the weakening of structural heterogeneity. On the other hand, Ni addition improved the stored energy of the material and intensified the distribution of loosely packed regions in the microstructure. Moreover, the mechanical test unveiled that Ni addition enhanced the viscoelastic response; however, it came at the expense of creep resistance. The evaluation of the magnitude of the derivative in the nanoindentation test also demonstrated that the Ni-added sample exhibited a multiple shear-band mode for plastic deformation.