Series Of Bulk Metallic Glasses Research Articles

Ductilization of bulk metallic glassy material and its mechanism

Bulk metallic glass has aroused intensive interest due to its unique atomic structure and properties, while its structural application is restricted by the shortcomings of its mechanical properties-room temperature brittleness and strain softening. To make up for these shortcomings, various approaches have been proposed, including tailoring intrinsic parameters such as elastic modulus and structural heterogeneity, and changing stress state or defect concentration. Bulk metallic glass composites with ex-situ added or in-situ formed crystallites have been fabricated, series of bulk metallic glasses and their composites with good mechanical properties have been designed, especially TRIP (Transformation-induced plasticity)-reinforced bulk metallic glass composites with large tensile ductility and work-hardening. In this paper, we review the ductilization of bulk metallic glass and its composites, as well as the related mechanism. Particularly, fabrication, properties, structure control and the ductilization mechanism of TRIP-reinforced bulk metallic glass composite are introduced in detail. A perspective of the challenges of ductilization of bulk metallic glassy materials is also mentioned briefly.

The material-dependence of plasticity in metallic glasses: An origin from shear band thermology

The material origin of plasticity in metallic glasses is a puzzled question for decades. In this work, we tackled this question from a perspective of excessive heating. With a simultaneous heat generation and dissipation model to describe the spatial and temporal distribution of temperature-rise in shear bands, an upper bound of temperature-rise of about tens of Kelvins was noticed for the reported stable shear banding. These results implied the fracture of metallic glasses being triggered at some critical temperature-rise. Based on the thermal property data of a series of bulk metallic glasses (BMGs) with different plasticity, a trend of low temperature-rise in large plasticity BMGs was revealed. A new material-dependent parameter based on thermal properties was then suggested to estimate or predict the plasticity in metallic glasses. This study provides a reasonable physical picture to understand the origin of BMGs' fracture and their different plasticity, which sheds a light to the understanding of the complex mechanical properties of these materials.

A method for determining the crystallization temperature in studying internal friction behaviors of bulk metallic glasses

As well known, internal friction (Q−1) is one of useful resorts for investigating the mechanical relaxation behaviors of bulk metallic glasses (BMGs). However, so far it has been controversial on ascertaining the authentic position of crystallization temperature (Tx) when the peak arises on Q−1-T heating curve of BMGs. Based on the isochronous measurement results of internal friction and resistivity (ρ) on a series of BMGs, a novel method for determining Tx of BMGs was proposed. By differentiating the curve of Q−1-T with respect to temperature to obtain dQ−1/dT-T curve, the inflexion temperature at the left side of the Q−1-T peak can easily be determined. It is interesting to find that, for all the investigated BMGs in this paper, this inflexion temperature (the peak position of the dQ−1/dT-T curve) is in correspondence with the Tx obtained from ρ-T curve (ρ is very sensitive to crystallization), with the temperature error of ±1.5K. These results suggest that in studying the internal friction behaviors of BMGs, the crystallization temperature can be determined with the inflexion temperature of the Q−1-T curve, and the position of Tx for BMGs locates at the left side of the Q−1-T peak, rather than at the Q−1-T peak temperature or others as pointed in some references.

Investigation on the structural characteristics of metallic glasses based on the first displacement excursion behavior in nanoindentation

► The first pop-in initiation becomes difficult with the BMG diameter. ► The first pop-in initiation becomes difficult with annealing temperature. ► Free volume decreases with the diameter and annealing temperature. ► The first pop-in behavior reflects the cluster bonding characteristic. ► Cluster bonding characteristic is significant in understanding BMG properties. The first displacement excursion (pop-in) behavior of bulk metallic glasses (BMGs) with different casting diameters and annealing conditions is studied by nanoindentation test using a spherical indenter. It is found that the load, displacement and the well-predicted shear stress corresponding to the first pop-in initiation distinctly increase with the sample diameter and annealing temperature. By using differential scanning calorimetry, it is revealed that the free volume decreases with the sample diameter and annealing temperature, indicating that the first pop-in initiation is greatly affected by the free volume amount in BMGs. Based on the distribution of free volume and cluster derived from a series of BMGs’ models, it is revealed that the first pop-in initiation reflects the breakdown of cluster bonds, viz., the cluster bonding characteristic in general, which plays a significant role in understanding of the mechanical properties of BMGs.

Sensitivity of the Hruby, Lu–Liu, Fan, Yuan, and Long glass stability parameters to the change of the ratios of characteristic temperatures Tx/ Tg and Tm/ Tg

The glass stability (GS) parameters, recently introduced by Fan ( Φ), Yuan ( β) and Long ( ω), which are based upon the three characteristic temperatures: T g —glass transition temperature, T x —onset of the crystallization peak (or T c —maximum of the crystallization peak), and T m —melting temperature, are expressed in this paper via the ratios r = T x / T g and m = T m / T g . In an earlier paper, we applied the same procedure on the Hruby ( K H ), Weinberg ( K W ) and Lu–Liu ( K LL ) parameters. Thus, the GS parameters are more directly related to the supercooled region and reduced glass transition temperature. The objective was to find out how these GS parameters are sensitive to the changes of r and m, and whether this is reflected on the correlation of the given parameter with the glass-forming ability (GFA). The theoretically derived relation dβ/ dr > dK H / dr > dK LL / dr always holds, and dβ/ dr > dK H / dr > dω/ dr > dK LL / dr is also probable, while the order of sensitivity to m is dβ/ dm > dω/ dm > dK LL / dm. Testing on one series of oxide glasses and two series of bulk metallic glasses confirmed in full these relations. The parameter β is the most sensitive to the changes of both r and m, while K LL is generally least sensitive. Partial sensitivity of a GS parameter to r and m is not related to the coefficient of correlation between the GS parameter and GFA, whereas the ratio dGS/ dr : dGS/ dm can explain the magnitude of the correlation coefficient.

High Glass-Forming Ability and Unusual Deformation Behavior of New Zr-Cu-Fe-Al Bulk Metallic Glasses

A new series of bulk metallic glasses were developed by addition of Fe into the ternary Zr60Cu30Al10 alloy. Although Fe-Cu element pair shows distinct immiscibility with a large positive heat of mixing, substitution of Fe for Cu significantly improves the glass-forming ability of the ternary Zr60Cu30Al10 alloy. The critical diameter for glass-formation increases from 8 mm for Zr60Cu30Al10 alloy to 20 mm for Zr60Cu25Fe5Al10 and Zr62.5Cu22.5Fe5Al10 alloys. As compared with the ternary Zr60Cu30Al10 alloy, the new quaternary Zr-Cu-Fe-Al alloys show lower liquidus temperatures. The Zr60Cu25Fe5Al10 and Zr62.5Cu22.5Fe5Al10 alloys, the best BMG-formers in this alloy system, are found to locate very near a Zr-Cu-Fe-Al eutectic point. The new Zr-Fe-Cu-Al bulk metallic glasses exhibit high strength of about 1700 MPa. The plastic strain increases from 7.8% to 11.3% with increasing the content of Fe from 0 to 12.5%. The finding of a Ni-free Zr-based bulk glassy alloy with the extremely high glass-forming ability is expected to extend the future application of bulk metallic glasses.

Wear behavior of a series of Zr-based bulk metallic glasses

Dry sliding wear behaviors of a series of bulk metallic glasses with nominal compositions of Zr 48Cu 45− x Al 7Ag x ( x = 0, 2, 5, 8 at.%) are investigated by pin-on-disk method at room temperature. Compared with Ag-free Zr 48Cu 45Al 7 glassy alloy, wear resistances of the Ag-doped bulk metallic glasses are significantly enhanced and increased with the content of Ag, and their microhardnesses also increase. The results of compression test show that the plastic strain decreases with the increase of Ag content for the quaternary Zr–Cu–Al–Ag alloys. SEM observations demonstrate that the cracks initiate and propagate perpendicular to the frictional direction during the debris formation.

Bulk metallic glasses based on rare-earth elements in lanthanum series

A series of bulk metallic glasses (BMGs) based on the rare-earth (RE) elements in lanthanum family have been obtained by a copper mold casting method. These chemical comparable RE elements with ‘continuous’ range of atomic size, electron structure and elastic constants may provide a good system for systematically exploring the BMG-forming characteristics. The glass-forming ability, elastic properties, thermal stability and their correlations in the RE-based BMGs have been investigated.

Composition rule of bulk metallic glasses and quasicrystals using electron concentration criterion

This paper aims at establishing a number of electrons/atom (e/a)-based criterion for searching bulk metallic glasses (BMGs) and quasicrystals with large forming abilities in the Zr-based multicomponent alloy systems. After discussions on the diffraction characteristics corresponding to the Fermi surfaces-Brillouin zone interaction in the Zr-based Hume-Rothery phases, the Hume-Rothery matching rule is well explained when the effective e/a value of the matrix element Zr is taken as 1.5. The BMG- and quasicrystal-related phases are pointed out to be a family of nearly e/a-constant phases in a given alloy system. An e/a-constant criterion is then used to predict the ideal composition of the quasicrystals and BMGs in the Zr-Ti-Ni, Zr-Al-Ni, and Zr-Al-Ni-Cu systems, respectively. Nearly pure bulk Zr-Ti-Ni quasicrystals and a series of BMGs with glass-forming abilities greater than that of the known Zr65Al7.5Ni10Cu17.5 alloy are found.

Glass-forming ability and crystallization of bulk metallic glass (Hf xZr 1− x) 52.5Cu 17.9Ni 14.6Al 10Ti 5

We have produced a series of bulk metallic glasses of composition (Hf x Zr 1− x ) 52.5Cu 17.9Ni 14.6Al 10Ti 5 (with x=0–1) by an arc melting/suction casting method. The density of these alloys increases by nearly 67% with increasing Hf content from 6.65 g/cm 3 ( x=0) to 11.09 g/cm 3 ( x=1). Over the same composition range the glass-forming ability decreases, as demonstrated by the size of the largest amorphous ingots that can be cast without crystallization. Although both the glass transition temperature and the melting temperature increase linearly with increasing Hf content, the reduced glass transition temperature ( T g/ T m) decreases, from 0.64 ( x=0) to 0.62 ( x=1), which suggests that the `confusion principle' correlating increased glass-forming ability with increased number of components, does not apply in this case due to the chemical similarity between Zr and Hf. A different crystallization behavior is observed for Zr-based and Hf-based glasses. The final crystalline phases are CuZr 2 and Zr 2Ni for Zr-based alloys, and Al 16Hf 6Ni 7 and CuHf 2 for Hf-based alloys.