Free Volume Changes in Bulk Amorphous Alloys During Structural Relaxation and in the Supercooled Liquid State

1998 ◽  
Vol 554 ◽  
Author(s):  
C. Nagel ◽  
K. Rätzke ◽  
E. Schmidtke ◽  
F. Faupel
Keyword(s):  
Free Volume ◽  
Metallic Glasses ◽  
Structural Relaxation ◽  
Amorphous Alloys ◽  
Excess Volume ◽  
Positron Lifetime ◽  
Supercooled Liquid ◽  
Mechanical Tests ◽  
Volume Changes ◽  
Shallow Traps

AbstractVolume changes in Zr46.7Ti8.3Cu7.5Ni10Be27.5 and Zr 65Al7.5Ni10Cu17.5 bulk metallic glasses have been observed by positron annihilation and density measurements. At low cooling rates excess volume of the order of 0.1 % is quenched in both glasses. Isothermal relaxation kinetics below the glass transition temperature obey a Kohlrausch law with exponents of β≈(0.3 ± 0.1). Structural relaxation is not accompanied by embrittlement, as indicated by simple mechanical tests. The outer surface plays a crucial role in annealing of excess volume, which can be restored by annealing above Tg. The observed free volume changes are at variance with the behavior of a perfectly strong glass. The temperature dependence of the positron lifetime is discussed in terms of thermal detrapping from shallow traps.

Free Volume Changes and Crack Tip Deformation in Bulk Metallic Glass Alloys and their Composites

2003 ◽  
Vol 806 ◽  
Author(s):  
Biraja P. Kanungo ◽  
Matthew J. Lambert ◽  
Katharine M. Flores
Keyword(s):  
Glass Transition ◽  
Metallic Glass ◽  
Bulk Metallic Glass ◽  
Free Volume ◽  
Metallic Glasses ◽  
Structural Relaxation ◽  
Strain Localization ◽  
Shear Bands ◽  
Inhomogeneous Deformation ◽  
Volume Changes

ABSTRACTThe free volume changes associated with deformation of metallic glasses play an important role in strain localization in shear bands. However the details of these structural changes during inhomogeneous deformation are unclear. In this study, the free volume changes in Cu60Zr30Ti10 and Zr58.5Cu15.6Ni12.8Al10.3Nb2.8 bulk metallic glasses were examined and quantified using differential scanning calorimetry following rolling and low temperature annealing. It was found that the height of the endothermic peak associated with the glass transition decreased following deformation whereas annealing resulted in an increase in the peak height. Additionally, the exothermic event associated with structural relaxation prior to the glass transition occurred at a lower temperature after rolling in the Zr-based system. Surprisingly, a similar shift in the onset temperature was not observed in the Cu-based system, suggesting a different structural relaxation mechanism. The Zr-based system was successfully modeled and the results indicated that the free volume increased ∼4% with inhomogeneous deformation and decreased ∼14% with annealing, consistent with expectations. In an effort to further characterize strain localization in shear bands, the development of a crack tip damage zone in a Zr-based bulk metallic glass composite was studied using scanning electron and atomic force microscopy. The first shear band developed at an angle of ∼60° from the crack propagation direction. This is discussed in light of the Mohr-Coulomb yield criterion for metallic glasses. The reinforcement phase arrested the growth of individual shear bands, while accumulated damage resulted in the shear bands cutting through the crystalline phase, ultimately resulting in crack branching and failure.

scholarly journals Metallic Glasses: A New Approach to the Understanding of the Defect Structure and Physical Properties

Metals ◽  
2019 ◽  
Vol 9 (5) ◽  
pp. 605 ◽  
Author(s):  
Vitaly Khonik ◽  
Nikolai Kobelev
Keyword(s):  
Shear Modulus ◽  
Physical Properties ◽  
Experimental Verification ◽  
Metallic Glasses ◽  
Structural Relaxation ◽  
Defect Structure ◽  
Relaxation Phenomena ◽  
Volume Changes ◽  
New Approach ◽  
Heat Effects

The work is devoted to a brief overview of the Interstitialcy Theory (IT) as applied to different relaxation phenomena occurring in metallic glasses upon structural relaxation and crystallization. The basic hypotheses of the IT and their experimental verification are shortly considered. The main focus is given on the interpretation of recent experiments on the heat effects, volume changes and their link with the shear modulus relaxation. The issues related to the development of the IT and its relationship with other models on defects in metallic glasses are discussed.

BULK AMORPHOUS AND NANOSTRUCTURED MATERIALS BY HIGH ENERGY BALL MILLING

2008 ◽  
Vol 22 (18n19) ◽  
pp. 2905-2913 ◽  
Author(s):  
CONSTANTIN POLITIS
Keyword(s):  
Ball Milling ◽  
Nanostructured Materials ◽  
Metallic Glasses ◽  
Amorphous Alloys ◽  
Glassy State ◽  
High Strength ◽  
Supercooled Liquid ◽  
High Energy ◽  
High Energy Ball Milling ◽  
Energy Ball

Mechanical alloying by high energy ball milling is a promising method for the production of bulk metallic glasses, amorphous alloys and nanostructured materials. Amorphous alloys reinforced by nanocrystals represent a big step in the optimization of new ultra high strength materials. Nano-scale W-Y solid solutions were synthesized by high energy ball milling. Only 1 at. % oxygen can stabilize the bulk metallic glassy state of Zr 54 Cu 19 Ni 8 Al 8 Si 5 Ti 5 O 1 to higher T x and to large supercooled liquid range Δ T xg .

Bulk Glass Formation in an Fe-Based Fe–Y–Zr–M (M = Cr, Co, Al)–Mo–B System

2004 ◽  
Vol 19 (3) ◽  
pp. 921-929 ◽  
Author(s):  
Z.P. Lu ◽  
C.T. Liu ◽  
C.A. Carmichael ◽  
W.D. Porter ◽  
S.C. Deevi
Keyword(s):  
Metallic Glasses ◽  
Glass Formation ◽  
Amorphous Alloys ◽  
High Strength ◽  
Supercooled Liquid ◽  
Glass Forming Ability ◽  
Bulk Glass ◽  
Bulk Amorphous Alloys ◽  
Glass Forming ◽  
Hardness Values

Several new bulk metallic glasses based on Fe–Y–Zr–(Co, Cr, Al)–Mo–B, which have a glass-forming ability superior to the best composition Fe61Zr10Co7Mo5W2B15 reported recently, have been successfully developed. The as-cast bulk amorphous alloys showed a distinctly high thermal stability with glass-transition temperatures above 900 K, supercooled liquid regions above 60 K, and high strength with Vickers hardness values larger than HV 1200. The suppression of the growth of primary phases in the molten liquids and the resultant low liquidus temperatures were found to be responsible for the superior glass-forming ability in these new alloys. It was found that the addition of 2% Y not only facilitated bulk glass formation, but the neutralizing effect of Y with oxygen in the molten liquids also improved the manufacturability of these amorphous alloys.

scholarly journals Rejuvenation of Zr-Based Bulk Metallic Glasses by Ultrasonic Vibration-Assisted Elastic Deformation

Materials ◽  
2020 ◽  
Vol 13 (19) ◽  
pp. 4397
Author(s):  
Yan Lou ◽  
Shenpeng Xv ◽  
Zhiyuan Liu ◽  
Jiang Ma
Keyword(s):  
Amorphous Alloy ◽  
Free Volume ◽  
Elastic Deformation ◽  
Ultrasonic Vibration ◽  
Metallic Glasses ◽  
Bulk Metallic Glasses ◽  
Supercooled Liquid ◽  
Deformation Region ◽  
Vibration Stress ◽  
The Relationship

The rejuvenation of Zr52.5Cu17.9Ni14.6Al10Ti5 bulk metallic glasses (BMGs) by ultrasonic vibration-assisted elastic deformation (UVEF) was studied herein. The UVEF-treated samples demonstrate an obvious rejuvenation and have a higher relaxation enthalpy and a smaller range of supercooled liquid regions than the as-cast samples. The fracture of the rejuvenated amorphous alloy is mainly ductile fracture, and shear deformation occurs in the deformation region. It is also found that as the amplitude increases, the free volume of the rejuvenated amorphous alloy increases, the yield strength and the elastic modulus decrease, and the formability increases. The free-volume content is used to characterize the degree of rejuvenation, and a mathematical model of the relationship between the ultrasonic amplitude and free volume is established. In addition, it is found that the ultrasonic vibration stress induces the additional free volume in the Zr-based bulk metallic glasses and improves the plasticizing behavior. The temperature rise caused by the ultrasonic thermal effect does not induce additional free volume.

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