Free Volume Relaxation Process in Zr50Cu40Al10 Bulk Metallic Glass Studied by Positron Annihilation Techniques

2007 ◽  
Vol 1048 ◽  
Author(s):  
Akito Ishii ◽  
Fuminobu Hori ◽  
Akihiro Iwase ◽  
Yoshihiko Yokoyama ◽  
Toyohiko J Konno
Keyword(s):  
Metallic Glass ◽  
Positron Annihilation ◽  
Bulk Metallic Glass ◽  
Free Volume ◽  
Structural Relaxation ◽  
Annealing Temperature ◽  
Volume Relaxation ◽  
Appreciable Change ◽  
Positron Annihilation Lifetime ◽  
Chemical Ordering

AbstractStructural relaxation around free volume in Zr50Cu40Al10 bulk metallic glass (BMG) during isothermal annealing at 473, 573 and 673 K which are below glass transition temperature Tg =675 K have been investigated by positron annihilation lifetime (PAL) and coincidence Doppler broadening (CDB) measurements. The trends of change in positron lifetime, which correspond to the size of free volume at each annealing temperature, have a good correlation with their density change. These annealing processes obey a stretched exponential relaxation function (KWW: Kohlrausch-Williams-Watts law). Fitting parameters of KWW function, with relaxation time t0 and β, in each temperature were determined. These relaxation parameters depend on the annealing temperature, suggesting the distribution of activation energy for structural relaxation. Moreover, the profile of electron momentum distribution around free volume derived by CDB spectrum during annealing showed no appreciable change at each temperature. These facts suggest that long range chemical ordering, particularly around the free volume, dose not take place essentially.

In situ high-energy x-ray diffraction observation of structural evolution in a Ti-based bulk metallic glass upon heating

2010 ◽  
Vol 25 (12) ◽  
pp. 2271-2277 ◽  
Author(s):  
N. Zheng ◽  
G. Wang ◽  
L.C. Zhang ◽  
M. Calin ◽  
M. Stoica ◽  
...  
Keyword(s):  
Metallic Glass ◽  
Bulk Metallic Glass ◽  
Free Volume ◽  
Structural Relaxation ◽  
Structural Evolution ◽  
High Energy ◽  
Rapid Quenching ◽  
X Ray Diffraction ◽  
X Ray

The structural evolution of the Ti40Zr10Cu34Pd14Sn2 bulk metallic glass (BMG) upon was investigated by means of in situ high-energy x-ray diffraction. The position, width, and intensity of the first peak in diffraction patterns are fitted through Voigt function below 800 K. All the peak position, width, and intensity values show a nearly linear increase with the increasing temperature to the onset temperature of structural relaxation, Tr = 510 K. However, these values start to deviate from the linear behavior between Tr and Tg (the glass transition temperature). The changes in free volume and the coefficient of volume thermal expansion prove that the aforementioned phenomenon is closely related to the structural relaxation releasing excess free volume arrested during rapid quenching of the BMG. Above 800 K, three crystallization events are detected and the first exothermic event is due to the formation of metastable nanocrystals.

Structural Relaxation and Crystallization in a Pd40Cu30Ni10P20 Bulk Metallic Glass

2003 ◽  
Vol 806 ◽  
Author(s):  
R. Raghavan ◽  
U. Ramamurty ◽  
J. Basu ◽  
S. Ranganathan ◽  
N. Nishiyama
Keyword(s):  
Differential Scanning Calorimetry ◽  
Glass Transition ◽  
Metallic Glass ◽  
Bulk Metallic Glass ◽  
Structural Relaxation ◽  
Short Range ◽  
Annealing Temperature ◽  
Scanning Calorimetry ◽  
Short Range Ordering ◽  
The Stability

ABSTRACTThe stability of a Pd40Cu30Ni10P20 bulk metallic glass (BMG) against structural relaxation is investigated by isothermal and isochronal annealing heat treatments below and above its glass transition temperature, Tg, for varying periods. Differential scanning calorimetry (DSC) of the annealed samples shows an excess endotherm at Tg, irrespective of the annealing temperature. This recovery peak evolves exponentially with annealing time and is due to the destruction of anneal-induced compositional short range ordering. The alloy exhibits a high resistance to crystallization on annealing below Tg and complex Pd- and Ni-phosphides evolve on annealing above Tg.

Characterization of Free Volume in a Bulk Metallic Glass Using Positron Annihilation Spectroscopy

2002 ◽  
Vol 17 (5) ◽  
pp. 1153-1161 ◽  
Author(s):  
K. M. Flores ◽  
D. Suh ◽  
R. H. Dauskardt ◽  
P. Asoka-Kumar ◽  
P. A. Sterne ◽  
...  
Keyword(s):  
Metallic Glass ◽  
Positron Annihilation ◽  
Bulk Metallic Glass ◽  
Free Volume ◽  
Positron Annihilation Spectroscopy ◽  
Relaxation Processes ◽  
Nickel Copper ◽  
Atomic Relaxation ◽  
Volume Decrease

The free volume of metallic glasses has a significant effect on atomic relaxation processes, although a detailed understanding of the nature and distribution of free volume sites is currently lacking. Positron annihilation spectroscopy was employed to study free volume in a Zr–Ti–Ni–Cu–Be bulk metallic glass following plastic straining and cathodic charging with atomic hydrogen. Multiple techniques were used to show that strained samples had more open volume, while moderate hydrogen charging resulted in a free volume decrease. It was also shown that the free volume is associated with zirconium and titanium at the expense of nickel, copper, and beryllium. Plastic straining led to a slight chemical reordering.

Relaxation Behavior of Zr-Cu-Al Ternary Bulk Glassy Alloy Studied by Using Positron Annihilation Techniques

2010 ◽  
Vol 654-656 ◽  
pp. 1070-1073 ◽  
Author(s):  
Akito Ishii ◽  
Shinya Mineno ◽  
Akihiro Iwase ◽  
Yokoyama Yoshihiko ◽  
Toyohiko J. Konno ◽  
...  
Keyword(s):  
Positron Annihilation ◽  
Free Volume ◽  
Isothermal Annealing ◽  
Glassy Alloy ◽  
Volume Ratio ◽  
Charpy Impact ◽  
Volume Changes ◽  
Appreciable Change ◽  
Positron Annihilation Lifetime ◽  
Bulk Glassy Alloy

Zr-based bulk glassy (BG) alloys show high tensile strength and a high Charpy impact value. In this study, the free volume changes for the hypoeutectic Zr60Cu30Al10 BG alloy during isothermal annealing below glass transition temperature (Tg) have been investigated by positron annihilation lifetime and coincidence Doppler broadening (CDB) measurements. The positron lifetime of hypoeutectic and eutectic BG alloys is almost the same, although the atomic volume ratio, estimated by the density for the eutectic BG alloy is different from that for the hypoeutectic BG alloy. The CDB spectra show a marked difference between eutectic and hypoeutectic BG alloys; that is, the spectrum of the hypoeutectic BG alloy is closes to that of Zr metal than that of the eutectic BG alloy. This result exhibits that the elemental fraction of Zr atoms around free volume in hypoeutectic BG alloy is greater than that in eutectic BG alloy. The CDB ratio profiles for the hypoeutectic BG alloy during annealing shows no appreciable change. The same trend was observed in the eutectic BG alloy.

Influence of Structural Relaxation on Compressive Plasticity of Zr64.13Cu15.75Ni10.12Al10 Bulk Metallic Glass

2014 ◽  
Vol 910 ◽  
pp. 48-52 ◽  
Author(s):  
Jian Sheng Gu ◽  
Hui Feng Bo
Keyword(s):  
Differential Scanning Calorimetry ◽  
Glass Transition ◽  
Transition Temperature ◽  
Glass Transition Temperature ◽  
Metallic Glass ◽  
Bulk Metallic Glass ◽  
Free Volume ◽  
Structural Relaxation ◽  
Isothermal Annealing ◽  
Scanning Calorimetry

Structural relaxation through isothermal annealing below the glass transition temperature was conducted on a Zr64.13Cu15.75Ni10.12Al10bulk metallic glass. Differential scanning calorimetry was used to quantify enthalpy differences between the as-cast and relaxed samples, which were then related to average free volume differences. The influence of structural relaxation on plasticity was examined. While the free volume decreasement can be clearly observed between the as-cast and relaxed samples, structural relaxation is not accompanied by severe embrittlement.

Effects of chemical composition on the structural relaxation in ternary Zr-Cu-Al bulk glassy alloys studied by EXAFS and positron annihilation techniques.

2011 ◽  
Vol 1300 ◽  
Author(s):  
A Ishii ◽  
S Mineno ◽  
A Iwase ◽  
Y Yokoyama ◽  
T J. Konno ◽  
...  
Keyword(s):  
Chemical Composition ◽  
Positron Annihilation ◽  
Free Volume ◽  
Structural Relaxation ◽  
Alloy System ◽  
Atomic Scale ◽  
Hypoeutectic Alloy ◽  
Positron Annihilation Lifetime ◽  
Glassy Alloys ◽  
Composition Ratios

ABSTRACTMechanical properties and thermal stability of bulk glassy alloys depend on their chemical composition ratios, although their detailed local structures especially around free volume have not been clarified yet. In order to know the origin of property dependence on alloy composition in Zr-Cu-Al ternary bulk glassy alloys in a view point of atomic scale, positron annihilation lifetime, coincidence Doppler broadening (CDB) and EXAFS (extended X-ray absorption fine structure) measurements have been employed for eutectic Zr50Cu40Al10 and hypoeutectic Zr60Cu30Al10 bulk glassy alloys before and after structural relaxation by annealing below glass transition temperature Tg.The result of CDB experiment, which represents the electron momentum distribution around free volume, shows that significant atomic reordering around free volume does not take place by the annealing in each alloy. Besides, CDB ratio profiles for each alloy suggest that the fraction of Zr atom around free volume does not match the chemical composition of each alloy system. Change in positron lifetime, which is proportional to the size of free volume, during annealing for hypoeutectic alloy almost remains unchanged.

Physical Aging and Isothermal Relaxation in Glassy Polycarbonate Measured by Positron Annihilation Lifetime Spectroscopy

1990 ◽  
Vol 215 ◽  
Author(s):  
A. J. Hill ◽  
P. L. Jones
Keyword(s):  
Heat Treatment ◽  
Glass Transition ◽  
Transition Temperature ◽  
Free Volume ◽  
Annealing Temperature ◽  
Physical Aging ◽  
Treatment Temperature ◽  
Relaxation Behaviour ◽  
Volume Relaxation ◽  
Positron Annihilation Lifetime

AbstractThe free volume behaviour of polycarbonates annealed above and below the glass transition temperature, Tg, is studied. The free volume behaviour as a function of temperature and as a function of time during isothermal relaxation is compared for the different heat treatments. The relaxations which occur during contraction experiments performed after cooling from the heat treatment temperature result in a decrease in free volume for both sets of samples; however, the general decrease is much greater in the polycarbonate annealed below Tg. For the polycarbonate annealed below Tg, the free volume is partially recoverable if the samples are reheated to the original annealing temperature. Differences in the free volume relaxation behaviour during contraction experiments are discussed.

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