Relaxation In Metallic Glasses Research Articles

Magnetic After-Effects and Structural Relaxation in Metallic Glasses

Magnetic After-Effects and Structural Relaxation in Metallic Glasses

Viscous relaxation in metallic glasses.

Recent theories of icosahedral ordering in supercooled liquids are used to define a model dynamics to describe the relaxation of momentum fluctuations in these systems. Glassy behavior of the system at microscopic distances is enforced by introducing a phenomenological relaxation parameter ${\ensuremath{\Gamma}}^{B}$ which is anomalously small and strongly dependent upon temperature. Macroscopic consequences of this microscopic slowing down are examined. It is found that there is an upper bound on the magnitude of the translational correlation length, below which microscopic sluggishness is ineffective in producing a large macroscopic viscosity. If the correlation length is larger than this upper bound, then the macroscopic viscosity acquires a strong temperature dependence increasing like 1/${\ensuremath{\Gamma}}^{B}$ as the temperature falls. Binary metallic glasses have a correlation length which is just above this bound.

New method of stress-free dilatometry to examine the structural relaxation of metallic glasses

A new type of dilatometer has been constructed which avoids any mechanical stress on the ribbon-shaped specimen and which measures the length change directly on the specimen on the furnace avoiding any transfer elements. The concept applies sensitive photometric measurement of the width of a slit machined into a reference plate of known material, which is partially covered by the end of the specimen ribbon clamped at the other end. The change of the width of the slit is a measure of the relative length changes of specimen and reference plate. The set-up has been tested by measuring known material and it is applied to monitor the structural relaxation of metallic glass ribbons which increase in density by atomic rearrangement in the amorphous state as well as during crystallisation. Examples for commercial FeNi-based amorphous alloys are given.

On the analysis of structural relaxation in metallic glasses in terms of different models

On montre qu'un modele qui separe les processus de relaxation structurale en une contribution de mise en ordre chimique a courte distance (CSRO) et une contribution de mise en ordre topologique a courte distance (TSRO) permet de tenir compte de toutes les donnees experimentales. Cas de Fe 40 Ni 40 B 20

A model for the kinetics of TSRO and CSRO structural relaxation in metallic glasses: Comparison with experimental results

Recently a model was developed for the description of topological and chemical structural relaxation in metallic glasses. In this paper we compare model calculations with experimentally studied relaxation effects, and we propose an extension of the model by introducing a spectrum of activation energies for the reversible chemical part of the relaxation processes. It is demonstrated that the results of the extended model agree well with experimental DSC results for both as-quenched and pre-annealed glasses.

Log time relaxation kinetics and the activation energy spectrum model

In order to test the assertions of our activation energy spectrum (AES) model for relaxation in metallic glasses, measurements of stress relaxation have been carried out. Data have also been generated by computer simulation, and it has been possible to calculate accurately the shape of relaxation curves even after complex thermo-mechanical treatments. The AES model is shown to be of considerable value in understanding relaxation kinetics in metallic glasses.

A DSC study of structural relaxation in metallic glasses prepared with different quenching rates

Sets of amorphous Fe-Ni-Cr-P-B, Fe-Ni-Mo-B, Fe-B-C alloys have been prepared by melt spinning using different rotation speeds of the wheel. The enthalpy of relaxation, the glass transition temperature Tg, the crystallization temperature are studied as a function of quenching rate. Structural relaxation takes place continuosly in a wide temperature range from 420–450 K up to the Tg region (650–670 K) and it is governed by a spectrum of activation energy described by the heat evolution curve at constant heating rate. The chemical and topological contribution to structural relaxation are separated by means of suitable thermal treatments.

Kinetics of structural relaxation in metallic glasses

Etude de la composante reversible de la relaxation structurale que l'on associe avec l'ordre chimique a courte distance. Etude sur les alliages Pd 78 Ge 22 et Fe 40 Ni 40 P 14 B 6 (Metglos 2826)

Atomic transport and structural relaxation in metallic glasses

Structural relaxation effects in metal-metalloid glasses are reviewed. Data on viscous flow and atomic diffusion are presented, and possible mechanisms of structural relaxation are discussed.

Thermal stresses and viscoelastic relaxation in metallic glasses prepared by liquid quenching

Thermal stresses and viscoelastic relaxation in metallic glasses prepared by liquid quenching

On the kinetics of structural relaxation in metallic glasses

A model is proposed to describe the simultaneous changes in topological (TSRO) and chemical (CSRO) short range order during structural relaxation of metallic glasses. Changes in free volume and order parameter during isothermal and isochronal annealing were calculated. Corresponding changes in internal energy and Curie temperature are—at least qualitatively—in good agreement with experimental observations. The amount of free volume and short range order frozen in during the quench from the liquid state were also calculated and found to be of the correct order of magnitude.

Study of structural relaxation in metallic glasses by modulus measurements

Study of structural relaxation in metallic glasses by modulus measurements

Relationship between specific heat and structural relaxation in Fe40Ni40B20metallic glass

The structural relaxation in metallic glasses influences many technically important properties. Calorimetric investigations of relaxation have been carried out to date using only continuous heating techniques. In the present work results of isothermal annealing experiments on Fe40Ni40B20 are reported. It was possible to divide the relaxation into reversible and irreversible contributions. The reversible relaxation occurs predominantly at higher temperatures and is ∼5–20% of the irreversible relaxation. The change in relaxation with time can be described by an exponential function. The relaxation times lay between 2·5 and 10 s. The specific heat changes by ∼1–3% for anneals between 400 and 600 K. The maximum change occurs at 500 K. The results are compared with those of other authors. Possible effects of the structural relaxation on the fracture toughness are discussed.

Use of elastic waves to study relaxation in metallic glasses

Metallic glasses may be formed in a large number of metal alloys by quenching the appropriate liquid at rates of the order of 106 K s−1. This is usually achieved by melt spinning which produces thin ribbons or tapes of the material. In their as-quenched state, metallic glasses are highly metastable with respect to not only the crystalline state, but also a denser glassy structure of lower energy. Consequently, on subsequent annealing these glasses undergo a number of subtle structural changes usually described as ‘structural relaxations’. We have used a sensitive pulse-echo technique to monitor the changes in Young's modulus during these relaxations. The total change in modulus is high (∼ 10%) and the change during isothermal annealing can be fitted to an expression of the type <disp-formula> <mml:math> <mml:mrow> <mml:mi>∆</mml:mi> <mml:mi>E</mml:mi> <mml:mo>=</mml:mo> <mml:mfrac> <mml:mrow> <mml:mi>k</mml:mi> <mml:mi>T</mml:mi> </mml:mrow> <mml:mi>α</mml:mi> </mml:mfrac> <mml:mo>(</mml:mo> <mml:mtext>ln</mml:mtext> <mml:mfrac> <mml:mi>t</mml:mi> <mml:mrow> <mml:msub> <mml:mi>t</mml:mi> <mml:mn>0</mml:mn> </mml:msub> </mml:mrow> </mml:mfrac> <mml:mo>+</mml:mo> <mml:mn>1</mml:mn> <mml:mo>)</mml:mo> </mml:mrow> </mml:math> </disp-formula> The value of E at full relaxation depends on the annealing temperature during relaxation. By subsequent temperature cycling it is possible to alter the values of E reversibly between those characteristic of different annealing temperatures. As a consequence it is possible to perform a crossover experiment commonly seen for the refractive index of oxide glasses. The results are discussed in terms of the topological defects and chemical short-range ordering present in metallic glasses.

Length changes during the structural relaxation of metallic glasses

Length changes during the structural relaxation of metallic glasses

The use of Young’s modulus to monitor relaxation in metallic glasses

The kinetics of change of Young’s modulus E during isothermal relaxation and crystallization of an all-metal glass Cu60Zr40 has been measured by a pulse-echo technique. E increases by about 10% between the as-quenched and fully relaxed states. Crystallization of the glass produces a further 15% increase in E. The kinetics of the relaxation process can be fitted to an expression of the form ΔE=a ln t+b. a)On leave from the Institute of Physics, Saragevo, Yugoslavia.

Ferromagnetic resonance observations of surface effects, magnetic ordering and inhomogeneous anisotropy in a metallic glass

Ferromagnetic resonance (FMR) and scanning electron microscope observations of surface effects in Metglas 2826 ribbons are presented. These effects are considered to be due to spin-wave scattering by surface pits. The considerable reduction in surface effects by a selected surface treatment allowed, for the first time, the FMR investigation of annealing effects and magnetic anisotropy. These observations are interpreted in terms of magnetic dipolar ordering and are related to recent experiments on structural relaxation in metallic glasses.

Structural relaxation in metallic glasses

Structural relaxation in metallic glasses