Papers by Keyword: Structural Relaxation

Abstract: The free volume relaxation just under the glass transition region was investigated by the high-resolution density measurement using the bulk metallic glasses with the compositions of Pd40Ni40P20 and Zr55Cu30Ni5Al10. The relaxation process was well described by a stretched exponential function with Kohlrausch exponent values less than unity. The reduced free volumes in an as-quenched state were estimated as 0.0117 and 0.0353 for Pd40Ni40P20 glass and Zr55Cu30Ni5Al10 glass, respectively. The specific heat curves Cp(T) for Pd42.5Cu30Ni7.5P20 alloy were obtained for the supercooled liquid, the equilibrium liquid and the crystallized alloy. The isenthalpic Kauzmann temperature TKH and isentropic Kauzmann temperature TKS were estimated as 471 K and 522 K, respectively, from the specific heat data.

Abstract: Hydrogenated Zr-Cu-base metallic glasses (MGs) are the potential high-damping and high-strength materials. On the other hand, the knowledge on the material parameters which govern the peak temperature, Tp, and the peak height, Q-1 p, of the hydrogen internal friction peak (HIFP) remains poor. In order to pursue this issue, the hydrogen concentration dependence of Tp and Q-1 p in the Zr-Cu-base MGs were investigated in the point of view of the hydrogen induced structural relaxation (HISR). It is found that the Tp vs. CH data and the Q-1 p vs. CH data are well fitted by the relationships of Tp =
Tp exp(-CH/τH) +Tp,0 and Qp -1 ∝ ln(CH/τH), respectively, for various Zr-Cu-base MGs including bulk MGs, Zr55Cu30Al10Ni5 and Zr60Cu30Al10. That is, the observed relationship between Tp and CH is mainly governed by HISR. It is suggested that Tp,0 in Zr-Cu-base MGs is the highest among various MGs resulting in the highest Tp in Zr-Cu-base MGs. In other words, the control of Tp,0 is the key issue to find the high-Tp MGs.

Abstract: By means of the vibrating reed technique, measurements of internal friction have been performed in the temperature range of 120 K < T < Tg (= glass temperature) on two amorphous alloys, each produced as ribbon and bulk material. The different contents of free volume result in an only slight shift of the onset of irreversible structural relaxation to lower temperatures (i.e., lower activation energies) for the ribbons, while considerably different amounts of structural relaxation occur. After correcting for the thermoelastic effect, the reversible structural relaxation, i.e., an approximately exponential increase of damping with rising temperature, is well described by KWW kinetics (β ≈ 0.3). For the Zr-based alloy only, a clear relaxation peak occurs in the range from 270 K to 320 K (for the first flexural vibration mode between 100 Hz and 400 Hz) induced by hydrogenation. In addition, the effect of plastic deformation on the damping behavior by cold rolling of the bulk materials has been examined.

Abstract: A set of the techniques, including large- and small-angle X-ray scattering, differential scanning calorimetry, electrical resistance and microhardness measurements was used to study the changes in structure of the well-known Fe40Ni40P14B6 metallic glass under continuous heating up to the crystallization onset temperature. The measurements performed in situ and after rapid cooling from different temperatures revealed that structural relaxation is a multi-stage process involving variations of the short-range order, relief of quenched-in stresses, changes of the free volume concentration and enhancement of the concentration inhomogeneities. The temperature ranges of each process have been established. Using proposed approximate equation describing the scattering particles growth at a constant heating rate, it has been shown that the enhancement of phase separation in the glass investigated is governed by diffusion-limited growth mechanism.

Abstract: We will discuss the stress release phenomena, structural relaxation and interdiffusion processes during annealing. The [Co(4nm)/Ta(4nm)]38 multilayers were prepared by dc magnetron sputtering on Si substrate. The multilayers were annealed at various temperatures (523 - 673K) in vacuum (under 10-5 torr) furnace. The effective interdiffusion coefficients were determined from the slope of the best straight line fit of the first peak intensity versus annealing time [d ln(I(t)/I(0)) /dt] by X-ray diffraction (XRD) low angle measurements. The drastic decrease of the relative intensity in the initial stage shown due to the structural relaxation was excluded in the calculation of effective interdiffusion coefficients. The temperature dependence of interdiffusion in the range of 523 - 673K is described by D = 3.2×10-19 exp(-0.51±0.11 eV/kT) m2s-1.