H. Mizubayashi

Young`s modulus of single phase cementite

The Young`s modulus of cementite, Fe{sub 3}C, is one of the physical quantities which are inevitably required to understand the mechanical properties of the high strength steels. Thus, efforts have been devoted to estimate the Young`s modulus of cementite from the mechanical tests on cast iron containing cementite. Very recently, the electron-shower-assisted physical vapor deposition (ES-PVD, hereafter) has been applied to prepare single phase cementite films, and their Young`s modulus and Poisson`s ratio have been evaluated using the surface wave method. On the other hand, the vibrating reed method to measure the Young`s modulus of a thin film deposited on a reed-substrate has been established recently. In the present paper, the authors applied the vibrating reed method to the single phase cementite films deposited on silicon reed-substrates to determine the Young`s modulus of cementite.

Mechanical property of high density nanocrystalline gold prepared by gas deposition method

Abstract High density nanocrystalline gold (n-Au) specimens were prepared by the gas deposition method. The Youngs modulus of n-Au is higher than 0.94Ecrys, suggesting E GB E crys ≈ 0.7 to 0.8 , where EGB and Ecrys denote the Youngs modulus of the grain boundary region and bulk-Au, respectively. Plastic deformation process at 300K in n-Au is governed not only by mean grain size but also by strain rate. The deformation map is proposed.

Effects of passing electric current on structural relaxation, crystallization and elastic property in amorphous Cu50 Ti50

For the amorphous Cu50Ti50, we investigated the effects of passing electric d.c.-current (PEC) other than joule heating on Youngs modulus M below 300 K, the structural relaxation (SR) at ∼ 500 K and the crystallization at ∼ 650 K for the current density id below 5 × 103 A/cm2. Under PEC, M shows an increase with increasing id, which is reversible for changing id and shows no temperature dependence. All the features of the effects of PEC on M are very similar to those reported for the effects of applied strain et on M, when the effects of PEC are assumed to be identical to those of et. On the basis of the scaling found between id and et, we estimateed the apparent charge a—Z*e (e=the elementary charge) measuring the electromigration force as 7 × 104e, which is the order of 104 times larger than the values reported in crystalline metals and alloys. SR is accredited under PEC for id > 2.5 × 103A/cm2, where the pre-exponential frequency-factor νvSR,O and the activation energy ESR show a strong increase and a small increase, respectively. For the crystallization, its early stage is accelerated under PEC when the crystallization proceeds rapidly at higher temperatures. This is found to reflect the acceleration of the homogenoeus nucleation under PEC. These features found for the effects of PEC are very similar to those reported for various a-alloys, suggesting that they reflect the common characteristics in a-alloys.

Effects of passing electric current on the elastic property of amorphous Cu50Zr50 and Cu50Ti50

For both amorphous Cu50Zr50 and Cu50Ti50, the dynamic Youngs modulus M was found to increase under passing electric d.c.-current (PEC) with the current density id below 5 × 103 A/cm2, suggesting that PEC induces internal stress. The id dependence of M observed at low strain amplitude et was found to be identical to the et dependence of M without PEC after scaling between id and et, giving Z* in the order of 105, where Z* is the apparent charge number measuring the electromigration force (EM-force) under PEC. We surmise that such a large Z* reflects the concentration of EM-force through the collective motion of many atoms, Z* = z*ξ, for ξ atoms with the charge number z* per atom. Application of this view to the observed effect of annealing on Z* gives ξ as several hundreds in the as-quenched state. Based on the present results, the effects of PEC on the structural relaxation and crystallization processes reported are also discussed.

Feasibility study of high-strength and high-damping materials by means of hydrogen internal friction in amorphous alloys

Abstract Exploring the feasibility of high-strength and high-damping materials, we investigated the hydrogen internal friction peak (HIFP) in amorphous (a-) Zr 60 Cu 40− x Al x ( x =0, 5, 10) and a-Zr 40 Cu 50 Al 10 and the tensile strength, σ f , of a-Zr 60 Cu 30 Al 10 as a function of the hydrogen concentration. Results are discussed relative to the HIFP reported in a-Zr 50 Cu 50 , a-Zr 40 Cu 60 and a-Ti 50 Cu 50 . σ f of a-Zr 60 Cu 30 Al 10 increases from 1.5 GPa in the no-charged state to 2 GPa at about 15 at.% H. The HIFP in the a-alloys is observed as a very broad peak, where the peak temperature found varies from 350 K in a-Zr 40 Cu 60− x Al x with 1 at.% H to 200 K in a-Ti 50 Cu 50 with 15 at.%. Although the HIFP with the peak height, Q −1 peak , beyond 3×10 −2 is observed in a-Zr 60 Cu 40− x Al x ( x =0, 10) in the as charged state, its Q −1 peak shows a decrease after aging at 350 K due to the hydrogen induced structural relaxation (HISR). However, for all the present a-alloys, Q −1 peak observed in the thermally stable state after the HISR can be still as high as 2×10 −2 . The present results suggest that the hydrogen-charged a-alloys are potential high-strength and high-damping materials.

Study of hydrogenated amorphous alloys as high-strength and high-damping materials

Abstract We investigated the hydrogen internal friction peak (HIFP) in the Zr–Cu base a-alloys. From the high-strength and high-damping materials point of view, the available range for T p is between 250 and 400 K at 300 Hz, and that for Q −1 p is between 0.5×10 −2 and 2×10 −2 for the Zr–Cu base a-alloys with a tensile strength beyond 1.5 GPa, where T p and Q −1 p are the peak temperature and peak height of the HIFP, respectively. For the HIFP mechanism, almost all the hydrogen atoms contribute to the HIFP in Zr 60 Cu 40 and Zr 60− y Cu 30 Al 10 Si y ( y =0, 1) a-alloys [a-alloys(I)] and the hydrogen atoms sitting in the hydrogen sites near the chemical potential can contribute to the HIFP in Zr 50 Cu 50 , a-Zr 40 Cu 60 and a-Zr 40 Cu 50− x Al 10 Si x ( x =0,1) [a-alloys(II)]. T p is considerably higher for a-alloys(II) than for a-alloys(I). The drastic increase in T p due to the Si addition by 1% is found for a-alloys(II) (a-Zr 40 Cu 49 Al 10 Si 1 ). The small increase in T p due to the Si addition by 1% is found for a-alloys(I) (Zr 59 Cu 30 Al 10 Si 1 ) The migration path for the HIFP is discussed.

Hydrogen internal friction peak and hydrogen induced structural relaxation in amorphous Cu60Zr40

Abstract Hydrogen internal friction peaks (HIFP) and hydrogen thermal desorption (HTD) for amorphous (a-) Cu 60 Zr 40 were investigated. The hydrogen concentration ( C H ) dependence of the relaxation strength of HIFP suggests that hydrogen occupies the tetrahedral sites under the nearest neighbor blocking. HIFP is found to be composed of seven constituent peaks, suggesting that in a-Cu 60 Zr 40 , there exist seven representative atomic structures which can be distinguishable by the activation energy of hydrogen migration. These features are very similar to those reported for a-Cu 50 Ti 50 and a-Cu 50 Zr 50 , indicating that they reflect the common characteristics of the a-alloys. The results of HTD show that the hydrogen induced structural relaxation (HISR) proceeds at room temperature for C H above 7 and 17 at.%, and the onset temperature, T x,s , for the precipitation of ZrH 2 decreases linearly with C H,R remaining in the specimens at T x,s . These results are discussed in the view of the effect of volume expansion on the stability of the a-alloys.

Elastic behaviors of high density nanocrystalline gold prepared by gas deposition method

Abstract Porosity-free nanocrystalline (n-) gold was prepared by the gas deposition method. Above 200 K, the anelastic strain associated with the grain boundary regions (GBs) starts to increase and, as the component, two processes with different stress dependence are found. This study demonstrates that the various atomic processes are excited in the GBs in n-metal.

Low temperature crystallization of amorphous alloys under electropulsing

Abstract The crystallization under electropulsing was studied for amorphous (a-) Zr 60 Cu 30 Al 10 , a-Cu 50 Ti 50 and a-Pd 80 Si 20 using the discharge of a condenser, with an initial current density, i d0 of ∼10 9 A/m 2 and a decay time, τ , between 2 and 0.1 ms. The crystallization proceeds when i d0 increases beyond the threshold i d0,c . i d0,c shows a minimum value at τ ∼1 ms, where the maximum increase in temperature is lower than 120 K. We surmise that density fluctuations exist in amorphous alloys and that a high density region undergoes a resonant collective motion under electropulsing, which induces a migration of atoms in the low density matrix around it. On the other hand, the electrical resistivity, R , decreases in the early stages of crystallization due to electropulsing, and then increases with increasing i d0 suggesting that electropulsing also modifies the thermodynamic free energy of the phases.

Local strain around hydrogen in amorphous Cu50Zr50 and Cu50Ti50

Abstract The hydrogen-induced volume expansion, a change in the X-ray diffraction first peak due to hydrogen charging and the hydrogen Gorsky effects were measured for amorphous (a-) Cu 50 Zr 50 and Cu 50 Ti 50 and discussed together with the hydrogen Snoek peak reported. The hydrogen-induced volume expansion is similar between a-Cu 50 Zr 50 and a-Cu 50 Ti 50 . In contrast, anisotropy of the elastic distortion around hydrogen appears to be much larger in a-Cu 50 Zr 50 than in a-Cu 50 Ti 50 . It is surmised that the local atomic structures are more deformable in a-Cu 50 Zr 50 than in a-Cu 50 Ti 50 .