Shigeru Asano

Phase stability of Fe3Al with addition of 3d transition elements

In the (Fe1−x Mx)3Al system, the lattice parameter of the DO3 phase decreases with composition for M = V and Cr, maintaining the single phase state up to x = 0.4 and x = 0.25, respectively, whereas it increases for M = Ti and Mn at a smaller rate than those expected from bee Fe solid solutions. Both the cases consistently indicate an enhanced cohesion of the DO3 superlattice. In particular, the phase stabilization induced by M = V, as well as by M = Ti, is closely related to a strong preference of the substituted atoms for the FeI site (with eight Fe nearest neighbors) in the DO, structure. The electrical resistivity for M = Ti, V, Cr and Mn shows an abnormal negative temperature dependence. At a temperature higher than 800 K, an inflection appears on the resistivity curves as a sign of the D03-B2 transformation. The substitution of Ti and V is particularly effective for stabilizing the DO3 phase at high temperatures up to 1200 K and above, whereas M = Mn causes a modest increase and M = Cr gives no change in the transformation temperature. The solute effect on the transformation temperature could be related to both the atomic size mismatch and the variation of electron concentration.

Phase stability and mechanical properties of Fe3Al with addition of transition elements

Abstract The mechanical properties of D0 3 -type (Fe 1 − x M x ) 3 Al alloys with M = Ti, V, Cr, Mn and Mo have been investigated using a Vickers microhardness indentation technique. Electrical resistivity measurements demonstrate that the substitution of M = Ti, V and Mo results in a remarkable stabilization of the D0 3 structure relative to the B2 structure, probably because of the site preference of the substituents. At temperatures above 600 K, the hardness increases with increasing temperature and reaches a maximum at around 800 K. The anomalous peak in hardness extends to higher temperatures in parallel with increase in the D0 3 -B2 phase transformation temperature. In particular, the substitution of M = V leads to a significant improvement in the high-temperature strength up to 1000 K and above, maintaining the peak hardness almost constant.

Electronic, magnetic and transport properties of (Fe1-xVx)3Al alloys

We report electronic, magnetic and transport properties of (Fe1-x Vx )3 Al alloys with x = 0 - 0.38 and analyse the results on the basis of the measured electronic specific-heat coefficient, the Debye temperature and the magnetic stiffness constant. As the V composition increases, the electrical resistivity increases rapidly at low temperatures and the magnetization decreases significantly in parallel with a sharp reduction in the Curie temperature. In particular, the Heusler-type Fe2 VAl compound (x = 0.33) is found to be in a marginally magnetic state and to exhibit a semiconductor-like behaviour with the resistivity reaching 3000 µ cm at 2 K. Low-temperature specific heat studies demonstrate a substantial decrease in carrier concentration with the V substitution, being consistent with recent band calculations, which predict that Fe2 VAl is a nonmagnetic semimetal with a sharp pseudogap at the Fermi level. A large mass enhancement deduced from the electronic specific-heat measurements suggests that Fe2 VAl is a possible candidate for a 3d heavy-fermion system. The unusual electron transport is mainly attributed to the effect of strong spin fluctuations, in addition to the existence of very low carrier concentrations.

Analytical expressions of intrinsic internal friction based on damping data under inhomogeneous strains

Abstract The effect of a strain distribution in a vibrating specimen on the amplitude-dependent damping is analysed for several kinds of measurements. An analytical procedure is given for converting damping data measured as a function of the maximum strain amplitude under inhomogeneous strains to intrinsic internal friction expressed as a function of the homogeneous strain amplitude. On the basis of the analysis by Povolo and Gibala, correct mathematical expressions of internal friction are derived for longitudinal, flexural and torsional modes of free resonant vibrations. The formulae obtained are applied to an experimental curve of damping which increases according to a power of the maximum strain amplitude.

Temperature dependence of electrical resistivity in (Fe1-xTix)3Al alloys

We report on the temperature dependence of electrical resistivity in (Fe1-xTix)3Al alloys with Ti compositions x = 0-0.33. Samples in the composition range 0≤x≤0.15 are found to exhibit ferromagnetism with the Curie temperature TC decreasing from 770 K for x = 0 to 145 K for x = 0.15. The electrical resistivity below about 400 K for these Ti-poor samples increases rapidly with increasing x, but a negative temperature derivative of resistivity (dρ/dT) dominates above TC up to 1000 K and above. In contrast, samples in the range 0.20≤x≤0.33 are in a paramagnetic state, at least down to 2 K, and exhibit a rapid decrease in the low-temperature resistivity with increasing Ti composition x. In particular, the Heusler-type Fe2TiAl (x = 0.33) shows a large positive dρ/dT with the residual resistivity of only about 20 µΩ cm, in sharp contrast to a closely related system Fe2VAl reminiscent of a semiconductor-like behaviour with the resistivity reaching 3000 µΩ cm at 2 K. This can be explained by the fact that Fe2TiAl possesses a much higher density of states at the Fermi level than Fe2VAl, as deduced from the low-temperature specific-heat measurements supplemented by the band calculations in literature. The reason for the possession of a large positive dρ/dT in Fe2TiAl is discussed in relation to the Bloch-Gruneisen law.

Influence of impurity content on the acoustoplastic effect, internal friction, and Young's modulus defect during deformation of Cu-Ni single crystals

Abstract Oscillatory stress amplitude dependences of the acoustoplastic effect, absorption of ultrasonic vibrations (frequency of about 100 kHz) causing this effect, and Youngs modulus defect were simulataneously measured in situ during quasistatic deformation of Cu-1·3–7·6 at.% Ni single crystals. The time dependences of the magnitude of the acoustoplastic effect at constant oscillatory stress amplitudes were also obtained. The amplitude-dependent internal friction and Youngs modulus defect diminish drastically with increasing Ni content. The dependence of the magnitude of the acoustoplastic effect on the Ni concentration is much less pronounced and is reversed with increase in oscillatory stress amplitude. Data on the kinetics of the acoustoplastic effect revealed ‘instant’ (time-independent) and ‘relaxational’ (time-dependent) components. Both components show a similar dependence on Ni concentration, thus indicating their common origin. It is concluded that, while the amplitude—dependent internal fri...

Strain-amplitude-dependent internal friction and microplasticity in alumina with microcracks

Abstract Internal friction in polycrystalline alumina subjected to thermal shock has been measured as a function of strain amplitude by means of the free-decay method of flexural vibration. The curves of the amplitude dependence show a more rapid rise with increasing thermal shock damage. The data have been analysed on the basis of the phenomenological theory of microplasticity assuming a friction-type hysteresis. Thus the internal friction in alumina with microcracks is transformed into a microplastic strain of the order of 10—9. The stress-strain responses show that the microplastic strain increases nonlinearly with increasing stress under conditions where macroscopic plastic flow can never be observed. The variation in the microplastic flow stress corresponds well to the decrease in the macroscopic fracture strength resulting from the formation of microcracks and crack propagation.

STRAIN AMPLITUDE-DEPENDENT ANELASTICITY IN CU-NI SOLID SOLUTION DUE TO THERMALLY ACTIVATED AND ATHERMAL DISLOCATION-POINT OBSTACLE INTERACTIONS

Experimental investigations of the internal friction and the Young’s modulus defect in single crystals of Cu-(1.3–7.6) at. % Ni have been performed for 7–300 K over a wide range of oscillatory strain amplitudes. Extensive data have been obtained at a frequency of vibrations around 100 kHz and compared with the results obtained for the same crystals at a frequency of ∼1 kHz. The strain amplitude dependence of the anelastic strain amplitude and the average friction stress acting on a dislocation due to solute atoms are also analyzed. Several stages in the strain amplitude dependence of the internal friction and the Young’s modulus defect are revealed for all of the alloy compositions, at different temperatures and in different frequency ranges. For the 100 kHz frequency, low temperatures and low strain amplitudes (∼10−7–10−5), the amplitude-dependent internal friction and the Young’s modulus defect are essentially temperature independent, and are ascribed to a purely hysteretic internal friction component. ...

Analysis of strain-amplitude-dependent internal friction in thin-layer materials

Abstract Internal friction in aluminium thin films on a silicon substrate has been measured as a function of strain amplitude by means of a free-decay method of flexural vibration. Procedures for analysing the strain amplitude dependence of internal friction in thin-layer materials are presented, firstly for evaluating the internal friction in the film separately from the measured damping of the composite system, and secondly for converting the internal friction in the film into the plastic strain as a function of effective stress on dislocations. The stress-strain responses thus obtained for the aluminium films show that plastic strain of the order of 1019 increases nonlinearly with increasing stress. The microflow stress at a constant level of plastic strain is inversely proportional to the film thickness, which agrees with the variation in the macroscopic yield strengths.

Mechanical hysteresis due to microplasticity in alumina with microcracks

Abstract Stress-strain hysteresis in alumina with microcracks has been investigated by a loading–unloading test in the microstrain range around 10 −4 While there remains a permanent strain after the initial loading, steady-state cyclic loading results in a single closed hysteresis loop with a symmetrical shape. Such a stabilized hysteresis loop is responsible for internal friction and can be attributed to the microplasticity associated with a forerunning phenomenon of fracture.