Effect of cold work on anisotropic magnetoresistance of Co25Ni75

Various states of the polycrystalline Co₂₅Ni₇₅ sample have been achieved by cold rolling and heat treatments after cold rolling. At each metallurgical stage, the electrical resistivity

Full-size image

, measured in the saturated condition with a longitudinal field, and the resistivity

Full-size image

, obtained under a similar condition with a transverse field, were studied at 77K. We used the quantity

Full-size image

, defined as

Full-size image

, where

Full-size image

is the resistivity in zero field (or a demagnetized state), to check the magnetic anisotropy in the sample. It is found that cold work can induce an easy axis parallel to the roll direction. This phenomenon is associated with the short-range order and/or the directional Co–Co pair order formed during a cold-rolling process. Recovery and recrystallization were observed, if the rolled samples were annealed at various temperatures T_Q. Both stress relief and change of texturing lead to an enhancement of magnetic anisotropy of the longitudinal type. The anisotropic magnetoresistance

Full-size image

of the cold-rolled sample (CR-0) is the lowest. When T_Q is increased,

Full-size image

becomes recovered. However,

Full-size image

of a plainly salt water quenched sample is always larger than that of a cold-rolled one.     

Nondestructive evaluation of formability in thin steel sheets using fundamental Lamb wave

This paper describes the nondestructive evaluation method of the Lankford value (

Full-size image

r" height="14" width="12">-value) in thin steel sheets using the transit time of the fundamental Lamb wave. The (

Full-size image

r" height="14" width="12">-value) in thin steel sheet depends on the texture, that is, the (

Full-size image

r" height="14" width="12">-value) increases as the (111) crystal plane contained in the rolling plane increases, while it decreases as the (100) crystal plane sheet increases. The (

Full-size image

r" height="14" width="12">-value) evaluation method using the averaged fundamental Lamb wave velocity in the rolling plane has already been developed by many researchers. However, this method needs different calibration curve for steel sheets produced by different manufacturing processes, because some sheets have the same (

Full-size image

r" height="14" width="12">-value) but different texture, leading to a different velocity distribution. This paper describes why different Lamb wave velocities would be observed for thin steel sheets having the same (

Full-size image

r" height="14" width="12">-value) and how to evaluate the (

Full-size image

r" height="14" width="12">-value) by utilizing a combination of the averaged fundamental Lamb wave transit time and the characteristics of the transit time distribution. This result provides a more flexible measurement than the conventional methods and simplifies the evaluation procedures in industrial application.     

Elastic properties of amorphous and crystalline B1−xCx and boron at low temperatures

We present measurements of the internal friction (Q⁻¹) and speed of sound variation (δ

Full-size image

/

Full-size image

₀) of amorphous boron (a-B) and amorphous B₉C (a-B₉C). The elastic properties of these materials, which can only be produced as thin films, are consistent with those of other amorphous solids measured to date and exhibit good agreement with the tunneling model (TM) of amorphous solids. The TM parameter

Full-size image

γ_t²/ρ

Full-size image

_t² extracted from the elastic data has the same order of magnitude as that observed for all amorphous solids studied to date; a review will be presented. Using the results from the elastic measurements, we calculate the T² thermal conductivity Λ expected in the TM regime (T≤1 K) for a-B. The predicted thermal conductivity falls within the expected range for amorphous solids and agrees with the thermal conductivity of the crystalline icosahedral boride MB_68-δ (M=Y, Gd), which has been previously shown to exhibit glass-like excitations. We have also measured the internal friction and speed of sound variation of bulk polycrystalline c-B_1−xC_x at low temperatures (0.07 K<T<10 K). The elastic properties evolve towards the behavior characteristics of amorphous solids for increasingly carbon-deficient (x<0.20) specimens. The magnitude of the internal friction for the most carbon-deficient crystalline c-B_1−xC_x sample (x=0.1, c-B₉C) is comparable to that for a-B and a-B₉C, thereby confirming the inherent glass-like vibrational properties of carbon-deficient c-B_1−xC_x. Such behavior supports the glass-like character of carbon-deficient c-B_1−xC_x high temperature (T>50 K) thermal transport reported previously and provides the first experimental evidence for the presence of two-level systems (TLS) in these crystalline solids. However, discrepancies with the tunneling model are present; the data for c-B_1−xC_x bear some similarity to those for amorphous metals in which electronic relaxation channels are active, although details are still unclear. Previous studies have shown that the TM quantity C=Pγ_t²/ρ

Full-size image

_t² (“tunneling strength”) is essentially independent of the material's shear modulus G=ρ

Full-size image

_t² over a factor of 17. The elastic data presented in this work now extend the observed independence of the tunneling strength, C, over a factor of 70 in shear modulus.     

Hydrogen diffusion in Sm2Fe17 and Sm2Fe14Ga3 compounds

The short-range and long-range diffusion of hydrogen in Sm₂Fe₁₇ and Sm₂Fe₁₄Ga₃ compounds was investigated by magnetic after-effect (MAE) and thermal desorption spectroscopy (TDS). The substitution of iron by gallium greatly reduces the uptake and diffusion of hydrogen in these compounds. After charging in a high-purity H₂ atmosphere of 0.13 MPa at 570 K for 1 h the H content was determined to be Sm₂Fe₁₇H₅ and Sm₂Fe₁₄Ga₃H_1.3. Sm₂Fe₁₇ shows a hydrogen-induced MAE relaxation maximum at 190 K with a mean activation enthalpy of Q=(0.48±0.02) eV and a pre-exponential factor of

Full-size image

s. In the case of the Ga-substituted compound this maximum is replaced by a double maximum at 200 and 250 K corresponding to activation ethalpies of (0.52±0.02) eV and (0.64±0.02) eV with a pre-exponential factor of

Full-size image

s. These relaxation maxima are attributed to the short-range diffusion of hydrogen, since they are absent in the degassed compounds. TDS measurements of Sm₂Fe₁₇H₅ and Sm₂Fe₁₄Ga₃H_1.3 were performed in the temperature range from 291 to 515 K yielding activation enthalpies of Q=(0.59±0.02) eV and Q=(0.75±0.03) eV, respectively. The results are explained by different interstitial sites for hydrogen and the impact on the hydrogen disproportionation process is discussed.     

New technique of VAR investigations of thin films on thick substrates

A new technique of variable angle reflectometry (VAR) investigations of thin films on thick, transparent, parallel-sided substrates is presented. This technique uses spatial distribution of intensity of reflected radiation of a sample illuminated with a light beam of finite diameter. The experimental results obtained for amorphous silicon (a-Si) were fitted with theoretical dependencies taking into account the optical inhomogeneity over the film thickness. This inhomogeneity was described by values n_f, α_f, n_b and α_b of the real part of the refractive index and absorption coefficient at the surfaces of the film. The investigated film was also characterized by the average over its thickness values of the real part of the refractive index and absorption coefficient . For the investigated a-Si

Full-size image

. It can be suggested that the presented investigations of optical inhomogeneity of thin films of a-Si should be taken into serious consideration for optimized technological conditions.     

Thermochemistry of holmium bismuthides

Thermodynamic properties of Ho–Bi intermediate phases (HoBi and Ho₅Bi₃) have been studied by means of calorimetric and tensimetric techniques. The heats of formation at T=298 K were determined by high temperature direct synthesis calorimetry and the molar heat capacity of HoBi was measured by differential scanning calorimetry (DSC) in the temperature range 330–920 K. The equilibrium vapour pressures over the two-phase region HoBi+Ho₅Bi₃ were measured by Knudsen Effusion–Mass Spectrometry in the temperature range 1357–1631 K. These data were analyzed by the second-law method to obtain the enthalpy changes for the atomization processes and, thereafter, the heats of formation for the two compounds. From the calorimetric measurements the heats of formation at 298 K were determined to be −93±3 and −112±4 kJ/mol atoms, respectively for the Ho₅Bi₃ and HoBi compounds, consistent with

Full-size image

and obtained from the tensimetric measurements.     

Kinetics and mechanism of the nickel electrode—I. Acid solutions containing a high concentration of chloride and nickel ions

The kinetics of the Ni electrode in acid solutions with a high chloride ion concentration has been investigated in the range of 25–75°C. Dissolution occurs uniformly only at low anodic potentials. When the latter exceeds a critical value, E_crit, net localized metal corrosion takes place. The plot at E < E_crit corresponds to a curve approaching two limiting slopes, namely, at (

Full-size image (1K)

. The cathodic Tafel slope is . These results, including their pH dependence, are explained with a reaction mechanism involving the participation of adsorbed hydroxo-species.     

Crystal structure of R3Ge4 compounds (R Er, Ho, Tm, Lu)

The crystal structure of binary germanides R₃Ge₄ (R Er, Ho, Tm, Lu) has been determined by means of powder X-ray diffraction. For Er₃Ge₄ a full-structure determination has been performed using the Rietveld method (306 reflections, space group Cmcm,

Full-size image (2K)

). The location of the atoms in Er₃Ge₄ is similar to that in the W₃CoB₃ structure, with the Ge atoms substituting for Co and B. For the other R₃Ge₄ compounds (RHo, Tm and Lu) the lattice parameters are given.     

Crystal structure of 3R-Ta1.08S2

Single crystal of nonstoichiometric Ta_1+xS₂ with 3R-type structure has been obtained by chemical vapor transport method with NH₄Cl as transport agent. Single crystal of 3R-Ta_1+xS₂ grew as thin platelet with metallic luster. The X-ray Laue photograph has shown that the sample obtained has trigonal symmetry with

Full-size image

m1 Laue group. The structure has been refined with 3R-type model with R3m space group. The lattice constants refined are a=3.3169(3), c=18.0141(13)Å and c/a is 3×1.810. It has been found that a small excess of Ta atom (x=0.08(1)) is statistically distributed in the interstitial site located between TaS₂ sandwiches of 3R-TaS₂.     

Enhanced corrosion resistance of carbon steel in normal sulfuric acid medium by some macrocyclic polyether compounds containing a 1,3,4-thiadiazole moiety: AC impedance and computational studies

We report here the use of macrocyclic polyether compounds containing a 1,3,4-thiadiazole moiety (n-MCTH) in the corrosion inhibition of C38 carbon steel in 0.5 M H₂SO₄ acid medium.

Full-size image (8K)

The aim of this work is devoted to study the inhibition characteristics of these compounds for acid corrosion of C38 steel using electrochemical impedance spectroscopy (EIS). Data obtained from EIS show a frequency distribution and therefore a modeling element with frequency dispersion behaviour, a constant phase element (CPE) has been used. The experimental results obtained revealed that these compounds inhibited the steel corrosion in acid solution and the protection efficiency increased with increasing inhibitors concentration. The difference in their inhibitive action can be explained on the basis of the number of oxygen atoms present in the polyether ring which contribute to the chemisorption strength through the donor acceptor bond between the non bonding electron pair and the vacant orbital of metal surface. Adsorption of n-MCTH was found to follow the Langmuir’s adsorption isotherm. The thermodynamic functions of adsorption process were calculated and the interpretation of the results is given. These results are complemented with quantum chemical study in order to provide an explanation of the differences between the probed inhibitors. Correlation between the inhibition efficiency and the structure of these compounds are presented.     

First-Principles Studies on Twinnability of Magnesium Alloys: Effects of Yttrium and Lithium on $$\left( {10\bar{1}1} \right)\left[ {\bar{1}012} \right]$$ Compression Twinning Deformation Processes

We investigate the energetics involved in the \(\left( {10\bar{1}2} \right)\left[ {\bar{1}011} \right]\) tension and \(\left( {10\bar{1}1} \right)\left[ {\bar{1}012} \right]\) compression twinning deformation processes in magnesium via first-principles studies. Through identification of structural changes associated with each deformation process, we study the energetics of each deformation process and the local instability in the twin boundary region. We observe that the energy barrier in the \(\left( {10\bar{1}1} \right)\left[ {\bar{1}012} \right]\) compression twinning deformation pathway is higher than that in the \(\left( {10\bar{1}2} \right)\left[ {\bar{1}011} \right]\) tension twinning deformation pathway, even though the \(\left( {10\bar{1}1} \right)\) compression twin boundary is more stable than the \(\left( {10\bar{1}2} \right)\) tension twin boundary. We extend our study to examine the effects of Y and Li as alloying elements on each twinning deformation process. Our calculations predict that the addition of Y causes a reduction in the probability of fracture by an order of magnitude when the twinning deformation occurs and weakening of the resistivity to twinning deformation. However, the effect of Li addition on the twinning deformations is weaker than that of Y addition.     

A substitution of nickel by antimony:: Crystal and electronic structure of the new antimonide Hf6Ni1−xSb2+x

The ternary antimonides Hf₆M_1−xSb_2+x (M=Fe, Co, Ni) were prepared by arc-melting of stoichiometric mixtures of Hf, HfSb₂ and M. According to the single crystal structure analyses, performed on Hf₆NiSb₂ and Hf₆Ni_0.76Sb_2.24, Hf₆M_1−xSb_2+x crystallizes in an ordered variant of the Fe₂P structure type with the M and Sb atoms occupying the two P positions on 1b and 2c of space group P

Full-size image

2m, respectively (Zr₆CoAl₂ type). The 3d metal atoms M can partially be replaced by antimony, leading to significant, anisotropic changes in the lattice dimensions which are a=765.6(1) pm, c=362.10(7) pm, V=183.81(5)×10⁶pm³ for Hf₆NiSb₂, and a=760.5(1) pm, c=372.40(7) pm, V=186.53(5)×10⁶pm³ for Hf₆Ni_0.76Sb_2.24 as determined by single crystal data. Calculations of the electronic structure of Hf₆NiSb₂ using the Extended Hückel approximation show strong bonding Hf–Hf, Hf–Ni, and Hf–Sb interactions.     

Determination of the continuous cooling transformation diagram of a high strength low alloyed steel

The continuous cooling transformation diagram of a high strength low alloyed steel was determined by a dilatometer and microscopic analysis (OM, SEM) as well as thermodynamic analysis. As expected, Widmanstätten ferrite, bainite and martensite coexisted for most cooling rates, which made it difficult to determine the transformation kinetics of individual phases. However, peaks were clearly observed in the dilatometric

$$\frac{{d\left( {LVDT} \right)}}{{dT}}$$

curves. By overlapping the

$$\frac{{d\left( {LVDT} \right)}}{{dT}}$$

curves, which were determined using various cooling rates, peaks were separated and the peak rate temperatures, as well as the temperature at the start of transformation (5%) and the end of transformation (95%) of an individual phase, were determined. A SEM analysis was also conducted to identify which phase existed and to quantify the volume fraction of each phase. It was confirmed that the additional

$$\frac{{d\left( {LVDT} \right)}}{{dT}}$$

curve analysis described the transformation behavior more precisely than the conventional continuous cooling transformation diagram, as determined by the volume measured from the microstructure analysis.

     

Pressure–composition isotherms in the Mg2Ni–H2 system

A relatively pure Mg₂Ni intermetallic compound was prepared by partial melting and sintering. Absorption and desorption pressure–composition isotherms for the Mg₂Ni–H₂ system were obtained. The relationships between the equilibrium plateau pressure (P_eq) and the temperature were

and

The procedure to obtain the pressure–composition isotherms was explained and a method to calculate the composition for pressure–composition isotherms (“the summation method”) was also suggested.     

A New Finding About Conditions for More Than One Kirkendall Marker Plane in Binary Single Phase Diffusion Couples

It is now well known that there are experimental results of bifurcate, trifurcate or more Kirkendall marker planes (K-plane) in a multiple phase diffusion couple (M-couple). In the case of Au-Zn binary alloy system, for example, even in a β’/β’ single phase diffusion couple (S-couple) there is a possibility of the bifurcate K-planes because the ratio R = D _Zn/D _Au of the intrinsic diffusion coefficients in the β’ phase is smaller than 1 in the Au rich side and larger than 1 in the Zn rich side. It has been reported that the positions of the K-planes in a diffusion zone can be found graphically as intersections between the plot of marker moving distance \(2t\upsilon_{\text{k}}^{\text{D}}\) versus X _k and the plot of a straight line \(2t\upsilon_{\text{k}}^{\text{EX}}\) versus X _k. Here, \(\upsilon_{\text{k}}^{\text{D}}\) is the marker velocity with respect to the volume fixed frame of reference (V-frame) defined by,

$$\upsilon_{\text{k}}^{\text{D}} = \upsilon_{\text{k}} - \upsilon_{\text{V}} = V_{\text{B}} \left( {D_{\text{B}}^{\text{V}} - D_{\text{A}}^{\text{V}} } \right)\left( {\frac{{\partial C_{\text{B}} }}{\partial X}} \right),$$

and \(\upsilon_{\text{k}}^{\text{Ex}}\) is that determined experimentally by the following equation,

$$\upsilon_{\text{k}}^{\text{Ex}} = \upsilon_{\text{k}} - \upsilon_{0} = \frac{{X_{k} - X_{0} }}{2t}.$$

In this work, we studied the alignments of multiple markers (M-Ms) after diffusion anneal embedded in a S-couple for widely different constant values of ratio of intrinsic diffusion coefficients, R = D _B /D _A, with respect to the mole fixed frame of reference (N-frame) by our numerical technique taking the change in molar volume into account. For this purpose, new two plots to know the K-plane(s) for the N-flame were derived. A possibility was indicated that Kirkendall markers can locate not only at the intersection(s) between these new two plots but also at an unexpected place where the intersection cannot be found.

     

Thermodynamic stability of barium thorate, BaThO3, from a Knudsen effusion study

The Gibbs energy of formation of barium thorate was determined using the Knudsen effusion forward collection technique. The evaporation process could be represented by the equation

BaThO₃(s)=ThO₂(s)+BaO(g)

The vapour pressure of BaO(g) over the two-phase mixture of BaThO₃(s) and ThO₂(s) was obtained from the rate of effusion of BaO(g) and could be represented as

ln(p/Pa) (±0.39)=−50526.5/T/K+26.95 (1770≤T/K≤2136)

The Gibbs energy of formation of BaThO₃(s) could be derived from this data and represented as

Δ_fG°(BaThO₃(s))/kJ mol⁻¹±8.0=−1801.75+0.276T/K