Electron irradiation effects on iron-nickel invar alloys

Electron irradiation was used as a means of accelerating the diffusion in Fe-Ni alloys. Mössbauer effect, X-ray and electron microscopy experiments on samples with 28 to 50% Ni show that the Invar character disappears after irradiation up to 250°C, in particular the variation of the lattice parameter versus temperature becomes linear around room temperature. At the same time, two phases appear in the alloy, one rich in nickel and ordered with FeNi (AuCu) superstructure, the other rich in iron and probably ordered (Fe₃Ni). The Invar state is therefore shown to be a metastable state. A diagram of the Fe-Ni alloy is proposed.     

Lattice dynamics in ferromagnetic invar alloys

The lattice dynamical properties of the Invar alloys Fe₆₅Ni₃₅ and Fe₇₂Pt₂₈ are discussed. The experiments on the lattice vibration by inelastic neutron scattering have shown an apparent correlation of phonon anomalies with the ferromagnetic long range order. The elastic softening below the Curie temperature is attributed to the dynamical aspects, at least for the [ςς0]TA₁ mode. The lattice dynamical features are derived from the electronic structure of the Invar alloys. They are consistent with the theoretical model that Invar characters are closely related to the detailed band structure of the d electrons near the Fermi level. The present studies indicate significant contributions of phonon anomalies to the Invar problem.     

Fe-Pt invar alloys—homogeneous strong ferromagnets

The thermal expansion and magnetic properties of Fe-Pt Invar alloys in both ordered and disordered states indicate that inhomogeneities play no essential role in determining large magnetovolume effects in Fe-Pt alloys. On the other hand, the concentration dependence of the magnetization, the hyperfine field at Fe nuclei and other related properties clearly show the strong ferromagnetism in Fe-Pt Invar alloys. Comparing the Invar behaviour found in Fe-Pt alloys with that in Fe-Ni alloys, it has been concluded that the so-called Invar effect generally consists of two types of anomalies. One is the essential effect, i.e., the large magnetovolume effect arising from the 3d band polarization and the other is the secondary or additional effect manifested as various magnetic anomalies associated with heterogeneities or weak ferromagnetism.     

The effect of interstitial hydrogen on the electronic structure of Fe-Pd alloys

The electronic structure and bonding in Fe-Pd alloys were computed using a tight binding method. Two phases have been identified for these alloys, a high temperature fcc and a low temperature fct structure. The hydrogen absorption turns out to be a favorable process in both structures. The hydrogen at tetrahedral interstitial site for the fct structure is 2.2 eV more stable than that impurity atom located at an octahedral interstitial site in the fcc structure.The density of states curves show a peak below the d metal band which is made up mostly of hydrogen based states (>50% H_1s) while the metal contribution includes mainly s and p orbitals.In the fcc structure, both Fe-H and Pd-H bonds are developed while the Fe-Pd interface shows antibonding filled states near the Fermi level. When the fct phase is considered, the Fe-H overlap population (OP) decreases, while the Pd-H remains similar to the previous case. The Fe-Fe OP decreases and the Pd-Pd bonds are almost unaltered. The interfacial Fe-Pd bonds are almost unaffected by hydrogen. The band structure of the hydrogenated alloys in the fcc and fct phases were also computed.     

Single crystalline elastic constants of Fe-Ni invar alloys

The single crystalline elastic constants of Fe-Ni alloys containing 30 – 50 wt.% Ni are reported. The anomalous temperature dependence in the ferromagnetic state is due to a large magnetic contribution to the elastic constants.     

The effect of hydrogen on the superconducting and structural properties of b.c.c. Nb-Ru alloys

The superconducting transition temperature (T_c) has been measured before and after the introduction of hydrogen into Nb_(1?x)Ru_x$\text{(0.20?x?0.33)}$. In all cases, the presence of appreciable amounts of this interstitial component led to a sharp increase in the T_c. All the evidence suggests that conversion of the host metal lattice to f.c.c. is necessary for the appearance of the elevated T_c.     

Elastic and magnetoelastic effects in invar alloys

A review of the elastic behaviour of Invar alloys is given. This includes (a) ferromagnetic alloys (Fe-Ni, Fe-Pt, stainless Invar); (b) antiferromagnetic alloys (Fe-Mn, Mn- and Cr-based alloys); (c) very weak ferromagnets (ZrZn₂, Ni₃Al, Ni-Pt); (d) amorphous alloys (Fe-B). It is shown that elastic anomalies (ΔE effects) can but need not occur simultaneously with a large thermal expansion anomaly. Various magnetoelastic contributions exist (ΔE_λ, ΔE_ω, ΔE_m) which are discussed in terms of existing theoretical models. The effect associated with a volume distortion, i.e. the bulk modulus anomaly, is shown to fit into the framework of the itinerant electron model.     

The effect of chromium on the magnetic properties of elinvar alloys

A study was made of the magnetic properties of alloys of the Fe-Ni-Cr system with varying chromium content in strong fields at room temperature. The processes which govern the magnetization of these alloys were determined. It is shown that the presence of chromium in the alloy has a marked effect on its magnetic properties. The chromium content determines the saturation magnetization, the anisotropy constant and the susceptibility of the paraprocess.     

High-field susceptibility and magnetization in Fe-Ni invar alloys

The high-field susceptibility of Fe-Ni Invar alloys does not give rise to a sudden increase at the Curie temperature. The decrease in magnetization with increasing temperature is attributed to the T² term as well as to the spin wave term for Fe-Ni Invar alloys.     

Effects of pressure on magnetization of Fe-Ni and Fe-Pt invar alloys

The changes of magnetization under hydrostatic pressure up to about 20 kbar have been measured on f.c.c. Fe₆₅Ni₃₅ and f.c.c. disordered Fe₇₂Pt₂₈ Invar alloys in a pulse magnetic field up to 50 kOe with temperature down to 4.2 K. Although the pressure coefficients of the magnetization at room temperature are almost the same for both specimens, the coefficients at 4.2 K of Fe₇₂Pt₂₈ alloys is about one order smaller than that of Fe₆₅Ni₃₅ alloy. These results are coincident with those obtained by the recent measurements of the forced volume magnetostriction.     

Effects of hydrogen on the electronic properties of dilute GaAsN alloys

Nitrogen has profound effects on the electronic structure of GaAs, as only a few percent of N can drastically lower the band gap. It is, however, not recognized that the same amount of N can also qualitatively alter the electronic behavior of hydrogen: First-principles calculations reveal that, in GaAsN, a H atom bonds to N and can act as a donor in its own right, whereas in GaAs and GaN, H is amphoteric, causing passivation instead. At high Fermi energy and H concentration, a N complex with two H was found to have lower energy than the single-H configuration. By removing the effect of N, this electrically inactive complex restores the gap of GaAs.     

The effect of isotopic substitution on the thermodynamic properties of palladium-hydrogen alloys

An attempt has been made to predict the thermodynamic properties of the Pd-D and Pd-T systems from those of the Pd-H system. By considering only the isotopic dependence of the optic modes, a satisfactory interpretation of the infinitely dilute solutions is not possible. However, using only the isotopic dependence of the optic modes together with an empirical equation for the infinitely dilute solution yields calculated results for the concentrated solutions in both the single and two phase regions which are in excellent agreement with the experimental results for the deuteride and tritide systems.     

时效工艺对PtCo合金磁性能的影响

研究了时效温度对PtCo合金磁性能的影响.磁性能测量结果显示,随着时效温度的增加合金的剩磁逐渐减小,时效温度为690 ℃时,合金的矫顽力达到最大值.第一步时效处理后,合金的有序度S随时效温度的提高而增加,长程有序度的增加说明合金有序相的晶粒尺寸也在增加,这是合金矫顽力变化的根本原因.第二步时效处理后,PtCo合金的微观组织结构不发生改变,有序相的各向异性场增大,使合金的矫顽力增大. 关键词： 时效温度 PtCo合金 磁性能 有序度     

Volume and shape magnetostriction of ferromagnetic invar type alloys

The volume and shape magnetostriction ω_V(H) and ω_S(H) of an Invar alloy and a technical constant-modulus alloy were measured with a strain gauge technique at room temperature. The considerable shape magnetostriction amounts to 0.1 of the volume effect. The itinerant model of ferromagnetism and Kanamori's formula for correlation effects is applied. The observed magnetostriction implies a deformation potential of about 0.3 eV.     

Origin of the anomalies and thermodynamic aspects in iron-nickel invar alloys

The thermodynamic properties of Fe-Ni Invar alloys are analyzed in terms of the theoretical results obtained in the itinerant electron model accompanying in the mixing of the ferromagnetic and paramagnetic phases with different atomic volumes. All the anomalies in Fe-Ni Invar alloys are explained by the effect of a large magnetovolume coupling and this large coupling is attributed to the magnetic transformation due to the changes in temperature, magnetic field and pressure. There is also an enhancement due to the magnetovoume coupling to the high-field susceptibility, compressibility and forced magnetostriction. The pressure dependence of T_c is also discussed.     

The effect of scale factor on mechanical properties of lead alloys

The effect of scale factor on mechanical and physical properties of metals and alloys is of both scientific and practical interest. Its study permits determination of the role in formation of physical properties of such factors as surface quality, character and distribution of internal and surface defects, types of processing, grain size, etc. As is well known, scale factor manifests itself to a greater degree, the stronger the material in question. Possibly because of this, data on the effect of scale factor on the properties of lead alloys with their relatively low mechanical strength are absent from the literature. However, such an omission is not justifiable, since lead, which is widely used in industry, is a scarce and expensive material, and proper determination of optimum dimensions for lead products is of major importance. The present study will clarify in greater detail the role of grain size and general level of mechanical properties on the relative effect of scale factor. The practical value of the study lies in the following. The alloys studied are used in manufacture of protective cable shields. The shield thickness can vary over wide limits, depending on the properties of the alloy, construction of the cable, and conditions of transportation and use. Therefore, by increasing the strength and other desirable properties of the alloy, significant reductions can be made in shield thickness, producing considerable economic savings. However, this cannot be done without a knowledge of the dependence of the alloy's mechanical properties on dimensions of the final product or specimen. Commencing from conditions of cable shield transportation and use, the effect of scale factor on alloy properties was studied for tensile loading, creep, and cyclical bending. The data gathered permit evaluating the validity of calculations for change in cable shield thickness for replacement of one alloy by another.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 7, pp. 103–109, July, 1977.     

The effect of hydrogen on the magnetic properties of quenched Ti-Zr-Ni rods

Ti-Zr-Ni quenched rods of 3, 2 and 1.5 mm diameter, prepared by vacuum-casting, were analyzed by X-ray diffraction (XRD) and vibrating sample magnetometry (VSM) before and after hydrogenation. Samples with two different compositions were prepared, i.e., Ti₄₀Zr₄₀Ni₂₀ and Ti₅₃Zr₂₇Ni₂₀. The as-cast rods were pulverized and hydrogenated from the gas-phase at 45 bar and 300 °C for 1000 min. The mass spectra of the desorbed hydrogen revealed the distribution of the hydrogen desorption temperatures from these alloys, whereas using thermogravimetry we obtained the mass% of desorbed H. We found that the ratio between the i-phase and the C14 Laves phase depends on the master alloy composition and the cooling rate, i.e., the rod diameter. VSM measurements revealed an about 30% decrease in paramagnetic susceptibility upon hydrogenation for all six investigated samples.