Effect of reactive stresses on the heat of martensitic transformations in titanium nickelide

Calorimetric studies of titanium nickelide show that thermally reversible prestraining does not affect the heat of the B2 → R and R → B2 martensitic transformations. At the same time, reactive stresses induced by straining under constrained conditions are found to decrease the heat of the B19′ → B2, R → B19′, B2 → R, and R → B2 transformations by a factor of 1.16–1.40. A formula describing this effect is proposed.     

On the pressure dependence of martensitic and superconducting transition temperature in intermetallic compounds

In order to explain the large pressure dependence of the cubic to tetragonal transition temperature T_M in LaAg an expression has been derived from ?T_M/?P for a two-fold degenerate electronic band interacting with the tetragonal strain mode. Analogy with the pressure dependence of the ferromagnetic transition temperature T_c in an itinerant system is pointed out. The nature of variation of the superconducting transition temperature with pressure is also discussed.     

Narrow band in the intermetallic compounds MNiSn (M=Ti,Zr, Hf)

The presence of a narrow band below conduction band of nonmagnetic compounds MNiSn (M=Ti, Zr, Hf) is assumed to explain their low temperature properties such as the heat capacity, IR optics, electronics transport. A computation of the Seebeck coefficient supplies support for this assumption.     

Influence of neutron irradiation on the martensitic transformations and shape-memory effect in a TiNi alloy

The paper reports measurements of the strains and electrical resistance of a TiNi shape-memory alloy under irradiation in the low-temperature helium circuit of a nuclear reactor. Irradiation of the alloy in martensitic state at 170 K revealed that the transition temperatures from cubic to rhombohedral and from rhombohedral to monoclinic phase decrease exponentially with increasing dose. No change in the shape-memory effects and transformation plasticity was observed up to a dose of 6.7×10²² n/m². Keeping the sample at 340 K without irradiation restores (increases) partially the transition temperatures. The relations observed can be assigned to a change in the degree of long-range order in the lattice caused by neutron irradiation. Fiz. Tverd. Tela (St. Petersburg) 40, 1705–1709 (September 1998)     

Mechanisms of martensitic transformations in boron nitride and conditions of their development

Abstract

The dependence of the pressure threshold of martensitic transformations on the disordering degree of starting structures is considered for graphite-like BN into diamond-like BN modifications transitions. The effect of loading conditions on transformation mechanisms of rhombohedral BN into zinc blende or wurtzite modifications is analyzed also. Analytical relations obtained allow to explain the experimental data and to predict a behavior of various graphite-like structures under different p, T conditions.     

An57Fe Mössbauer study of rare-earth intermetallic compounds R(Fe11Ti)

⁵⁷Fe Mössbauer spectra are reported for the ThMn₁₂ structure series of intermetallic compounds R(Fe₁₁Ti) (R=Y, Nd, Sm, Gd, Tb, Dy, Ho, Er, Tm, Lu). The Mössbauer spectroscopy of oriented absorbers has been used to study the spin reorientation transitions exhibited by the members of the series where the second-order Stevens coefficient α_J of the rare-earth (Nd, Tb and Dy) is negative. A simple model has been established to deduce the canting angle from the Mössbauer spectra of oriented absorbers. The results are analyzed in terms of a crystal-field model. The crystal field parameters must be increased significantly to account for the observed large anisotropy in the Sm(Fe₁₁Ti) compound, which may find applications as a permanent magnet.     

The determination of crystal field levels in the intermetallic compound HoRh by inelastic neutron scattering

Inelastic neutron time of flight measurements have been carried out on the intermetallic compound HoRh at different temperatures. Well resolved transitions between crystal field levels were observed at 4.0 and 9.7 meV. The complete crystal field level scheme was deduced and the crystal field parameters were found to be A₄⁰ 〈r⁴〉 = ?10.98 meV and A₆⁰ 〈r⁶〉 = ?1.59 meV. These values deviate considerably from point charge estimates.     

Gap at the Fermi level in the intermetallic vacancy system RBiSn(R=Ti,Zr,Hf)

The new class of intermetallic compounds RNiSn(R=Ti,Zr,Hf) may be characterised by the presence of an ordered sublattice of Ni atom vacancies in comparison with normal metals RNi₂Sn with no Ni vacancies. We report unusual transport and optical properties of the RNiSn system. The electrical resistivity of RNiSn is very high (3<p<100) mOhm*cm; the temperature coefficient of resistivity (TCR) is negative and strongly dependent on the annealing conditions. For some samples ZrNiSn and for a single crystal of TiNiSn the resistivity can be described by the Mott's law at temperatures 0.1<T<20 K. A phase transition nearT=100 K without change of crystal structure was deduced from Hall effect data and the temperature dependence of the lattice constant. Preliminary data on transport phenomena in RPtSn and RPdSn(R=Ti,Zr,Hf) compounds are also reported. The unusual properties of RNiSn system might be related to a gap of the electron spectrum near the Fermi energy.     

Influence of argon ion bombardment on the formation of intermetallic compounds in the nickel-aluminum system

The formation of Ni _x Al _y intermetallic compounds in two-layer (Ni/Al) structures (nickel films deposited on aluminum substrates in vacuum) under bombardment by Ar⁺ ions has been studied experimentally. The method based on Rutherford backscattering of He⁺ ions is used to demonstrate that argon ion bombardment causes the formation of intermetallic compounds in the near-surface layer. The thickness of the intermetallic layer formed in the near-surface region substantially exceeds the projective ion path. The composition and thickness of the intermetallic layer depend mainly on the implantation dose and the substrate temperature, rather than on the ion current density. In the intermetallic layer, the content of nickel increases with increasing temperature. It has been established that, in the absence of bombardment, intermetallic phases are not observed at temperatures lower than T = 400°C and that, in the presence of bombardment, the Ni₃Al intermetallic layer arises at a temperature of 320°C.     

Pseudogap formation in the intermetallic compounds (Fe1-xVx)3Al

Optical conductivity data of the intermetallic compounds (Fe1-xVx)3Al ( 0相似文献   

Structural phase transformations and physical properties of intercalation compounds in the Cr0.5Ti(Se1−x Tex)2 system

The atomic structure and magnetic and electric properties of the Cr_0.5TiSe₂-Cr_0.5TiTe₂ system of intercalated phases were studied in detail by gradually replacing selenium by tellurium. It was revealed that this replacement changes the crystalline structure from monoclinic in the initial compounds to hexagonal in the compounds containing various types of chalcogen atoms; this is accompanied by disordering of chromium atoms in the van der Waals gaps. The electrical resistance and magnetic characteristics vary nonmonotonically on replacement of selenium by tellurium, which is associated with a change in the degree of atomic disordering during the transition from Cr_0.5TiSe₂ to Cr_0.5TiTe₂.     

Magnetic susceptibility of intermetallic compounds in the Er-In system at high temperatures

The temperature dependence of the magnetic susceptibility (T) of intermetallic compounds of Er with In in a wide temperature range from 20 to 1600°C inherent in the solid state and melting process of the materials under review was studied for the first time by the Faraday method. For all test compounds, the temperature dependence was found to be approximated by the Curie-Weiss linear law both in a solid and liquid state. The Curie paramagnetic temperature, Curie-Weiss constants, and effective magnetic moment numbers per Er atom were calculated by computer processing of the ^–1(T) data, using the least-squares technique. A semiempirical estimation of the indirect exchange interaction parameter showed the test compounds to be characterized by exchange interactions of the Ruderman-Kittel-Kasuya-Yosida type.__________Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 12, pp. 7–10, December 2004     

Influence of Ti/TiAlN-multilayer designs on their residual stresses and mechanical properties

In this research work, Ti/TiAlN multilayers of various designs were deposited onto substrates pretreated by different etching procedures. The influence of multilayer design and substrate pretreatment on multilayers adhesion, hardness, wear and friction coefficients was systematically analyzed and correlated with residual stresses of these multilayers as well as with residual stresses on the coating-near substrate region, which were analyzed by synchrotron X-ray diffraction at HZB-BESSYII. These investigations show that the adhesion can be improved by a specific etching procedure, which cause increased compressive stress in the coating-near the substrate region. Additionally, it was found, that the multilayer with the thickest ceramic layers has the highest hardness and the lowest wear coefficients as well as the lowest compressive residual stress within studied multilayers.     

金属间化合物YFe11Ti中替代元素的致稳机理与系统磁性的理论研究

基于密度泛函理论(DFT),采用线性缀加平面波展式结合改进的局域轨道方法(APW+lo),对具有ThMn12结构的永磁材料YFe11 Ti的结构和磁性进行了计算和分析.计算了YFe12,Y3Fe17,YFe11 Ti的生成能,探讨了替代元素Ti的加入使YFe12系统能够保持稳定的ThMn12结构的原因以及Ti在系统中的最佳可能占位.给出了系统的晶体磁矩和各晶位原子的磁矩以及系统的电子态密度,分析了系统磁性的来源和各晶位原子磁矩的大小与其配位数和平均近邻原子距离的关系.     

Influence of reactive stresses on thermodynamics and kinetics of martensitic transitions in single crystals of the shape memory Cu-Al-Ni alloy

The heat of the β′₁-β₁-martensitic transition in single crystals of the alloy Cu-13.5 wt % Al-4.0 wt % Ni was studied under conditions of a constrained shape memory deformation and emergence of reactive stresses. The experiments were performed with samples bended in the form of a clamp. The sample was put into a continuous stainless steel ring, and this construction was placed in the capsule of a differential calorimeter. It was found that, with an increase in the magnitude of preliminary bend deformation, the maximum in the heat release (or heat absorption) curves decreases noticeably and its position shifts to higher temperatures. It was revealed that the latent heat of the transition decreases by a factor of 2 and 3 during heating and cooling, respectively. It was assumed that the observed effects are related to the influence of reactive stresses on the parameters of martensitic transitions. A quantitative analysis of the data obtained was performed in terms of the theory of diffuse martensitic transitions taking into account both the thermodynamic and kinetic factors.     

X-ray topographic identification and measurement of plastic strains and elastic stresses in single crystallites of polycrystalline diamond layers

The well-known phenomenon of asterism is used as the basis for the development of an X-ray topographic method to identify and measure plastic strains and residual elastic stresses in single crystallites more than 3 μm in size in polycrystalline diamond layers. The amount of asterism is used as a quantitative measure of plastic strains in crystallites. The distribution of crystallites over the amount of asterism in 40-to 670-μm-thick microwave-plasma-deposited polycrystalline diamond layers is obtained. Shear plastic strains, which cause a misorientation from 0.4′ to 1.5° between different areas of a crystallite, are observed for the first time. The residual elastic stresses calculated in plastically strained crystallites vary between 2.7 kPa and 0.84 GPa.     

Magnetic properties and magnetocaloric effects in Er_(1-x)Gd_xCoAl intermetallic compounds

The magnetism and magnetocaloric effect in Er1-xGdxCoAl(x = 0, 0.1, 0.2, 0.4, 0.6, 0.8, 1) were investigated. The Er1-xGdxCoAl compounds were synthesized by arc melting. With the increasing Gd content, the N′eel temperature(T N)linearly increases from 14 K to 102 K, while the magnetic entropy change(-?S M) tends to decrease nonmonotonously.Under the field change from 0 T to 5 T, the-?S M of the compounds with x = 0.2–1 are stable around 10 J/kg·K, then a cooling platform between 20 K and 100 K can be formed by combining these compounds. For x = 0.6, 0.8, 1.0, the compounds undergo two successive magnetic transitions, one antiferromagnetism to ferromagnetism and the other ferromagnetism to paramagnetism, with increasing temperature. The two continuous magnetic transitions in this series are advantageous to broaden the temperature span of half-peak width(δT) in the-?S M–T curve and improve the refrigeration capacity.