Temperature dependence of electrical resistivity of deformed and undeformed V-rich V3Si single crystals

The electrical resistivity (T) of V-rich V₃Si single crystals (T _c-11.4 K) was measured from 4.2 to 300 K along the directions of [1 0 0] and [1 1 1] before and after plastic deformation at 1573 K. Anisotropy of (T) was observed although V₃Si has the cubic A15 structure. Plastic deformation does not affect the normal-state (T) behaviour but changes the normal-superconducting transition width T_c. At low temperatures (T _c<T 40 K), (T) varies approximately as T ⁿ where n-2.5 and this behaviour does not contradict the (0)- phase-diagram plot proposed by Gurvitch, where is the electron-phonon coupling constant and (0) is the residual resistivity.     

A note on the solution of a differential equation arising in boundary-layer theory

Summary The differential equation f + ff + f² = 0 (where dashes denote differentiation with respect to the independent variable ) subject to the boundary conditions f(0)=0, f()=0 and either f(0)=1 or f(0)=–1 is considered. It is shown that by using pf as dependent variable and =C–f (where C=f()) as independent variable and then expanding in powers of , a very good approximation to the solution can be obtained using only a few terms in the expansion.     

A universal dependence for thermal conductivity of metals and dilute alloys

A universal curve relating the maximum of thermal conductivity and its respective temperature with the residual electrical resistivity has been proposed for metals and dilute alloys. Based on the equation of that curve, a comparative analysis of selected literature data of thermal conductivity of metals, which have residual electrical resistivity in the range 10^–11<₀<10^–5. cm, have been performed. Using the data for 33 metals, confirmation of the Wiedemann-Franz law for the impurity component/T of thermal conductivity was obtained, which means that _th/_el1, where _th and _el are the parameters of the electron-lattice defect interaction obtained from measurements of thermal and electrical conductivity, respectively. Examples of the failure of the Wiedemann-Franz law are also presented, exhibiting the values of _th/_el in the range 0.16 to 25. Measurements of thermal conductivity in the range 2 to 20 K and determination of the residual electrical resistivity for the samples of Cd doped with Zn and quenched were performed, resulting in values _th/_el1.     

1 : 2 Long-range ordering and defect mechanism of WO3-doped perovskite Ba(Mg1/3Ta2/3)O3

The nature of the B-site cation ordering and the associated defect process necessary to stabilize the ordered domains were investigated using the WO₃-doped BaMg_1/3Ta_2/3O₃ BMT system as a typical example of BaB_1/3B_2/3O₃-type complex perovskites. It was shown that only the 1 : 2 long-range ordering of the B-site cation existed in both undoped and WO₃-doped BMT perovskites. The atomic defect mechanism associated with the stoichiometric 1 : 2 long-range ordering was systematically investigated. It is concluded that the substitution of W⁶⁺ for Ta⁵⁺ in the WO₃-doped BMT enhances the degree of the 1 : 2 long-range ordering and produces the positively charged W _Ta sites with a concomitant generation of tantalum vacancies V_Ta and mobile oxygen vacancies V _O for the ionic charge compensation.     

Tensile properties and plastic deformation modes ofβ Zr-Nb alloys

Tensile properties and plastic deformation modes of zirconium-niobium alloys were investigated at 290 and 77 K in the wide composition range from metastable to stable phase. Three types of plastic deformation modes, {332}113 twinning, {112}111 twinning and slip, were observed depending on alloy composition and temperature. {332}113 twinning, which occurs in metastable zirconium alloys, is related to the stability of phase to decomposition and leads to low yield stress and large elongation. On the other hand, {112}111 twinning, which appears in stable zirconium alloys, results from high critical stress for slip due to solution hardening and high Peierls stress and does not affect tensile properties significantly. The results obtained for zirconium-alloys are similar to those for titanium alloys, strongly suggesting that {332}113 twinning is an important plastic deformation mode which is common to phase alloys containing athermal phase.     

The morphology of α′ martensite in a two-phase (α+γ) Fe-Cr-Ni stainless steel

Both lath-shaped and martensites are induced by tensile deformation within of a two-phase ( + ) Fe-Cr-Ni stainless steel, forms from the through the at an intersection of two crystals. These are observed both when is surrounded by and when borders . The amount of strain at which both and nucleate, increases with test temperatures in the range –196 to 50° C. Adjacent laths are either twin-related, or 5, 9, 15 or 19° off the twin relationship, as found by analysing electron diffraction patterns.     

Mechanical and Corrosion Characteristics of Zr + 2.5% Nb Zirconium Reactor Alloy

The results of structural and phase hardening of pipes made of Zr + 2.5% Nb alloy show that ultrahigh-frequency thermal treatment of pipes (fast heating to the temperature of existence of the -phase followed by sharp cooling and annealing in the high-temperature range of the -phase) destroys the texture and forms a fine-grained structure (the grain diameter is about 1 m) with numerous transitional twins and a high density of precipitations of the secondary -niobium phase ( 10¹⁶cm^–3). In this state, the alloy is rather strong and plastic (at room temperature, _u 650 MPa, _0.2 550 MPa, and 20% both in the longitudinal and transverse directions). The efficiency of hardening by ultrahigh-frequency thermal treatment is not reduced with increase in the temperature of testing up to 500°C. Corrosion tests of channel pipes made of Zr + 2.5% Nb alloy subjected to ultrahigh-frequency thermal treatment in water containing various amounts of oxygen (from 0.1–0.3 to 600 mg/kg) at temperatures of 285–350°C for 700–6600 h under static conditions and in reactor water of the Ignalina Nuclear Power Plant for 5000 h under dynamic conditions showed that the corrosion resistance of this alloy is on a par with the corrosion resistance of the material of assembly channels of high-power channel reactors subjected to a standard treatment.     

The effect of an added seed on the phase transformation and the powder properties in the fabrication of Al2O3 powder by the sol-gel process

-Al₂O₃ powder was produced by the sol-gel process. The prepared sol-gels were seeded with 1.5 wt% powder (0.12m). The phase transformation of Boehmite into -Al₂O₃ and also the particle size distribution of the transformed -Al₂O₃ were strongly influenced by seeding and the heating rate during calcination. -Al₂O₃ seed particles have been shown to act as a nuclei for the transition of - to -Al₂O₃ and also to increase the driving force of the phase transformation, which consequently lowers the transformation temperature by about 200 °C. The particles derived from the seeded sol-gels retarded the formation of vermicular microstructures and were finer than those in the unseeded case. The seeding and the control of the heating rate during calcination could inhibit the grain growth due to transformation into -Al₂O₃. Fine particles which are homogeneous and have a high sinterability at lower temperatures could be obtained.     

A high-resolution-electron-microscopy study of a γ/γ′-α directionally solidified eutectic alloy

The microstructure of a /- directionally solidified (DS) eutectic alloy with a nominal composition of Ni-30.26Mo-6.08Al-1.43V (wt%) was investigated by means of high-resolution electron microscopy (HREM) and analytical electron microscopy. The -fibres exhibited a typical morphology with a rectangular cross-section and they displayed the Bain orientation relationship (OR) with the / matrix; that is, [001][001] and (110)(010). Misfit dislocations and lattice strain fields existed at the / interface for different habit planes; that is, (110)(010) and (100)(110) were analysed. EDAX (Energy dispersive X-ray) analysis showed that the composition of the -phase was approximately Ni₄(Mo, Al, V); it contained 90° rotational domains of Ni₃(Mo, Al, V) with a DO₂₂ structure and Ni₂(Mo, Al, V) with a Pt₂Mo structure.     

Anisotropy in the hardness and friction of calcium fluoride crystals

Anisotropy in the Knoop indentation hardness and the friction of diamond cones on calcium fluoride crystals has been investigated at experimental temperatures from 20 to 300° C. It is shown that the directions of minimum and maximum indentation hardness, on the (001) plane, are 110 and 100 respectively whilst the 1¯10 are harder than the 11¯2 directions on the (111) plane. Also, the sliding friction in the (001) plane is greatest in the 110 directions and least in the 100 and, on the (111) cleavage plane, [¯1¯12] sliding leads to higher friction than [11¯2]. The nature of anisotropy, for both hardness and friction measurements, does not change over the experimental temperature range covered in this work. Observations on the resultant deformation are made and these anisotropic properties are explained in terms of the effective resolved shear stresses developed on the {100} 011 primary slip systems at all experimental temperatures.     

Hydraulic characteristics and vapor content in a channel with boiling of a liquid underheated up to the saturation temperature

A method is proposed for calculating the hydraulic characteristic and vapor content in a channel with underheated boiling.Notation H heated length of channel - d_t thermal diameter - d_h hydraulic diameter - _t thermal perimeter - _h hydraulic perimeter - s through cross section - N power of channel - q heat flux - G weight flow rate - W velocity - coefficient of heat transfer - t, T temperatures - t temperature difference - i enthalpy - P pressure - P pressure drop - x weight vapor content - volumetric vapor content - C_p heat capacity - r heat of vaporization - coefficient of thermal conductivity - coefficient of surface tension - liquid density - vapor density - g acceleration of gravity - _o coefficient of friction of liquid against the channel wall - shear stress - density of two-phase medium averaged over a channel cross section - dynamic viscosity Indices s on saturation line - en at channel entrance - l liquid - v vapor - w wall Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 37, No. 5, pp. 784–792, November, 1979.     

Internally Consistent Thermodynamic Description of Three-Component Liquid-Metal Systems at High Temperatures in the Entire Region of Concentration Triangle

A method is suggested for the investigation of the thermodynamic properties of ternary liquid-metal alloys at high temperatures in the entire region of concentration triangle. The method is demonstrated for a Na–K–Cs ternary system. Data are obtained for the enthalpy and Gibbs energy of formation of alloy in the temperature range of 200 T 1200 K and concentration range of 0 x _{i (j, k)} 1. The results reveal a very fine effect associated with the temperature rise, namely, the inversion of excess partial Gibbs energy G¯ _i ^*= RTln _i ( _i is the activity coefficient of the liquid component) and the change of sign of deviation of partial pressure, as well as of total pressure, from the respective values in accordance with Raoult's law. The obtained results may be used to interpret the available literature data on independent measurements of the saturation pressure.     

Characterization of strength and microstructure in deformation processed Al-Mg composites

The microstructures, mechanical properties and electrical resistivity have been evaluated for deformation processed Al-20 vol%Mg and Al-13 vol%Mg composites. The Mg second phase adopts a convoluted, ribbon shape filamentary morphology after deformation. Both the size and spacing of these filaments decreases with deformation. The strength of these composites increases exponentially with reduced spacing of Mg filaments. The electrical resistivity of these Al-Mg composites is slightly higher than that of pure Al.     

A high-temperature solid-state potentiometric sensor for nitrogen based on ceramic LaAl12O18N

The nitrogen-sensing properties of LaAl12O18N are described for the first time. Positive e.m.f. measurements at high temperature across the cells -Nb (N), -Nb2N, -Al2O3, LaAl12O18NLaAl11O18 (or LaAl12O18N)LaAl12O18N, -Al2O3, -Nb2N, -Nb4N3, were in agreement with PN2(-Nb2N, -Nb4N3)>PN2(-Nb(N), -Nb2N) for the idealized stoichiometric cell reaction -Nb4N3+2-Nb(N)3-Nb2N, thus demonstrating the nitrogen-sensing property of these cells. The e.m.f. for a variety of cells with electrodes containing -V2N, -Nb2N, -Ta2N and Ti2N, were consistent with the predicted equilibrium nitrogen partial pressures.     

Formulas for evaluating the stabilization time of sluggish measuring instruments

Conclusions In this article formulas are suggested for calculating the stabilization time in ranges of 0<1 and 1.04<. These formulas are universal, they have a higher precision than has been hitherto obtained and they reflect the actual nature of the relationship between t_s and .Translated from Izmeritel'naya Tekhnika, No. 11, pp. 58–60, November, 1966.     

Effect of annealing upon decomposition of electrodeposited iron-zinc alloy coatings

As-deposited electrodeposited iron-zinc alloy coatings containing phase, decompose upon heating through a sequence of metastable phases. The h c p phase transforms to b c c G, or -like phase via a rapid diffusional phase transformation in the vicinity of 150 °C. For bulk iron contents of 8–13 wt%, transforms to 100% G phase. The G phase subsequently transforms at 240 °C to phase, which in turn transforms to or ₁ phase near 300 °C by depletion of iron from the surrounding matrix. The decomposition process may be driven by supersaturation of with iron.     

Plastic deformation of linear polyethylene containing row structures

The mechanical and thermal properties of highly oriented polyethylene films containing shish kebab type morphology are studied. At low deformations (strain<10%) strong work hardening is observed. Higher deformations ((40%) give rise to strain softening of the material and a decrease in the Young's modulus of as much as one-third of its initial value. In addition, the high melting component of the material originating from the shish-type crystals vanishes on higher deformation. The deformation processes are discussed from the point of view of a fibre-composite material and structural changes during the deformation are followed by transmission electron microscopy.     

Multi-length scale modeling of CVD of diamond Part II A combined atomic-scale/grain-scale analysis

Chemical vapor deposition of polycrystalline diamond films is studied by combining an atomic-scale kinetic Monte Carlo model with two one three-dimensional and one two-dimensional grain-scale models. The atomic-scale model is used to determine the growth rates of 111- and 100-oriented surface facets, the surface morphology of the facets and the extent of incorporation of the crystal defects. Using the atomic-scale modeling predicted growth rates for the 111- and 100-oriented facets, grain-scale modelling is carried out to determine the evolution of grain structure, surface morphology and crystallographic texture in the polycrystalline diamond films. It is found that depending on the relative growth rates of the 111- and 100-oriented facets, which can be controlled by selecting the CVD processing conditions, one can obtain either 110-textured films with a relatively smooth faceted surface or 100-textured films with a highly pronounced deep facets. In both cases, however, the film surface is composed entirely of the 111 facets. This findings are found to be fully consistent with the available experimental results.     

Use of adjoint functions in investigations of heat conduction and transfer processes

An examination is made of the use of adjoint functions in heat conduction and convection theory. Formulas of perturbation theory are obtained for steady and unsteady cases, an interpretation of the physical meaning of adjoint temperature is given, and some applications of the theory are discussed.Notation (r,) thermal conductivity - t(r,) temperature - t *(r,) adjoint temperature - q_V(r,) density of heat release sources - p(r,) a parameter of adjoint equation - r generalized coordinate - time - (r_s, ) heat transfer coefficient - I linear functional of temperature - (r,;r₀,₀) and *(r,; r₀,₀) Green's function for t(r, ) and t *(r, ) - C(r,) volume specific heat - W(r, ) vector distribution of flow velocities - V, S volume and surface areas of body - R radius of HRE - r, radial and angular coordinates - F_in, F_out inlet and outlet flow areas of channel     

γ ? α2 Phase transformation in fractured high temperature stress rupture Ti-48Al-2Nb(at.%)

The ₂ phase transformation in fractured high temperature stress rupture Ti-48Al-2Nb(at.%) alloy has been studied by analytical electron microscopy. ₂ and phases were found at grain boundaries. ₂ layers that suspended in layers and interfacial ledge higher than 2d ₍₁₁₁₎ at /₂ interfaces were observed in the lamellar grains. These facts indicated that ₂ phase transformation and dynamic recrystallization have occurred during high temperature stress rupture deformation. It can be concluded that deformation induced ₂ phase transformation and dynamic recrystallization resulted in the presence of particles at grain boundaries. A structural and compositional transition area between deformation-induced ₂(or ) and its adjacently original (or ₂) phases was found by HREM and EDS and is suggested as a way to transform between and ₂ phase during high temperature stress rupture deformation. The transition area was formed by slide of partial dislocations on close-packed planes and diffusion of atoms.