Transport properties of (La,Pr)Sn3 alloys at low temperatures

We report on measurements concerning the transport properties of polycrystalline (La_1–x Pr _x )Sn₃samples with impurity concentrations 0.07 x 0.2 in the temperature range 0.3 T 12 K. The experimental results of the electrical resistivity, the thermopower, and the thermal conductivity show pronounced anomalies which are referred to crystal-field effects and a Kondo effect of excited levels. A quantitative comparison with existing theories confirms the importance of the aspherical Coulomb scattering in addition to the isotropic spin-exchange scattering of the conduction electrons by the magnetic ions. Taking into account the Kondo effect in a phenomenological ansatz, we are able to fit the magnetic part of the resistivity. Furthermore, we present the first experimental proof of the theoretically predicted influence of crystal-field split impurities on the thermal conductivity in dilute magnetic alloys. The thermopower is qualitatively discussed by a model including both the effect from inelastic scattering on the crystal-field levels and the Kondo effect. Finally the temperature dependence of the Lorenz number is compared with a calculation in the framework of crystal-field theory.Work supported by the Deutsche Forschungsgemeinschaft.     

Mechanical properties of the Sn-Zn eutectic alloys

The structure and mechanical properties of Sn-Zn unidirectionally frozen eutectic alloys have been examined over the growth range 5 to 4000mm h^–1. The structure is predominantly broken-lamellar below 750mm h^–1 but becomes increasingly fibrous at higher growth rates. The yield and ultimate strengths when tested in tension and compression were found to increase monotonically with growth rates up to 1000 mm h^–1 above which they assumed near constant values. This behaviour is attributed to some loss of axial growth at higher growth rates. The hardness measured on transverse sections increased over the entire growth rate range. Annealing at near eutectic temperatures followed by quenching increased the strength of alloys grown at less than 750 mm h^–1 and decreased that of those grown at higher rates. Similar behaviour was observed in selected Cd-Zn eutectic alloys. The increase in strength is attributed to solid solution hardening and the reduction to structural degradation during annealing. The Sn-rich matrix in this broken-lamellar eutectic appears to contribute significant strengthening to the composite.     

Mechanical properties of unidirectionally transformed Cu-In alloys

Comprehensive hardness measurements and limited tensile tests have been made on eutectoid and off-eutectoid Cu-In alloys. The alloys were transformed by unidirectional heat-treatment techniques using a range of imposed growth rates which resulted in alignment of the pearlite microstructure and a range of interlamellar spacing. Room temperature hardness of the as-transformed alloys was found to vary linearly as a function of ^–1/2, where is the pearlite interlamellar spacing; the alloys were calculated to have cooled from the decomposition temperature at rates in the range 0.047 to 18.6 K min^–1, which could result in variations of precipitation/coarsening reactions in the pearlitic phases contributing towards strength, as well as the lamellae interfaces. Hardness was also measured as a function of temperature and indicated a change in strengthening mechanism at 550 K, thought to indicate the temperature above which no significant strengthening was contributed by the pearlitic interfaces. Tensile failure of the lamellar structure occurred in a manner identical to directionally aligned Al-CuAl₂ eutectics.     

Mechanical properties of alloys with reversible martensitic transformation

Characteristics of the formation of properties of alloys with reversible martensitic transformation are examined from positions of the theory of structure formation in open, highly nonequilibrium, thermodynamic systems. It is shown that strain hardening of a metal is linearly connected with change in entropy and is a measure of the nonequilibrium state of the system and that it can be used for calculating the entropy change. Based on analysis of the energy state of the material, the article establishes that it is possible to determine stress levels corresponding to instant of loss of the form memory effect with plastic deformation and to failure under a simple type of stress. Calculated values of these characteristics of alloys are in good agreement with experimental data of the authors and other published data. The thermodynamics of reversible martensitic transformation are examined.Translated from Problemy Prochnosti, No. 3, pp. 34–42, March, 1992.     

Superconductivity in dilute Cu-Nb-Sn alloys containing Nb3Sn precipitates

The dilute Cu-Nb-Sn alloys containing small amounts of Nb and Sn less than 1 at % exhibited superconductivity after quenching from the liquid state and ageing. The best superconducting properties ( andJ _c=130 A cm^–2) in a Cu-0.30 at % Nb 0.15 at % Sn alloy were obtained when the sample was aged at 550° C for 384 h. This sample exhibited a structure of fine Nb₃Sn precipitates of 200 to 500Å diameter distributed homogeneously in the Cu matrix, and therefore it was concluded that superconductivity in these alloys resulted from the proximity effect of Nb₃Sn particles. In spite of the similar structure obtained by ageing at 800° C, the Cu-Nb-Sn alloys showed inferior superconducting properties compared to the Cu-0.4 at % Nb alloy and this would be explained qualitatively by the difference in the mean free path in the two alloys.     

Mechanical properties of alloys consisting of two ductile phases

A large number of engineering alloys consist of two ductile phases; for example α/β titanium alloys, α/β brasses and dual phase steels. Whenever a material consisting of two or more component phases with different properties is subjected to stress, in general, the phases deform differently. This results in additional interaction stresses and strains and their magnitude depends on such factors as the property difference between phases, and morphology and volume fraction of phases. Due to these complexities, the properties of two-phase materials, in general, cannot be predicted on the basis of simple laws such as the law of mixtures. The aim of this review paper is to describe how the various parameters such as morphology and volume percent of phases affect the mechanical properties of two-phase materials. Such information will be of great use in designing and selecting two-phase materials for various engineering applications.     

Mechanical properties of Al-Zn-Mg alloys investigated by microhardness measurements

One of the most simple and economic methods of testing the mechanical properties of alloys is the microhardness measurement. In the present paper we report on the results and the interpretation of experiments carried out on a series of AI-Zn-Mg alloys prepared from high purity base materials. The following results were obtained: (a) the incremental microhardness,HV, was related to the microhardness,HV, of high purity Al and can be given asHV=264(C_mg–0.25C_zn) wherec _mg andC _zn are the concentrations of Mg and Zn respectively, in the as-quenched state after solution heattreatment, (b) the ultimate tensile strength and the microhardness were correlated by the approximation:HV3_u.HV was investigated in the light of the average radius and the volume fraction of zones forming at room temperature. On the basis of the micromechanism of plastic deformation further evidence was found to show that the shearing mechanism is responsible for strengthening by GP zones in AI-Zn-Mg alloys.     

Mechanical properties and deformation behaviour of some zirconium-nickel amorphous alloys

A series of zirconium-nickel alloys have been melt-spun under identical conditions to produce partly crystalline and fully amorphous ribbons. The mechanical properties: hardness and fracture strength of these ribbons have been determined. The deformation and fracture behaviour in bending and tension have been studied and the effect of the crystalline particles on the deformation and fracture processes has been examined. The structure of the deformation defects has also been investigated.     

Mechanical properties of zinc-aluminium alloys extruded in the liquid-solid state

Zinc-aluminium alloy bars and wires were successfully extruded in the liquid-solid state with a liquid fraction higher than 15%. Fully dense materials were obtained in this way with pressure lower than 100 MPa. The relationship between flow stress and solid fraction was obtained and the role of the liquid component in the deformation behaviour was clarified. Mechanical properties of the extruded material are presented and discussed with regard to the initial microstructure of the metals before deformation, i.e. the conventional dendritic structure and non-dendritic structure composed of solid spheroids dispersed in the remaining liquid obtained by stir-casting techniques. The microstructure of the extruded products was generally fine and a fibrous structure was easily observed particularly for the stir-cast material where primary solid spheroids were highly deformed. Optimization of these parameters leads to a desirable high-strength material.     

Mechanical and electronic properties of Ag3Sn intermetallic compound in lead free solders using ab initio atomistic calculation

First principle calculations based on density functional theory (DFT) are used to calculate the structural, elastic and electronic properties of tin–silver intermetallic compound (Ag₃Sn), found mainly in lead free solder joints. In present work, for the exchange-correlation energy, generalized gradient approximation (GGA) functional is used. The calculated lattice constants are found to be within 2% error of the experimental values. All single crystal elastic constants are computed from which values of shear modulus, bulk modulus, Young's modulus and Poisson's ratio for polycrystalline Ag₃Sn are calculated using Voigt and Hill approximations. To explain the scatter in the experimentally determined values of elastic constants, directional dependence of bulk modulus and Young's modulus are estimated. The values of Young's modulus calculated along different planes are found to be in same range as experimentally determined values. Various anisotropic indices like universal anisotropic index, Zener anisotropic index, shear anisotropic index and others are calculated to study elastic anisotropy. Further anisotropy in Poisson's ratio is studied by calculating their values along six lower-index planes. The value of Debye temperature calculated using elastic data of present work is found be to higher than the values obtained using resistivity measurement, which can be attributed to temperature dependence. Electronic properties are studied via the band structure and total and partial density of states. The density of state (DOS) of Ag₃Sn has a characteristic main peak which is mainly dominated by Ag-d states. At the Fermi level, the total DOS value is found to be 1.97 states/eV with major contribution coming from Sn p states and minor contribution from Sn s and Ag s, p and d states.     

Mechanical and magnetic load effects in Nb3Sn cable-in-conduit conductors

Recent electromagnetic analyses of Nb₃Sn cables have suggested that cyclic longitudinal bending strain due to transverse magnetic loads could explain the observed low ‘n’ values and drop in critical current compared to the strand. The paper uses finite element modelling to simulate the strand strain states in the cable, including friction and plasticity effects (which cause permanent strand bending). These results are used to calculate the expected behaviour of the overall cable and of strands extracted from the cable after experiencing operational loads. Comparisons with experimental results are made.     

Precipitation hardening of Cu-Fe-Cr alloys part I Mechanical and electrical properties

This research is part of a project whose scope was to investigate the engineering properties of new non-commercial alloy formulations based on the Cu rich corner of the Cu-Fe-Cr ternary system with the primary aim of exploring the development of a new cost-effective high-strength, high-conductivity copper alloy. The literature indicated that Cu rich Cu-Cr and Cu-Fe alloys have been thoroughly investigated. A number of commercial alloys have been developed and these are used for a variety of applications requiring combinations of high-strength, high-conductivity and resistance to softening. Little evidence was found in the literature that the Cu rich corner of the Cu-Fe-Cr system had previously been investigated for the purpose of developing high-strength, high-conductivity copper alloys resistant to softening. The aim of these present investigations was to explore the possibility that new alloys could be developed that combined the properties of both sets of alloys, ie large precipitation hardening response combined with the ability to stabilise cold worked microstructures to high temperatures while at the same maintain high electrical conductivity. To assess thefeasibility of this goal the following alloys were chosen for investigation: Cu-0.7wt%Cr-0.3wt%Fe, Cu-0.7wt%Cr-0.8wt%Fe, Cu-0.7wt%Cr-2.0wt%Fe. This paper reports on the mechanical property investigation which indicated that the Cu-0.7wt%Cr-0.3wt%Fe, and Cu-0.7wt%Cr-2.0wt%Fe alloys were worthy of further investigation.     

Mechanical and corrosion properties of binary Mg-Dy alloys for medical applications

Microstructure, mechanical and corrosion properties of binary magnesium-dysprosium (Mg-5, 10, 15, 20 wt.% Dy) alloys were investigated for medical applications. In the as-cast condition, the distribution of Dy is quite inhomogeneous. Mg-10Dy alloy exhibits a moderate tensile and compression yield strength, and the best elongation and corrosion resistance. After T4 (solutionizing) treatment, the distribution of Dy becomes homogeneous. The tensile and compression yield strength of all Mg-Dy alloys decreases. The elongation remains unchanged, while the corrosion resistance is largely improved after T4 treatment.     

Mechanical properties of the Ni3(Si,Ti) alloys doped with carbon and beryllium

The Ni₃(Si, Ti) alloys doped with small amounts of carbon and beryllium were tensile tested in two environments, vacuum and air, over a wide range of test temperatures. The yield stresses of the carbon-doped alloys were almost identical to the undoped alloys while those of the beryllium-doped alloys were slightly higher than the undoped Ni₃(Si, Ti) alloys. The doping with carbon enhanced the elongation and ultimate tensile strength (UTS) whereas doping with beryllium reduced the elongation over the entire temperature range tested. The fracture patterns were primarily associated with the ductility behaviour. As the elongation (or UTS) increased, the fracture pattern changed from the intergranular to the transgranular fracture patterns. No environmental embrittlement of the ductility of the carbon-doped alloys was found at ambient temperatures but it was evident at elevated temperatures. Ductilities were reduced at high temperatures when the carbon-doped alloys were tensile tested in air. At high temperatures the environmental embrittlement observed is suggested to be due to the penetration of (free) oxygen into the grain boundaries causing the ductility loss in the carbondoped alloys.     

Thermodynamics and surface properties of liquid Ga-X (X = Sn, Zn) alloys

The mixing behaviour of Ga-Sn and Ga-Zn segregating alloy systems has been investigated by the Quasi-Chemical Approximation (QCA) in the frame of the Quasi-Lattice Theory (QLT) combined with a statistical mechanical theory. Assuming the order energy parameters as temperature dependent, various thermodynamic quantities are calculated at different temperatures. Thermodynamic properties of both systems deviate positively from the Raoult’s law. The energetics of mixing in liquid alloys has been analysed through the study of surface properties (surface tension and surface composition) and microscopic functions (concentration fluctuations in the long-wavelength limit and chemical short-range order parameter). Theoretical results are in a good agreement with the corresponding literature data and support a weak demixing tendency in Ga-Sn and Ga-Zn liquid alloys.