Structure, mechanical properties and electrical resistivity of rapidly solidified Pb-Sn-Cd and Pb-Bi-Sn-Cd alloys

A series of Pb-Sn-Cd alloys containing up to 60 wt % Bi were quenched from the melt to room temperature by melt spinning. The structure of rapidly solidified (melt spun), Pb-30 wt % Sn-10 wt % Cd, Pb-30 wt % Bi-20 wt % Sn-10 wt % Cd, and Pb-60 wt % Bi-10 wt % Sn-10 wt % Cd have been investigated by means of an X-ray diffraction technique. From X-ray analysis a crystalline metastable phase, designated (Pb-Bi) is detected. The formation of a metastable crystalline phase in the range of composition investigated causes a pronounced increase in the electrical resistivity. Desirable values of hardness and elastic constants are critically evaluated. It is also observed that the values of the Fermi energy are a few electron volts. Calculated values for the concentration of the conduction electrons, N, m_-3 of Pb -60 wt % Bi-10 wt % Sn-10 wt % Cd rapidly solidified is found to be 0.985×10₂₈ m_-3.     

Microstructure and mechanical properties of rapidly solidified Al-Si-Fe-X base alloys

The effects of Ti and V additions on microstructure and mechanical properties of rapidly solidified Al-20w/oSi-5w/oFe alloy were investigated, respectively. The hypereutectic Al-Si-Fe base alloys were gas-atomized and hot-extruded to make the consolidated bars. The addition of 2w/oTi increased wear resistance and mechanical properties such as tensile strength, hardness and elongation. Based on TEM analyses, it can be concluded that the improved properties in the Al-Si-Fe alloys containing Ti were caused by the formation of DO₂₂-(Al,Si)₃ Ti phase finely dispersed in the matrix. On the contrary, V addition was less effective than Ti, in that V could not decompose as the expected Al₁₀V phase with a large v/o of precipitates; V was mostly solid-solutionized in the other unknown phase.     

Structure of rapidly solidified aluminum alloys

This paper is a summary of an extensive research program carried out by the authors on the structure of rapidly solidified aluminum alloys; and a comparison with the work of others also involved in this field. The paper discusses the changes in the dendritic and non-dendritic structure of the matrix at cooling rates from 10^–3 to 10¹⁰ K/s and discusses the hetergeneity of the structure caused by interdendritic-segretion during solidification.     

Structure of rapidly solidified aluminium-silicon alloys

This paper present results obtained on rapid solidification of aluminium-silicon alloys from the liquid state. It shows that the limit of primary solid solubility is extended almost to the eutectic composition and that the large supersaturation is relieved on raising the annealing temperature to the range 110 to 450° C. This conclusion is based on measurements of lattice parameter and is also supported by corresponding changes in hardness and metallographic features.     

Microstructural evaluation of rapidly solidified Al-Li-Be alloys

Aluminium-lithium-beryllium alloys are a group of low-density, high-modulus materials that potentially have technological importance in aerospace structures. In this paper, a series of such alloys has been produced using rapid solidification processing via melt spinning. The microstructures of the alloys have been investigated in the as-melt-spun condition, after consolidation and heat treatment to peak hardness, and after tensile testing in the heat-treated condition. In particular, changes in the size and distribution of primary beryllium particles and Al₃Li precipitates are described after consolidation and processing. The mechanical properties of the alloys in the heat-treated condition are also presented.     

Structure and properties of rapidly solidified Al-Zr-Ti alloys

The Al-Zr-Ti system has recently been suggested as a candidate for Al-based materials capable of retaining a high strength during a long term exposure to high temperatures up to 700 K. The Al-1.25 at.% (Zr+Ti) alloys with a variable Zr : Ti ratio were rapidly solidified using the melt spinning method. The solidification structure was found inhomogeneous along the direction perpendicular to the ribbon plane and dependent on the Zr : Ti ratio. The microhardness values were correlated with the structure and chemical composition. The presence of second phase particles in the as melt-spun ribbons was proved by SAXS experiments. X-ray and electron diffraction experiments enabled to identify most of particles as the metastable Al₃(Zr_xTi_1–x) phase with the cubic L1₂ structure. Especially in the Zr-rich alloys, these particles precipitated preferentially in a fan-shaped morphology. The grains of the Ti-rich alloys were nearly free of these particles.     

Structure and properties of rapidly solidified Mg-Al alloys

Three binary Mg-Al alloys containing nominally 5, 15, and 30 at % Al were prepared in the ingot and rapidly solidified flake conditions using the twin roll technique. The microstructure, mechanical properties, and electrochemical behavior of the extruded alloys in both the conditions were investigated. The hardness, tensile strength, and corrosion resistance increased with increasing Al content. Further, the hardness, tensile strength, and corrosion resistance of the rapidly solidified alloys were superior to the ingot-metallurgy alloys and this is attributed to the microstructural refinement and increased homogeneity in the rapidly solidified alloys.     

High-temperature properties of rapidly solidified Al-Be alloys

Rapidly solidified Al-Be binary alloys (10%, 20%, and 40%, Be by weight) have been produced by melt-spinning techniques. The microstructures have been evaluated and the elevated temperature mechanical properties have been characterized over a range of strain rates. Despite the fact that the materials exhibited duplex microstructures resulting from high-temperature processing, they showed behaviour typical of dispersion strengthened alloys. The mechanical properties at elevated temperature can accurately b8 described by the equation exp (–120 kJ mol^–1/RT), where is the deformation rate, is the stress,E is the modulus,A is 8 material constant, andRT has its usual meaning. A direct comparison of the deformation properties was made between binary Al-Be composition and pure aluminium as baseline, as well as between Al-Be and some high temperature aluminium alloys. The Al-Be alloys do not exhibit good high-temperature strength when compared with other high-temperature aluminium alloys, e.g. Al-Fe-Co alloys. This is a result of particle coarsening and agglomeration during processing and testing.     

Structure and microhardness of rapidly solidified Al-Ni-Cr alloys

Al-Ni-Cr foils prepared by rapid quenching from the liquid state are studied. The surface of the foils is found to have a cellular morphology, with a microcrystalline, large-block structure and (111) texture. The effect of annealing on the microhardness of the foils is analyzed. The aging behavior of the microhardness is shown to depend on the Ni/Cr ratio.     

Zero and negative temperature coefficients of resistivity of rapidly solidified Bi–Sn alloys using melt-spinning technique

Pure Bi was rapidly solidified using melt-spinning technique and was alloyed with low concentrations of Sn (1, 2, 3, and 4 wt.%). X-ray diffraction analysis (XRDA), differential thermal analysis (DTA), and temperature dependence of resistivity (TDR) were performed. The resistivity was increased largely, also zero and negative temperature coefficients of resistivity (TCR) were obtained. An intermediate phase SnBi was formed which was not usually obtained under equilibrium conditions, or by rapid solidification using gun technique.     

Grain refinement in rapidly solidified W-Si alloys

Grain refinement in rapidly solidified W-Si alloys has been investigated with respect to silicon content and solidification rate. Solid-solution W-Si alloys with varying silicon content were prepared into small buttons by arc melting, from which rapidly quenched foils of various thickness were made by the hammer and anvil technique. The grain size of the foils was studied with respect to thickness and silicon content. The results show that the grain size is inversely proportional to the thickness of a foil and also is an exponential function of silicon content on an empirical basis. The combined effect of cooling rate and silicon content on the grain size can be expressed by an exponential function.     

Metastable microstructures in rapidly solidified zirconium alloys

Zirconium alloys exhibit a wide variety of phase transformations. The present review outlines some aspects of phase transformations, which are encountered in rapidly solidified zirconium alloys. The possibility of solidification of unalloyed zirconium directly into the low temperature phase is examined and the role that solidification microstructure plays in modifying the to martensitic transformation in rapidly solidified material is discussed. Zirconium alloys undergo two types of displacive transformations, namely, the martensitic transformation and the transformation. The influence of rapid solidification on the transition from the martensitic to the transformation is also discussed. Addition of transition metals are known to depress the melting point of zirconium alloys very drastically. As a consequence, glass forming abilities of a number of binary and ternary zirconium alloys are quite strong. A number of zirconium based metal-metal amorphous alloys have been synthesized using rapid solidification. In recent years, this work has been extended to bulk metallic glasses, which usually contain a larger number of alloying elements. Crystallization of these glasses and quasi-crystalline phase formation in these systems is also discussed.     

On precipitation in rapidly solidified aluminium-silicon alloys

The precipitation of silicon in rapidly solidified AlSi alloys was studied. For alloys with 2.4 and 11.0 wt % Si (2.3 and 10.3 at % Si, respectively) the lattice parameters of the Alrich and of the Si-rich phases were measured after ageing at 397,425 and 448 K. For alloys with 2.6 and 13.0 wt % Si crystallite sizes and lattice strains were determined by analysis of the X-ray diffraction line broadening. After ageing the lattice parameters of the Al-rich and the Si-rich phases were influenced by the difference in thermal expansion between both phases. After correction for this effect the amount of silicon dissolved in the Al-rich phase was estimated as a function of ageing time. Quenched-in (excess) vacancies influenced the precipitation kinetics. Activation energies for precipitation appeared to depend on the extent of transformation. Further, quenched-in vacancies caused anomalous maxima in the lattice parameter curves. The behaviour of the lattice microstrains on ageing was explained as a result of the disappearance of stresses due to quenching and the introduction and subsequent dissipation of stresses due to precipitation. After completed precipitation stresses due to the difference in thermal expansion between both phases still exist at room temperature.     

Phase selection in rapidly solidified niobium-silicon alloys

X-ray diffraction analysis of rapidly solidified Nb-10 at.% Si and Nb-15 at.% Si alloy ribbons produced by electron beam melting and splat quenching shows that the phases present are primarily Nb + Nb₃Si, rather than the stable Nb + Nb₅Si₃ structure. The level of Nb₅Si₃ phase present is a function of the cooling rate and degree of undercooling.