Structure, mechanical metallurgy and electrical transport properties of rapidly solidified Pb50Sn50-xBix alloys

Electrical transport properties, structure and mechanical properties of Pb₅₀Sn_50-xBi_x(0≤x≤50) alloys have been studied and analyzed. The addition of bismuth in the amounts of 30 wt % and 50 wt % results in the appearance of the crystalline metastable χ(Pb-Bi) phase. Y phase is also identified and it is found at 50 wt % bismuth. Electrical transport is sensitive to the alloys composition, decreasing as the bismuth content increases. The Vickers hardness number is sensitive to the structure of the quenched ribbons. The lowest value of H_v is 55 MPa for the Pb₅₀Sn₂₀Bi₃₀ alloy, which is attributed to the formation of the metastable χ(Pb-Bi) after a rapid quench from the melt. Values of the equivalent Fermi temperature, T_F Fermi velocity, V_F and the Fermi wave vector, K_F , are also computed. © 2000 Kluwer Academic Publishers     

Microstructure formation and electrical resistivity behavior of rapidly solidified Cu-Fe-Zr immiscible alloys

The immiscible Cu-Fe alloy was characterized by a metastable miscibility gap. With the addition element Zr, the miscibility gap can be extended into the Cu-Fe-Zr ternary system. The effect of the atomic ratio of Cu to Fe and Zr content on the behavior of liquid-liquid phase separation was studied. The results show that liquid-liquid phase separation into Cu-rich and Fe-rich liquids took place in the as-quenched Cu-Fe-Zr alloy. A glassy structure with nanoscale phase separation was obtained in the as-quenched(Cu_(0.5) Fe_(0.5))40Zr_(60) alloy sample, exhibiting a homogeneous distribution of glassy Cu-rich nanoparticles in glassy Fe-rich matrix. The microstructural evolution and the competitive mechanism of phase formation in the rapidly solidified Cu-Fe-Zr system were discussed in detail. Moreover, the electrical property of the as-quenched Cu-Fe-Zr alloy samples was examined. It displays an abnormal change of electrical resistivity upon temperature in the nanoscale-phase-separation metallic glass. The crystallization behavior of such metallic glass has been discussed.     

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.     

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 and mechanical properties of rapidly solidified magnesium based Mg-Al-Zn-RE alloys consolidated by extrusion

Magnesium based Mg-9Al-lZn-5RE (RE = La or Nd) alloys were rapidly solidified by chill block melt spinning. The resulting ribbons were cold packed into an aluminium alloy can and extruded at temperatures of 230 and 340°C and ratios of 20:1 or 25:1. Tensile and hardness tests of the extruded and heat treated materials were carried out. The tensile strength and elongation to fracture of the as extruded material were 478 MN m^?2 and 6·5% respectively and those of the material heat treated for 2 h at 350° C were 420 MN m^?2 and 20% respectively. The microstructure of these specimens was studied by X-ray diffraction and transmission electron microscopy. Intermetallics of Al₁₁ La₃ or Al₂Nd were found at grain boundaries and in the matrix which had a grain size of between 0–26 and 0–8 μm, while Mg₁₇Al₁₂ precipitates were present in the specimens extruded at a lower temperature (230° C). Yield strengths were consistent with the Hall-Petch relationship with grain size established earlier for this class of material.

MST/3495     

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.     

Structural investigations of mechanical properties of Al based rapidly solidified alloys

In this study, Al based Al–3 wt.%Fe, Al–3 wt.%Cu and Al–3 wt.%Ni alloys were prepared by conventional casting. They were further processed using the melt-spinning technique and characterized by the X-ray diffraction (XRD), scanning electron microscopy (SEM) together with energy dispersive spectroscopy (EDS), transmission electron microscope (TEM), differential scanning calorimetry (DSC) and the Vickers microhardness tester. The rapidly solidified (RS) binary alloys were composed of supersaturated α–Al solid solution and finely dispersed intermetallic phases. Experimental results showed that the mechanical properties of RS alloys were enhanced, which can be attributed to significant changes in the microstructure. RS samples were measured using a microhardness test device. The dependence of microhardness H_V on the solidification rate (V) was analysed. These results showed that with the increasing values of V, the values of H_V increased. The enthalpies of fusion for the same alloys were determined by DSC.     

Structure and mechanical properties of age-hardened directionally solidified AlSiCu alloys

The structure of directionally solidified Al-Si hypoeutectic alloys are generally composed of Al-matrix and Si-reinforcing phase. The growth direction of the both phases was near 200. The strength properties of an Al-Si alloy with additions of 2 wt.% and 4 wt.% copper have been investigated. These alloys were solution treated, quenched in water and aged at 200°C. Large Al₂Cu precipitates present in D.S. samples dissolved partly, and after ageing, they precipitated as the Θ′ platelets, significantly increasing the mechanical properties of the alloys. Hardness, strength and elongation were measured in the course of ageing. The structure was investigated by means of: XSAS, X-ray phase analysis, lattice parameter measurements and scanning microscopy.     

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.     

Structure and mechanical properties of unidirectionally solidified Zn-Ge eutectic alloys

The Al-Si eutectic alloys are known to undergo various structural transitions when unidirectionally solidified. This paper describes another metal/non-metal combination, Zn-Ge, which undergoes closely similar morphological changes. The tensile and compressive properties of the unidirectionally solidifed Zn-Ge eutectic have been examined and compared with those of the Al-Si eutectic. It is shown that the marked compressional stiffness of Al-Si alloys containing 〈100〉 type branched silicon dendrites only arises because of the lateral constraints of the aluminium matrix and does not occur in the Zn-Ge system.     

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 mechanical properties of rapidly solidified Al-(Fe,Cr) and Al-Mg-(Fe,Cr) alloys

For Al-(Fe,Cr) and Al-Mg-(Fe,Cr), by employing a combination of X-ray diffraction, metallography and transmission electron microscopy, detailed understanding of microstructural transformations that occur during rapid solidification and consolidation has been achieved. A major decrease in the solid solubility extension of Fe in an Al-Mg system with an increase of Mg concentration has been found. The decrease in solubility of Fe results in the reduction of strength and hardness of the Al-Mg-Fe alloys in comparison with Al-Mg-Cr alloys.     

Structure and decomposition behaviour of rapidly solidified Al-Fe alloys

The structure and decomposition behaviour of rapidly solidified Al-5, 10 and 15 at% Fe alloys have been investigated by detailed transmission electron microscopy and differential scanning calorimetry. Rapid solidification produces a variety of metastable phases: microquasicrystalline, decagonal, Al _m Fe, Al₆Fe and Al₁₃Fe₄, in order of increasing thermodynamic stability. The rapidly solidified microstructure depends upon the alloy composition and cooling rate. Primary and cellular particles of the microquasicrystalline phase are preferred at higher cooling rates, and primary or eutectic particles of the Al _m Fe phase are preferred at lower cooling rates. With increasing iron content, the microquasicrystalline phase is replaced with primary particles of the decagonal phase. After annealing at moderate temperatures, the microquasicrystalline phase in Al-5 and 10 at% Fe decomposes into Al _m Fe and Al₆Fe, and the microquasicrystalline phase in Al-15 at% Fe decomposes into Al _m Fe. After annealing at higher temperatures, the Al _m Fe, Al₆Fe and decagonal phases then decompose into stable Al₁₃Fe₄.     

Structure and decomposition behaviour of rapidly solidified AI-Cu-Li-Mg-Zr alloys

The microstructural characteristics of AI-Cu-Li-Mg-Zr alloys have been studied after rapid solidification by melt spinning and after subsequent annealing at temperatures in the range 160 to 500°C, by using a combination of optical microscopy, scanning and transmission electron microscopy, X-ray diffraction, differential scanning calorimetry and microhardness measurements. The as-melt-spun alloys consist of a cellular microstructure with fine scale precipitates and icosahedral particles distributed within the cells and at cell boundaries. The icosahedral structure is equivalent to the T₂ phase reported by Hardy and Silcock. Annealing the melt-spun alloys leads to a complex precipitation sequence: + I + + I + S + + I + + T₁ + T₂ (bcc) + two other phases. The icosahedral particles coarsen progressively during annealing, especially at higher annealing temperatures. Fine-scale precipitates grow during annealing at low temperature, dissolve at higher annealing temperatures below 500°C, and then reprecipitate during cooling after annealing at 500°C. During annealing at low temperature, plates of and S precipitate and then dissolve, providing solute atoms for icosahedral particle growth. Stable T₁, T₂ (bcc) and two other phases precipitate after decomposition of the icosahedral particles during annealing at 500°C.     

Structure and properties of rapidly solidified Sn-Zn foils

We have studied the phase composition, chemical homogeneity, surface morphology, aging behavior, thermal stability, and grain structure of rapidly solidified Sn-Zn foils. The surface of the foils is found to have a cellular structure. The effect of solidification rate on the properties of the foils is examined. Data are presented on the microhardness of the foils as a function of zinc content. The microhardness data are interpreted in relation to the microstructure of the foils.     

Structure and properties of rapidly solidified Al rich Al-Mn-Si alloys Part I Melt spun ribbons

The evolution of microstructure as-spun and during subsequent heat treatment at 200 to 500°C for up to 1000 h has been studied for Al-6.3 Mn-3.3 Si, Al-8.3 Mn-3.7 Si and Al-14.5 Mn-5.8 Si (wt %) alloys, containing 17, 26 and 48 vol % AlMnSi at equilibrium respectively. Microstructure as-spun ranged from primary icosahedral phase nucleating radial cellular Al arrays to less regular duplex arrays of Al and AlMnSi with decreasing alloy content and decreased section thickness or reduced distance from the chill surface. Heat treatment in the range 200 to 500°C transformed any icosahedral phase present to AlMnSi along with spheroidization and coarsening/coalescence of AlMnSi, to produce isolated spheroids when volume fraction f was lower and very stable interlinked chains at higher f. Measured coarsening rates of AlMnSi were a factor of 10 below predictions of LSW theory at lower f but were within a factor of 2 of prediction at highest f. Hardness was governed by a combination of Hall-Petch and matrix solid solution hardening as-spun supplanted by particle-radius dependent Orowan combined with matrix Hall-Petch hardening for the evolution of hardness during prior long term heat treatment at 425°C.