Influence of an axial uniform magnetic field on the solid/liquid interface curvature and macrosegregation in directionally solidified the Al–0.85 wt.% Cu alloy

Effect of a uniform magnetic field on the solid/liquid interface curvature and macrosegregation in directionally solidified the Al–0.85 wt.% Cu alloy has been investigated. Results show that the interface curvature and macrosegregation increase to a maximum when B is about 0.1 T; and then decreases as B still increases. This is good agreement with the computed velocities of the thermoelectric magnetic convection. Above results reveal that the uniform magnetic field induces the new convection and further modifies the interface curvature and macrosegregation.     

Anisotropy in wetting of oriented sapphire surfaces by liquid Al–Cu alloys

The coexistence of a liquid with a solid and a gas phase causes a contact angle at the triple line and results in a certain work of adhesion. These properties were studied for liquid Al, Cu, and their alloys on single-crystalline sapphire surfaces with C(0001)-, A(11-20)-, and R(1-102)- orientation. Measurements were performed at 1100 °C and under $3 \cdot 10^4\, \hbox{Pa}$ Ar atmosphere in a sessile drop apparatus. There, the sample was heated and melted separately from the substrate within a drop dispenser. Only after the desired measurement conditions were reached, the liquid metal was released. Depending on the alloy composition, the wetting angle approached a constant value within few minutes after the contact of droplet and substrate was established: For pure Cu the contact angle increased to an equilibrium value of 116° ± 5°, which is identical for all the studied sapphire surfaces. For pure Al an anisotropy of the contact angle with regard to these surfaces is found: time evolution of the Al contact angle is only observed for wetting of C-surfaces. Wetting of A- and R-surfaces shows no pronounced time dependence. In these cases, a smaller contact angle of about 90° is observed. Wetting of the different sapphire surfaces by Al–Cu alloys corresponds qualitatively to their wetting by pure Al: again, only for C-surfaces a time-dependent increase of the contact angle is observed. On A- and R-surfaces wetting is not time-dependent and the contact angle increases with Cu content of the alloy.     

Decomposition of supersaturated solid solutions in Al–Cu–Mg–Si alloys

The Al–Cu–Mg–Si alloying system is a base for a diverse group of commercial alloys which acquire their properties after quenching and aging. Therefore, the knowledge of the phase composition of hardening precipitates and the conditions under which they are formed is very important. ast reference data were analyzed along with experimental results and calculations of phase equilibria. Different alloys were compared based on the composition of the supersaturated solid solution. It is shown that the phase composition of aging products in alloys with Mg : Si > 1 agrees well with the equilibrium phase composition at a temperature of annealing. However, the sequence of precipitation in the alloys with Mg : Si < 1 is more complicated. The hardening in these alloys occurs with precipitation of the and phases and their precursors. The former phase may contain copper and later transforms either to and (Mg₂Si) or to Q phase depending on the amount of copper and annealing temperature.     

Modification of eutectic silicon in Al–Si alloys

The mechanical properties of Al–Si alloys are strongly related to the size, shape and distribution of eutectic silicon present in the microstructure In order to improve mechanical properties, these alloys are generally subjected to modification melt treatment, which transforms the acicular silicon morphology to fibrous one resulting in a noticeable improvement in elongation and strength. Improper melt treatment procedures, fading and poisoning of modifiers often result in the structure which is far from the desired one. Hence it is essential to assess the effectiveness of melt treatment before pouring. A much investigated reliable thermal analysis technique is generally used for this purpose. The deviation from the standard curve in thermal analysis helps in assessing the level of refinement of the Si structure. In the present review an attempt is made to discuss various aspects of modification, including mechanism, interaction of defects and non-destructive assessment by thermal analysis.     

Surface tension of liquid Al–Cu–Ag ternary alloys

Surface tension data of liquid Al–Cu–Ag ternary alloys have been measured contactlessly using the technique of electromagnetic levitation. A digital CMOS-camera (400 fps) recorded image sequences of the oscillating liquid sample and the surface tension was determined from an analysis of the frequency spectra. Data were obtained at temperatures above the melting point. Samples covered a broad range of compositions. In all cases, the surface tensions could be described as linear functions of temperature with a negative slope. The data were compared to thermodynamic model calculations using the ideal- and subregular solution approximation. It was found that, apart from samples where the composition is close to one of the binary margin phases, the surface tensions of the ternary alloys can be described by the ideal solution model.     

Effect of strontium and phosphorus on solid/liquid interface of Al–Si eutectic

Abstract

A high resolution quenched interface technique has been used to study the solid/liquid interface of the Al–Si eutectic solidified at extremely low growth rates. The interface morphology of the pure eutectic and also that of samples doped with Sr or P were studied. The observations were consistent with the twin plane re-entrant edge (TP RE) growth model for the pure eutectic and with a change to non-TPRE growth in the presence of Sr. On the other hand, P was found to have an effect on the relative tendencies towards faceting of the two phases.

MST/923     

Density and viscosity of ternary Al–Cu–Si liquid alloys

Densities and viscosities of ternary Al–Cu–Si liquid alloys have been investigated over a wide temperature and composition range. Density was measured using electromagnetic levitation as a container-less technique, while viscosity was measured by means of a high-temperature oscillating cup viscometer. In this ternary system, binary interaction parameters as well as a third (ternary) interaction parameter need to be taken into account for the excess volume to describe the liquid densities. The temperature dependences of the viscosities are well described by the Arrhenius law. A maximum of the activation energy of viscous flow is found in that compositional range in which intermetallic phases exist in the solid state.     

Corrosion resistance of directionally solidified Al–6Cu–1Si and Al–8Cu–3Si alloys castings

The aim of this article is to compare the electrochemical corrosion resistance of two as-cast Al–6 wt.% Cu–1 wt.% Si and Al–8 wt.% Cu–3 wt.% Si alloys considering both the solutes macrosegregation profiles and the scale of the microstructure dendritic arrays. A water-cooled unidirectional solidification system was used to obtain the as-cast samples. Electrochemical impedance spectroscopy (EIS) and potentiodynamic anodic polarization techniques were used to analyze the corrosion resistance in a 0.5 M NaCl solution at 25 °C. It was found that the Al–8Cu–3Si alloy has better electrochemical corrosion resistance than the Al–6Cu–1Si alloy for any position along the casting length. At the castings regions where the Cu inverse profile prevailed (up to about 10 mm from the castings surface) the corrosion current density decreased up to 2.5 times with the decrease in the secondary dendrite arm spacing.     

Viscosity of Al–Cu liquid alloys: measurement and thermodynamic description

In the present work a high temperature oscillating cup viscometer has been used to measure the viscosities of liquid binary Al–Cu alloys. The dependence of viscosity on temperature is well described by the Arrhenius law. For constant temperature, the viscosity as a function of copper concentration exhibits a maximum at a mole fraction x _Cu = 0.7. This might be due to a pronounced chemical short range order in the liquid phase at this composition. As the comparison of existing phenomenological models describing viscosity as a function of composition to the experimental data is unsatisfactory, a new model for the viscosity has been developed within this work based only on a few assumptions and using the enthalpy of mixing as input parameter which is easily accessible. The agreement between model calculation and experimental data is excellent.     

Modeling of the solid–liquid bubble interface in partial nucleate boiling

Several models of heat transfer in partial nucleate boiling are identified in order to determine the relationship between the dominant physical parameters. The correlations are different for different models, so the main goal of this analysis is to determine the validity of each model and to identify the most dominant physical phenomenon in the nucleate boiling heat transfer. This is done by comparing the results of different models with a vast range of reliable experimental data. The comparison shows that the Sakashita and Kumada model gives the best results in the nucleate boiling heat transfer. It is also shown that the most dominating phenomenon in isolated partial bubbles zones is the transient conduction taking place mainly under the bubbles. This is in contradiction with a majority of the models that consider convection as the most important mode in the nucleate boiling heat transfer. The selected model can also be extrapolated and used in the case of fully developed bubbles zones.     

Growth direction and Si alloying affecting directionally solidified structures of Al–Cu–Si alloys

The roles of growth direction and Si content on the columnar/equiaxed transition and on dendritic spacings of Al–Cu–Si alloys still remain as an open field to be studied. In the present investigation, Al–6 wt-%Cu–4 wt-%Si and Al–6 wt-%Cu alloys were directionally solidified upwards and horizontally under transient heat flow conditions. The experimental results include tip growth rate and cooling rates, optical microscopy, scanning electron microscopy energy dispersive spectrometry and dendrite arm spacings. It was found that silicon alloying contributes to significant refinement of primary/secondary dendritic spacings for the upward configuration as compared with corresponding results of the horizontal growth. Experimental growth laws are proposed, and the effects of the presence/absence of solutal convection in both growth directions are discussed.     

Theoretical study on the dislocation structure of parent–martensite interface in a magnetic shape memory alloy

Ferromagnetic shape memory alloys have received increasing interest and have great potential for actuator and sensor applications, the mobility of the parent–martensite interphase interface in such alloys is determined by its interfacial structure and the migration mechanism; therefore, a thorough understanding of its nature is essential. In the present paper, the parent–martensite interface in a Ni₂MnGa alloy is studied in the light of the topological model of martensite transformation crystallography, where the habit plane is envisaged comprising coherent terraces and steps. The coherency strains arising on the terrace plane are accommodated by a network of interfacial dislocations, e.g., twinning dislocations originating in the martensite phase, and disconnections. The topological parameters of these defects, i.e., the Burgers vectors, line directions, and dislocation spacings are quantified via rigorous crystallographic analysis and matrix algorithm based on the Frank-Bilby equation. Consequently, martensite transformation crystallographic features, e.g., the habit plane index and the orientation relationship, in the Ni₂MnGa alloy are determined and found to be in good agreement with the results predicted by the well-established phenomenological theory.     

Two novel calixarene functionalized iron oxide magnetite nanoparticles as a platform for magnetic separation in the liquid–liquid/solid–liquid extraction of oxyanions

This article focuses on the syntheses of 25,27-bis[3-(N-ethylsulfonic acid)aminopropxy]-26,28-dihydroxy-5,11,17,23-tetra-tert-butyl-calix[4]arene (3) and 25,27-bis[3-(N-ethyl-dihydrogen phosphate)aminopropxy]-26,28-dihydroxy-5,11,17,23-tetra-tert-butyl-calix[4]arene (4) as well as their immobilization onto [3-(2,3-epoxypropoxy)-propyl]-trimethoxysilane-modified Fe₃O₄ magnetite nanoparticles, and the extraction abilities of four new extractants which were characterized by a combination of FTIR, ¹H NMR, elemental analyses, transmission electron microscopy (TEM) and thermogravimetric analyses (TGA) involving electrostatic and hydrogen bonding interactions between the calixarene and oxide anions such as arsenate and dichromate anions. The extraction results indicate that these new calixarene derivatives having high extraction capabilities would be used as effective extractants for the removal of the dichromate/arsenate ions from water.     

Influence of chemical composition on the damping characteristics of Cu–Al–Ni shape memory alloys

Cu–XAl–4Ni shape memory alloys (SMAs) are capable of martensitic transformation across a wide temperature range through the precise adjustment of their chemical composition from X = 13.0 to 14.5. In addition, the variations in chemical composition significantly influence the internal friction characteristics of Cu–XAl–4Ni SMAs. Cu–XAl–4Ni SMAs with a higher content of Al exhibit lower internal friction peaks due to decreases in the amount of transformed martensite and the formation of γ₂ phase precipitates. The damping capacity of the inherent and intrinsic internal friction for Cu–13.5Al–4Ni SMA is extremely low due to the fact that the transformed β^′₁(18R)${{\beta }^{\prime }}_1(18\text{R})$ martensite has only an ordered 9R structure with stacking faults. The Cu–14.0Al–4Ni SMA exhibits a relative increase in the inherent and intrinsic damping capacity because the transformed γ^′₁(2H)${{\gamma }^{\prime }}_1(2\text{H})$ martensite exhibits twinning with abundant moveable twin boundaries.     

Phase transformation and fracture behavior of Cu/In/Cu joints formed by solid–liquid interdiffusion bonding

In this paper, microstructure evolution and phase transformation of Cu–In intermetallic compounds in Cu/In/Cu joints formed by solid–liquid interdiffusion bonding at 260 and 360 °C were investigated respectively. The shearing properties and fracture behaviors of the Cu/In/Cu joints formed under different bonding conditions were also studied. For Cu/In/Cu joints bonded at 260 °C, Cu₁₁In₉ phase firstly generated and then Cu₂In phase formed between Cu₁₁In₉ layer and Cu substrate. For Cu/In/Cu joints bonded at 360 °C, Cu₂In phase firstly formed and then parts of Cu₂In grains transformed to Cu₇In₃ phase, and this transition from incomplete to complete coverage of Cu₂In/Cu₂In grain boundaries by Cu₇In₃ phases was observed with the bonding time increasing. The shear test results show that Cu₂In was high-quality phase which could improve the mechanical properties of Cu/In/Cu joints. After shear test, the fractures in Cu/In/Cu joints bonded at 260 °C were found at Cu₁₁In₉ layers and the fracture mode was cleavage fracture. In the case of the joints bonded at 360 °C, the intergranular fractures were found at the interface between Cu₂In layer and Cu₇In₃ layer while the cleavage fractures were found at Cu₇In₃ layer.     

Correlation of microstructure and magnetic properties in Cu–Co–Ni alloys

The present study concerns correlation of microstructure and magnetic properties of nanocrystalline binary 50Cu–50Co and ternary 50Cu–25Co–25Ni (wt%) alloys prepared by ball milling and subsequent isothermal annealing of the ball milled alloys. High resolution transmission electron microscopic (HR-TEM) investigation has shown deformation-induced microstructural features. Field emission scanning electron microscopy (FE-SEM) has revealed a distinct change in morphology of as-milled CuCoNi alloys after annealing. Differential scanning calorimetric (DSC) and X-ray diffraction (XRD) analysis have revealed that annealing of the CuCoNi alloy above 350 °C results into precipitation of nanocrystalline Co (fcc) in the CuNi matrix by spinodal decomposition. It is also demonstrated that isothermal annealing of the ball milled alloys in the temperature range between 350 and 650 °C significantly influence the magnetic properties, e.g. coercivity (H_c), remanence (M_r) and magnetic saturation (M_s) due to annihilation of defects such as stacking and twin fault along with dissolution and/or precipitation of magnetic phases in the Cu-rich matrix.     

Study of a reaction at the solid Cu/α-SiC interface

A solid-state wetting technique has been used to investigate the interface between solid Cu and -SiC at high temperatures. An intermediate phase is found to form as an interfacial reaction product between Cu and SiC at high temperature, and to thicken upon further heating at 1123 K. The interfacial phase has an approximate composition of Cu–19 at%Si–5 at%C and displays an f.c.c. structure. Such a phase is not present in the published Cu–Si phase diagram, and forms under conditions which cannot be explained from that phase diagram. It is postulated that this phase represents a previously unreported silicide of Cu which may be stabilized by the presence of C in solution. © 1998 Chapman & Hall     

Microstructure,mechanical properties and shape memory effect of Cu–Hf–Al–Ni alloys

The influence of hafnium element’s incorporation on a Cu–xHf–13.0Al–4.0Ni (wt-%) (x?=?0.5, 1.0 and 2.0) high-temperature shape memory alloy was investigated systematically. The results show that the matrix of Cu–xHf–13.0Al–4.0Ni (x?=?0.5, 1.0 and 2.0) alloys is 18R martensite, and an orthorhombic-structured Cu₈Hf₃ phase is formed and distributed at the grain boundaries. The grain size is significantly reduced with increasing Hf content. The mechanical properties of Cu–xHf–13.0Al–4.0Ni (x?=?0.5, 1.0 and 2.0) alloys are improved by Hf doping due to the combination of refinement strengthening, solid solution strengthening and second phase strengthening. After heating under pre-strain of 10%, the shape memory effect of the Cu–1.0Hf–13.0Al–4.0Ni alloy reaches 5.6%, which is obviously higher than that of the Cu–13.0Al–4.0Ni alloy.     

Structure factors of modified liquid Al–Si alloys

The structure factor and the coordination numbers of liquid Al–Si alloys with different Si content have been measured by a high temperature X-ray diffractometer. Radial distribution functions (RDFs), the nearest atomic distance and the coordination numbers of eutectic Al–Si alloys before and after being modified with Sr and Sb were studied. The RDFs of the liquid alloy were decomposed by five Gaussian peaks. The results show that a Si–Si covalent bond exists in the liquid of eutectic and hyper-eutectic alloys. Sr in the liquid Al–Si has a capability to weaken the covalent bonds of Si–Si, suppressing the nucleation of the eutectic silicon phase. On the other hand, Sb in the liquid Al–Si increases the order degree of Si atoms, decreasing the supercooling degree of the nucleation and promoting the nucleation of eutectic silicon.