Mechanical properties of rapidly solidified ribbons of some AI–Si based alloys

Continuous uniform ribbons of Al–16 Si, Al–12.5 Si–1 Ni and Al–12.5 Si–1 Mg were prepared by melt spinning. Microhardness was measured. The as-melt spun values were 1280, 1370 and 1500 MN m-2 which relax on thermal ageing to 700, 700 and 800 MN m-2 for Al–16 Si, Al–Si–Ni and Al–Si–Mg, respectively. The hardness values of the melt spun ribbons are higher than the as-cast rods from which the ribbons were produced by a factor ranging from 1.8–2.2 times. Tensile testing at room temperature shows that the load–elongation curves are linear with a change of slope occurring in some of the specimens. These curves also show serrations in the case of as-melt spun and the intermediately annealed Al–Si specimens, while no serration was observed in the fully annealed samples. No serration was observed in the Al–Si–Ni and Al–Si–Mg alloys. UTS values were 420, 270 and 100 MN m-2 for Al–16 Si, Al–Si–Ni and Al–Si–Mg, respectively. These values show that the rapid solidification process improved the tensile properties significantly in Al–16 Si and Al–Si–Ni alloys while no significant improvement can be detected for Al–Si–Mg alloy. A discussion is given on hardness relaxation and tensile testing results in terms of silicon precipitation. This revised version was published online in November 2006 with corrections to the Cover Date.     

Properties of SnAgCu/SnAgCuCe soldered joints for electronic packaging

For quad flat packages (QFP256), lead-free soldered joints reliability in service is a critical issue. In this paper, soldering experiments of quad flat package (QFP256) devices were carried out by means of infrared reflow soldering system with Sn–3.8Ag–0.7Cu and Sn–3.8Ag–0.7Cu–0.03Ce lead-free solders, respectively, and the mechanical properties of micro-joints of the QFP devices were tested and studied by STR micro-joints tester. The results indicate that the tensile strength of Sn–Ag–Cu–Ce soldered joints is better than that of Sn–Ag–Cu soldered joints. In particular, the addition of trace Ce to the Sn–Ag–Cu solder can refine the microstructures and decrease the thickness of the intermetallic compound layer of Sn–Ag–Cu solder alloys. In addition, the stress–strain response of Sn–Ag–Cu/Sn–Ag–Cu–Ce soldered joints in quad flat packaging was investigated using finite element method based on Garofalo–Arrhenius model. The simulated results indicate creep distribution of soldered joints is not uniform, the heel and toe of soldered joints, the area between soldered joints and leads are the creep concentrated sites. The creep strain of Sn–Ag–Cu–Ce soldered joints is lower than that of Sn–Ag–Cu soldered joints.     

Subcritical crack growth and power law exponent of Y–Si–Al–O(–N) glasses in aqueous environment

The subcritical crack growth resistance in water of a Y–Si–Al–O and Y–Si–Al–O–N glasses has been investigated with three point bending experiments. It has been shown that the SCG behaviour of the Y–Si–Al–O–N glass is superior to that of the Y–Si–Al–O glass. This is reflected by the power law exponent n which is 21 for the Y–Si–Al–O glass and 63 for the Y–Si–Al–O–N glass. Mechanistic implications of these observations are discussed.     

Correlation between interfacial microstructure and shear behavior of Sn–Ag–Cu solder ball joined with Sn–Zn–Bi paste

Sn–8Zn–3Bi solder paste was applied as a medium to joint Sn–3.2Ag–0.5Cu solder balls and Cu/Ni/Au metallized ball grid array substrates at 210 °C. Sn–Ag–Cu joints without Sn–Zn–Bi addition were also conducted for comparison. The shear behavior of the specimens was investigated after multiple reflow and thermal aging. For each strength test, more than 40 solder balls were sheared. The shear strength of Sn–Ag–Cu specimens kept constant ranging from 15.5 ± 1.3 N (single reflow) to 16.2 ± 1.0 N (ten reflows) and the fractures occurred in the solder. Shear strength of Sn–Ag–Cu/Sn–Zn–Bi specimens fell from 15.9 ± 1.7 N (single reflow) to 13.4 ± 1.6 N (ten reflows). After single reflow, Sn–Ag–Cu/Sn–Zn–Bi specimens fractured in the solder along Ag–Au–Cu–Zn intermetallic compounds and at Ni metallization. After ten reflows, fractures occurred in the solder and at solder/Ni–Sn–Cu–Zn intermetallic compound interface. The shear strengths of the Sn–Ag–Cu and Sn–Ag–Cu/Sn–Zn–Bi packages changed little after aging at 150 °C. Sn–Ag–Cu/Sn–Zn–Bi joints kept higher strength than Sn–Ag–Cu joints. Sn–Ag–Cu joints fractured in the solder after aging. But the fractures of Sn–Ag–Cu/Sn–Zn–Bi specimens shifted to the solder with aging time.     

Influence of arsenic, antimony and phosphorous on the microstructure and corrosion behavior of brasses

The effect of minor additions of As, Sb and P on phase distribution and corrosion behavior has been studied in brasses. The alloys investigated were 60Cu–39Zn–1Pb, 48.95Cu–45Zn–5Pb–1Sn–0.05As, 48.90Cu–45Zn–5Pb–1Sn–0.05As–0.05Sb and 48.85Cu–45Zn–5Pb–1Sn–0.05As–0.05Sb–0.05P. Immersion tests in 1% CuCl₂ solution indicated that the addition of As improved corrosion resistance while the combined addition of As + Sb and As + Sb + P was not beneficial. The hardness increased significantly with the addition of As, Sb and P. Microstructural observations indicated an increase in β phase fraction in the As, Sb and P containing alloys. X-ray diffraction studies confirmed the formation of intermetallic compounds in As, Sb and P containing alloys. Based on the microstructural observations, the intermetallic compounds appear to be primarily precipitated in the β phase with As + Sb and As + Sb + P additions. The lower corrosion resistance of the alloys 48.90Cu–45Zn–5Pb–1Sn–0.05As–0.05Sb and 48.85Cu–45Zn–5Pb–1Sn–0.05As–0.05Sb–0.05P has been related to increase in β phase volume fraction and precipitation of intermetallic compounds in the β phase.     

Suppressing the growth of interfacial Cu–Sn intermetallic compounds in the Sn–3.0Ag–0.5Cu–0.1Ni/Cu–15Zn solder joint during thermal aging

Evolution of interfacial phase formation in Sn–3.0Ag–0.5Cu/Cu (wt%), Sn–3.0Ag–0.5Cu–0.1Ni/Cu, Sn–3.0Ag–0.5Cu/Cu–15Zn, and Sn–3.0Ag–0.5Cu–0.1Ni/Cu–15Zn solder joints are investigated. Doping Ni in the solder joint can suppress the growth of Cu₃Sn and alter the morphology of the interfacial intermetallic compounds (IMCs), however it shows rapid growth of (Cu,Ni)₆Sn₅ at the Sn–3.0Ag–0.5Cu–0.1Ni/Cu interface. In comparison with the Cu substrates, the Cu–Zn substrates effectively suppress the formation of Cu–Sn IMCs. Among these four solder joints, the Sn–3.0Ag–0.5Cu–0.1Ni/Cu–15Zn solder joint exhibits the thinnest IMC, and only (Cu,Ni)₆(Sn,Zn)₅ formed at the interface after aging. It is revealed that the presence of Ni acts to enhance the effect of Zn on the suppression of Cu–Sn IMCs in the SAC305–0.1Ni/Cu–15Zn solder joint. The limited formation of IMCs is related to the elemental redistribution at the joint interfaces during aging. The Sn–3.0Ag–0.5Cu–0.1Ni/Cu–15Zn joint can act as a stabilized interconnection due to the effective suppression of interfacial reaction.     

Wear characteristics of a new type austenitic stainless steel

In order to solve the problem of the poor wear resistance in conventional austenitic stainless steels, a new type austenitic stainless steel was designed based on Fe–Mn–Si–Cr–Ni shape memory alloys in this article. Studies on its wear resistance and wear mechanism have been carried out by comparison with that of AISI 321 stainless steel using friction wear tests, X-ray diffraction, scanning electron microscope. Results showed that the wear resistance of Fe–14Mn–5.5Si–12Cr–5Ni–0.10C alloy was better than that of AISI 321 stainless steel both in dry and oily friction conditions owing to the occurrence of the stress-induced γ → ε martensitic phase transformation during friction process. This article also compared the corrosion performance of the two stainless steels by testing the corrosion rate. Results showed that the corrosion rate of Fe–14Mn–5.5Si–12Cr–5Ni–0.10C alloy was notably lower in NaOH solution and higher in NaCl solution than that of AISI 321 stainless steel.     

Wettability of NiAl by a liquid Ni–Si–B alloy

An investigation of the wettability of the intermetallic compound NiAl by a liquid Ni–4.5 wt% Si–3.2 wt% B filler metal is presented in this paper. Dynamic observations of spreading of Ni–Si–B droplets, conducted using hot-stage light microscopy, are correlated with post-cooling microscopy and analysis. The paper examines the influence of the oxide layer on the NiAl substrates, on the progression of spreading of the Ni–Si–B liquid. Termination of spreading of the Ni–Si–B droplets by the onset of isothermal solidification at the spreading front is considered. Spreading of the Ni–Si–B droplets was found to be rapid until the onset of isothermal solidification at the spreading front. However, once isothermal solidification commenced, negligible further spreading was observed. The Ni–Si–B filler metal was observed to spread by undermining of the substrate oxide. However, a marked reaction occurred between the substrate oxide and the Ni–Si–B filler metal. This reaction served to remove the substrate oxide layer. The paper contrasts the mechanisms of substrate oxide undermining and isothermal solidification of liquid Ni–Si–B droplets on NiAl with those occurring during the spreading of the same liquid on pure nickel and Ni–Cr alloys. This revised version was published online in November 2006 with corrections to the Cover Date.     

Creep and fatigue behaviors of the lead-free Sn–Ag–Cu–Bi and Sn60Pb40 solder interconnections at elevated temperatures

Creep and fatigue behaviors of the interconnections soldered by the lead-free Sn–Ag–Cu–Bi solder were investigated at different elevated temperatures (with the homologue temperature in the range of 0.71– 0.82), with a comparison to that of a traditional Sn60Pb40 solder. The results show that the lead-free Sn–Ag–Cu–Bi solder shows a superior anti-creep performance over the Sn60Pb40 solder, in terms of a much lower creep strain rate and a vastly elongated creep fracture lifetime; in the secondary creep regime, the calculated creep-activation energy for two solders is reasonably close to other published data. In addition, it has also been shown that the joints soldered by the lead-free Sn–Ag–Cu–Bi solder exhibits a superb fatigue property.     

TLP bonding of SiCp/2618Al composites using mixed Al–Ag–Cu system powders as interlayers

Mixed Al–Ag–Cu and Al–Ag–Cu–Ti powders were used as interlayers for transient liquid phase diffusion bonding (TLP bonding) of SiC particulate reinforced 2618 aluminum alloy matrix composite (SiCp/2618Al MMC). The results show that by using mixed Al–Ag–Cu powder with the eutectic composition as an interlayer, SiCp/2618Al MMC can be TLP bonded at 540 °C, however, the joining layer is porous. Adding a certain amount of titanium into the Al–Ag–Cu interlayer, the TLP bonding quality can be improved. The titanium added into the Al–Ag–Cu interlayer has an effect of shortening the solidification time of the joining layer, thus decreasing SiC particles from the parent materials entering into the joining layer. The joints bonded using Al–Ag–Cu–Ti interlayers have a maximum shear strength of 101 MPa when 2.1% titanium is added.     

Corrosion behaviour of aluminium alloys in ethanol fuels

In this study, the corrosion behaviour of several aluminium alloys in ethanol fuels was investigated by immersion and polarization tests. The corrosion properties of cast aluminium alloys (Al–17wt%Si–4wt%Cu–Mg, Al–8wt%Si–3wt%Cu, Al–7wt%Si–Mg and Al–17wt%Si–4wt%Cu–Mg with a chemically deposited nickel layer) in ethanol blended gasoline fuels were examined at various ethanol and water contents and various temperatures. Electrochemical and gravimetric measurements revealed a pronounced acceleration of the corrosion process above the boiling point. Additions of water restrain the corrosion. Increasing the ethanol content and the temperature leads to a higher corrosion sensitivity of the aluminium alloys. Furthermore, the nickel layer is very protective in all tested fuels. For aluminium alloys, a theory of the corrosion process in ethanol blended gasoline fuels is proposed.     

Mechanical properties of calcium silicate hydrates

The dynamic mechanical properties of compacted samples of synthetic calcium silicate hydrate (C–S–H) were determined at variable stoichiometries (C/S ratio). The stiffness and damping properties of the C–S–H systems were monitored at various increments of mass loss from 11%RH following the removal of the adsorbed and interlayer water. The changes in the storage modulus (E′) and internal friction (tan δ) were discussed in terms of the state of water present in the nanostructure of C–S–H, the evolution of the silicate structure and the interaction of calcium ions in the interlayer region. Results were compared to those for the hydrated Portland cement paste and porous glass. It was shown that the C–S–H in the hydrated Portland cement has a complex yet analogous dynamic mechanical behavior to that of the synthetic C–S–H. The response of these systems upon the removal of water was explained by a layered model for the C–S–H. A mechanistic model was proposed to describe the changes occurring at various stages in the dynamic mechanical response of C–S–H.     

Microstructure and corrosion properties of as sub-rapid solidification Mg–Zn–Y–Nd alloy in dynamic simulated body fluid for vascular stent application

Magnesium alloy stent has been employed in animal and clinical experiment in recent years. It has been verified to be biocompatible and degradable due to corrosion after being implanted into blood vessel. Mg–Y–Gd–Nd alloy is usually used to construct an absorbable magnesium alloy stent. However, the corrosion resistant of as cast Mg–Y–Gd–Nd alloy is poor relatively and the control of corrosion rate is difficult. Aiming at the requirement of endovascular stent in clinic, a new biomedical Mg–Zn–Y–Nd alloy with low Zn and Y content (Zn/Y atom ratio 6) was designed, which exists quasicrystals to improve its corrosion resistance. Additionally, sub-rapid solidification processing was applied for preparation of corrosion-resisting Mg–Zn–Y–Nd and Mg–Y–Gd–Nd alloys. Compared with the as cast sample, the corrosion behavior of alloys in dynamic simulated body fluid (SBF) (the speed of body fluid: 16 ml/800 ml min⁻¹) was investigated. The results show that as sub-rapid solidification Mg–Zn–Y–Nd alloy has the better corrosion resistance in dynamic SBF due to grain refinement and fine dispersion distribution of the quasicrystals and intermetallic compounds in α-Mg matrix. In the as cast sample, both Mg–Zn–Y–Nd and Mg–Y–Gd–Nd alloys exhibit poor corrosion resistance. Mg–Zn–Y–Nd alloy by sub-rapid solidification processing provides excellent corrosion resistance in dynamic SBF, which open a new window for biomedical materials design, especially for vascular stent application.     

Phase Diagrams of Pb-Free Solders and their Related Materials Systems

Replacing Pb–Sn with Pb-free solders is one of the most important issues in the electronic industry. Melting, dissolution, solidification and interfacial reactions are encountered in the soldering processes. Phase diagrams contain equilibrium phase information and are important for the understanding and prediction of phase transformation and reactive phase formation at the solder joints. This study reviews the available phase diagrams of the promising Pb-free solders, and their related materials systems. The solders are Sn–Ag, Sn–Cu, Sn–Ag–Cu, Sn–Zn, Sn–Bi, Sn–In and Sn–Sb. The materials systems are the solders with the Ag, Au, Cu, Ni substrates, such as Sn–Ag–Au, Sn–Ag–Ni, Sn–Cu–Au, and Sn–Cu–Ni ternary systems. For the Pb-free solders and their related ternary and quaternary systems, preliminary phase equilibria information is available; however, complete and reliable phase diagrams over the entire compositional and temperature ranges of soldering interests are lacking.     

Formation of dendritic precipitates in the beta phase of Cu-based alloys

The isothermal treatment of the β phase in some Cu-based alloys produces its decomposition by an earlier precipitation of γ phase. During their growth, by means of a diffusion-controlled process, the precipitates show evidences of morphological changes. In the first stages and for a Cu–Zn–Al alloy, the morphology is spherical and cuboidal, but develops more complex shapes such as dendrites, owing to composition fields, interphase overlapping, crystallography characteristics, and relative orientation. In this work, a dendritic γ precipitate characterization is done and morphological theoretical predictions are applied, for Cu–Zn–Al and Cu–Al–Be alloys.     

Using direct hot-rolling approach to obtain dual-phase weathering steel Cu–P–Cr–Ni–Mo

A weathering steel Cu–P–Cr–Ni–Mo has been developed which exhibits special continuous cooling transformation characteristics which permit the desired dual-phase (DP) microstructure to be obtained by direct hot-rolling. Hot-rolling procedures to obtain DP microstructures have been designed based on the continuous cooling transformation diagram of weathering steel Cu–P–Cr–Ni–Mo. The results show that the microstructures of DP weathering steels Cu–P–Cr–Ni–Mo are characterized by an irregular distribution of island-shaped martensite–austenite in the matrix of polygonal ferrite grains. DP weathering steel Cu–P–Cr–Ni–Mo with favorable corrosion resistant property, weldability and mechanical properties, such as, high strain hardening exponent values, a lower ratio of yield to tensile strength, and higher strengths; and is obtained successfully by direct hot-rolling.     

Study of thermodynamic properties of liquid binary alloys by a pseudopotential method

On the basis of the Percus–Yevick hard-sphere model as a reference system and the Gibbs–Bogoliubov inequality, a thermodynamic perturbation method is applied with the use of the well-known model potential. By applying a variational method, the hard-core diameters are found which correspond to a minimum free energy. With this procedure, the thermodynamic properties such as the internal energy, entropy, Helmholtz free energy, entropy of mixing, and heat of mixing are computed for liquid NaK binary systems. The influence of the local-field correction functions of Hartree, Taylor, Ichimaru–Utsumi, Farid–Heine–Engel–Robertson, and Sarkar–Sen–Haldar–Roy is also investigated. The computed excess entropy is in agreement with available experimental data in the case of liquid alloys, whereas the agreement for the heat of mixing is poor. This may be due to the sensitivity of the latter to the potential parameters and dielectric function.     

The variation of beta phase morphology after creep and negative creep for duplex titanium alloys

The creep resistance of SP700 (Ti–4.5Al–3V–2Mo–2Fe) is superior to Ti–6–4 (Ti–6Al–4V) at 500 °C under a constant load corresponding to an initial stress of 100 MPa. The β phase grains in the SP700 alloy prefer to orient along the loading axis in contrast to the Ti–6–4 alloy. The grain growth occurs during the stress drop incubation period. The observation of different amounts of negative creep/anelasticity upon loading is closely associated with the difference in the amount of grain/subgrain coarsening.     

Melting Temperatures of Eutectic Fixed-Point Cells Usable for the Calibration of Contact Thermometers

The objective of the present investigation was the determination of the melting temperatures of the eutectic compounds Fe–C, Co–C, and Ni–C. Six eutectic fixed-point cells of the Physikalisch-Technische Bundesanstalt (PTB) (Fe–C1, Fe–C2, Co–C1, Co–C2, Ni–C1, and Ni–C2) and two cells of the Brazilian National Metrological Institute (Inmetro) (Fe–C1V and Ni–C1V), useable for the calibration of contact thermometers, were investigated. Their melting temperatures were calculated by extrapolation of the emf-temperature characteristics of four stable Pt/Pd thermocouples, which were calibrated at the eutectic fixed points and at conventional fixed points of the International Temperature Scale of 1990 (ITS-90). On the basis of the eight eutectic fixed-point cells and seven independent calibration runs, the melting temperatures of the Fe–C, Co–C, and Ni–C eutectics resulted in 1153.67 ± 0.15°C, 1323.81 ± 0.27°C, and 1328.48 ± 0.20°C, respectively, with expanded uncertainties corresponding to a coverage factor of k = 2.     

Influence of granulated blast furnace slag on the reaction,structure and properties of fly ash based geopolymer

Ground granulated blast furnace slag (GBFS) has been used to alter the geopolymerisation behaviour of fly ash. The influence of varying amount of GBFS (5–50%) on the reaction kinetics has been studied using isothermal conduction calorimetry. It was observed that the reaction at 27 °C is dominated by the GBFS activation, whereas the reaction at 60 °C is due to combined interaction of fly ash and GBFS. The reaction product of geopolymerisation has been characterised using X-ray diffraction and scanning electron microscopy–X-ray microanalysis. Alumino–silicate–hydrate (A–S–H) and calcium–silicate–hydrate (C–S–H) gels with varying Si/Al and Ca/Si ratio are found to be the main reaction products. Coexistence of A–S–H and C–S–H gel further indicates the interaction of fly ash and GBFS during geopolymerisation. Attempt has been made to relate the microstructure with the properties of the geopolymers.