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.     

Influence of the mechanism and parameters of hardening of modified novolac phenol-formaldehyde resins on the physicomechanical properties of the composite

We study the influence of concentrations of the components of reactive compositions and the conditions of production and hardening of phenol-formaldehyde resins with the help of epoxy resins in the presence of polyvinylpyrrolidone on the physicomechanical, thermal, adhesion, insulation, and anticorrosion properties of the composites. The positive effect of modifications with polyvinylpyrrolidone and epoxy resin manifests itself within the following ranges of concentrations: 0.5–1 wt.% of polyvinylpyrrolidone and 25–30 wt.% of ED-20 in the presence of 1 wt.% of N, N-dimethylaniline. Thus, the adhesion strength of a glue based on the developed composition becomes four times higher and constitutes 5–6 MPa; the impact strength, static strength in bending, surface hardness, and the specific bulk electric resistance of the specimens hardened at 150–160°C for 25–30 min become 1.5–2.5 times higher and are equal to 5–6J/m², 15–17 MPa, 350–420 MPa, and (5.5–6.5)⋅10¹⁰ Ω⋅m, respectively. The behavior of these characteristics strongly depends on the conditions of hardening. We optimized the composition of modified phenol-formaldehyde resins, which made it possible to produce materials with predicted properties.     

Effect of polymers on the nanostructure and on the carbonation of calcium silicate hydrates: a scanning transmission X-ray microscopy study

This study investigated the effects of organic polymers (polyethylene glycol and hexadecyltrimethylammonium) on structures of calcium silicate hydrates (C–S–H) which is the major product of Portland cement hydration. Increased surface areas and expansion of layers were observed for all organic polymer modified C–S–H. The results from attenuated total reflectance–Fourier transform infrared (ATR–FTIR) spectroscopic measurements also suggest lowered water contents in the layered structures for the C–S–H samples that are modified by organic polymers. Scanning transmission X-ray microscopy (STXM) results further supports this observation. We also observed difference in the extent of C–S–H carbonation due to the presence of organic polymers. No calcite formed in the presence of HDTMA whereas formation of calcite was observed with C–S–H sample modified with PEG. We suggest that the difference in the carbonation reaction is possibly due to the ease of penetration and diffusion of the CO₂. This observation suggests that CO₂ reaction strongly depends on the presence of organic polymers and the types of organic polymers incorporated within the C–S–H structure. This is the first comprehensive study using STXM to quantitatively characterize the level of heterogeneity in cementitious materials at high spatial and spectral resolutions. The results from BET, XRD, ATR–FTIR, and STXM measurements are consistent and suggest that C–S–H layer structures are significantly modified due to the presence of organic polymers, and that the chemical composition and structural differences among the organic polymers determine the extent of the changes in the C–S–H nanostructures as well as the extent of carbonation reaction.     

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.     

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.     

Effects of modification and heat-treatment on the abrasive wear behavior of hypereutectic Al–Si alloys

In the present study, Al–Si alloys with Si contents of 23, 26, 28 and 31 wt.%, respectively, were modified with a new modifying agent. The results show that the primary silicon size decreased about 8–10 times after modification. The wear rates of the modified and heat-treated Al–Si alloys are lower than those of the unmodified and non-heat-treated Al–Si alloys, respectively. The silicon content in the range of 23–31 wt.% has a significant effect on the wear rates of the same processed Al–Si alloys (modification and heat treatment). Under the same load, the wear rates of the same processed Al–Si alloys decreased with the increasing silicon content. The abrasion took place mainly by cutting and partly by ploughing actions for the non-heat-treated Al–Si alloys, or on the contrary, mainly by ploughing and partly by cutting actions for heat-treated Al–Si alloys.     

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.     

Materials behaviour and intermetallics characteristics in the reaction between SnAgCu and Sn–Pb solder alloys

The paper compares theoretical calculations with experimental data, to identify the metallurgical mechanisms with respect to the rework or repair that may be encountered in the transition period from Sn–Pb to Pb-free soldering. Thermodynamic calculations have been carried out to study material behaviour and possible formation of intermetallic precipitates during the reaction between Sn–Pb and Sn–Ag–Cu Pb-free alloys. Two Sn–Ag–Cu alloys that are relevant to current industrial interests, namely Sn–3.9Ag–0.6Cu* (known as ‘405 alloy’ in Europe and North America), and Sn–3.0Ag–0.5Cu (known as ‘305’ alloy in Asia), were reacted with different contamination levels of eutectic Sn–37Pb solder. The variables examined included those related to both the materials and processes, such as composition, temperature and cooling rate. Together these are the primary drivers with respect to the resultant solder microstructures, which were studied using scanning electron microscopy (SEM). Nanoindentation, which is suitable for the ultra-fine and complex microstructures, was also used to investigate the micromechanical properties, including hardness and elastic modulus, at both ambient and elevated temperatures. The results from this work provide guidance as to the consequence for microstructural evolution and hence mechanical integrity when small amounts of Pb exist in Pb-free alloys. The composition of alloys in this paper is in weight percentage (wt%)     

Antagonistic effect of superplasticizer and colloidal nano-silica in the hydration of Alite and Belite pastes

The dependence on the hydration rate for Alite and Belite clinker phases in the presence of a polycarboxylate superplasticizer PC SP upon addition of colloidal nano-silica CNS were monitored by means of Diffuse Reflectance Infrared spectroscopy DR-FTIR. Spectral signatures of clinker dissolution and product formation were acquired for both materials. The rates for the build-up of product vibrational band intensities were found to depend sensitively on addition of CNS. The hydration product was proposed to be calcium-silicate-hydrate C–S–H. Details in the spectral signatures were found to differ. Quantum chemical calculations were employed and found to be consistent with the interpretation that small clusters dominate the Alite C–S–H spectrum, whereas the Belite C–S–H spectrum results from extended polymers.     

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.     

Optimization of composition and heat treatment design of Mg–Sn–Zn alloys via the CALPHAD method

This work is focused on the application of the calculation of phase diagrams method for alloy and heat treatment design. We analyzed the influence of Zn content on the precipitation of Mg₂Sn in Mg–Sn–Zn alloys. A comparison with previous studies in the Mg–Sn–Zn system was made according to the published results and computational thermochemistry simulations. The phase evolution in the Mg–Sn–Zn system was evaluated for the different compositions, and the simulations were used for precise alloy and heat treatment design. The composition of the ternary alloy was set as Mg–8wt%Sn–1.25wt%Zn. The Sn and Zn content was designed and confirmed to be within the α-Mg solubility limit at the solution treatment temperature. The addition of Zn and the heat treatment applied resulted in the enhancement and refinement of the Mg₂Sn precipitation. Three Vickers micro-hardness maxima were detected: precipitation of metastable Mg–Zn phases, heterogeneous precipitation of Mg₂Sn on the Mg–Zn precipitates, and Mg₂Sn precipitation in the α-Mg matrix. The CT simulations were found to be a valuable alloy design tool.     

Low temperature fabrication of high strength porous calcium phosphate and the evaluation of the osteoconductivity

Porous NaO₂–MgO–CaO–P₂O₅ bioglass doped beta-tri-calcium phosphate (β-TCP) bioceramic possessing high mechanical properties and well pore structure with high porosity and high pore connectivity has been prepared through dipping method with the porous polyurethane as the pore forming template. The sintering mechanism and the mechanical properties of the bioglass doped β-TCP scaffold have been investigated by the X-ray diffraction (XRD) analysis, Scanning electron microscope (SEM) and thermal differential analysis (DTA). The scaffold’s in vivo osteoconductivity has been evaluated by implantation of scaffolds into the femurs of New Zealand rabbits. The results show that the porous structure can achieve the densification process at a low temperature about 950°C by a solid solution sintering mechanism and hence dense macropore scaffold with a compressive strength of 4.32 MPa when the porosity is 75% has been obtained. The in vivo test shows that the Na₂O–MgO–CaO–P₂O₅ bioglass doped porous β-TCP bioceramic has a relatively fast bone formation after implantation; after 1 month implantation new deposited bone tissue has been detected on the strut of the porous scaffold and degraded particles also has been found on the surface of the new formed bone. After 6 months implantation the porous scaffold has been thoroughly covered with new formed bone. Results show that the Na₂O–MgO–CaO–P₂O₅ bioglass doped porous β-TCP bioceramic is potential bone tissue engineering scaffold for orthopedic use.     

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.     

Determination of the weight and composition of the precipitates formed in the course of dissolution of irradiated WWER oxide fuel

The amount and composition of insoluble precipitates formed in the course of dissolution of spent fuel samples with the burn-up from 15 to 54 MW day (kg U)⁻¹ were examined. The weight of the insoluble precipitates was from 0.03 to 0.44% of the fuel weight. The major elements determining the composition of the precipitates were platinum group metals (Pd, Rh, Ru), Zr, and Mo. The specific β- and α-activity of the precipitates obtained was 30–840 and 0.01–8 Ci kg⁻¹, respectively. The major factor determining the concentration of α-emitting nuclides is the fuel burn-up. Depending on the dissolution conditions, the U content was 0.2–4, and the Pu content, 0.1–3%. The weight of secondary precipitates was from 0.005 to 0.3% of the irradiated fuel weight, or 11–50% of the total weight of the precipitates obtained in the experiments. The specific β-activity of the secondary precipitates obtained varies from 5 to ∼300 Ci kg⁻¹ and is determined by the same radionuclides as in the primary precipitates. The α-activity of the secondary precipitates increases with the burn-up and amounts to 0.1–30 Ci kg⁻¹. The values obtained vary only slightly depending on the dissolution conditions and on the time of solution keeping before control filtration.     

Effect of strain rate and environment on the mechanical properties of the Ni–19Si–3Nb–0.15B–0.1C intermetallic alloy at high temperatures

The effect of strain rate and environment on the mechanical behavior at different temperatures of the Ni–19Si–3Nb–0.15B–0.1C alloy is investigated by atmosphere-controlled tensile testing under various conditions at different strain rates and different temperatures). The results reveal that the Ni–19Si–3Nb–0.15B–0.1C alloy exhibits ductile mechanical behavior (UTS ∼ 1250 MPa, ε ~ 14%) at temperatures below 873 K under different atmosphere conditions. However, the alloy without boron and carbon addition shows ductile mechanical behavior only when the sample is tested in vacuum. This indicates that the microalloying of boron and carbon does overcome the environmental embrittlement from water vapor at test temperatures below 873 K for the Ni–19Si–3Nb base alloy. However, the boron and carbon doped alloy still suffers from embrittlement associated with oxygen at a medium high temperature (i.e. 973 K). In parallel, both of the ultimate tensile strength and elongation exhibit quite insensitive response with respect to the loading strain rate when tests are held at temperatures below 873 K. However, the ultimate tensile strength exhibits high dependence on the strain rate in air at temperatures above 873 K, decreasing the ultimate tensile strength with decreasing strain rate.     

Temperature dependences of the mechanical properties of austenitic and martensitic steels in hydrogen

The influence of gaseous and preliminarily dissolved hydrogen on the characteristics of short-term static strength, crack resistance, and low-cycle durability of martensitic and austenitic steels is studied within the temperatures range 293–1073°K, under pressures of hydrogen varying within the range 0–35 MPa, for the strain rates of 0.01–100 mm/min, and the strain amplitudes of 0.8–1.6%. We determine the loading rates and the conditions of action of hydrogen leading the maximum possible hydrogen degradation of each material. The influence of the chemical composition and structural state on the degree of embrittlement and fractographic features of the fracture of steels in the presence of hydrogen is analyzed. __________ Translated from Fizyko-Khimichna Mekhanika Materialiv, Vol. 43, No. 5, pp. 53–64, September–October, 2007.     

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.     

The effects of calcium and yttrium additions on the microstructure,mechanical properties and biocompatibility of biodegradable magnesium alloys

In this study, the effects of calcium (Ca) and yttrium (Y) on the microstructure, mechanical properties, corrosion behaviour and biocompatibility of magnesium (Mg) alloys, i.e. Mg–xCa (x = 0.5, 1.0, 2.0, 5.0, 10.0, 15.0 and 20.0%, wt%, hereafter) and Mg–1Ca–1Y, were investigated. Optical microscopy, X-ray diffractometry (XRD), compressive and Vickers hardness testing were used for the characterisation and evaluation of the microstructure and mechanical properties. The in vitro cytotoxicity of the alloys was assessed using osteoblast-like SaOS2 cells. The corrosion behaviour of these alloys was evaluated by soaking the alloys in simulated body fluid (SBF) and modified minimum essential medium (MMEM) at 37 °C in a humidified atmosphere with 5% CO₂. Results indicated that the increase of the Ca content enhances the compressive strength, elastic modulus and hardness of the Mg–Ca alloys, but deteriorates the ductility, corrosion resistance and biocompatibility of the Mg–Ca alloys. The Y addition leads to an increase in the ductility; but a decrease in the compressive strength, hardness, corrosion resistance and biocompatibility of the Mg–1Ca–1Y alloy when compared to the Mg–1Ca alloy. Solutions of SBF and MMEM with the immersion of Mg–xCa and Mg–1Ca–1Y alloys show strong alkalisation. Our research results indicate that Mg–xCa alloys with Ca additions less than 1.0 wt% exhibited good biocompatibility, low corrosion rate as well as appropriate elastic modulus and strength; whilst the Y is not a proper element for Mg alloys for biomedical application due to its negative effects to the corrosion resistance and biocompatibility.     

On the distribution of preliminary stresses and the optimal shape of an anchor joint for reinforced concrete

By the methods of mathematical simulation and optimization, we determine the optimal geometry of the anchor with regard for its action upon reinforced concrete. __________ Translated from Problemy Prochnosti, No. 1, pp. 144–149, January–February, 2007. Report on International Conference “Dynamics, Strength, and Life of Machines and Structures” (1–4 November 2005, Kiev, Ukraine).     

Strain–life curves of steels and methods for determining the curve parameters. Part 2. Methods based on the use of artificial neural networks

The authors look into the possibility of using artificial neural networks for predicting the deformation characteristics of steels (the parameters of the Basquin–Manson–Coffin strain–life curve equation) based on static strength and plasticity characteristics, by constructing four independent neural networks with different configurations of input and output data. The prediction of parameters of the Basquin–Manson–Coffin equation and the fatigue life calculations by means of artificial neural networks are demonstrated to provide a better accuracy in comparison to the available conventional methods.