Effects of electromigration on resistance changes in eutectic SnBi solder joints

The motivation of this study is tried to explore the relationship between resistance changes and microstructure evolution of eutectic SnBi solder joints under 10⁴ A/cm² of current density and 50 °C of ambient temperature. A novel type of one-dimensional solder joints was employed to achieve a true uniform distribution of current density, and a real-time data acquisition system was employed to investigate the voltage changes of the eutectic SnBi solder joints during electromigration process. This study suggested that the resistance remained initially due to the interaction between coarsened phase and Joule heating effect, and then increased due to the formation of continuous Bi-rich phase at anode interface, finally remained again due to the phase segregation of Bi- and Sn-rich phases.     

The effect of solutes on grain boundary mobility during recrystallization and grain growth in some single-phase aluminium alloys

The effect of solutes (Si, Mn, Mg) in quantities typical of commercial aluminium alloys, on grain boundary mobility in aluminium, has been investigated with in situ annealing and electron backscattered diffraction in the SEM, and grain growth experiments. The in situ experiments provided information on the migration of the high mobility tilt boundaries of misorientations close to 40°〈1 1 1〉. Grain growth experiments were used to investigate boundary migration in alloys of high solute content (1-5wt%Mg), and a comparison between the in situ and bulk experiments is made. The relationship between boundary velocity and driving pressure was found to be linear in all cases, and the activation energies for boundary migration were higher than those controlled by lattice diffusion of the solutes at higher solute concentrations.     

Metallurgical characterization of pulsed current gas tungsten arc,friction stir and laser beam welded AZ31B magnesium alloy joints

This paper reports the influences of welding processes such as friction stir welding (FSW), laser beam welding (LBW) and pulsed current gas tungsten arc welding (PCGTAW) on mechanical and metallurgical properties of AZ31B magnesium alloy. Optical microscopy, scanning electron microscopy, transmission electron microscopy and X-Ray diffraction technique were used to evaluate the metallurgical characteristics of welded joints. LBW joints exhibited superior tensile properties compared to FSW and PCGTAW joints due to the formation of finer grains in weld region, higher fusion zone hardness, the absence of heat affected zone, presence of uniformly distributed finer precipitates in weld region.     

Effect of small amount of rare earth addition on electromigration in eutectic SnBi solder reaction couple

Effect of small amount of rare earth (RE) addition on electromigration behavior of Cu/SnBi/Cu solder reaction couple (SRC) was investigated with current density of 5 × 10³ A/cm² at room temperature and 100 °C, respectively. Results indicate that tiny RE addition to eutectic SnBi solder alloy can make the energy of interfaces and grain boundaries decrease, restrain the movement of dislocations and grain boundary sliding. Therefore, phase segregation and IMC growth will be effectively suppressed which enhances the electromigration resistance.     

Pore evolution and microstructure with heating profile in BaTiO3-based Ni-MLCCs with Y5V specification

The effects of the heating profile in the burnout and sintering processes, especially the heating rate and holding time, on the pore evolution and microstructure in multilayer ceramic capacitors (MLCCs) showing Y5V characteristics, were investigated in order to optimize the fabrication process. The heating rate was controlled as 1, 3, and 5 °C/min in both burnout and sintering processes or the sintering process was carried out with and without the holding time of 3 h at the final sintering temperature of 1200 °C. The pore size distribution and cumulative pore surface area became broad and small, respectively, as the heating rate and sintering temperature were increased. The microstructure revealed that the MLCCs were effectively densified in the slow heating rate of 1 °C/min in both processes with the holding time of 3 h. The heating rate in the burnout process predominantly affected the pore evolution and microstructure more so than that in the sintering process, showing the effects of the holding time on removing the residual pores and on developing the final microstructure.     

Mechanical and microstructural characteristics of detonation gun sprayed NiCrAlY + 0.4 wt% CeO2 coatings on superalloys

The microstructure and mechanical properties of detonation gun sprayed NiCrAlY + CeO₂ alloy coatings deposited on superalloys were investigated. The morphologies of the coatings were characterized by using the techniques such as optical microscopy, X-ray diffraction and field emission scanning electron microscopy/energy-dispersive analysis. The coating depicts the formation of dendritic structure and the microstructural refinement in the coating was due to ceria. Average porosity on three substrates was less than 0.58% and surface roughness of the coatings was in the range of 6.17–6.94 μm. Average bond strength and microhardness of the coatings were found to be 58 MPa and 697–920 H_V, respectively.     

Effect of ageing on the mechanical properties of directly quenched copper bearing microalloyed steels

The present work aims to study the ageing behaviour of directly quenched Cu-added microalloyed steels. Temperatures related to precipitation of Cu and recovery of dislocations retained in the microstructure after quenching of the steels from finish rolling temperature are determined by differential scanning calorimetric method. Ageing of the directly quenched steels has resulted in the reduction in hardness and strength with concomitant improvement of ductility. 1.5 wt% Cu-added Ti–B microalloyed steel has yielded the most attractive combination of strength and ductility. Presence of Ni in the 1.5 wt% Cu-added Ti–B microalloyed steel indicates sluggish kinetics of Cu precipitation. Ageing has generally deteriorated the impact toughness except for Ni containing Cu-added microalloyed steel above −25 °C temperature. Formation of recovered dislocation cells and fine ?-Cu precipitates during ageing have contributed to the microstructural softening and hardening, respectively.     

Influence of microstructural inhomogeneity of individual sides of Fe81Si4B13C2 amorphous alloy ribbon on thermally induced structural transformations

As a result of the preparation process of Fe₈₁Si₄B₁₃C₂ amorphous alloy ribbon, a difference has been observed between the opposite sides of the ribbon in microstructure and surface morphology. Influence of these differences on thermally induced structural transformations was studied. Thermal treatment below 600 °C had a significant influence on the evolution of the microstructure, as well as phase composition of individual sides of the ribbon. Treatment at higher temperatures caused the microstructural differences between two sides to decrease significantly. Phase composition of the alloy samples showed the opposite trend: the differences observed were the greatest in the fully crystallized alloy, after treatment at 700 °C. These differences are the result of different numbers of nucleation sites for Fe₂B phase on respective sides of the ribbon, leading to 30% difference in its content on different sides in the fully crystallized alloy.     

Thermal and microstructural characterization and crystallization kinetic studies in the TeO2−B2O3 system

Thermal, phase and microstructural characterization of the (1−x)TeO₂−xB₂O₃ system, where 0.05 ≤ x ≤ 0.40 in molar ratio, was realized by applying differential thermal analysis, differential scanning calorimetry, X-ray diffraction and scanning electron microscopy/energy dispersive X-ray spectrometer techniques to investigate the glass forming region, phase equilibria, microstructural characterization of the TeO₂−B₂O₃ system and to study the crystallization kinetics of the boro-tellurite glasses. Samples were prepared using a conventional melt quenching technique at 750 °C. Glass forming range of the system was determined as 5–25 mol% B₂O₃ and thermal behavior of the glasses were examined by running thermal analysis. In order to obtain the thermal equilibrium, as-cast samples were heat-treated above all crystallization reaction temperatures at 520 °C and the phase equilibria investigations were realized with the heat-treated samples. Monotectic reaction of the binary system: liquid₁ → liquid₂ + TeO₂, was detected at 666 ± 2 °C. A stable phase separation region where the samples show two different phases, white colored opaque and light yellow transparent, was investigated in terms of the phase equilibria and the morphology. Non-isothermal investigation of crystallization kinetics of the boro-tellurite glasses were realized in terms of the crystallization mechanism and the activation energy by using the Ozawa and the modified Kissinger techniques, respectively. The activation energy of the crystallization reaction was calculated as around 300 kJ mol⁻¹.     

The characterization and formation mechanism of nanosized insoluble intermetallic phase in 2024Al alloy

The coarse insoluble intermetallic phase in 2024Al was refined to nanometer scale by an effective powder metallurgy approach, which involved atomization to form oversaturated solution powder, high energy ball milling to produce a high dislocation density and fine grains in the powder, and sintering to generate highly dispersed nanosized intermetallic particles. The structure of refined nanosized intermetallic particles have been determined to be an ordered body center cubic with a lattice parameter of a = 12.65 Å for the first time. The nanosized intermetallic particles play a positive role in enhancing dispersion-strengthening effect and thermal stability of 2024Al alloy. This refined approach can be applied to many commercial alloy systems that contain insoluble coarse intermetallic phases.     

TiC as heterogeneous nuclei of the (Fe, Mn)3C and austenite intergrowth eutectic in austenite steel matrix wear resistant composite

By calculation of thermodynamics, analysis of crystal structure and study of transmission electron microscope (TEM), scanning electron microscope (SEM) and electron probe microanalyzer (EPMA), it has been discovered that TiC is formed preferentially between austenite dendrites at the end of the solidification to act as heterogeneous nuclei for the crystallization of the (Fe, Mn)₃C (cementite) and γ₂-Fe (austenite) intergrowth eutectic in the austenite steel matrix wear resistant composite.     

Effect of nanocarbides and interphase hardness deviation on stretch-flangeability in 998 MPa hot-rolled steels

By performing various laboratory hot-rolling simulation tests, effective rolling conditions for steel with a composition (mass %) of 0.06C–2.0Mn–0.5Si–0.5Cr–0.2(Ti + Nb + V) was studied. Very remarkable mechanical properties were obtained when the coiling simulation temperature was 650 °C: a hole-expanding ratio of 65%, total elongation of 19%, and ultimate tensile strength of 998 MPa were achieved in the hot-rolled state. These results were associated with the Ti–Nb–V multi-microalloyed carbides (10–50 nm in size) precipitated in the ferrite matrix, and with the minimized deviation in interphase hardness.     

Effect of nanoscale boron carbide particle addition on the microstructural evolution and mechanical response of pure magnesium

In this study, the effect of nano-B₄C addition on the microstructural and the mechanical behavior of pure Mg are investigated. Pure Mg-metal reinforced with different amounts of nano-size B₄C particulates were synthesized using the disintegrated melt deposition technique followed by hot extrusion. Microstructural characterization of the developed Mg/x-B₄C composites revealed uniform distribution of nano-B₄C particulates and significant grain refinement. Electron back scattered diffraction (EBSD) analyses showed presence of relatively more recrystallized grains and absence of fiber texture in Mg/B₄C nanocomposites when compared to pure Mg. The evaluation of mechanical properties indicated a significant improvement in tensile properties of the composites. The significant improvement in tensile ductility (∼180% increase with respect to pure Mg) is among the highest observed when compared to the pure Mg based nanocomposites existing in the current literature. The superior mechanical properties of the Mg/B₄C nanocomposites are attributed to the uniform distribution of the nanoparticles and the tendency for texture randomization (absence of fiber texture) achieved due to the nano-B₄C addition.     

Grain growth and microstructural evolution of yttrium aluminum garnet nanocrystallites during calcination process

An yttrium aluminum garnet (YAG) precursor precipitate was synthesized by urea method using yttria (Y₂O₃) and aluminum nitrate (Al(NO₃)₃·9H₂O) as raw materials. The fresh wet precipitate was dried by supercritical carbon dioxide (CO₂) fluid and the resulting powder was calcined at temperatures from 600 to 1600 °C. Crystallization of YAG was detected at 800 °C, and completed at 900 °C. HRTEM images of the YAG product obtained above 900 °C revealed crystallographically specific oriented attachment along the [1 1 2] direction. Based on the observation of the particle morphology a possible growth mechanism of YAG nanoparticles was presented. The fast increase on the average crystallite size of YAG at temperatures from 900 to 1300 °C is attributed to the crystallographically specific oriented attachment growth process. As the growth process proceeds at higher temperatures, oriented attachment based growth becomes less important because of the increase on particle size, and the self-integration assisted by the Ostwald ripening becomes dominant.     

Study of SHI induced recrystallization effects in SOI structures synthesized by nitrogen and oxygen ion implantation in silicon

Silicon oxynitride (Si_xO_yN_z) buried insulating layers were synthesized by implantation of nitrogen (¹⁴N⁺) and oxygen (¹⁶O⁺) ions sequentially in the ratio 1:1 at 150 keV to ion-fluences ranging from 1 × 10¹⁷ to 5 × 10¹⁷ cm⁻² to prepare silicon on insulator (SOI) structures. The as implanted samples were held at 270 °C and irradiated to total fluence of 1 × 10¹⁴ cm⁻² by 60 MeV Ni⁺⁵ to study the structural changes/recrystallization of SOI structures induced by swift heavy ion (SHI) irradiation. Fourier transform infrared (FTIR) measurements on the as implanted samples (≤1 × 10¹⁸ cm⁻²) show a single absorption band in the wavenumber range 1300-750 cm⁻¹ attributed to the formation of silicon oxynitride (Si-O-N) bonds in the implanted silicon. It is observed that a nitrogen rich silicon oxynitride structure is formed after SHI irradiation. The study of X-ray rocking curves on the samples show the formation of small silicon crystallites due to swift heavy ion irradiation.     

Quantitative study of the dispersion degree in carbon nanofiber/polymer and carbon nanotube/polymer nanocomposites

Quantitative measurements of the filler dispersion degree of carbon nanofiber (CNF) and nanotube (CNT) reinforced polymer nanocomposites have been made by transmission electron microscopy. Samples were prepared by either high-shear mixing or twin-screw extrusion processing. It was found that the filler dispersion degree was largely influenced by the filler size. As the filler dimension became smaller, the dispersion parameter D_0.1 largely decreased as quantified, which demonstrated the challenges associated with improving the dispersion of smaller fillers. This work provided a method to quantitatively compare the dispersion degrees of CNF/CNT polymer nanocomposites.     

Effect of filament and substrate temperatures on the structural and electrical properties of SiC thin films grown by the HWCVD technique

The effect of varying filament and substrate temperatures on the structure and electrical conductivity of crystalline SiC films prepared by HWCVD technique are described in this paper. At a constant filament temperature, the electrical conductivity of the SiC films increases with increasing substrate temperature. However, TEM studies show that there is no change in the size of the SiC columnar grains. On the other hand, a significant variation in filament temperature at constant substrate temperature leads to a variation of structure and conductivity. Raman spectroscopy and TEM studies reveal that crystallinity improves with increase in filament temperature. Furthermore, a μc-Si phase exists alongside SiC at low filament temperature (1750 °C).     

Influence of current density on crystalline structure and magnetic properties of electrodeposited Co-rich CoNiW alloys

The influence of current density, at the interval 5–100 mA cm⁻², on the structural and magnetic properties of electrodeposited (Co_100−xNi_x)_100−yW_y alloys (x = 23–33.5 at. % Ni, y = 1.7–7.3 at. % W) was studied from a glycine-containing bath. W-content decreases with the increase of the current density magnitude. X-ray data have shown stabilization of hexagonal close packed, face centered cubic or a mixture of these structures by modulating the applied cathodic current density, for values lower than 50 mA cm⁻². Two structural phase transitions were observed: one from hexagonal close packed to face centered cubic structural transition occurring for a current density of 20 mA cm⁻², and another one, from cubic crystalline phase to amorphous state, which happens for values higher than 50 mA cm⁻². These structural phase transitions seem to be associated with the W-content as well as average crystalline grain sizes that reduce with increasing the current density value. The grain size effect may explain the face centered cubic stabilization in Co-rich CoNiW alloys, which was initially assumed to be basically due to H-adsorption/incorporation. Magnetic properties of Co-rich CoNiW alloys are strongly modified by the current density value; as a result of the changes on the W-content and their structural properties.     

Effect of carbon steel microstructure and molecular structure of two new Schiff base compounds on inhibition performance in 1 M HCl solution by DC,SEM and XRD studies

In this investigation, attempts have been made to study the inhibitive effect of N,N′-ortho-phenylen acetyle acetone imine (S1) and 4-[(3-{[1-(2-hydroxy phenyl) methylidene] amino} propyl) ethanemidol]-1,3-benzenediol (S2) in the concentration range of 50–400 ppm for mild steel with two different microstructures resulted from two different heat treatments (annealed (A) and quenched and tempered (Q&T)) in 1 M hydrochloric acid solution. Both Schiff bases acted as a mixed type inhibitors. The S1 inhibitor for both microstructures showed better inhibition efficiency than S2. The A samples indicated slightly less corrosion than Q&T samples in 1 M HCl solution in absence of inhibitor due to the formation of duplex γ-Fe₂O₃/Fe₃O₄.     

Performance and testing of joined Crofer22APU-glass-ceramic sealant-anode supported cell in SOFC relevant conditions

This paper aims to investigate the performance and testing of joined Crofer22APU/glass-ceramic sealant/anode-supported solid oxide fuel cell (SOFC) in dual atmosphere in order to study the stability and effectiveness of the sealant.The sealant was able to prevent corrosion effects of the Crofer22APU after thermal treatments in SOFC relevant conditions at 800 °C for 460 h; an effective gas stream separation between the anode and cathode side was also obtained, as indicated by a very high measured open circuit potential, close to the theoretical one. Chromium poisoning was found to degrade the fuel cell performance, whereas the sealant was chemically and physically stable, as shown by post-mortem analysis.