A Sn–58Bi (SB)/Sn–3Ag–0.5Cu (SAC) composite solder was developed to overcome the challenges, e.g., the low ductility, deterioration of bonding properties and joint reliability, associated with SB eutectic solder and enhance its mechanical bonding properties. Specifically, four types of SB/SAC composite solder samples with different SB/SAC mixing ratios (100:0, 50:50, 20:80, and 0:100) were formulated. Two types of mechanical property investigations, i.e., ball shear and microhardness tests, were conducted to explore the influence of the SB/SAC mixing ratios on the mechanical properties of SB/SAC composite solder joints. The results indicated that the mechanical properties of the joint that containing both SB and SAC were superior to that with only SB or SAC. Furthermore, the mechanical properties of SB/SAC composite solder joint increased linearly with increasing SAC content. This improvement was attributable to the precipitation hardening and dispersion strengthening induced by the presence of fine intermetallic compounds and Bi-rich phase particles dispersed in the SB/SAC composite solder joint.
It is well known that the types of automotive corrosion can be divided into perforation and cosmetic corrosion. Although many studies concerning the mechanism of perforation corrosion have been conducted so far, very few have investigated the mechanism of cosmetic corrosion. In our previous work, the authors found that the initial corrosion behavior in cosmetic corrosion consists of three steps by conducting in-situ observation during a cyclic corrosion test. In the present work, in-situ observation of painted samples with a scratch was performed during an exposure test in Okinawa to examine the cosmetic corrosion behavior under an actual environment. It was found that corrosion started at the moment of salt deposition around the scribed part from air containing salts, and the initial corrosion behavior in the exposure test consisted of three steps, which were the same as in the cyclic corrosion test. In the 1st step, black rust of Fe3O4 formed at the scribed part, and in the 2nd step, under-film corrosion progressed from the scribed part where the black rust had formed. In the 3rd step, the tip of the under-film corrosion displayed swelling behavior. The behavior of each step was also discussed by combining the in-situ observation results with an analysis of environmental factors such as relative humidity and an EPMA analysis.
In recent years, to reduce manufacturing costs and alleviate the rare-earth supply/demand imbalance in the Nd–Fe–B magnet market, researchers have actively pursued the development of (Nd,Ce)–Fe–B magnets, in which Nd is replaced by Ce. In the present study, we focused on magnetic powders treated by the hydrogenation–disproportionation–desorption–recombination (HDDR) process and explored the relationship between the hydrogen pressure and temperature (PH2–T curves) in the Ce–Fe–B system, which is essential for the development of (Nd,Ce)–Fe–B magnets. It was confirmed that the disproportionation and recombination reactions of both Ce2Fe14B and CeFe2 take place in the Ce–Fe–B system. Furthermore, compared with Nd2Fe14B, the PH2–T curve of Ce2Fe14B was found to be shifted to higher pressure and lower temperature, suggesting a corresponding shift in the HDDR conditions under which good magnetic properties can be obtained.
We attempted to calculate the hydrogen trapping energies at the incoherent interfaces of MgZn2 precipitates and Mg2Si crystallites in aluminum alloys from first-principles calculations. Since the unit cell containing the incoherent interface does not satisfy the periodic boundary condition, resulting in a discontinuity of crystal blocks, the hydrogen trapping energy was calculated in a region far from the discontinuity (vacuum) region. We found considerable trapping energies for hydrogen atoms at the incoherent interfaces consisting of assumed atomistic arrangement. We also conducted preliminary calculations of the reduction in the cohesive energy by hydrogen trapping on the incoherent interfaces of Mg2Si in the aluminum matrix.
Al-Zn-Mg alloys with different precipitate sizes were investigated to determine the influence of the precipitate size on the flow stress and dislocation density change during tensile deformation. The dislocation density was measured using in-situ X-ray diffraction at the SPring-8 synchrotron radiation facility with a time resolution of about 2 s. In region II with rapid dislocation multiplication, from under-aging to peak aging, the dislocation density increased with increasing aging time. Under over-aging conditions, the amount of dislocation multiplication in region II decreased with increasing aging time. Even in region III, the increase in dislocation density with plastic deformation was the largest for the peak aging conditions. However, the amount of work hardening was small and the contribution of dislocation hardening to the strength of the material was minimal. For over-aging conditions, the increase in dislocation density in region III was smaller than for the other regions, but the amount of work hardening was relatively large. It is considered that the influence of the dislocation density on work hardening is determined by the effectiveness of precipitates as obstacles to dislocation motion.
We used two deep learning methods, convolutional neural networks (CNN) and deep neural networks (DNN), to classify three common metal crystal structures (FCC, BCC, and HCP). The training, validation, and test datasets were created by Atomsk and Python scripts, and the data structure was transformed to meet the input requirements of CNN and DNN. To fully train and test CNN and DNN, we constructed four crystal structure datasets using random parameters. The results show that the accuracy of CNN and DNN algorithms on the test set is 100%, indicating that deep learning methods are effective for metal crystal structure classification. Compared with DNN, CNN has fewer parameters, faster training, and faster classification. It lays the foundation for further studying alloy structure detection and phase transition.
In this study, microstructure and phase transformation behavior in Fe20Co20Ni20Cr20B20-xSix alloys prepared by the mechanical alloying (MA) method were investigated by X-ray diffraction (XRD) measurements, scanning electron microscopy, transmission electron microscopy, and differential scanning calorimetry (DSC). The Fe20Co20Ni20Cr20B20-xSix alloys prepared by the melt-spinning method were composed of FCC and compounds, and the FCC and BCC phases predicted by the valance electron concentration parameter were not formed. However, alloy powders prepared by the MA method were revealed to be composed of the FCC and BCC phases. Small amounts of unreacted pure B and Si particles were observed in alloy powders with high and low B content, respectively. XRD and DSC measurements revealed that the BCC phase in MA powder disappeared, and compounds were formed by heating up to 700 °C. Especially the compound formation temperature was higher than that of the same alloy prepared by the melt-spinning method, suggesting that the thermal stability of the alloy powders prepared by the MA method was higher than that of the alloy ribbons prepared by the melt-spinning method.
This work investigated the Microstructure and corrosion behavior of wire arc additive manufactured Ti-6Al-xV (x = 0, 2, 4 wt.%) alloys with varying vanadium content. It was found that Ti-6Al with pure α phase showed irregular plate-like grains, which was distinct from the grains obtained in α+β alloys. Vanadium additions in the Ti-6Al-xV alloys promoted the formation of martensitic phase. The width of lamellae decreased and the size of prior β grains, the β phase content increased with the increase of Vanadium content. Electrochemical results suggested that Ti-6Al alloy possessed higher corrosion resistance than Ti-6Al-4V. The difference in corrosion behavior could be attributed to grain size and orientation and phase distribution.
An as-cast Mg-6Zn-0.9Zr-0.9Nd (mass%) alloy was isothermally heat treated to form semi-solid microstructure, and its corrosion behaviors before and after heat treatment were revealed. During the isothermal heat treatment, the microstructure transformed into homogenous spheroidized structure, and the liquid phase presented network-shaped morphology. The electrochemical results showed that there is no passivation behavior and obvious local corrosion in the semi-solid formed alloy, and homogeneous general corrosion is the primary corrosion form. The network-shaped liquid phase prevented the flow of corrosion media between solid phases, and therefore inhibited the formation of pitting corrosion.
Most Mg-based composites are reinforced with ceramic particles such as aluminum oxide and silicon carbide, which leads to relatively high strength and elastic modulus but moderate plasticity, especially when ceramic reinforcements are present at elevated concentrations. We offer a novel type of Mg-based composite reinforced micro-sized spherical Fe-based metallic glass powders (FMGP) that positively mix heat with the matrix element to avoid the development of brittle intermetallic compounds. The composites are sintered at the temperature between the glass transition temperature and the first commencing crystallization temperature of metallic glass, i.e., the supercooled liquid region, to obtain improved densification due to lower sintering resistance. The results reveal that when the FMGP concentration increases, so do the composites' strength, plasticity, and densification. For example, adding 30 wt.% spherical FMGP to pure magnesium increases yield strength, ultimate compressive strength, and fracture strain by 105%, 228%, and 450%, respectively. This intriguing discovery might provide valuable guidance for developing a novel kind of composite with great durability and flexibility for real engineering applications.
Announcement Concerning Article Retraction The following paper has been withdrawn from the database of Mater. Trans., because a description based on a misinterpretation of the experimental results was found by the authors in advance of publication after acceptance. Mater.Trans. 52(2011) Advance view. Improvement in Fatigue Strength of Biomedical β-Type Ti-Nb-Ta-Zr Alloy while Maintaining Low Young’s Modulus through Optimizing ω-Phase Precipitation