•Corrosion behaviors of Hastelloy-N and -B3 in molten FLiNaK salt at 700°C.•The alleviated corrosion rate of alloys was observed after long-hour immersion.•Long-term corrosion rate was limited by ...diffusion from matrix to alloy surface.•Corrosion pattern transferred from intergranular corrosion into general corrosion.•Presence of minor H2O did not greatly influence the long-term corrosion behavior.
This study investigated long-term corrosion behaviors of Ni-based Hastelloy-N and Hastelloy-B3 under moisture-containing molten alkali fluoride salt (LiF–NaF–KF: 46.5–11.5–42%) environment at an ambient temperature of 700°C. The Hastelloy-N and Hastelloy-B3 experienced similar weight losses for tested duration of 100–1000h, which was caused by aggregate dissolution of Cr and Mo into FLiNaK salts. The corrosion rate of both alloys was high initially, but then reduced during the course of the test. The alleviated corrosion rate was due to the depletion of Cr and Mo near surface of the alloys and thus the long-term corrosion rate was controlled by diffusion of Cr and Mo outward to the alloy surface. The results of microstructural characterization revealed that the corrosion pattern for both alloys tended to be intergranular corrosion at early stage of corrosion test, and then transferred to general corrosion for longer immersion hours.
In this study, AlCrSiNbZr nitride thin films were deposited on Si substrate by reactive radio frequency magnetron sputtering under the substrate bias from 0 V to −100 V at room temperature. The ...effect of substrate bias on structure, morphology, hardness and resistivity of the films was investigated. The results show that (111) preferred orientation was dominant phases for samples under bias of 0 V, −25 V, −50 V and − 75 V whereas amorphous-like feature was observed for samples under the bias of −100 V. In addition, crystallinity of film was enhanced when the substrate bias increased from 0 V to −50 V, but decreased when substrate bias further increased from −50 V to −100 V, suggesting that the optimized crystallinity of films was achieved under the substrate bias of −50 V. The oxygen contents of the thin films decreased significantly when the substrate bias was higher than −25 V. The hardness of the films was divided into two regions and samples under bias of −75 V and −100 V possessed higher hardness than those under bias of 0 V, −25 V and −50 V, which was mainly attributed to less oxynitride phases for samples under bias of −75 V and −100 V. The resistivity of thin films decreased as the substrate bias increased, which was mainly affected by the concentration of oxygen in films. The optimized substrate bias was −75 V with the maximum hardness and lowest resistivity.
•(AlCrSiNbZr)N thin films fabricated by reactive RF magnetron sputtering•Effect of substrate bias on structure and properties of film was studied.•Amorphous and FCC structures can be achieved by adjusting substrate bias.•Optimized substrate bias is −75 V with the maximum hardness and low resistivity.
High entropy alloys (HEAs) have recently attracted considerable interest and attention due to their novel properties of good corrosion resistance and superior mechanical strength at high ...temperatures. In this study, we investigated the oxidation behavior of a new high entropy alloy, Al4Co3Cr25Cu10Fe25Ni33, by using thermogravimetric analyzer at temperatures ranging from 800 °C to 950 °C under atmosphere of Ar and O2 for 24 h. The results showed that the oxidation kinetics of Al4Co3Cr25Cu10Fe25Ni33 alloy followed a parabolic regime with its rate constant steadily increased with increasing temperature. The activation energy of Al4Co3Cr25Cu10Fe25Ni33 alloy was found to be 178 kJ/mol. In addition, the bilayer scales and the internal oxidation behavior at the grain boundaries of Al4Co3Cr25Cu10Fe25Ni33 alloy were also examined and discussed.
•Oxidation of Al4Co3Cr25Cu10Fe25Ni33 HEA under Ar and O2 atmosphere for 24 h.•Oxidation of HEA at 800 °C to 950 °C using thermo-gravimetric analyzer.•Oxidation kinetics of Al4Co3Cr25Cu10Fe25Ni33 alloy followed a parabolic behavior.•The activation energy of HEA oxidation was found to be 178 kJ/mol.•Cr2O3/Al2O3 bilayer scales and copper-rich phases were observed after oxidation.
The growth of Ni3Sn4 intermetallic compound (IMC) between liquid–solid interface in micro-scale Ni/SnAg/Ni system was investigated under a temperature gradient of 160 °C/cm at 260 °C on a hot plate. ...In contrast to a symmetrical growth of Ni3Sn4 on both interfaces under isothermally annealed at 260 °C, the interfacial Ni3Sn4 IMC exhibited asymmetric growth under a temperature gradient; the growth of Ni3Sn4 at cold interface was faster than that at hot side because of temperature gradient induced mass migration of Ni atoms from the hot end toward the cold end. It was found that two-stage growth behavior of Ni3Sn4 IMC under a temperature gradient. A growth model was established and growth kinetic analysis suggested that the chemical potential gradient controlled the growth of Ni3Sn4 at stage I (0–120 min) whereas the dynamic equilibrium between chemical potential gradient and temperature gradient forces was attained at the hot end at stage II (120–210 min). When dynamic equilibrium was achieved at 260 °C, the critical length-temperature gradient product at the hot end was experimentally estimated to be 489.18 μm × °C/cm and the moving velocity of Ni3Sn4 interface due to Ni consumption was calculated to be 0.134 μm/h. The molar heat of transport (Q*) of Ni atoms in molten SnAg solder was calculated to be +0.76 kJ/mol.
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•Interfacial reaction in Ni/SnAg solder/Ni system under thermal gradient.•Growth rate of Ni3Sn4 at cold end is faster than that at hot end.•Critical length-temperature gradient product at hot end is 489.2 μm°C/cm at 260 °C.•Velocity of Ni3Sn4 moving interface is 0.134 μm/h during dynamic equilibrium.•Molar heat of transport (Q*) of Ni in molten SnAg was +0.76 kJ/mol.
Materials with nanotwinned structures have been known to possess high strength, high ductility, and low resistivity. Tailoring their mechanical and thermal stabilities has become a critical technique ...based on their practical applications in the electronic industry. In this study, we propose to manipulate the thermal stability of the nanotwinned Ag thin films with the assistance of ion bombardment. The {111}-oriented nanotwinned Ag films were fabricated on Si (100) substrate with 100 nm-thick Ti adhesion layer using different applied ion bombardment energies. We found that the thermal stability of highly {111}-oriented nanotwinned Ag films can be tailored by using different levels of ion bombardment during deposition. The sample with the highest ion bombardment energy exhibits exceptional thermal stability, which can sustain {111}-oriented nanotwinned structure and high mechanical strength after 450 °C annealing. On the other hand, the {111} to {100} texture transformation with large grain coarsening can be triggered at low temperature of 150 °C without introducing ion bombardment during the deposition. This study not only advances the fundamental understanding of the thermal stability of the nanotwinned Ag films after high-temperature annealing but also provides valuable insights into manipulating the thermal stability of sputtered nanostructured Ag films through ion bombardment based on the demands of their applications.
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•Thermal stability of nanotwinned Ag films manipulated by ion bombardment.•{100} abnormal grain growth occurred at 150 °C without ion bombardment.•{111} nanotwinned structure still sustained at 450 °C with highest ion bombardment.
Materials with nanotwinned structures have drawn much attention due to their unique properties. The high-density nanotwinned Cu films are generally deposited at room temperature with high deposition ...rate. In this study, we report nanotwins can be formed in the Cu films at 150 °C with the aid of the ion bombardment effect caused by applied substrate bias. Cu thin films were deposited on Si (100) substrate by the unbalanced magnetron sputtering system using different applied substrate biases ranging from 0 V to −160 V. The results show that, with a suitable applied substrate bias of −120 V, the twinning density of the Cu films can reach over 80 % and exhibit a high hardness of 3.1 GPa. This study provides a concept to tailor the microstructure of the sputtered Cu films by tuning applied substrate biases and realizing the mechanism of substrate bias on the twin formation during deposition.
•Nanotwinned Cu films were fabricated with the aid of ion bombardment effect.•Twin formation at low deposition rate and high deposition temperature•Twin density over 80 % and high hardness over 3 GPa using proper substrate bias•Sufficient ion bombardment enhances the formation probability of twinned structures.
We demonstrate a systematic study optimizing the properties of CoCrFeNi medium entropy alloy (MEA) thin films by tuning the deposition parameters of the pulsed direct current (DC) magnetron ...sputtering process. The chemical composition and microstructure of thin films were studied with energy dispersive X-ray spectroscopy (EDS), an X-ray diffractometer (XRD) and a transmission electron microscope (TEM). Abundant nanotwins and the dual face-centered cubic-hexagonal close-packed (FCC-HCP) phases were formed in some specimens. The Taguchi experimental method and analysis of variance (ANOVA) were applied to find the optimized parameters. The control factors are five deposition parameters: substrate bias, substrate temperature, working pressure, rotation speed and pulsed frequency. According to the signal-to-noise ratio results, the optimized parameters for low electrical resistivity (98.2 ± 0.8 μΩ·cm), low surface roughness (0.5 ± 0.1 nm) and high hardness (9.3 ± 0.2 GPa) were achieved and verified with confirmed experiments.
A series of composite coatings (Ni60-Ti3SiC2) were prepared by laser cladding on 304 stainless steel (SUS304). Then the tribological properties were investigated at room temperature (RT) and 600 °C. ...From the results, because of the fine-grain and dispersion strengthening caused by the presence of small-sized hard phases, the hardness of coatings was much higher than substrate. Benefiting from the addition of Ti3SiC2 lubricant, the friction reduction and wear resistance were decreased greatly, especially the wear rate and friction stability were enhanced 88.9% and 61.5% respectively at the high temperature. The wear mechanisms changed from serious oxidation adhesive wear on the substrate to the slight abrasive wear under the auxiliary lubrication of oxide films and Ti3SiC2 on the composite coatings.
•The ternary layered ceramic MAX phase Ti3SiC2 played the role of lubricant in the coating.•The hardness and tribological properties of 304 stainless steel were greatly improved.•The strengthening mechanisms of the coating with different amount of Ti3SiC2 are quite different.•The formation of specific oxides has positive effects in the high-temperature tribological process.
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•Pd particles ranging from single sites to nanoparticles were prepared and thoroughly characterized.•Direct synthesis of H2O2 over Pd/HAp catalysts showed remarkable size ...effects.•H2O2 selectivity of 94% over a Pd (dpd: 1.4nm) catalyst was observed.•The structure of active sites could be tailored simply by tuning Pd particle size.
A series of size-controlled Pd/hydroxyapatite (HAp) catalysts ranging from single sites (Pd clusters) to nanoparticles (dPd:∼30nm) was prepared and examined for the H2O2 synthesis directly from H2 and O2. A Pd/HAp (dPd:∼1.4nm) showed a high selectivity of 94% toward H2O2 under mild conditions (283K and atmospheric pressure). The crystal phase, morphology, surface electronic states and coordination number of Pd particles from atomic level to nano scale were characterized in detail using multiple techniques such as X-ray diffraction, scanning transmission electron microscopy, and extended X-ray absorption fine structure. Density functional theory calculations indicated that Pd clusters of subnano size have the most effective active sites for the selective activation of oxygen hydrogenation, thus resulting in high catalytic efficiency for H2O2 synthesis. This work elucidates why those smaller Pd particles in a proper size range show the best catalytic performance for H2O2 synthesis.
The mechanical properties of electronic devices in packaging technology are significantly affected by intermetallic compounds (IMCs). This study investigates the interfacial reaction between Ni under ...bump metallization and In solder at aging temperatures of 125°C, 135°C, and 145°C for different periods. Based on the energy dispersive x-ray spectrometry analysis, the growth of the IMCs is mainly Ni
3
In
7
. In addition, the square thickness of the IMCs is proportional to the aging time, which is consistent with volume diffusion control. The activation energy of the Ni
3
In
7
IMC is calculated as 165.9 kJ/mol.
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