Formation Of Oxide Film Research Articles

Influence of conditions for the formation of hafnium oxide films on the structural and electrical properties of heterostructures.

Hafnium oxide (HfO_2) films were synthesized onto silicon substrates by magnetron sputtering under various technological conditions. Research results presented structural composition of HfO2 films and electrical properties of heterostructures metal-insulator-semiconductor (Ni–HfO_2–Si) based on them.

Exploration of microstructural, chemical states and electrical features of the Au/Er2O3/n-GaN MIS diode with a Er2O3 interlayer

The study involved the formation of high-k erbium oxide (Er2O3) films on the n-GaN surface and evaluated their microstructural and chemical states by XRD, TEM and XPS approaches. By employing Er2O3 as an interlayer between the Au and n-GaN substrate, the metal/insulator/ semiconductor (MIS) diode is developed and explored its electrical features by I–V and C–V procedures. The electrical properties of the MIS diode demonstrate a better rectification nature with a lower leakage current compared with the Au/n-GaN Schottky diode (SD). The MIS diode's derived barrier height (BH) is higher than the SD, suggesting that Er2O3 plays a momentous role in altering the BH. The BH was determined using Cheung’s and Norde techniques, and the measurements showed a high degree of consistency, indicating the methods used are valid. The derived density of states (NSS) value for the MIS diode is beneath the SD, suggesting that the Er2O3 layer significantly contributes to the reduction of NSS. Under reverse bias, the PFE is a dominant current mechanism in the lower-bias, whereas the SE is the leading current mechanism in the higher-bias region of the SD. However, the PFE is the prevailing conduction mechanism in the lower-bias and higher-bias regions of the MIS diode. Outcomes of the investigation reveal that the Er2O3 thin films are favorable interfacial layers for fabricating MIS/MOS diodes.

Influence of chromium of low content on the corrosion behavior of SA106B carbon steels in high-temperature pressurized LiOH medium

The corrosion of carbon steel (CS) pipelines widely troubles the primary circuit system of pressurized heavy water reactors. The element chromium (Cr) plays a crucial role in resisting corrosion. However, the mechanism of oxide film formation and dissolution on low Cr-content CS remains unclear. A comparison study in corrosion behavior between SA106B with 0.02 wt% and 0.36 wt% Cr was carried out with weight loss tests, electrochemical measurements, and morphology observations. Immersion tests were performed in deaerated lithium hydroxide solution at 553 K and 6.3 MPa for 30 days. The results showed that although the content of Cr was as low as 0.36 wt%, it exhibited relatively high corrosion resistance to the SA106B with 0.02 wt% Cr. Two layers of oxide film were formed on both the two CSs and chromium oxide was present in the inner oxide layer of 0.36Cr CS. The possible formation mechanism of oxidation film with low content of Cr in high-temperature water was discussed.

Study on the role of solution treatment on corrosion behavior of duplex lightweight steel in different environments

Diverse microstructure and complex application environments increases the uncertainty of the corrosion resistance of lightweight steels. The effect of solution treatment on the corrosion behavior of Fe–16Mn–10Al–1.5C–0.1Ti lightweight steel in Cl−, HSO3− and Cl−–HSO3− environments was investigated using electrochemical measurement, scanning electron microscope (SEM) and X–ray photoelectron spectroscopy (XPS). The lightweight steels are dominated by austenite and contain a small amount of ferrite. The increase in solution treatment temperature leads to more ferrite formation, but it has less effect on grain size. The decrease in austenite content results in more corrosion microcells and a porous oxide film; therefore, the corrosion resistance of the steel deteriorates with increasing temperature. In addition, in the Cl−–HSO3− environment, the synergistic effect of Cl− and HSO3− leads to the formation of a weak protective oxide film, resulting in a significant increase in corrosion rate compared to the Cl−and HSO3− environment.

Morphological and semiconductive properties of the anodic oxide layers made on Fe3Al alloy by anodizing in tartaric-sulfuric acid mixture

It has recently been found that the anodizing of FeAl alloys allows the formation of iron-aluminum oxide layers with interesting semiconducting properties. However, the lack of systematic research on different anodizing regimes is hampering their full exploitation in numerous photoelectrochemical-related applications. This study address, for the first time, the systematic effect of the electrolyte composition on the formation of self-ordered oxide films by anodizing on cast Fe3Al alloy. The Fe3Al alloy was anodized in 3 electrolytes with different water-ethylene glycol (EG) ratios (pure water, 25 vol.%-EG, and 50 vol.%-EG solutions) at a constant tartaric-sulfuric acids concentration, different voltages (10–20 V) and treatment times (2–60 min). After anodizing, all anodic oxide layers were annealed at 900 °C to form semiconductive iron-aluminum crystalline phases. Conventional techniques were used to systematically ascertain the morphological (SEM/EDS, XRD, eddy-current measurements) and semiconductive (UV–VIS reflectance spectroscopy) properties of these oxide layers. The results confirmed the formation of homogeneous and self-ordered anodic oxide layers at 10 and 15 V, regardless of the electrolyte composition. Namely, anodic films formed in electrolytes containing EG showed lower pore sizes, growth rates, and film thicknesses than those anodic films formed in the aqueous-based electrolyte. The annealing post-treatment results in different Fe-Al oxides (FexOy, FeAl2O4, etc.) with superior band gap values than those for non-annealed films.

Microstructural evolution and corrosion behavior of Al-20Mg2Si composites with trace La addition

Trace La element was introduced in Al-20Mg2Si composites to regulate the microstructure and corrosion performance. The modification mechanism of trace La and the corrosion behavior of the newly developed composites were systematically investigated by thermal analysis, microstructural observations and electrochemical tests. Our study reveals that the addition of only 0.10% La can refine the size of the primary Mg2Si phase from 77.6 to 26.7 µm, modify its morphology from a coarse dendrite to a fine truncated octahedron and reduce the corrosion current density from 5.96 μA cm−2 to 3.03 μA cm−2. Trace La refines the primary Mg2Si phase size by forming a tiny LaAlSi phase which can provide effective heterogeneous nuclei for the primary Mg2Si phase during solidification. Excess La atoms can selectively adsorb on the {100} facets of the primary Mg2Si phase and suppress the preferential growth of the Mg2Si phase, eventually resulting in the morphological transition of the primary Mg2Si phase from dendrite to truncated octahedron shape. The enhanced corrosion resistance of the La micro-alloyed Al-20Mg2Si composites can be attributed to the formation of stronger protective surface oxide films and finer primary Mg2Si phase. The protective oxide films can effectively hinder the penetration of the corrosive medium and the finer primary Mg2Si phase can weaken the localized corrosion tendency of the Al-Mg2Si composites.

Hot salt corrosion behavior of Ti–6Al–4V alloy treated with different surface deformation strengthening processes

In this study, the effects of shot peening (SP) and ultrasonic surface rolling process (USRP) on the high-temperature oxidation and hot salt corrosion (HSC) behavior of the Ti–6Al–4V alloy were systematically investigated. The results showed that the high-temperature oxidation resistance of this titanium alloy can be significantly improved by the above two treatments. However, the hot salt corrosion resistance of Ti–6Al–4V alloy cannot be improved by SP due to surface roughness increasement, the surface defects and the complete relaxation of compressive residual stress (CRS) at high temperature. On the contrary, the hot salt corrosion resistance of USRP treated specimen was remarkably improved because USRP treatment significantly reduced the surface roughness and introduced deep CRS field with good thermal stability. In addition, the refined surface microstructure promoted the formation of a protective oxide film, which was also beneficial for inhibiting hot salt corrosion.

Effect of Mo on the high-temperature oxidation behavior of Cr-Ni-Mo hot-work die steels

To investigate the effect of molybdenum (Mo) on the high-temperature oxidation behavior of low-carbon hot-work die steels in a Cr-Ni-Mo system, five 3Cr3MoxNiW steels were prepared. The addition of Mo resulted in a decrease in the grain size of the 3Cr3MoxNiW steel, as well as an improvement in its oxidation resistance. The addition of Mo to 3Cr3MoxNiW steel reduces the inward diffusion of oxygen and the outward diffusion of iron, which accelerates the formation of chromium oxide. The oxide of Mo can then also participate in the process of protective oxide film formation, thus improving its oxidation resistance.

Performance and Properties of a Ti-Al Composite Anodic Oxide Film on AC-Etched Al Foil

AC-etched aluminum foils for an Al electrolytic capacitor were covered with a TiO2 film by a sol–gel coating and then anodized to 25 V in an ammonium adipate solution. The structure, properties, and performance of the anodic oxide films were examined by transmission electron microscopy (TEM), scanning electron microscopy (SEM), electrochemical impedance measurements (EIS), a general digital LCR meter, a TV characteristic tester, and multicycle pulse charging–discharging. It was found that the anodizing of aluminum coated with TiO2 films led to the formation of Al-Ti composite anodic oxide films, which consist of an outer Al-Ti composite oxide layer and an inner Al2O3 layer on the metal substrate. The capacitance (C25V) of the anodic oxide films formed on specimens with a TiO2 coating was about 10% larger than without a TiO2 coating. The specific resistance (Rox) of the Al-Ti composite film measured by EIS was lower than the blank one, accounting for a greater increase in the rise time (Tr) and a slight reduction in the withstand voltage (Vt). After hydration and a multicycle pulse charging–discharging destructive test, the Al-Ti composite anodic oxide film maintained the same good, comprehensive dielectric properties and performance as the blank one, thereby proving to be promising for acting as dielectric layers.

Enhancing the wear and high-temperature oxidation behavior of NiCrBSi coatings by collaboratively adding WC and Cr3C2

A composite coating was deposited by collaborative modification with tungsten carbide (WC) and Cr3C2 ceramic particles to improve the wear resistance of NiCrBSi coating over a wide temperature range. The original NiCrBSi coating and the composite coatings with WC and Cr3C2 collaboratively (NiCrBSi +20 wt% WC–Cr3C2–Ni) and exclusively (NiCrBSi +20 wt% WC and NiCrBSi +20 wt% Cr3C2–NiCr) added were designed and deposited by plasma spraying. The microhardness of the composite coatings added with the ceramic phase was higher than that of the NiCrBSi coating. The composite coating with the addition of WC showed the maximum microhardness (896.8 HV). The wear mechanism of the four coatings at room temperature was dominated by fatigue spalling, whereas oxidative and abrasive wear prevailed at 700 °C. The composite coating (NiCrBSi +20 wt% WC–Cr3C2–Ni) showed excellent abrasion resistance at room temperature and 700 °C. The wear volume of the composite coating (NiCrBSi +20 wt% WC–Cr3C2–Ni) decreased by 83.5 % and 46.9 % at room temperature and 700 °C, respectively, compared with the wear volume of the NiCrBSi coating. In general, high WC hardness was favorable for improving the microhardness of the coating. The preferential oxidation of Cr3C2 instead of WC promoted the formation of a dense oxide film on the surface of the coating and reduced oxidation within the coating. This study revealed the mechanism of the collaborative enhancement of NiCrBSi coatings by WC and Cr3C2 and the improved wear resistance of the NiCrBSi coatings at room and high temperatures.

High‐Performance Flexible MoS2 Transistors Using Au/Cr/Al/Au as Source/Drain Electrodes

Abstract2D transition metal dichalcogenides such as molybdenum disulfide (MoS2) are promising candidates for flexible electronics because of their bandgap tunability, high carrier mobility, and mechanical flexibility. However, flexible MoS2 field effect transistors (FETs) are typically faced with high contact resistance which is identified as a critical limiting factor to their potential applications. The present work successfully addresses this challenge by using Al contacts without any annealing process. It is found that the contact resistance is strongly coupled to the Al thickness, increasing the Al thickness is beneficial to reduce the contact resistance. The observed variation in the device electrical characteristics can be associated with the formation of the natural aluminum oxide (AlxOy) film at the interface. An ultrathin Au insert layer can further advance the device performance. An optimal contact resistance of 2.03 kΩ and an on/off current ratio of 1.57 × 109 can be achieved in the flexible MoS2 FETs using Au/Cr/Al/Au as source/drain electrodes. Furthermore, no apparent degradation in the device properties is observed under systematic cyclic bending testing with bending radii of 18 and 15 mm. The successful integration of Au/Cr/Al/Au source/drain electrodes into MoS2 FETs promises its potential application in flexible electronic devices.

3D Impedance Analysis on Dissolution Behavior of Additive-Manufactured Al-12%Si Alloy

Laser Powder Bed Fusion (LBPF) is one of the additive manufacturing techniques using a laser beam to melt and fuse layers of metal powder particles forming various metal products with complex shapes. Because the Al-Si alloy manufactured by LPBF has good mechanical properties compared to conventionally cast Al alloys, it is important to investigate the dissolution behavior of Al-Si alloy manufactured by LPBF for wider usage in industry.In the present study, the film resistance of oxide film formed on additive-manufactured Al-12%Si alloys were investigated by a three-dimensional(3D) impedance spectroscopy1-5. This method allows for the estimation of the film resistance with time information because the impedance is plotted on the 3D diagram whose axes are real, imaginary and time, namely, the instantaneous impedance at arbitrary time can be determined from 3D impedance. To investigate the dissolution behavior of additive-manufactured Al alloys, the non-annealed sample (Al-12Si) and annealed samples at different temperatures ranging from 200 to 350 ℃ (Al-12Si300) and 530 ℃ (Al-12Si530) with arbitrary holding time were used for the electrochemical measurements. The 3D impedance of Al-12Si, Al-12Si300 and Al-12Si530 could be successively measured in the immersion conditions. The 3D impedance of Al-12Si and Al-12Si300 demonstrated that the impedance of both samples was increased with time. The 3D impedance of Al-12Si530 indicated small values during measurement. These results imply that the increase of impedance of Al-12Si and Al-12Si300 is associated with the formation of oxide film on the surface. The film resistance estimated from impedance spectra determined from 3D impedance and the morphology of samples after the measurement were correlated discussed.

2D Amorphous GaOX Gate Dielectric for β-Ga2O3 Metal-Insulator-Semiconductor Field-Effect Transistors

Beta gallium oxide (β-Ga2O3) is an n-type ultra-wide bandgap semiconductor material with a reported bandgap from 4.5 eV to 4.9 eV. β-Ga2O3 is a frontrunner in the research for next-generation power devices owing to its numerous merits including the wide range of donor doping concentrations, large bandgap, high theroretical value of critical electric field (~8 MV/cm) leading to substantial Baliga’s figure of merit of ~1900, and the low production cost for crystalline wafers. The last is enabled by the commercial development of several bulk growth techniques, namely, melt growth methods including Czochralski and edge-defined film-fed growth, and epitaxial growth. The metal-insulator-semiconductor field-effect transistor (MISFETs) is the most widely used device structure since it often requires less complicated fabrication process and offers better device scaling and faster switching speed than their counterparts such as junction field-effect transistors or bipolar junction transistors. Various dielectric materials, such as silicon dioxide, hafnium oxide, and aluminium oxide, have been explored for incorporation into β-Ga2O3 MISFETs. However, many of the dielectrics require high-temperature and/or high-vacuum processes during fabrication. Recent studies have reported on the self-limiting formation of native oxide film on the surface of liquid gallium at room temperature and the application of the oxide film as a passivation or a dielectric layer in a nano-scale device. In this study, two-dimensional (2D) amorphous gallium oxide (a-Ga2O3) film is fabricated through the liquid gallium squeezing technique and is integrated with a β-Ga2O3 field-effect transistor (FET) to demonstrate an a-Ga2O3/β-Ga2O3 MISFET.In this work, β-Ga2O3 nano-flakes were obtained through mechanical exfoliation and were dry-transferred onto Si/SiO2 substrates. Electron-beam lithography and electron-beam evaporation were performed to define and deposit Ti/Au electrodes, respectively, where rapid thermal annealing was performed afterward to form Ohmic source and drain contacts. Polypropylene carbonate (PPC) solution was spin-coated and baked on a polydimethylsiloxane (PDMS) film, placed on a glass slide for mechanical support, to form a uniform PPC layer on the PDMS film. A liquid gallium droplet was placed on the PPC/PDMS film and was squeezed with a cleaned glass slide to form a uniform 2D a-Ga2O3 layer. The fabricated a-Ga2O3 layer was dry-transferred onto a β-Ga2O3 FET during which temperature of 90 °C was applied to the sample chuck to completely release the PPC layer with the a-Ga2O3 layer from the PDMS layer. The resulting a-Ga2O3/β-Ga2O3 FET was submerged in acetone to remove the PPC layer. The above dry-transfer process of the a-Ga2O3 layer was conducted twice to form double-layered a-Ga2O3 on the β-Ga2O3 FET, before performing electron-beam lithography and electron-beam evaporation to respectively define and deposit the Ni/Au top-gate electrode.The electrical properties of the fabricated device is characterized as a Ni/a-Ga2O3/β-Ga2O3 heterojunction and an a-Ga2O3/β-Ga2O3 MISFET at temperatures of 25 °C, 150 °C, and 250 °C. The Ni/a-Ga2O3/β-Ga2O3 heterojunction of the device shows a clear rectification characteristic with a wider operating voltage compared to those of standard Ni/β-Ga2O3 devices in literatures. The double-layered a-Ga2O3 The a-Ga2O3/β-Ga2O3 MISFET exhibits normally-on n-type conductivity with stable operation at temperatures from 25 °C to 250 °C, where the obtained on/off current ratio and mobility range from 5.3×108 to 4.8×107 and 4.7 cm2/V·s to 6.9 cm2/V·s, respectively. The subthreshold swing and the threshold voltage of the a-Ga2O3/β-Ga2O3 MISFET showed increases and negative shifts at higher temperatures, respectively. This work demonstrates the facile fabrication process of the a-Ga2O3/β-Ga2O3 MISFET and its high-temperature stability through the integration of the 2D amorphous Ga2O3 gate dielectrics with a β-Ga2O3 semiconductor.

Hot corrosion behavior of a novel TiC/GTD222 nickel-based composite prepared by selective laser melting

In this study, a novel TiC/GTD222 nickel-based composite with enhanced hot corrosion resistance was designed by incorporating appropriate amounts of C, Al, and Ti elements into the GTD222 superalloy. The composite was successfully prepared using the selective laser melting (SLM) technique. The hot corrosion behavior of GTD222 superalloy and the TiC/GTD222 composite in a salt mixture of 75% Na2SO4 + 25% NaCl (wt%) at 900 °C was systematically studied. The results show that the TiC/GTD222 composite exhibits much better hot corrosion resistance than the GTD222 superalloy. This is because a continuous and dense double-layer oxide film is formed in the composite (The inner layer is TiO2 and the outer layer is Cr2O3), while oxide film of the superalloy is loose and porous, and has a discontinuous TiO2 and Al2O3 distribution. The adding alloy elements can promote the formation of more γ' phase and TiC particles in the TiC/GTD222 composite, and also result in the refined grain and formation of more dislocations. The above microstructures increase the diffusion channels of elements, and the higher contents of Al and Ti can enhance the diffusion potential energy of these elements, leading to the formation of continuous and dense double-layer oxide film of the composite. This work provides new ideas for the design of additive manufactured superalloy.

Evaluation of microstructure, mechanical properties, and corrosion resistance for Ti-doped inconel 625 alloy produced by laser directed energy deposition

Additive manufacturing (AM) technology has opened up new opportunities to efficiently synthesize alloys and produce near-net shape components. In this study, Ti-doped Inconel 625 materials were produced to promote in-situ alloying between pre-alloyed Inconel 625 and elemental Ti powders by laser directed energy deposition, a predominant metal AM technique. The microstructure, mechanical properties, and corrosion resistance were evaluated before and after Ti addition and heat treatment (solutionization followed by aging). It was found that Ti addition alone did not cause significant change in microstructure. However, heat treatment caused migration of segregation species from interdendritic regions to intermetallic precipitates which occupy grain boundaries, and it modestly increased the average grain size for Ti-doped samples. Crystallographic analysis revealed a very strong cubic texture of Ti-doped Inconel 625 which only slightly decreased after heat treatment. Without heat treatment, the addition of Ti was not found to be beneficial to tensile properties of Inconel 625, due to the formation of thin Ti oxide films. However, the combination of Ti addition and heat treatment led to modest increase in hardness and tensile strength compared to the as-built Ti-free case, which is believed to result from the effects of Ti solid solution hardening, precipitation hardening, and dissolution of oxide films. Also, the combined effects can explain the pronounced increase of ductility for Ti-doped Inconel 625 after heat treatment, where the beneficial effect from oxide film dissolution could be dominant. In addition, under the as-built condition, corrosion resistance was found to be slightly higher for Ti-doped materials, but after heat treatment it dropped for Ti-doped materials while almost did not change for Ti-free case.

Influence of layer number and sintering temperature on microstructural, tribological, and corrosion behavior of Al2O3–TiO2 multilayer coatings

The effects of layer number (2, 4, and 6-layer) and sintering temperature (800, 900, 1000, and 1100 °C) on the microstructure, wear, and corrosion properties of Al2O3–TiO2 multilayer coatings deposited on 316L stainless steel plates using the sol-gel dip coating technique were investigated. The wear characteristics were measured through ball-on-disc type dry sliding tests using an Al2O3 ball under a 1 N load, whereas the corrosion features were determined by potentiodynamic polarization tests conducted in a 3.5 wt% NaCl solution. Anatase, rutile, α-Al2O3, and γ-Al2O3 phases were obtained in the hybrid coatings, depending on the sintering temperatures. However, at 1100 °C, the coating did not adhere well to the substrate due to passive oxide film formation on the 316L plate, leading to spalling. Besides, the surface homogeneity deteriorated in the 6-layer coated sample due to higher organic removal and residual stresses. The corrosion rate decreased with the increasing number of layers, but the sensitivity to corrosion varied due to changes in surface properties. The 4-layer coated sample sintered at 1000 °C achieved the highest wear strength (improved by up to 71.1%) and corrosion resistance (increased by up to 90.4%) due to its decreased porosity and homogeneously distributed finer particles.

Tribocorrosion behavior of Co-based self-lubricating composites with varying contents of Ag in NaCl solution

Majority of self-lubricating composites exhibit a high wear rate due to corrosion. In this study, Co-based self-lubricating composites with addition of Ag were prepared via spark plasma sintering to manage their tribocorrosion resistance. No interfacial reaction occurred after sintering. Their tribocorrosion behavior in 3.5 wt.% NaCl solution was characterized as a function of applied potentials. In corrosion-free conditions, i.e. applying a cathodic potential (−1 V), the addition of Ag enhances wear rate of the Co-based composites. While in a state of OCP or applying an anodic potential, galvanic corrosion occurs between Ag and Co-matrix. It promotes the formation of a loose oxide film and reserves most silver debris, which contributes synergistically to reduced friction coefficient and wear rate. With the addition of 12 wt.% Ag, Co-based self-lubricating composite exhibits the lowest friction coefficient of 0.09 and wear rate of 3.8 × 10−5 mm3/(Nm) at OCP.

Electrochemical and surface characterization of anodized and fs-laser treated Ti6Al4V for osseo-repellent bone screws and dental implants

The surfaces of titanium grade 5 (Ti6Al4V) samples were altered on a micro and nano scale by femtosecond laser irradiation and subsequent electrochemical anodization. The produced micro-cones and nano-ripples covered by the additional oxide layer were characterised and their influence on osteoblast-like Saos-2 cell growth was studied. Surface topography and morphology were studied by Atomic Force Microscopy (AFM) and Scanning Electron Microscopy (SEM). From the wettability experiments, it was found that the contact angle vs. roughness follows the Wenzel equation and that the wettability increases after the anodization. The composition of the formed oxide layer was determined by X-ray photoelectron spectroscopy (XPS) and oxide incorporation of phosphate ions could be confirmed. Moreover, estimated electrochemical surface area (ECSA) of the femtosecond laser treated sample was 14 times larger compared to a polished sample. The anodic oxide film formation factors for different electrolytes were determined and were in the range of 1.3 nm V−1–2.0 nm V−1. Finally, the samples anodized with 0.1 M H2SO4 and 3 M H3PO4 showed decreased Saos-2 cell growth.

Improving corrosion resistance of Mg–Li alloys by Sn microalloying

It is well known that the corrosion resistance of ultra-light Mg–Li alloys is inferior to traditional Mg alloys due to the rapid oxidation of reactive Li on the surface. In this study, microalloying Sn has been found to improve the corrosion resistance of Mg–Li alloys due to the formation of Mg2Sn on the corrosion pits and reduction of electro-potential difference. Indeed, the addition of Sn not only reduced the corrosion rate to the minimum value of 4.27 mmpy but also promote the formation of dense corrosion oxide films. The volt potential difference between the matrix (α-Mg and β-Li) and Al-X (Gd, Y, Mn) phases has also been measured to reduce from 260 mV (α-Mg) and 343 mV (β-Li) to 220 mV (α-Mg) and 220 mV (β-Li). After homogenization, pitting was significantly reduced, as shown by the in-situ observation of the corrosion process using X-ray tomography. By quantifying the secondary phases, it has been found that the corrosion expansion was restricted by the Mg2Sn and Al-X phases. The corrosion products are primarily MgO, SnO, and Li2O oxides and the corrosion mechanism follows three stages: I. Breakthrough of MgO protective layer by corrosive fluid; II. Hydrogen evolution reaction (HER) between matrix phase and water immersion; III. Segregation of secondary phases and corrosion products. It has been found that all three processes are highly dependent on the Sn solutes and Mg2Sn precipitates, showing the bright future development of corrosion-resistant Mg–Li alloys by Sn microalloying.

Direct bonding of Ni nanoparticles to a semiconductor Al electrode in air and its form

This research group evaluated the bondability of sinter bonding using Ni nanoparticles, which have a high melting point and excellent corrosion resistance, as a new metal nanoparticle bonding material, and found that bonding is possible at bonding temperatures below 400 °C when the particle size is less than 100 nm. Furthermore it was found that Ni nanoparticles can be directly bonded to Al, which is considered difficult to bond directly with solder materials containing tin (Sn) or lead (Pb), and that high bonding strength can be obtained. In addition, the bonding strength of Ni nanoparticles to Al was higher when bonded in air than in a reduction atmosphere of N2+H2 (3%), indicating that there were differences in bonding properties depending on the bonding atmosphere. In this study, we compared the bonding properties to Al in different bonding atmospheres. In the N2+H2 (3%) reducing atmosphere, the bonding strength was not increased even when the bonding temperature was increased. On the other hand, the bonding strength was significantly increased with increasing bonding temperature over 330 °C in air. The failure mode was also rupture in the bonding layer, and good bonding was achieved at the Ni/Al bonding interface. Observation of the bonding interface between Ni nanoparticles and Al using Transmission electron microscope (TEM) showed the presence of an interlayer of oxide film at both bonding interfaces in air and in the N2+H2 (3%) reduction atmosphere. And the oxide layer at the interface bonded in air was thicker, indicating that the structure at the interface between the Ni layer, the oxide layer and the Al layer has changed. It was suggested that the difference in oxide film formation behavior, structure, and thickness affects the bondability due to the difference in the bonding atmosphere.