Austenitic stainless steels are employed in many industrial fields, due to their excellent corrosion resistance, easy formability and weldability. However, their low hardness, poor tribological ...properties and the possibility of localized corrosion in specific environments may limit their use. Conventional thermochemical surface treatments, such as nitriding or carburizing, are able to enhance surface hardness, but at the expense of corrosion resistance, owing to the formation of chromium-containing precipitates. An effective alternative is the so called low temperature treatments, which are performed with nitrogen- and/or carbon-containing media at temperatures, at which chromium mobility is low and the formation of precipitates is hindered. As a consequence, interstitial atoms are retained in solid solution in austenite, and a metastable supersaturated phase forms, named expanded austenite or S phase. Since the first studies, dating 1980s, the S phase has demonstrated to have high hardness and good corrosion resistance, but also other interesting properties and an elusive structure. In this review the main studies on the formation and characteristics of S phase are summarized and the results of the more recent research are also discussed. Together with mechanical, fatigue, tribological and corrosion resistance properties of this phase, electric and magnetic properties, wettability and biocompatibility are overviewed.
Lithium–sulfur (Li–S) batteries have been recognized as one of the most promising candidates for next-generation portable electronic devices, owing to their extremely high energy density and low ...cost. However, the dissolution of lithium polysulfides (LiPSs) and consequent “shuttle effect” seriously hinder the practical deployment of Li–S batteries. Herein, multi-metal oxide nanorods named attapulgite are proposed as multifunctional ionic sieve to immobilize LiPSs and further promote the regulation of LiPSs. Attapulgite, consisting of Al, Mg, Fe, Si and O ions, possesses more polar sites to immobilize LiPSs in comparison with single metal oxides. In addition, the catalytic nature (Fe ions) of attapulgite avails the LiPSs conversion reaction, which is further confirmed by the linear sweep voltammetry and electrochemical impedance spectroscopy. Benefited from the synergistic effect of multi-metal oxide and conductive carbon, the Li–S battery with the modified separator delivers remarkable discharge capacities of 1059.4 mAh g−1 and 792.5 mAh g−1 for the first and 200th cycle at 0.5 C, respectively. The work presents an effective way to improve the electrochemical performance of Li–S batteries by employing attapulgite nanorods assisted separator surface engineering.
Attapulgite nanorods have excellent chemical adsorption and physical barrier to LiPSs. Besides, the high catalytic nature of attapulgite further promotes the LiPSs conversion. Therefore, the battery with attapulgite-modified separator shows excellent electrochemical performance. Display omitted
A coating can be a deciding factor for machining performance of a tool by improving its tool life and wear resistance. Additionally, a variety of elements, including coating thickness, composition ...ratio, layer sequencing in multilayer coatings, and deposition process, affect the coating's performance. In this study, the properties of single-layer AlTiCrN and AlTiN coatings deposited using PVD high-power impulse magnetron sputtering (HiPIMS) and scalable pulse power plasma (S3p) and multilayer TiN/TiAlN- and AlTiN/TiAlN-coated carbide tools deposited using PVD cathodic arc evaporation (CAE) were investigated. Initially, the coatings were characterized for physical properties. Moreover, the performance of these coatings for dry machining of DSS2205 steel are described with respect to tool wear and tool life. It was observed that the AlTiCrN coating deposited by the HiPIMS technique exhibited excellent properties, including low surface roughness 0.19 µm, coefficient of friction 0.35 µm, higher adhesion strength 110 N, and maximum operating temperature 1150 °C, followed by the S3p AlTiN coating with surface roughness 0.21 µm, adhesion strength 107 N, coefficient of friction 0.34 µm, and 850 °C maximum operating temperature. The TiN/TiAlN coating exhibited poor properties among all the tools used. Machining performance confirmed the excellent results obtained through characterization for the AlTICrN coating during dry machining of the DSS2205.
Cathodic plasma electrolytic nitriding (c-PEN) technique has been utilized to modify a low-alloy ferritic steel (2.25Cr-1Mo) surface and assess the effect of the c-PEN layer on corrosion, hydrogen ...permeation, and tribological behavior of the steel. The surface morphology and phase composition of the c-PEN-treated surface were analyzed, and it was found that the surface exhibits a globular network morphology of iron nitride and expanded ferrite. The potentiodynamic polarization results showed that the c-PEN treatment created an electrochemically noble surface compared to the untreated steel. Next, electrochemical hydrogen permeation experiments carried out on the nitrided surface exhibited a noticeable drop in hydrogen permeability, diffusivity, and reversible trap density of the steel. Furthermore, based on nanomechanical and tribological characterization, the c-PEN treatment was found to create a noticeably harder and wear-resistant surface. Overall, these findings demonstrate the applicability of c-PEN treatment to create a multi-functional coating for low-alloy steels that can assist in mitigating the effect of various harsh environments.
The purpose of this article is to investigate the relationship among the material design, in situ synthesis, microstructure and mechanical properties of arc-sprayed Al-Ni-Ti amorphous coatings. The ...precursor reactants were designed by aluminium strip and low-purity industrial alloy powders. The results show that the Al-Ni-Ti coating displays a lamellar structure with porosity up to 1%. The volume fraction of the amorphous, crystallization temperature and hardness of the coatings are 85.9%, 365°C and 4.87 GPa, respectively. The microstructure analysis reveals that the grey region in the coating has a glassy structure and the white region has a crystalline structure of α-Al phase. In 0.6 M NaCl solution, compared with the crystalline structure of the arc-sprayed Al coating and 6061-Al alloy, the Al-Ni-Ti amorphous coating demonstrates an extraordinarily higher pitting potential (− 0.12 V) and lower corrosion current density (4.54 × 10
−8
A/cm
2
). These investigations show that the present Al-Ni-Ti amorphous coating furnishes valuable guidance for expanding engineering applications with an inexpensive, high glass formation ability and prominent performance.
This study demonstrated the sensing performance of surface-patterned poly(dimethylsiloxane) (PDMS)/carbon nanotube (CNT: 3–5 wt%) nanocomposite pads. PDMS/CNT nanocomposite pads as a flexible sensing ...platform were prepared by employing a series of techniques: 3-roll milling for mixing, 2-roll for pad formation, and imprinting for pattern development. Then, tailored surface engineering strategy was introduced. First, the silane coupling agent was incorporated to improve the surface compatibility of the nanocomposite pads. The change in surface property was monitored by shift in contact angle from 132 to 141°. Subsequently, the beta-cyclodextrin (CD) molecules were introduced as a sensing medium through a simple bio-conjugation reaction. The nanocomposite pads showed a sensitive response to methylparaben (MePRB), a representative preservative for cosmetics through host-guest interactions between CD and MePRB in the range of 1–100 nmol. Owing to the surface hydrophobicity of the nanocomposite pads, the sensor was found most effective under nonpolar solvents. The feasibility of surface engineered PDMS/CNT pad as a flexible sensor was demonstrated by measurement after 50 times manual bending. This study can be a useful example for the application of nanocomposites that show unique surface structure and properties.
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•An optimized Ge-rich GeSbTe alloy shows high crystallization temperature (T ~ 380 °C).•Oxidation in Ge-rich GeSbTe reduces the crystallization temperature by ~50 °C.•The phase change ...in GeSbTe is studied via in-situ Transmission Electron Microscopy.•Oxidized and non-oxidized Ge-rich GeSbTe present different nucleation mechanisms.•Chemical phase separation produces the formation of Ge and rocksalt GST phase.
We have studied the effect of surface oxidation on the crystallization of Ge-rich Ge-Sb-Te materials, promising for Phase Change Memories working at high temperatures (>350 °C). For this, we have compared the structural and chemical characteristics of films left exposed to air with those shown by TiN-encapsulated films. The effect of air exposure is to lower the temperature at which the onset of crystallization starts by 50–60 °C. Instead of homogeneous nucleation observed in encapsulated films, crystallization proceeds from the surface towards the bulk of the film and results in a massive redistribution of the chemical elements, forming Ge grains which grow until Ge concentration is low enough to allow the Ge2Sb2Te5 rocksalt phase to nucleate. In the air-exposed films, Ge crystallization preferentially occurs at the film surface while the Ge2Sb2Te5 grains develop later, at higher temperature, and deeper in the film. Our results strongly suggest that “seeds” are formed in or below the oxide during the early stage of annealing, promoting the heterogeneous nucleation of the Ge cubic phase at a lower temperature than observed in encapsulated films. These seeds necessarily involve oxygen and we speculate that crystalline Sb2O3 nuclei formed in the surface layer during annealing play this role.
•We introduced N into Ti3C2Tx at low temperature by a one-step plasma treatment method.•Ti3C2Tx-N acted as an effective host and a catalyst for buffering polysulfide shuttle effect.•The S/Ti3C2Tx-N ...showed excellent electrochemical performances.
Ti3C2Tx MXene has attracted great attention in lithium-sulfur batteries (LSBs) because of its multi-layer structure. However, the low adsorption strength between pure Ti3C2Tx and lithium polysulfides (LiPSs) causes inferior capacity. Surface modification is a promising methode to improve LiPSs adsorption strength of Ti3C2Tx.Herein, we report afast method for rationalsurface engineering of Ti3C2Tx in this paper. One-step plasma treatment strategy is applied to prepare nitrogen-doped Ti3C2Tx (Ti3C2Tx-N) in the first time. SEM and EDS mapping images show that the homogenous nitrogen doped on Ti3C2Tx. Due to the strong interaction between nitrogen in Ti3C2Tx with LiPSs along with high electronical conductivity, the S/MXene-N composite demonstrates excellent electrochemical performances, including high initial reversible capacity (1281.2 mAh g−1 at 0.5 C) and high cycling stability (420.3 mAh g−1 at 2.0 C after 1000 cycles). Overall this work offers a simple surface engineering strategy to manipulate Ti3C2Tx towards high-performance LSBs’ cathodes host.
The surface morphology in polycrystalline silicon (poly-Si) film is an issue regardless of whether conventional excimer laser annealing (ELA) or the newer metal-induced lateral crystallization (MILC) ...process is used. This paper investigates the stress distribution while undergoing long-term mechanical stress and the influence of stress on electrical characteristics. Our simulated results show that the nonuniform stress in the gate insulator is more pronounced near the polysilicon/gate insulator edge and at the two sides of the polysilicon protrusion. This stress results in defects in the gate insulator and leads to a nonuniform degradation phenomenon, which affects both the performance and the reliability in thin-film transistors (TFTs). The degree of degradation is similar regardless of bending axis (channel-length axis, channel-width axis) or bending type (compression, tension), which means that the degradation is dominated by the protrusion effects. Furthermore, by utilizing long-term electrical bias stresses after undergoing long-tern bending stress, it is apparent that the carrier injection is severe in the subchannel region, which confirms that the influence of protrusions is crucial. To eliminate the influence of surface morphology in poly-Si, three kinds of laser energy density were used during crystallization to control the protrusion height. The device with the lowest protrusions demonstrates the smallest degradation after undergoing long-term bending.
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