Search Results (13)

Today, the machining of heat-resistant alloys based on triple, quad, or penta equilibria high-entropy alloy systems of elements (ternary, quaternary, quinary iron-, titanium-, or nickel-rich alloys), including dual-phase by Gibb’s phase rule, steels of the austenite class, and nickel- and titanium-based alloys, are highly relevant for the airspace and aviation industry, especially for the production of gas turbine engines. Cutting tools in contact with those alloys should withstand intensive mechanical and thermal loads (tense state of 1.38·10⁸–1.54·10⁸ N/m², temperature up to 900–1200 °C). The most spread material for those tools is cutting ceramics based on oxides, nitrides of the transition and post-transition metals, and metalloids. This work considers the wear resistance of the cutting insert of silicon nitride with two unique development coatings — titanium–zirconium nitride coating (Ti,Zr)N and complex quad nitride coating with TiN content up to 70% (Ti,Al,Cr,Si)N with a thickness of 3.8–4.0 µm on which microtextures were produced by the assisted electric discharge machining with the electrode-tool of ø0.25 mm. The microtextures were three parallel microgrooves of R0.13^+0.02 mm at a depth of 0.025₋₀.₀₅. The operational life was increased by ~1.33 when the failure criterion in turning nickel alloy was 0.4 mm. Full article

Ultraviolet light-emitting diodes (LEDs) based on Aluminum Gallium Nitride (AlGaN) suffer from poor carriers’ confinement effect, one possible solution to this problem is to increase the barrier heights for carriers by increasing Aluminum content in quantum barriers (QBs), which results in a higher turn-on voltage. Keeping this in mind, we have improved the carriers’ confinement by introducing a small amount of Boron nitride (BN) (2%) in ternary QBs and an electron injecting layer, which results in higher barriers that restrict the out-of-active region movement of electrons and holes. With quaternary B_xAl_yGa_zN QBs, significantly enhanced electrons and hole concentrations can be observed in the active region of quantum wells (QWs), which leads to a 4.3 times increased radiative recombination rate with a 68% better internal quantum efficiency (IQE) than the referenced conventional LEDs. Relying on the fairly improved IQE and radiative recombinations, other optoelectronic characteristics such as luminous power, emission intensity, etc., are also enhanced. Our whole analysis is based on numerical techniques but we believe that fabricating the proposed type of LEDs will result in desirable light extraction and external quantum efficiencies. Full article

The recent advancements in the field of superconductivity have been significantly driven by the development of nitride superconductors, particularly niobium nitride (NbN). Multicomponent nitrides offer a promising platform for achieving high-temperature superconductivity. Beyond their high superconducting transition temperature (Tc), niobium-based compounds are notable for their superior superconducting and mechanical properties, making them suitable for a wide range of device applications. In this work, machine learning is used to identify ternary and quaternary nitrides, which can surpass the properties of binary NbN. Specifically, Nb_0.35Ta_0.23Ti_0.42N shows an 84.95% improvement in Tc compared to base NbN, while the ternary composition Nb_0.55Ti_0.45N exhibits a 17.29% improvement. This research provides a valuable reference for the further exploration of high-temperature superconductors in diversified ternary and quaternary compositions. Full article

Secondary caries is one of the leading causes of resin-based dental restoration failure. It is initiated at the interface of an existing restoration and the restored tooth surface. It is mainly caused by an imbalance between two processes of mineral loss (demineralization) and mineral gain (remineralization). A plethora of evidence has explored incorporating several bioactive compounds into resin-based materials to prevent bacterial biofilm attachment and the onset of the disease. In this review, the most recent advances in the design of remineralizing compounds and their functionalization to different resin-based materials’ formulations were overviewed. Inorganic compounds, such as nano-sized amorphous calcium phosphate (NACP), calcium fluoride (CaF₂), bioactive glass (BAG), hydroxyapatite (HA), fluorapatite (FA), and boron nitride (BN), displayed promising results concerning remineralization, and direct and indirect impact on biofilm growth. The effects of these compounds varied based on these compounds’ structure, the incorporated amount or percentage, and the intended clinical application. The remineralizing effects were presented as direct effects, such as an increase in the mineral content of the dental tissue, or indirect effects, such as an increase in the pH around the material. In some of the reported investigations, inorganic remineralizing compounds were combined with other bioactive agents, such as quaternary ammonium compounds (QACs), to maximize the remineralization outcomes and the antibacterial action against the cariogenic biofilms. The reviewed literature was mainly based on laboratory studies, highlighting the need to shift more toward testing the performance of these remineralizing compounds in clinical settings. Full article

Hard and wear-resistant coatings created utilizing physical vapor deposition (PVD) techniques are extensively used in extreme tribological applications. The friction and wear behavior of coatings vary significantly with temperature, indicating that advanced coating concepts are essential for prolonged load-bearing applications. Many coating concepts have recently been explored in this area, including multicomponent, multilayer, gradient coatings; high entropy alloy (HEA) nitride; and functionally modified coatings. In this review, we highlighted the most significant findings from ongoing research to comprehend crucial coating properties and design aspects. To obtain enhanced tribological properties, the microstructure, composition, residual stress, hardness, and HT oxidation resistance are tuned through doping or addition of appropriate materials at an optimized level into the primary coatings. Such improvements are achieved by optimizing PVD process parameters such as input power, partial pressure, reactive gas flow rates, substrate bias, and temperature. The incorporation of ideal amounts of Si, Cr, Mo, W, Ag, and Cu into ternary and quaternary coatings, as well as unique multilayer designs, considerably increases the tribological performance of the coatings. Recent discoveries show that not only mechanical hardness and fracture toughness govern wear resistance, but also that oxidation at HT plays a significant role in the lubrication or wear failure of coatings. The tribo-induced metal oxides and/or Magnéli phases concentrated in the tribolayer are the key governing factors of friction and wear behavior at high temperatures. This review includes detailed insights into the advancements in wear resistance as well as various failure mechanisms associated with temperature changes. Full article

Despite III-nitride and silicon carbide being the materials of choice for a wide range of applications, theoretical studies on their quaternary alloys are limited. Here, we report a systematic computational study on the electronic structural properties of (SiC)_x (AlN)_1−x and (SiC)_x (AlN)_1−x quaternary alloys, based on state-of-the-art first-principles evolutionary algorithms. Trigonal (SiCAlN, space group P3m1) and orthorhombic (SiCGaN, space group Pmn2₁) crystal phases were as predicted for x = 0.5. SiCAlN showed relatively weak thermodynamic instability, while that of SiCGaN was slightly elevated, rendering them both dynamically and mechanically stable at ambient pressure. Our calculations revealed that the Pm31 crystal has high elastic constants, (C₁₁~458 GPa and C₃₃~447 GPa), a large bulk modulus (B₀~210 GPa), and large Young’s modulus (E~364 GPa), and our results suggest that SiCAlN is potentially a hard material, with a Vickers hardness of 21 GPa. Accurate electronic structures of SiCAlN and SiCGaN were calculated using the Tran–Blaha modified Becke–Johnson semi-local exchange potential. Specifically, we found evidence that SiCGaN has a very wide direct bandgap of 3.80 eV, while that of SiCAlN was indirect at 4.6 eV. Finally, for the quaternary alloys, a relatively large optical bandgap bowing of ~3 eV was found for SiCGaN, and a strong optical bandgap bowing of 0.9 eV was found for SiCAlN. Full article

With the growth of the automobile, machinery, and aerospace industries, demand for high-performance surface coatings having multifunctional characteristics for use in mechanical parts is increasing. In this study, ternary/quaternary Mo–Cu–Cr–(N) nanocomposite coatings were deposited at different N₂ gas flow rates using direct current magnetron sputtering from a multicomponent single-alloy target. The use of a single-alloy target simplifies the deposition process and improves the coating uniformity. The influence of the nitrogen content was investigated regarding the microstructural, mechanical, and tribological properties, and corrosion resistance of these coatings. The Mo–Cu–Cr–N coating containing 30.5 at.% nitrogen showed a nanocomposite structure comprising transition metal nitride phases (Mo–N/Cr–N) having high mechanical properties and corrosion resistance, while retaining the excellent tribological properties of ternary Mo–Cu–N coatings. Full article

Poly(methyl acrylate)-b-poly(N-vinyl pyrrolidone/maleic anhydride/styrene) (PMA-b-P (NVP/MAH/St)) quaternary amphiphilic block copolymer prepared by reversible addition-fragmentation chain transfer (RAFT) was used to improve the anti-hydrolysis and dispersion properties of aluminum nitride (AIN) powders that were modified by copolymers. Its structure was characterized by Fourier transform infrared spectroscopy (FT-IR) and Hydrogen nuclear magnetic spectroscopy (¹H-NMR). The results demonstrate that the molecular weight distribution of the quaternary amphiphilic block copolymers is 1.35–1.60, which is characteristic of controlled molecular weight and narrow molecular weight distribution. Through charge transfer complexes, NVP/MAH/St produces a regular alternating arrangement structure. After being treated with micro-crosslinking, AlN powder modified by copolymer PMA-b-P(NVP/MAH/St) exhibits outstanding resistance to hydrolysis and can be stabilized in hot water at 50 °C for more than 14 h, and the agglomeration of powder particles was improved remarkably. Full article

Nitride and carbide ternary coatings improve the wear and corrosion resistance of carbon steel substrates. In this work, Ti-W-N and Ti-W-C coatings were deposited on AISI 1060 steel substrates using reactive radio frequency (RF) magnetron sputtering. The coatings were designed as monolayers, bilayers, and multilayers of 40 periods. The coatings were obtained with simultaneous sputtering of Ti and W targets. The microstructure, composition, and electrochemical properties were investigated by techniques such as X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), atomic force microscopy (AFM), electrochemical impedance spectroscopy (EIS), and potentiodynamic polarization. XRD results shower a mix of binary TiN and W₂N structures in the Ti-W-N layer, a ternary phase in Ti-W-C layers, in addition of a quaternary phase of Ti-W-CN in the multilayers. The analysis of the XPS demonstrated that the atomic concentration of Ti was more significant than W in the Ti-W-N and Ti-W-C layers. The lowest corrosion rate (0.19 mm/year⁻¹) and highest impedance (~10 kΩ·cm²) out of all coatings were found in n = 40 bilayers. In the simulation of equivalent electrical circuits, it was found that the Ti-W-N coating presented three processes of impedance (Pore resistance + Coating + Inductance). However, the multilayer (n = 40) system presented a major dielectric constant through the electrolyte adsorption; therefore, this caused an increase in the capacitance of the coating. Full article

Multi-element material coating systems have received much attention for improving the mechanical performance in industry. However, they are still focused on ternary systems and seldom beyond quaternary ones. High entropy alloy (HEA) bulk material and thin films are systems that are each comprised of at least five principal metal elements in equally matched proportions, and some of them are found possessing much higher strength than traditional alloys. In this study, CrVTiNbZr high entropy alloy and nitrogen contained CrVTiNbZr(N) nitride coatings were synthesized using high ionization cathodic-arc deposition. A chromium-vanadium alloy target, a titanium-niobium alloy target and a pure zirconium target were used for the deposition. By controlling the nitrogen content and cathode current, the CrNbTiVZr(N) coating with gradient or multilayered composition control possessed different microstructures and mechanical properties. The effect of the nitrogen content on the chemical composition, microstructure and mechanical properties of the CrVTiNbZr(N) coatings was investigated. Compact columnar microstructure was obtained for the synthesized CrVTiNbZr(N) coatings. The CrVTiNbZrN coating (HEAN-N165), which was deposited with nitrogen flow rate of 165 standard cubic centimeters per minute (sccm), exhibited slightly blurred columnar and multilayered structures containing CrVN, TiNbN and ZrN. The design of multilayered CrVTiNbZrN coatings showed good adhesion strength. Improvement of adhesion strength was obtained with composition-gradient interlayers. The CrVTiNbZrN coating with nitrogen content higher than 50 at.% possessed the highest hardness (25.2 GPa) and the resistance to plastic deformation H³/E*² (0.2 GPa) value, and therefore the lowest wear rate was obtained because of high abrasion wear resistance. Full article

Orthodontic adhesives with antimicrobial and remineralizing properties may be an alternative to control white spot lesions around brackets. The aim of this study is to develop an experimental orthodontic adhesive containing boron nitride nanotubes (BNNT) and alkyl trimethyl ammonium bromide (ATAB). Methacrylate (BisGMA and TEGDMA) monomers were used to formulate the adhesives. Four experimental groups were produced with the addition of 0.1 wt.% BNNT (G_BNNT); 0.1 wt.% ATAB (G_ATAB); and 0.2 wt.% BNNT with ATAB (G_BNNT/ATAB); in the control group, no fillers were added (G_Ctrl). The degree of conversion, cytotoxicity, softening in solvent, contact angle and free surface energy, antibacterial activity, shear bond strength, and mineral deposition were evaluated. Adhesives achieved degree of conversion higher than 50% and cell viability higher than 90%. G_BNNT and G_ATAB adhesives exhibited reduced softening in solvent. Mean free surface energy was decreased in the G_BNNT adhesive. Significant reduction in bacterial growth was observed in the G_BNNT/ATAB. No statistical difference was found for shear bond strength. Mineral deposition was found in G_BNNT, G_ATAB, and G_BNNT/ATAB groups after 14 and 28 days. The addition of 0.2% BNNT/ATAB to an experimental orthodontic adhesive inhibited bacterial growth and induced mineral deposition without affecting the properties of the material. Full article

SrLi₂{Li[CoN₂]}, an isostructural variant of Li₄SrN₂, has been synthesised as black single crystals from a reaction between Li₂[(Li,Co)N] and Sr₂N, at 973 K using a Li flux in a sealed tantalum ampoule. Single crystal diffraction refinements gave a tetragonal unit cell, which upon closer inspection showed a monoclinic supercell. This supercell allowed, for the first time, the refinement of the occupation of metal atoms along the infinite chains in the structure, resulting in the chemical formula SrLi₂{Li_0.65Co_0.35[Co_0.65Li_0.35N₂]}. This revealed a clear preference for the Li and Co atoms to alternate along the chains. Magnetic measurements showed the sample to be a Curie paramagnet, with Co(I) being in a high-spin S = 1 configuration. Full article

The quaternary series Zn₂NCl_1−yBr_y and Zn₂NBr_1−yI_y were synthesized from solid-liquid reactions between zinc nitride and the respective zinc halides in closed ampoules, and the evolution of their crystal structures was investigated by single-crystal and powder X-ray diffraction. Zn₂NX_1−yX′_y (X, X′ = Cl, Br, I) adopts the anti-β-NaFeO₂ motif in which each nitride ion is tetrahedrally coordinated by four zinc cations, and the halide anions are located in the voids of the skeleton formed by corner-sharing [NZn₄] tetrahedra. While Zn₂NCl_1−yBr_y crystallizes in the acentric orthorhombic space group Pna2₁ (No. 33), isotypic to Zn₂NX (X = Cl, Br), the structure of Zn₂NBr_1−yI_y is a function of the iodide concentration, namely, Zn₂NBr (Pna2₁) for low iodine content and Zn₂NI (Pnma) for higher (y ≥ 0.38). Full article