Search Results (14)

In the manufacturing sector, energy loss often stems mainly from wear. By improving the surface characteristics of alloys, we can substantially cut down on this kind of loss, which in turn boosts the efficiency of energy use. In this study, Fe₄₀Mn₁₉Cr₂₀Ni₂₀Mo₁ high-entropy alloy (HEA) with a face-centered cubic (FCC) structure was subjected to aluminum–nitrogen co-infiltration treatment via pack aluminizing and plasma nitriding, forming an aluminum–nitrogen co-infiltrated layer with a thickness of approximately 17 μm. An analysis was carried out on the microstructure, growth dynamics, and tribological behavior of the Al-N co-infiltrated layer across a broad temperature spectrum. The results showed that the surface hardness of the samples treated by aluminizing and Al-N co-infiltration reached 592 HV and 993 HV, respectively, which were significantly higher than that of the hot-rolled alloy (178 HV). The Al-N co-infiltrated HEA exhibited a low and stable friction coefficient as well as wear rate over a wide temperature range (20–500 °C), which was attributed to the formation of the Al-N co-infiltrated layer composed of AlN, CrN, and FeN phases. This study demonstrates that Al-N co-infiltration treatment is an effective surface modification technique, which can significantly enhance the hardness and tribological properties of high-entropy alloys over a wide temperature range. Full article

In this work, by using density functional theory (DFT) and time-dependent DFT (TD-DFT) a comprehensive theoretical study on the structural, electronic, optical, and vibrational properties of aluminum nitride (Al_xN_x) nanoparticles (NPs) is presented. More than thirty nanostructures were constructed based on an initial cubic-like Al₄N₄ building block, including one-dimensional (1D), two-dimensional (2D), and three-dimensional (3D) configurations, as well as asymmetric and defected geometries (also known as exotic geometries). The absorption spectrum was evaluated using the CAM-B3LYP functional while geometry optimizations and vibrational frequencies were performed using the PBE functional. All calculations were performed using the triple-ζ valence plus polarization basis set def2-TZVP. The optical spectra revealed strong geometry-dependent modulation of absorption, with red-shifted and broadened UV–Vis features emerging in elongated and low-symmetry geometries. IR analysis indicates a growing number and intensity of vibrational modes with increasing dimensionality, particularly in the 300–470 cm⁻¹ range, which corresponds to Al–N stretching and bending vibrations. Testing different exchange–correlation functionals showed that CAM-B3LYP is a good choice for excited-state calculations, matching well with the EOM-CCSD functional, which, while offering higher precision, imposes significantly higher computational requirements. Overall, the results demonstrate that structural variation in Al_xN_x NPs leads to tunable optoelectronic and spectroscopic behavior. These findings and calculations highlight the potential of AlN-based nanomaterials for applications in ultraviolet photonics, sensors, and future nanoscale optoelectronic devices. Full article

The rapid growth in population and industrialization have significantly increased global energy demand, placing immense pressure on finite and environmentally harmful conventional fossil fuel-based energy sources. In this context, the development of hybrid electrocatalysts presents a crucial solution for energy conversion and storage, addressing environmental challenges while meeting rising energy needs. In this study, the fabrication of a novel bifunctional catalyst, copper nickel aluminum spinel (Cu_0.5Ni_0.5Al₂O₄) supported on graphitic carbon nitride (GCN), using a solid-state synthesis process is reported. Because of its effective interface design and spinel cubic structure, the Cu_0.5Ni_0.5Al₂O₄/GCN nanocomposite, as synthesized, performs exceptionally well in electrochemical energy conversion, such as the oxygen evolution reaction (OER), the hydrogen evolution reaction (HER), and energy storage. In particular, compared to noble metals, Pt/C- and IrO₂-based water-splitting cells require higher voltages (1.70 V), while for the Cu_0.5Ni_0.5Al₂O₄/GCN nanocomposite, a voltage of 1.49 V is sufficient to generate a current density of 10 mA cm⁻² in an alkaline solution. When used as supercapacitor electrode materials, Cu_0.5Ni_0.5Al₂O₄/GCN nanocomposites show a specific capacitance of 1290 F g⁻¹ at a current density of 1 A g⁻¹ and maintain a specific capacitance of 609 F g⁻¹ even at a higher current density of 5 A g⁻¹, suggesting exceptional rate performance and charge storage capacity. The electrode’s exceptional capacitive properties were further confirmed through the determination of the roughness factor (Rf), which represents surface heterogeneity and active area enhancement, with a value of 345.5. These distinctive characteristics render the Cu_0.5Ni_0.5Al₂O₄/GCN composite a compelling alternative to fossil fuels in the ongoing quest for a viable replacement. Undoubtedly, the creation of the Cu_0.5Ni_0.5Al₂O₄/GCN composite represents a significant breakthrough in addressing the energy crisis and environmental concerns. Owing to its unique composition and electrocatalytic characteristics, it is considered a feasible choice in the pursuit of ecologically sustainable alternatives to fossil fuels. Full article

Enhanced hard coatings with exceptional mechanical and thermal qualities have prompted substantial study into multicomponent nitride systems. TiAl(Si)N coatings have emerged as viable possibilities owing to their remarkable hardness, thermal stability, and oxidation resistance. This work involved the fabrication of thickness-varied TiAl(Si)N gradient coatings using reactive magnetron sputtering, employing a controlled modulation of aluminum and silicon content across the film thickness. Three samples, with thicknesses of ~400 nm, ~600 nm, and ~800 nm, were deposited under uniform Ar/N₂ gas flow ratios, and their microstructural, mechanical, and tribological characteristics were rigorously examined. SEM investigation demonstrated a significant change across thicknesses. XRD results validated the emergence of a predominant cubic TiAl(Si)N phase alongside a secondary hexagonal AlN phase, signifying partial phase segregation. The nanoindentation results indicated that Sample 2 exhibited the maximum hardness (~38 GPa) and Young’s modulus (~550 GPa) due to an optimized equilibrium between solid solution strengthening and nanocomposite production. Tribological testing revealed that Sample 1 displayed the lowest and most consistent friction coefficient, corresponding to its superior H/E and H3/E2 ratios, which signify improved elasticity and resistance to plastic deformation. The findings emphasize that the implementation of a compositional gradient, especially in the distribution of Si and Al, markedly affects the microstructure and performance of TiAl(Si)N coatings. Gradient structures enhance the microstructure, optimize hardness, and increase the friction coefficient. Ongoing refinement of gradient profiles and deposition parameters may further improve the characteristics of TiAl(Si)N coatings, facilitating their wider industrial use. Full article

Nitrides of aluminum (Al) and titanium (Ti) mixtures have long been studied and used as commercial coatings because of their high hardness and high oxidation resistance due to the formation of an alumina layer on the coating surface. To fully understand the contribution of Al and Ti to the properties of the film, a combinatorial deposition approach was employed using half-disk targets. Film growth was carried out using a magnetron sputtering system powered by a 13.56 MHz radio frequency power supply with varying argon (Ar) and nitrogen (N₂) gas ratios. Depending on the location of the substrate relative to the target, atomic percent gradients of 0.60–0.70 Al and 0.30–0.40 Ti across the substrate surface were obtained from energy dispersive X-ray spectral analysis. X-ray diffraction peaks at 43.59°, 74.71° (face-centered cubic), and 50.60° (wurtzite) confirmed the presence of aluminum titanium nitride (AlTiN) mixtures, with an increasing amount of wurtzite phase at higher Al concentrations. For all samples, cauliflower-like nanograins were obtained and samples of the 80:20 Ar:N₂ gas pressure ratio showed the smallest grain size among the three gas ratio combinations. The 80:20 Ar:N₂ films revealed a relatively high hardness compared to the other gas ratios. All thin films exhibited good adhesion to 304 stainless steel substrates. Full article

The next generation of all-solid-state batteries can feature battery safety that is unparalleled among conventional liquid batteries. The garnet-type solid-state electrolyte Li₇La₃Zr₂O₁₂ (LLZO), in particular, is widely studied because of its high Li-ion conductivity and stability in air. However, the poor interface-contact between Li and the electrolyte (garnet) severely limits the development of solid electrolytes. In this study, we synthesize cubic phase Li_6.4La₃Zr_1.4Ta_0.6O₁₂ (LLZTO) using a secondary sintering method. In addition, a thin aluminum nitride (AlN) layer is introduced between the metal (Li) and the solid electrolyte. Theoretical calculations show that AlN has a high affinity for Li. Furthermore, it is shown that the AlN coating can effectively reduce the interface impedance between Li and the solid electrolyte and improve the lithium-ion transport. The assembled symmetric Li cells can operate stably for more than 3600 h, unlike the symmetric cells without AlN coating, which short-circuited after only a few cycles. The hybrid solid-state battery with a modified layer, which is assembled using LiFePO₄ (LFP), still has a capacity of 120 mAh g⁻¹ after 200 cycles, with a capacity retention rate of 98%. This shows that the introduction of an AlN interlayer is very helpful to obtain a stable Li/solid-electrolyte interface, which improves the cycling stability of the battery. Full article

The friction stir lap welding of AA5083 H111 aluminum alloy and S355J2 grade DH36 structural steel was investigated. A polycrystalline cubic boron nitride with tungsten and rhenium additives tool was used. According to visual inspection, radiographic examination, and tensile test, it was observed that the best results were obtained for rotation speeds of about 700–800 rpm, with a feed speed ranging between 1.3 and 1.9 mm/s. From the fatigue tests, it is possible to state that there was a preferential propagation of cracks in the part of the aluminum alloy base material. Furthermore, a different response to fatigue stress for samples extracted from the same weld at different positions was observed, which introduces an overall variability in weld behavior along the welding direction. The specimens obtained in the second part of the weld endured a larger number of cycles before reaching failure, which can be related to progressively varying thermal conditions, dissipation behavior, and better metal coupling as the tool travels along the welding line. Full article

A simple process to synthesize metal nitride particles was proposed using submerged arc discharge plasma in liquid nitrogen. Gibbs standard free energy was considered for the selection of the nitride-forming materials. In this study, titanium (Ti) and aluminum (Al) electrodes were used as raw materials for nitride particle preparation. Liquid nitrogen acted as a dielectric medium as well as a nitridation source in this process. A copper electrode was also used as a non-reactive material for comparison with the reactive Ti and Al electrodes. As the operating conditions of the experiments, the arc discharge current was varied from 5 A (low-power mode) to 30 A (high-power mode). The formation of titanium nitride (TiN) and aluminum nitride (AlN) was confirmed in the particles prepared in all experimental conditions by X-ray powder diffraction (XRD). The observation using a field emission scanning electron microscope (FE-SEM) and a field emission transmission electron microscope (FE-TEM) indicated that the synthesized TiN particles showed a cubic morphology, whereas AlN particles containing unreacted Al showed a spherical morphology. The experiments using different metal electrode configurations showed that the anode generated most of the particles in this process. Based on the obtained results, a particle formation mechanism was proposed. Full article

Thermal spraying of aluminum nitride (AlN) is a challenging issue because it decomposes at a high temperature. In this work, the use of suspension plasma spray (SPS) technology is proposed for the in situ synthesis and deposition of cubic-structured AlN coatings on metallic substrates. The effects of the nitriding agent, the suspension liquid carrier, the substrate materials and the standoff distance during deposition by SPS were investigated. The plasma-synthesized coatings were analyzed by X-ray diffraction (XRD), optical microscopy (OM) and scanning electron microscopy (SEM). The results show higher AlN content in the coatings deposited on a carbon steel substrate (~82%) when compared to titanium substrate (~30%) or molybdenum (~15%). Melamine mixed with pure aluminum powder produced AlN-richer coatings of up to 82% when compared to urea mixed with the Al (~25% AlN). Hexadecane was a relatively better liquid carrier than the oxygen-rich liquid carriers such as ethanol or ethylene glycol. When the materials were exposed to a molten aluminum–magnesium alloy at 850 °C for 2 h, the corrosion resistance of the AlN-coated carbon steel substrate showed improved performance in comparison to the uncoated substrate. Full article

Presented is a study on the original preparation of individual and in situ intimately mixed composite nanocrystalline powders in the titanium nitride-aluminum nitride system, Ti:Al = 1:1 (at.), which were used in high pressure (7.7 GPa) and high temperature (650 and 1200 °C) sintering with no binding additives for diverse individual and composite nanoceramics. First, variations in precursor processing pathways and final nitridation temperatures, 800 and 1100 °C, afforded a pool of mixed in the nanosized regime cubic TiN (c-TiN) and hexagonal AlN (h-AlN) composite nanopowders both with varying average crystallite sizes. Second, the sintering temperatures were selected either to preserve initial powder nanocrystallinity (650 °C was lower than both nitridation temperatures) or promote crystal growth and recrystallization (1200 °C was higher than both nitridation temperatures). Potential equilibration towards bimetallic compounds upon solution mixing of the organometallic precursors to nanopowders, monomeric Ti[N(CH₃)₂]₄ and dimeric {Al[N(CH₃)₂]₃}₂, was studied with ¹H and ¹³C NMR in C₆D₆ solution. The powders and nanoceramics, both of the composites and individual nitrides, were characterized if applicable by powder XRD, FT-IR, SEM/EDX, Vicker’s hardness, and helium density. The Vicker’s hardness tests confirmed many of the composite and individual nanoceramics having high hardnesses comparable with those of the reference h-AlN and c-TiN ceramics. This is despite extended phase segregation and, frequently, closed microsized pore formation linked mainly to the AlN component. No evidence was found for metastable alloying of the two crystallographically different nitrides under the applied synthesis and sintering conditions. The high pressure and high temperature sintering of the individual and in situ synthesis-mixed composite nanopowders of TiN-AlN was demonstrated to yield robust nanoceramics. Full article

To meet the requirements for high-performance products, the aerospace industry increasingly needs to assess the behavior of new and advanced materials during manufacturing processes and to ensure they possess adequate machinability, as well as high performance and an extensive lifecycles. Over the years, industrial research works have focused on developing new alloys with an increased thermal conductivity as well as increased strength. High silicon content aluminum (Al–Si) alloys, due to their increased thermal conductivity, low coefficient of thermal expansion, and low density, have been identified as suitable materials for space applications. Some of these applications require the use of intricate parts with tight tolerances and surface integrity. These challenges are often tied to the machining conditions and strategies, as well as to workpiece materials. In this study, experimental milling tests were performed on a rapidly solidified (RS) Al–Si alloy with a prominent silicon content (over 50%) to address challenges linked to material expansion in deep space applications. The tests were performed using a polycrystalline cubic boron nitride (PCBN) tool coated with amorphous diamond to reduce tool wear, material adhesion, surface oxidation, and particle diffusion. The effects of cutting parameters on part surface roughness and microstructure were analyzed. A comparative analysis of the surface with a conventionally utilized Al6061-T6 alloy showed an improvement in surface roughness measurements when using the RS Al–Si alloy. The results indicated that lower cutting speed and feed rate on both conventional and RS Al–Si alloys produced a better surface finish. Reduced vibrations were also identified in the RS Al–Si alloy, which possessed a stable cutting time at low cutting speeds but only displayed notable vibrations at cutting speeds above 120 m/min. Full article

The performance of transition metal nitride based coatings deposited by magnetron sputtering, in a broad range of applications including wear-protective coatings on cutting tools and components in automotive engines, is determined by their phase content. The classical example is the precipitation of thermodynamically-favored wurtzite-AlN while alloying TiN with Al to obtain ternary single phase NaCl-structure films with improved high-temperature oxidation resistance. Here, we report on reactive high-power impulse and direct current magnetron co-sputtering (HiPIMS/DCMS) growth of Ti_0.31Al_0.69N and Zr_0.48Al_0.52N thin films. The Al concentrations are intentionally chosen to be higher than theoretically predicted solubility limits for the rock salt structure. The goal is to investigate the effect of the incident Al⁺ energy E_Al⁺, controlled by varying the amplitude of the substrate bias applied synchronously with the Al⁺-rich portion of the ion flux from the Al-HiPIMS source, on the crystalline phase formation. For E_Al+ ≤ 60 eV, films contain predominantly the wurtzite phase. With increasing E_Al⁺, and thus, the Al subplantation depth, the relative fraction of the NaCl structure increases and eventually for E_Al⁺ > 250 eV, Ti_0.31Al_0.69N and Zr_0.48Al_0.52N layers contain more than 95% of the rock salt phase. Thus, the separation of the film forming species in time and energy domains determines the phase formation of Ti_0.31Al_0.69N and Zr_0.48Al_0.52N layers and enables the growth of the cubic phase outside of the predicted Al concentration range. The new film growth concept can be applied to the entire family of multinary transition metal aluminum nitrides, where one of the metallic film constituents is available in the ionized form while the other arrives as neutral. Full article

This work compares the deposition of aluminum nitride by magnetron sputtering on silicon to multilayer ceramic substrates. The variation of sputter parameters in a wide range following a fractional factorial experimental design generates diverse crystallographic properties of the layers. Crystal growth, composition, and stress are distinguished because of substrate morphology and thermal conditions. The best c-axis orientation of aluminum nitride emerges on ceramic substrates at a heater temperature of 150 °C and sputter power of 400 W. Layers deposited on ceramic show stronger c-axis texture than those deposited on silicon due to higher surface temperature. The nucleation differs significantly dependent on the substrate. It is demonstrated that a ceramic substrate material with an adapted coefficient of thermal expansion to aluminum nitride allows reducing the layer stress considerably, independent on process temperature. Layers sputtered on silicon partly peeled off, while they adhere well on ceramic without crack formation. Direct deposition on ceramic enables thus the development of optimized layers, avoiding restrictions by stress compensating needs affecting functional properties. Full article

Reactive plasma spraying is a promising technology for the in situ formation of aluminum nitride (AlN) coatings. Recently, it became possible to fabricate cubic-AlN-(c-AlN) based coatings through reactive plasma spraying of Al powder in an ambient atmosphere. However, it was difficult to fabricate a coating with high AlN content and suitable thickness due to the coalescence of the Al particles. In this study, the influence of using AlN additive (h-AlN) to increase the AlN content of the coating and improve the reaction process was investigated. The simple mixing of Al and AlN powders was not suitable for fabricating AlN coatings through reactive plasma spraying. However, it was possible to prepare a homogenously mixed, agglomerated and dispersed Al/AlN mixture (which enabled in-flight interaction between the powder and the surrounding plasma) by wet-mixing in a planetary mill. Increasing the AlN content in the mixture prevented coalescence and increased the nitride content gradually. Using 30 to 40 wt% AlN was sufficient to fabricate a thick (more than 200 µm) AlN coating with high hardness (approximately 1000 Hv). The AlN additive prevented the coalescence of Al metal and enhanced post-deposition nitriding through N₂ plasma irradiation by allowing the nitriding species in the plasma to impinge on a larger Al surface area. Using AlN as a feedstock additive was found to be a suitable method for fabricating AlN coatings by reactive plasma spraying. Moreover, the fabricated coatings consist of hexagonal (h-AlN), c-AlN (rock-salt and zinc-blend phases) and certain oxides: aluminum oxynitride (Al₅O₆N), cubic sphalerite Al₂₃O₂₇N₅ (ALON) and Al₂O₃. The zinc-blend c-AlN and ALON phases were attributed to the transformation of the h-AlN feedstock during the reactive plasma spraying. Thus, the zinc-blend c-AlN and ALON phases were not included in the feedstock and were not formed through nitriding of the Al. Full article