Formation Of AlN Research Articles

Influence of the reactive gas mixture on the superconducting properties of nitrogen-doped aluminum thin films

We present a correlation between disorder and superconducting properties in nitrogen-doped aluminum thin films, ranging from a few nitrogen impurities to the insulating limit due to AlN formation. Samples were deposited via reactive sputtering on (100) silicon substrates with native oxide at room temperature. Our findings show that adding nitrogen increases the superconducting critical temperature (Tc) compared to pure metal films. By varying the nitrogen/argon ratio up to 6 %, we observed a dome-like Tc behavior: 2 K at low concentrations, peaking at 3.3 K at intermediate concentrations, and then dropping as the samples become insulating (≈ 4.4 %). Increasing nitrogen raises resistivity and shifts the material from metallic to semiconductor-like behavior. Disorder impacts the upper critical field, starting at 0.2 T for low nitrogen content and reaching up to 3.2 T for nitrogen-rich samples with Tc = 2.2 K. Current-voltage curves reveal typical vortex dissipation, as expected for type II superconductors.

Enhanced mechanical properties of SPS sintered h–BN based ceramics with Al3BC3 addition

A novel h–BN based ceramics, fabricated through spark plasma sintering, was developed by incorporating varying Al3BC3 additives. At high temperatures, Al3BC3 reacted with h–BN, resulting in the in–situ formation of AlN, B4C, and C. AlN acted as the primary reinforcement distributed along the grain boundaries of h–BN, creating a structural framework that filled internal pores and improved material density. DFT calculations highlighted favorable bonding at the interfaces between h–BN (100) and AlN (100) surfaces, and this robust bonding contributed to further enhancing their thermodynamic stability and mechanical properties. Upon reaching the Al3BC3 addition of 30 wt%, the h–BN–based composite ceramics exhibited optimal comprehensive performance, and the corresponding relative density, flexural strength, fracture toughness, and vickers hardness reached values of 96.86 %, 229.36 ± 2.14 MPa, 2.81 ± 0.03 MPa·m1/2, and 175.87 ± 8.81 kg·mm−2 respectively.

Low-defect and stress-free AlN(0001) nanoprisms and microrods selectively grown on micro-patterned c-sapphire substrate by plasma-assisted molecular beam epitaxy

This paper describes different growth modes of AlN layers on micro-cone patterned c-sapphire substrates (μ-PSSs) using plasma-assisted molecular beam epitaxy. Ordered arrays of AlN nanoprisms and microrods were selectively grown on the tips of μ-PSS's microcones according to a bottom-up formation mechanism using sequential migration enhanced and metal-modulated epitaxy (MME) under metal-rich growth conditions at 820 °C. Transmission electron microscopy revealed structurally perfect AlN regions above the tips of the μ-PSSs, which initiate as inverted nanopyramids with {1011¯} side faces, evolving into hexagonal nanoprisms with orientations of {11¯00} and (0001) for side and top surfaces, respectively. The diameter and height of these ordered hexagonal nanoprisms, which have a 60% probability of nucleating, were about 1 μm. Long-term MME growth of these nanoprisms in both vertical and lateral directions led to the formation of AlN(0001) microrods with a maximum possible diameter of two micrometers and a height of up to 6 μm. Atomic force microscopy revealed a mixed step-flow and 2D nucleation growth mechanism for the flat tops of these AlN nanoprisms and microrods with an average surface roughness of 1–2 monolayers. Micro-Raman spectroscopy demonstrated narrow E2 (high) linewidths of 3.8 and 4.2 cm−1 for essentially stress-free AlN nanoprisms and microrods, respectively.

Van der Waals epitaxial AlGaN/GaN growth on hexagonal BN via two-dimensional N-induced dislocation slip

We demonstrate the epitaxial growth of nitride heterojunction structures on two-dimensional materials. The growth behavior of Al atoms on hexagonal boron nitride (h-BN) involves preferential adsorption and diffusion along the N-top position, considerably improving AlN formation in the early stage of nucleation. Preferential N adsorption enables h-BN to provide a natural N surface for the substrate. Moreover, the natural N surface provided by h-BN can induce three-dimensional island-like order merging of the upper AlN layer, promoting dislocation slip annihilation. The dislocations annihilation depth of GaN films was shortened to 870 nm, resulting in an order of magnitude decrease in the density of screw dislocations to 5.50 × 107 cm−2 and considerable improvement in the performance of HEMT devices on SiC. Therefore, h-BN films can be used as two-dimensional insertion layers to obtain high-quality van der Waals epitaxial nitride films in GaN-based HEMT devices.

Influence of nano-BN inclusion and mechanism involved on aluminium-copper alloy.

Taking advantage of the high specific surface area of the nanoparticles, boron nitride (BN) nanoparticles were incorporated into the semi-solidified aluminium-copper alloy Al-5Cu-Mn (ZL201) system during the casting process, and its properties and enhancement mechanism were studied. The results shown that the BN in the new composite material is more uniformly distributed in the second phase (Al2Cu), which can promote grain refinement and enhance the bonding with the aluminium-based interface, and the formation of stable phases such as AlB2, AlN, CuN, etc. makes the tensile strength and hardness of the material to be significantly improved (8.5%, 10.2%, respectively). The mechanism of the action of BN in Al2Cu was analyzed by establishing an atomic model and after calculation: BN can undergo strong adsorption on the surface of Al2Cu (0 0 1), and the adsorption energy is lower at the bridge sites on the two cut-off surfaces, which makes the binding of BN to the aluminum base more stable. The charge transfer between B, N and each atom of the matrix can promote the formation of strong covalent bonds Al-N, Cu-N and Al-B bonds, which can increase the dislocation density and hinder the grain boundary slip within the alloy.

High-Temperature Oxidation Behavior of FeCoCrNi+(Cu/Al)-Based High-Entropy Alloys in Humid Air

Previous studies showed some transition metal high-entropy alloy (HEA) compositions can have good oxidation resistance in air up to 800 °C. Four equiatomic HEAs have been developed based on FeCoCrNi with additions of Mn, Cu, Al or Al+Cu. The oxidation behavior of these HEAs was compared in humid (10 vol.% H2O) air at 800 °C for 100–500 h to investigate the influence of water vapor on the oxidation mechanisms. The Cu- and Al-containing alloys exhibited improved oxidation resistance over the Mn composition. For the Cu-containing alloy, a local attack of the Cu-rich phase was observed, which formed an Fe/Ni/Co/Cr spinel that was surrounded by Cr2O3. This oxide was thicker for the humid air atmosphere when compared to dry air, and the transition of the Cu oxide to the spinel was accelerated. The Al-containing HEA formed a thin Al2O3 scale with humidity suppressing AlN formation and forming a smoother oxide layer. The Al+Cu composition had the highest overall oxidation resistance (minimal local attack, no nitridation) and also showed a smooth oxide scale topography under humid air oxidation as opposed to a plate-like, rougher scale under dry air.

Strain and phase evolution in TiAlN coatings during high-speed metal cutting: An in operando high-energy x-ray diffraction study

We report on phase and strain changes in Ti1-xAlxN (0 ≤ x ≤ 0.61) coatings on cutting tools during turning recorded in operando by high-energy x-ray diffractometry. Orthogonal cutting of AISI 4140 steel was performed with cutting speeds of 360–370 m/min. Four positions along the tool rake face were investigated as a function of time in cut. Formation of γ-Fe in the chip reveals that the temperature exceeds 727 °C between the tool edge and the middle of the contact area when the feed rate is 0.06 mm/rev. Spinodal decomposition and formation of wurtzite AlN occurs at the positions of the tool with the highest temperature for the x ≥ 0.48 coatings. The strain evolution in the chip reveals that the mechanical stress is largest closest to the tool edge and that it decreases with time in cut for all analyzed positions on the rake face. The strain evolution in the coating varies between coatings and position on the rake face of the tool and is affected by thermal stress as well as the applied mechanical stress. Amongst others, the strain evolution is influenced by defect annihilation and, for the coatings with highest Al-content (x ≥ 0.48), phase changes.

Effect of nitrogen pressure on the fabrication of AlCrFeCoNiCu0.5 high entropy nitride thin films via cathodic arc deposition

In the past two decades, high entropy alloy (HEA) coatings have attracted great attention due to their superior mechanical properties, outstanding corrosion and oxidation resistance, and exceptionally high thermal stability. In comparison to HEA thin films, high entropy nitrides (HENs) exhibit higher mechanical strength and chemical inertness. In this work, AlCrFeCoNiCu0.5 HEA and HEN thin films were fabricated using a filtered cathodic arc. By regulating the deposition pressure from 0.0005 Pa (HEA thin film) to 0.05 Pa, the nitrogen concentration in each thin film was precisely controlled to tune the mechanical properties. Scanning transmission electron microscopy-energy dispersive spectroscopy revealed that the nitrogen concentration of the films was up to 21.2 at. % at the pressure of 0.05 Pa. The reduced effect of preferential sputtering increased aluminum concentration from 8.3 ± 1.5 to 12.9 ± 2.2 at. % as pressure increased up to 0.05 Pa. X-ray photoelectron spectroscopy further confirmed the formation of AlN and CrN at pressures of 0.01–0.05 Pa. The highest hardness and elastic modulus of the HEN film were 12.4 ± 0.6 and 347.3 ± 17.7 GPa, respectively, which were 84.8% and 131.4% higher than those of the HEA thin film.

Spectroscopy and Photochemistry of OAlNO and Implications for New Metal Chemistry in the Atmosphere.

A new aluminum-bearing species, OAlNO, which has the potential to impact the chemistry of the Earth's upper atmosphere, is characterized via high-level, ab initio, spectroscopic methods. Meteor-ablated aluminum atoms are quickly oxidized to aluminum oxide (AlO) in the mesosphere and lower thermosphere (MLT), where a steady-state layer of AlO then builds up. Concurrent formation of nitric oxide (NO) in the same region of the atmosphere will lead to the bimolecular formation of the OAlNO molecule. Molecular orbital analysis provides fundamental insights into the chemical bonding and energetic arrangement of the triplet (1 3A″) ground state and singlet (1 1A') excited-state species of OAlNO. Additionally, unpaired electrons on the terminal oxygen atom of triplet (1 3A″) OAlNO cause it to be reactive to atmospheric species, potentially impacting climate science and high-altitude chemistry. The triplet (1 3A″) ground-state species exhibits a large permanent dipole moment useful for rotational spectroscopic detection; however, similar rotational constants to the singlet (1 1A') excited-state species will hamper differentiation in a spectrum. Strong infrared intensities will assist in detection and discrimination of the different spin states and isomers. Repulsive electronic excited states of OAlNO will lead to photolysis of the Al-N bond and formation of various electronic states of AlO + NO through nonadiabatic pathways. Reaction through the OAlNO intermediate represents a means for the production of electronically excited AlO, leading to new chemistry in the atmosphere. Excitation to higher-lying electronic states will lead to fluorescence with a minor Stokes shift, useful for laboratory investigation. Such physical properties of this molecule will allow for new, unexplored chemical pathways in the MLT to be considered.

Decomposition pathways in nano-lamellar CVD Ti0.2Al0.8N

Recent progress in chemical vapour deposition (CVD) technology has enabled synthesis of metastable cubic Ti1−xAlxN coatings with x as high as 0.8–0.9. These coatings have unique micro- and nano-structures consisting of grains with epitaxially grown nanolamellae with different Al/Ti ratios, and exhibit exceptional hardness and resistance to wear and oxidation. Here, the thermal stability and decomposition of nano-lamellar CVD Ti0.2Al0.8N at temperatures between 800 and 1000 °C have been investigated using a combination of cross-sectional transmission X-ray nano-diffraction and scanning transmission electron microscopy. The decomposition started by formation of hexagonal AlN (h-AlN) in the grain boundaries throughout the coating. Below 900 °C, only limited further decomposition of the grain interiors occurred. At higher temperatures the formation of grain boundary h-AlN was followed by a bulk transformation of the nano-lamellar structure, starting at the top of the coating and subsequently sweeping inwards. The bulk transformation occurred initially through spinodal decomposition, followed by transformation of the Al-rich cubic phase to h-AlN, leading to a coarsened structure with Ti-rich domains in a h-AlN matrix. The behaviour is explained by the higher capability of grain boundaries and free surfaces to accommodate the volumetric expansion from the h-AlN formation. The results increase our understanding of the complicated decomposition processes in these metastable cubic coatings, which are of utmost importance from both technological and scientific perspectives.

Thermal-induced decomposition and mechanical properties of AlN/CrN superlattice coating

Here, the thermal-induced decomposition and mechanical properties of AlN/CrN superlattice coating with modulation period of ∼8 nm are investigated in detail. Introduction of CrN template layers stabilizes the cubic growth of AlN layers, where the coherent AlN/CrN coating exhibits the higher hardness value of ∼24.1 GPa than CrN (∼16.9 GPa) and AlN (∼18.5 GPa) monolithic coatings. After thermal exposure, the AlN/CrN coating decomposes into stable body-centered cubic Cr and wurtzite AlN via intermediate phases of hexagonal Cr2N and cubic AlN. Especially, the formation of metastable cubic AlN is observed due to the destruction of coherent interfaces. Meanwhile, the thermal load leads to the grain deformation, which causes the change of AlN and CrN sublayers from the crossover to pinch-off to finally dissociation. The driving force of grain deformation mainly arises from the N-loss of CrN sublayers and the high-density stacking faults formation of AlN sublayers. Furthermore, the occurrence of stacking faults and h-Cr2N phase offset the softening effect caused by the thermal decomposition. Correspondingly, the hardness almost remains unchanged between 900 and 1100 °C.

Three bond modes of basic refractories used for Ruhrstahl Heraeus degassing process

AbstractMagnesia–spinel brick and unburnt periclase–spinel–Al brick are being employed as a substitution of traditional magnesia–chrome brick in the chromium‐free campaign of lining materials in Ruhrstahl Heraeus (RH) degasser. These three materials are investigated, in terms of physical properties, corrosion resistance and flexibility by wedge splitting test. Tracking their physical alterations and chemical reactions through burning or heating, three bond modes are discovered. Magnesia–chrome brick is subject to a series of phase transformation with rising temperature to yield a liquid envelop around chromite‐ore particles, to further form porous rim while liquid is gradually absorbed by surrounding magnesia and eventually to precipitate secondary chromite spinel lied between magnesia particles by thoroughly dissociating chrome ore. The precipitated chromite spinel functions as the featured bond that enhances hot strength and corrosion resistance to slag, and additionally liquid coexistence improves the flexibility. The direct bond mode of magnesia particles in magnesia–spinel brick endures slag penetration by immanent character of MgO. Spinel incorporation in magnesia effectively improves thermal shock resistance. Due to minor negative value of permanent linear change after reheating, further sintering (densifying) in using at high temperature would bring a risk of loosening and open joints of magnesia–spinel lining. While used in RH degasser, unburnt periclase–spinel–Al bricks undergo a miraculous process of metallic Al melting, gaseous AlN and AlON formation, MgAlON whiskers germination combined with gaseous Mg reduced, and micron‐size whisker network bond domination in their matrix. Such a whisker‐network bond renders the material a successful eco‐friendly alternative to magnesia–chrome refractory.

Superior oxidation resistance of the chemically complex but structurally simple Ti-Al-Ta-Ce-Si-La-B-nitride

Alloying (Ti,Al)N with Ta, CeSi2 or LaB6 is beneficial for both hardness and thermal stability. Here we show that their different mechanisms allow for a cumulative improvement when alloyed together, which is especially pronounced for the oxidation resistance. During isothermal oxidation treatments in ambient air at 900 °C (for up to 25 h), Ti0.44Al0.44Ta0.12N allows for a parabolic scale growth rate constant kp of 6.039 × 10-5 µm2/s. This is reduced to 2.074 × 10-5 and even 0.399 × 10-5 µm2/s when alloying with 2 mol% CeSi2 respectively CeSi2 + LaB6 (1 mol% each). The oxide scale growth kinetics for the latter can be even better described by a logarithmic or cubic law. In the as-deposited state the CeSi2 and CeSi2 + LaB6 alloyed (Ti,Al,Ta)N are single-phase fcc structured providing an indentation hardness of 32.6 ± 1.5 and 37.8 ± 1.5 GPa, combined with an indentation modulus of 496 ± 22 and 496 ± 14 GPa, respectively. After vacuum-annealing at 1000 °C, their hardness is still 33.0 ± 1.6 and 34.8 ± 1.1 GPa, and noticeable formation of hexagonal AlN and TaNx phases can only be detected by X-ray diffraction when annealed at temperatures above 1200 °C.Using CeSi2 and LaB6 instead of their elemental form is furthermore beneficial for the target production itself, as Ce and La are highly reactive.

Tribological Properties and Cutting Performance of AlTiN Coatings with Various Geometric Structures

The development of advanced machining techniques requires high-performance tool coatings. To improve the wear resistance and cutting performance of AlTiN coatings, a structure optimization strategy involving bias control and a nano-multilayer architecture strategy is presented. The investigated AlTiN coatings were deposited by cathodic arc evaporation and studied with regard to phase structure, hardness, adhesion, and tribological properties by a combination of X-ray diffraction, nanoindentation, scratch, and ball-on-disk friction tests. A high bias potential (up to −120 V) with enhanced adatom mobility suppressed the formation of the wurtzite structure AlN in AlTiN. In addition, the epitaxial growth of Al0.67Ti0.33N on Al0.5Ti0.5N in the AlTiN nano-multilayer could also promote the single-phase structure. The hardness of AlTiN-based coatings with a dominated cubic structure was 3–4 GPa higher than conventional ones. In addition, the interlayer interfaces in the Al0.67Ti0.33N/Al0.5Ti0.5N multilayer could deflect the cracks and thus improve the fracture toughness. As a consequence, the Al0.67Ti0.33N/Al0.5Ti0.5N multilayer with enhanced mechanical properties obtained the lowest wear rate of 1.1 × 10−5 mm3/N·m and the longest cutting lifetime of 25 min during dry turning the SUS304 stainless steel.

Formation, evolution and remove behavior of manganese-containing inclusions in medium/high manganese steels

The effect of manganese content, aluminium content, top slag and stirring on manganese-containing inclusions characteristics was investigated by laboratory thermal experiments and precipitation thermodynamics calculation. The results indicated that the types of manganese-containing inclusions in manganese steel were mainly single MnS, MnS–Al2O3, MnS–TiN and MnS–Al2O3–TiN complex inclusions. The morphology of manganese-containing inclusions was transformed from spherical and ellipsoidal to polyhedral as result of manganese content increased, which is attributed to large solidus-liquidus phase difference of high manganese steel, promoting the formation of type III MnS. It is also found that the manganese-containing inclusions shows irregular morphology with clear angularities after addition of aluminium, which was determined by both formation of flaky AlN and type III MnS with polygonal caused by increased of activity coefficient of S and the surface tension of molten steel. Furthermore, the manganese-containing inclusions in manganese steel is considered MnS–MnO type with top salg, in which patchy or multipoint shape MnS is embedded on the surface of oxide. The force field analysis in induction stirring demonstrated that the inclusion particles are removed by top slag and refractory adsorption under the action of strong electromagnetic force and buoyancy. This work provides an improved understanding for the controlling and removing of manganese-containing inclusions in high quality medium/high manganese steel.

Evolution of microstructure, mechanical and thermal properties with varied oxygen contents in TiAlON coatings

In recent years, TiAlON coatings have attracted broad attention in the machining field for their excellent toughness and machining performance. Here, we explore the microstructure, mechanical properties and thermal stability of Ti-Al-O-N coatings with the O/(O + N) ratio from 0 to 1. Combined experiments and first-principle calculations show that metal vacancies induced by charge balancing is the main incentive for increased non-metal/metal ratio and decreased lattice constant with increasing O concentration. Ti0.42Al0.58N0.95, Ti0.41Al0.59(O0.08N0.92)1.02 and Ti0.41Al0.59(O0.18N0.82)1.13 coatings reveal a single-phase face-centered cubic (fcc) structure and almost constant hardness of ∼32 GPa. Further increasing oxygen content leads to the formation of amorphous oxides. Attributed to the negative effect of metal vacancies, weaker metal‑oxygen bond and amorphous oxides, the hardness values of Ti0.42Al0.58(O0.57N0.43)1.25, Ti0.40Al0.60(O0.79N0.21)1.39 and Ti0.41Al0.59O1.52 are reduced to 27.7 ± 1.1, 22.5 ± 0.6 and 10.6 ± 0.7 GPa, respectively. All coatings present the age-hardening ability during annealing, where the temperatures of hardness peak for the O-containing nitride coatings are higher than that for Ti0.42Al0.58N0.95. This beneficial effect on the thermal stability can be attributed to the retarded wurtzite AlN formation and the precipitation strengthening of Al-containing oxides. However, for N-free Ti0.41Al0.59O1.52 coatings, the transformation of anatase-rutile TiO2 conduces to inferior thermal stability.

Effects of argon/nitrogen sputtering gas on the microstructural, crystallographic and piezoelectric properties of AlN thin films

The growth of highly crystalline c-plane AlN ‹002› is extremely difficult, entailing high temperature and ultra-high vacuum condition. In sputtering technique, the addition of nitrogen into argon sputtering gas can significantly assist the formation of AlN ‹002› at low temperature. We incorporated purified nitrogen gas and observed the consistent formation of single crystal ‹002› AlN thin film layer sputter-deposited on Mo/Si substrate from the AlN ceramic target. Small presence of oxygen content within AlN crystal relates to the preferential growth of AlN ‹002›. High oxygen content in AlN thin film due to the use of unpurified nitrogen and argon only sputtering gas prefers the formation of AlN ‹100›. Different AlN crystal structure has shown distinct thin film properties and piezoelectric response. This work provides a method to control the crystal structure of the sputter-deposited AlN thin film layer, either c-plane AlN ‹002›, a-plane AlN ‹100› or polycrystalline AlN.

Temperature dependence of crystal growth behavior of AlN on Ni–Al using electromagnetic levitation and computer vision technique

Bulk AlN single crystal has a great demand as a substrate material for AlGaN-based optical and electronic devices such as deep ultraviolet light-emitting diodes and high-power transistors. We have previously proposed a novel solution-growth method using Ni–Al solution with an in-situ observation system for solution growth of AlN crystal using electromagnetic levitation. In this paper, to investigate AlN formation behavior on 40 mol%Al–Ni droplets, two precisely synchronized high-speed cameras from the horizontal and vertical directions were installed. AlN formation behavior was evaluated quantitatively using computer vision image processing techniques. Based on the results, we demonstrated the growth of thick AlN film at 2030 K for 1 h. A 3.8-μm-thick c-axis oriented AlN film successfully formed on the droplet, and the film was also oriented in-plane. The + c-direction AlN film grew towards the droplet center from the surface by reacting dissolved nitrogen and Al atoms.

The roles of Al addition and heat treatment temperature on chloride corrosion of 9Cr alloy steel

The effects of 0.7% Al and heat treatment temperatures on chloride corrosion of 9Cr alloy steel were investigated through potentiodynamic polarization measurement and salt spray test. Al promoted the formation of Al2O3-rich inclusions and AlN, thus reducing the pitting potential at initial stage. However, Al addition reduced weight loss after longer time by optimizing the α/γ * value, compactness and element distribution of rust layer. The mechanism of corrosion resistance changing with heat treatment temperature was understood from the decrease in the pitting resistance equivalent number caused by (Fe, Cr)23C6 precipitation and the microgalvanic corrosion between fresh martensite and tempered martensite/ferrite.

Alloying and Processing of Medium Manganese Steels for Forging Applications

The processability of medium Mn-containing steels (MMnS) with 4–10% Mn is discussed in light of their continuous casting behavior. Precipitation, phase transformation, extension, or shift of solidification intervals induced by various alloying concepts are decisive in controlling the hot ductility. It turns out that the formation of complex AlN and MnS precipitates as well as δ‑ferrite solidification deteriorates the high temperature ductility. The concept of MMnS has been used to develop air-hardening forging steels with 4% Mn. The alloy design and the heat treatment parameters have been varied with a focus on the prevention of Mn embrittlement as well as the formation of fine austenite grains during intercritical annealing. It is shown that the addition of B and Mo increases the impact toughness, although the effectiveness of each element varies depending on the heat treatment conditions. The impact toughness can be significantly improved by the introduction of a globular metastable austenitic phase. Compared to conventional quenched+tempered steels, an improved cyclic strength for an ultimate tensile strength level of more than 1300 MPa can be achieved.