Papers by Keyword: AlN

Abstract: The influence of small contents of nitrogen present as an impurity in 0.3C Al-bearing steels, which were processed through thermomechanical rolling followed by direct quenching and partitioning (TMR-DQP), was examined in respect of room temperature tensile ductility and impact toughness. Two similar chemical compositions (in wt.%): Fe-0.3C-0.6Si-1.1Al (High-Al) with different N contents of 10 and 30 ppm were selected for this study. In addition, two other DQP steels with compositions: Fe-0.3C-1.0Si (High-Si) and Fe-0.3C-0.5Si-0.5Al (Al-Si), both containing about 30 ppm nitrogen, were also included in the study to compare the properties. Detailed metallographic studies using FESEM-EDS, TEM, EPMA and XRD combined with tensile testing and fractographic analysis indicated that already 30 ppm of nitrogen could impair tensile ductility of TMR-DQP processed High-Al steel in comparison to that with 10 ppm nitrogen. Similarly, the effect was adverse also in Al-Si steel (30 ppm N) despite its reduced Al content (0.5 wt.%), but High-Si steel (Al < 0.002 wt.%, N 30 ppm) did not show any such detrimental effect on tensile ductility. Extensive material characterization verified that even 30 ppm of nitrogen could impair ductility of Al-bearing steels, essentially due to the presence of AlN inclusions, despite that TMR-DQP processing enabled stabilization of 6–10% retained austenite (RA) in the steels. The capacity of RA in promoting improved ductility and strain hardening capacity was impaired by the presence of these inclusions. In contrast, impact toughness transition temperature T_28J was not clearly affected with Al-Si when compared to low-N High-Al steel, although excessive splitting in Al-Si caused pronounced scatter in the results and increase in upper shelf impact toughness.

Abstract: The article describes the methods for producing thin films and structures based on SiC, GaN and their SiC – AlN and Al – GaN solid solutions, as well as mathematical models of film growth and properties-behavior of the I–V characteristics of heterostructures. Two models were developed for producing thin films and heterostructures based on SiC, GaN and their solid solutions. The first model makes it possible to determine the sputtering coefficient when producing films by high-frequency magnetron sputtering. In the second quantum-mechanical model, the equation for the gap of the mean field of condensate was built and the growth rate of a film on the crystalline substrate was determined. The current-voltage characteristic of the transistor based on the AlGaN / GaN heterosystem was provided. The models for the growth of heterostructure films made it possible to modify the technologies for producing perfect SiC crystals and SiC – AlN solid solutions. It was possible to offer a pilot plant for growing SiC crystals with improved control over the modes of induction high-temperature heating of the growth crucible.

Abstract: At present, in connection with the implementation of the sustainable development program, the use of wind farms is increasing every year. Their low pollution of the atmosphere, land, and waters leads to their widespread distribution. The greatest pollution is the process of recycling wind turbines and their parts (blades, housings, etc.) since the main materials used in them are plastic and fiberglass, which are difficult or not at all recyclable. In this regard, the issue of increasing the life cycle of wind turbines is acute. In this article, the possibility of using AlN composite is considered. The main purpose of this article is to study the possibility of using AlN reinforced Al matrix composites to replace the currently used construction aluminum alloys. The main methodologies are theoretical research, analysis of domestic and foreign publications related to the topic, as well as an experiment. The result of this study is the conclusion about the impossibility of using this composite material, due to its low corrosion properties.

Abstract: In this study, the advantages of the AlN electron blocking layer (EBL) for InGaN/GaN blue light-emitting diodes (LEDs) were investigated. The LEDs with the AlN EBL exhibited better optical performance over a wide range of carrier concentration due to the suppression of electron overflow. Furthermore, the AlN EBL with a thicker last barrier layer was investigated. The thicker last barrier layer was used to enhance Electrostatic Discharge (ESD) characteristic by the better current spreading effect.

Abstract: The three-dimensional growth chamber model was established by GAMBIT software, and the FLUENT software was used to simulate the Vapor Phase Epitaxy ( VPE ) growth AlN material. By changing parameters, results of simulation were obtained, in turn described the effect of uniformity and concentration of AlN. The study mainly focuses on the research of flow velocities of nitrogen and argon gas, the distance from the substrate to the inner tube mouth, the substrate front-back angular height difference, the inner tube diameter, and the substrate thickness. It is discovered through the research: above parameters play a very important role in the crystal growth of AlN film, and there are optimal parameter values. The structure of growth chamber is designed and optimized according to the simulation result. By using the simulation software, experimental costs can be greatly saved, which provides a theoretical basis for the optimal growth process of high quality AlN film, and has a certain guiding role for the actual growth process.

Abstract: AlN crystals are one of the representative III-V group semiconductor materials. AlN has good electric field characteristics, thermal conductivity and thermal stability. Owing to its wide direct band gap of 6.2eV [1], it can achieve a luminescent wavelength of 210 nanometers in deep ultraviolet, which is an ideal material for UV and deep UV LED devices. But preparation of AlN crystals with PVT for growing conditions demanding, 0.3-0.5 atm of high purity nitrogen atmosphere of growth and the growth of 2100-2400 K temperature [2, 3]. In this paper, two kinds of growth chamber structures are designed and compared. In order to ensure that the temperature gradient between the source material surface and the seed surface satisfy the crystal growth and keep stability in the larger transverse region, [4, 5] the crystal grown on the seed crystal can get better quality.

Abstract: Band structure calculations for radiofrequency-sputtered AlN-films doped with various 3d-transition-metals (TM: V, Cr, and Mn) were conducted to investigate the origin of the characteristic optical absorption structures. Experimentally evaluated crystal structures and lattice constants of the synthesized films were adopted for supercells. The model calculations showed that additional energy bands mainly consisting of 3d e and t states of TMs are formed in the band gap of AlN (6.2 eV), and that their potentials depend on the TM species. It was also shown that the Fermi levels of Cr- and Mn-doped AlN lie within the spin-up t band, while the Fermi level of V-doped AlN lies between the spin-up e and t bands. These findings imply that the materials have TM species-dependent, multiple absorption paths with lower energy than the band gap energy of AlN, resulting in optical absorption in the near-ultraviolet, visible, and infrared regions.

Abstract: AlN single crystals were prevented from cracking by simultaneous growth and evaporation of SiC substrates. The freestanding crystals (<1 mm thick) were proved continuous by synchrotron phase contrast imaging and used as a model system to investigate the type of dislocation structure near AlN/SiC interface by x-ray diffraction techniques. We have found that, unlike the situation in GaN films, where predominantly edge-type threading dislocations cross the layer along its normal, the dislocations configure to form mosaic structure. We suggest a theoretical model that describes the misfit stress relaxation in growing AlN crystal.

Abstract: In this paper, In Situ AlN particles reinforced magnesium matrix composites were fabricated. The results show that the AlN phases can be In Situ synthesized in AZ91D alloy with the addition of Mg₃N₂. The microstructure and phases of the matrix alloys and the composites were investigated by OM, SEM and XRD. The hardness and mechanical properties of the matrix alloys and the composites were also obtained. Compared with those of the matrix alloy, the grains of composites were refined obviously and the mechanical properties of composites were improved significantly. The microstructural analysis indicates that the AlN particles can act as the heterogeneous nucleation of α-Mg phases in the composites. The strengthening mechanism of the composites with AlN particles was discussed.

Abstract: Aluminum nitride, AlN, and titanium diborite,TiB₂, are covalent-based ceramics with wide technological applications. However, sintering of these ceramics using conventional methods of high pressure requires not only elevated temperatures but also long processing time. This causes excessive grain growth, which impairs strength and hardness. In the present work, 70%AlN-30%TiB₂ ceramic composites were sintered to relatively higher density and hardness by means of the Spark Plasma Sintering (SPS) at temperatures in the interval from 1500 to 1900°C in order to improve the properties of both compounds and decrease the processing time. The SPS was applied for different sintering temperatures and the effects on density, hardness and surface structure were evaluated. Maximum values obtained for density and hardness were 98.8% of the theoretical value and 13.7 GPa, respectively.