Papers by Keyword: Boron

Abstract: In this paper, the temperature dependence of charge carrier lifetimes in n-type 4H-SiC epitaxial layers is studied in a temperature range of 300-500 K. It is assumed that shallow (B) and deep (D) boron-related defects are the dominating lifetime killers in as-grown epitaxial layers. The thermodynamic behavior of these two types of defects is obtained from DLTS measurements, and implemented in the Shockley-Read-Hall (SRH) model to calculate lifetimes, using Gibbs free energies to describe the accurate temperature dependence for capture and emission processes of the defects. Calculation results show that the lifetimes controlled by shallow boron defects increase with increasing temperature, while D-defects give the opposite temperature dependence. The theoretical results are also compared to measured data from 10 kV 4H-SiC PiN-structures, showing that the temperature dependence of the effective lifetime can be changed by proton implantations, which gives rise to additional Z_1/2 defects that have similar temperature effects on lifetimes as D-related defects.

Abstract: Polymethyl methacrylate (PMMA) is a polymer that is a suitable biomaterial for applications such as bone cement and replacement hip joints because it is inert, non-toxic, and has good mechanical properties. Hydroxyapatite (HA) is among the most thoroughly investigated bioceramics because its composition is similar to that of human bone and it has excellent biocompatibility and osteoconductive properties. Moreover, HA can be modified to regulate its physiochemical properties. In this study, boron and strontium were co-substituted into HA (SrBHA) to improve its biological characteristics. Previous studies have shown that strontium can increase bone density, although it negatively affects bone production. Moreover, boron helps to regulate the calcium balance to prevent bone loss. PMMA/SrBHA composites were prepared with different concentrations of SrBHA powder and the effects on the mechanical properties of the composites were investigated. The composites were fabricated using twin-screw extruders and compressed into test specimens using compression molding machinery. When the SrBHA powder concentration was <10 phr, the SrBHA particles were uniformly dispersed throughout the composite via a continuous polymer matrix reaction. Moreover, this concentration produced the greatest increase in compressive strength compared to the sample with no SrBHA (127.4 MPa). The composites were analyzed using energy-dispersive X-ray analysis, Fourier-transform infrared spectroscopy, and X-ray diffraction to determine the dispersion of the reinforced nanoparticles. Scanning electron microscopy (SEM) was used to analyze the dispersion of the SrBHA powder inside the matrix and to determine the causes of the fractures. The SrBHA powder improved the mechanical properties of PMMA, which is critical for applications in biomedical components. The mechanical tests and SEM analysis indicated that PMMA/SrBHA composites could be used for replacement joints and orthopedic implants.

Abstract: Graphenic carbon (GC) has been successfully synthesized from biomass (coconut shell charcoal) using the liquid phase exfoliation method. The dopants, in the form of light atoms such as boron (B-GC), were introduced with the aim of improving their magnetic properties. X-ray diffraction was used to identify the GC and B-GC, and the results show broad peaks around 24° and 43°, indicating the presence of graphene-like carbon structure. The bonding structure was also analyzed using X-ray photoelectron (XPS). It reveals the main bonds in GC consist of sp², sp³, and C=O. While the B-GC sample shows an additional bond, namely the B-C bond, as an indicator of the successful doping process of B into the GC structure. Both GC and B-GC show weak room temperature ferromagnetism. Furthermore, these findings show that introducing boron atoms into the graphenic structure can improve magnetization.

Abstract: Boriding is a thermochemical treatment that can be applied to improve the mechanical and chemical properties of steels by surface modification while stilling adequate substrate properties. This kind of treatment is widely used to protect the degradation of the mechanical parts’ surface against wear. The boride atoms introduced into the steel can produce a hard metallic compound formed by diffusion and precipitation. The present study has been conducted in order to obtain an iron borides layer on two types of steel substrates 16NC6 and 20MC5 by using a powder consisting of B4C, NaBF4 and, SiC. The solid boriding treatment was carried out in an electric furnace heated to 950°C for three holding times of 2h, 4h and, 6h. The present research work focuses an the effect studying of holding time as a parameter on the thickness, structure, morphology, and hardness of layers obtained on low carbon steels by the case boriding. As confirmed by structure and microstructure characterization, the hard boride layers produced form two phases of FeB and Fe2B.

Abstract: The effect of boron content on the transverse stress rupture properties of a directionally solidified columnar superalloy is studied in present research. The experimental results indicate that the transverse stress property of the alloy containing 0.015% boron reaches the peak value at 870^°C /380MPa while that of the alloy with 0.005% boron is the best at 1100^°C/40MPa. At 870^°C, dislocation slip is the main deformation mode. Stress concentration is induced when dislocations are hindered by precipitates at grain boundaries and interdendritic regions. And then cracks nucleate due to the stress concentration. In the alloy containing 0.015% boron, no borides precipitate and boron strengthens the grain boundary cohesion by solid solution. At 1100^°C, grain boundary movement becomes the main deformation mode. In the alloy with 0.005% boron, the strengthening of grain boundary cohesion decreases comparing with that of alloy with 0.015% boron, and the resistance to grain boundary movement reduces with decreasing B content. Therefore, it results in compatible deformation between adjacent grains, resulting in the longest stress rupture lifetime.

Abstract: The equilibrium interfacial distribution of sulfur and boron was estimated using the HSC 6.1 Chemistry software package (Outokumpu) and the simplex-lattice planning method. Adequate mathematical models have been constructed in the form of III degree polynomial, which describe the effect of the composition of the studied oxide system on the equilibrium distribution of sulfur and boron between the slag and the metal. Generalization of the results of experimental studies and thermodynamic modeling made it possible to obtain new data on the influence of the basicity and content of B₂O₃ in the slag of the CaO-SiO₂-B₂O₃-MgO-Al₂O₃ system on the interphase distribution of sulfur and boron. It was found that in the range of boron oxide concentration of 1.0-10%, an increase in slag basicity from 2 to 5 at 1600°C leads to an increase in the sulfur distribution coefficient from 1 to 20 and, as a consequence, a decrease in the sulfur content in the metal from 0.02 to 0.0014 %, i.e. an increase in slag basicity favorably affects the development of the metal desulfurization process. An increase in the B₂O₃ content from 2.0 to 10.0% in slags formed in the region of moderate basicity, not exceeding 2-3, is accompanied at 1600°C by a decrease in the boron interphase distribution coefficient from 450 to 150 and an increase in the boron concentration in the metal from 0.006 to 0.021 %, which indicates the progress of boron reduction from slag to metal. The shift of the formed slags to the area of ​​increased basicity up to 5.0 shows a high degree of boron reduction from slag to metal. The results of the laboratory experiment confirmed the results of thermodynamic modeling.

Abstract: One of the effective ways to improve the quality of semi-finished products made from aluminum alloys is to eliminate the columnar and fan-shaped structure in them, refine the grain and achieve homogeneity, is modification and alloying. Modification of the melt is carried out using ligatures and allows a significant increase in the casting rate without fear of an excessive increase in the degree of zonal segregation during crystallization, as well as ensuring the uniformity of the chemical composition over the section. An important role in the quality of modification is also played by the manufacturing technology of the master alloy itself, which should ensure an increase in the cooling rate during crystallization. To obtain an alloy with the required properties, the quality of the charge materials used must be considered. First of all, this concerns master alloys, which are used for alloying and modifying the alloy. The most common for the manufacture of ingots and shaped castings are master alloys containing boron or boron and titanium. The boron content in these ligatures is 1-5%. It is generally accepted that a large amount of boron (except for the rise in the cost of the alloy itself) upon accelerated cooling promotes the refinement of the internal structure of the grain, but can lead to an increase in large inclusions of TiB2.

Abstract: The paper presents the results of the effect of boron, manganese and sulfur on the microstructure and mechanical properties of pipe steel 17G1SU. It was shown that the microstructure of boron-free steel sample containing 1.4% Mn and 0.01% S consists mainly of ferrite and a small amount of perlite. Samples microalloyed by boron are represented by a dispersed ferritic-bainitic structure. A decrease in ferrite grain size from 8.7 μm, in a comparative sample without boron containing 1.4% Mn and 0.010% S to 5.8 μm in a sample of steel containing 0.006% B, 1.6% Mn and 0.011% S, shows increasing the dispersity of the ferritic-bainitic structure. A decrease in the manganese content to 1.4, sulfur to 0.004% and an increase in boron concentration to 0.0011%, despite an increase in grain size to 6.8 μm, retain a fine-grained structure. The effect of boron, manganese, and sulfur content on the microhardness of the structural phases of the studied pipe steel samples is noted. The smallest microhardness of ferrite and perlite is observed in the base sample without boron, reaching 180 and 214 HV10, respectively. The microalloying of pipe steel containing 1.6% Mn, 0.011% S with boron is accompanied by an increase in the microhardness of the bainitic phase to 314 HV10, which increases to 400 HV10 with an increase in boron concentration to 0.011%, and a decrease in the content of manganese and sulfur to 1.4 and 0.003%. In this case, the microhardness of the ferrite phase, reaching an increase to 260 HV10, is practically independent of the content of boron, manganese, and sulfur. The mechanical properties of the experimental metal rolling with a thickness of 10 mm provide the production of rolled steel of strength class X80, without heat treatment, regardless of the content of boron, manganese, and sulfur, as a result of the formation of a finely dispersed ferrite-bainitic structure.

Abstract: The ProENGINEER software is used to build a geometric model for the whole process cavity and internal structure and conduct the internal dynamic simulation of cavity with different diffusion temperatures of 1,000°C, 1,050°C, 1,100°C and 1,150°C, and different diffusion time of 5 min, 10 min, 15 min and 20 min. Analyze the process control indexes by combining with specific thermal diffusion test, and study the relationship between hydrodynamic parameters and diffusion uniformity, Comprehensively investigate the effects of the diffusion temperature and diffusion time on doping, achieving the requirements of impurity distribution in materials.

Abstract: This paper deals with the analysis of microstructure and substructure of 9CrNB steel, after normalization at temperature of 1070 °C and tempering at 790 °C / 240 min. The tube was second time tempered at the following temperatures and holding times: 760 °C / 30 min (A1), 760 °C / 120 min (C1), 800 °C / 30 min (G1) and 800 °C / 120 min (I1). Microstructure after tempering consists of tempered martensite and bainite with lath morphology, while inhomogeneous redistribution of precipitates is visible. Substructure analysis of state A1 and I1 show, that a relatively large number of irregular, rod-shaped and oval carbide particles, often arranged in clusters, were precipitated at the primary original austenite grain boundaries. In case of state A1, the average size of these carbide particles is 300 nm and in case of state I1 the average size is 350 nm. A relatively large number of rod-shaped and oval shaped particles were found at the interface of the tempered martensite and bainite mainly in the form of clusters and also inside the tempered bainite with higher particle distribution. In the case of the state A1, they reached an average size of 150 nm. In some regions of substructure of the state I1, the fine carbide particles with an average size of 200 nm and coarse carbide particles with an average size of 400 nm were presented within the areas of tempered bainite. Particles were identified by EDX analysis and by selection electron diffraction. The mechanical properties after tempering were evaluated and compared with properties of P91 and P92 steel.