Papers by Keyword: Nitrogen

Abstract: Because the well-known site-competition and step-controlled epitaxy rules cannot reasonably describe all the incorporation processes of the main impurities (Al and N) into 4H-SiC during epitaxy, the concept of replacement incorporation was proposed and applied to explain the experimental results published so far. In this model, the transient formation of C or Si vacancies at the surface or sub-surface of terraces is proposed to play a key role by destabilizing the impurities sitting on them. In addition to the availability of these vacancies at the surface, desorption was proposed to be a very important limiting process for Al incorporation while only occasionally relevant for N incorporation. The main 4H-SiC epitaxial growth parameters are reviewed and discussed according to the proposed replacement model.

Abstract: The chrome alloy has better affinity with nitrogen atom in nitriding process than any other alloy elements in steel. The higher content of chrome element binds larger number of nitrogen atoms. However, the higher concentration of nitrogen atom on the surface of the steel does not often make thicker case depth. This study clarified the phenomenon. The nitriding process was performed in two stages, namely the boost stage in the fluidized bed with the composition of 80 % NH₃ and 20 % of N₂ in 4 hours at 550 °C. Subsequently, the diffusion process was carried out in fluidized bed with the gas composition of 100 % N₂ HP (high purity) in 2 hours. The chemical composition was measured by spectrometry and EDAX. The case depth was identified by micro-Vickers, and metallography was observed by SEM. The concentration of nitrogen atom on the surface of AISI 316 L is twice higher than that on the AISI 4140. The result shows that 0.1 to 1 wt % of nitrogen atom creates diffusion layer, 1 to 5 wt % of nitrogen atom produces nitride layer of γꞌ and ε, and nitrogen atom above 5 wt % forms white layer. The layer strongly depends on the percentage of nitrogen atom concentration. The nitrogen atom concentration is determined by the concentration of chromium element within the steel (AISI 316 L). Meanwhile, the depth of nitrogen atom diffusion is highly determined by the alloy element of Fe (AISI 4140).

Abstract: This article discusses the problems of efficient removal of nitrogen in the vacuum tank degasser operating at the electric arc furnace shop of Uralskaya Stal (Ural Steel) OJSC in the course of manufacturing of high-quality low carbon steel grades by means of steel grades «2» and «T». In order to determine the reasonable and balanced treatment parameters that ensure the required level of nitrogen content in the above steel grades, an analysis of production data for the period of November-December 2016 has been carried out. This analysis is the basis for identifying the vacuum degassing parameters in compliance with the technological capabilities and well-balanced levels, which allow predicting the level of nitrogen content in steel. To assess the cumulative quantitative effect of the main parameters of vacuum degassing on nitrogen removal, there has been performed a regression analysis. As a result, there have been obtained multiple regression equations describing a rational combination of steel treatment parameters for achieving the required nitrogen removal level.

Abstract: An important factor in solving the problem of stainless steel corrosion resistance is carbon concentration reduction. However, a decrease in carbon content of austenitic steels leads to a drop in level of their strength properties. Theoretically, nitrogen alloying can lead to a strength increase in all types of austenitic corrosion-resistant steels. Practically, nitrogen alloying is effectively only with low-carbon compositions. This work shows the effect of nitrogen on the mechanical properties of middle-alloying nitrogen, containing stainless steel, and a study of AISI 304L and pilot steel with different nitrogen content (from 0.16 to 0.30 wt. %). Nitrogen increases strength of steel, which is approximately 30-60% higher than for steel without nitrogen, but reduces technological plasticity. Pilot steels show high corrosion resistance and fine austenite grains.

Abstract: Co-Cr-Mo alloys is the material used as a biomedical implant in human body. This material is widely used because they have excellent in corrosion and wear resistance. In this study, microstructure and results of tensile test that were affected by carbon and nitrogen were investigated. The specimens of Co-Cr-Mo alloy were made by investment casting. The compositions of the alloys are Co-28Cr-6Mo-0.8(Si, Mn, Fe)-0,2Ni-(0.08-0.25)C-(0-0.2)N. After that process, microstructure of the alloys is characterized by, SEM/EDX and XRD testing using bulk and electrolytic extracted specimens. The mechanical properties were determined by tensile test. The precipitate content in as-cast alloys was higher when carbon and nitrogen was added. The main precipitate formed in the specimens with variations in carbon and nitrogen is M₂₃X6 type, π-phase, χ-phase, and σ-phase. Carbon and nitrogen promoted M₂₃X₆ type and π-phase precipitation, respectively, meanwhile χ-phase was formed in the alloys with low carbon content. The addition of carbon and nitrogen shows an increased in yield strength, tensile strength and elongation of as-cast Co-28Cr-6Mo-0.8(Si, Mn, Fe)-0,2Ni-(0.08-0.25)C-(0-0.2)N alloys.

Abstract: The addition of oxygen or nitrogen in titanium alloys increases the hardness by the solid solution strengthening. Spinodal decomposition in titanium alloys is also the way to increase the hardness. This study aimed to reveal the effect of oxygen or nitrogen addition on spinodal decomposition in Ti-10at%V. Ti-10at%V-(0, 1, 3)at%O or N alloys were prepared by arc-melting. They were solution-treated at 1200 or 1300 °C for 0.6 ks and then quenched in iced brine. The solution treated specimens were aged at 375 °C. The increase of hardness was decreased by the oxygen or nitrogen addition in the alloys. The addition of nitrogen more suppressed the age-hardening than the case of oxygen addition. The modulated structure caused by spinodal decomposition in the laths was observed in all the aged specimens. The wavelength of spinodal decomposition of the aged specimens increased with the addition of oxygen or nitrogen, leading to a decrease in age-hardening by spinodal decomposition.

Abstract: The work investigates the properties of lead-free free-machining steel grade A30KhMAR, containing BN inclusions, in comparison with the base Cr-Mo steel 30KhM, lead-bearing AS30KhM, lead-calcium-bearing ASTs30KhM, calcium-bearing ATs30KhM, bismuth-calcium-bearing AVTs30KhM and tin-bearing AО30KhM. Effect of bismuth, calcium, lead, tin and boron nitride inclusions on steel susceptibility to temper brittleness and cold brittleness is studied. Contamination of steels with non-metallic inclusions is estimated. End-quench hardenability curves of the test steel A30KhMAR are obtained. Free-machining Cr-Mo structural steel, containing low-melting elements, has ASTM grain size of the number of 7–8. Hardenability and austenite grain size are satisfactory compared to the base steel 30KhM. Mechanical properties of the test steel in longitudinal direction (ultimate and proof stress, specific elongation, reduction in area, impact toughness, hardness) were also determined. It was found that bismuth, calcium, lead, tin, boron and nitrogen (in the form of boron nitride inclusions) within the studied limits do not have negative effect on mechanical properties of heat-treated ASTs30KhM, ATs30KhM, AVTs30KhM, A30KhMAR and AО30KhM steels, and the values of strength, plasticity and toughness characteristics satisfy the requirements of GOST standards for the base steel 30KhM and lead-bearing steel AS30KhM.

Abstract: During ion implantation into monocrystalline semiconductors, some of the implanted atoms will be deflected to crystal directions along which they may penetrate deeply into the crystal. We investigate such channeling effects for Al and N implantation into 4H-SiC by Monte Carlo simulations. The focus of the work is on the effects of channeling on doping profiles, the relevance for the net doping of typical power electronic devices, and the influence of scattering oxides.

Abstract: Natural rubber latex foam (NRF) was produced using nitrogen bubbling process. The process involved flowing of nitrogen with a constant flow rate of 80 cc/min through a bubble column, filled with latex compound, to generate a high bubble-volume inside the column. Microstructure of the finished product was examined using a scanning electron microscope (SEM), in comparison with that of the purchased Dunlop foam. The results showed characteristic of the as-produced foam that they composed of spherical pores with a uniform interconnected-cell structures. On the other hand, the Dunlop foam exhibited non-spherical pores and non-uniform cell structure with broken cells.

Abstract: One of the surface treatments to improve the hardness of the surface is by ion implantation process. This paper presents an equation to predict the surface hardness with the variable of the process time in ion implantation surface treatment. The hardness of three surfaces data were collected experimentally from various process times, i.e. 140 minutes, 280 minutes and 560 minutes. Lagrange polynomial interpolation was then used to generate quadratic mathematical formula of the surface hardness based on experimental data. The verification results show that the proposed equation accurately predict the surface hardness of commercially pure (cp) titanium under ion implantation process with the error less than 0.5 %. This equation can be used to set the appropriate treatment process time to achieve the expected surface hardness without costly trial experimental settings.