Papers by Keyword: Nitride

Abstract: In this paper, the phase compositions and microstructure of MgO-C samples containing Si powder in N₂ sintered at 1350-1500°C were investigated by X-ray diffraction (XRD) and scanning electron microscope (SEM). The α-Si₃N₄, β-Si₃N₄, MgSiN₂ and SiC phases have formed together with MgO and C phases in the sintered samples. The morphologies of β-Si₃N₄ crystals were almost in the shape of rod-like through the α-β phase transformation of Si₃N₄ by Mg-Si-O-N and silicon liquid. The morphologies of α-Si₃N₄ crystals were in the shape of equiaxed. The morphology of MgSiN₂ crystals was in the shape of polyhedron with the size of 5 μm.

Abstract: In this paper characteristics of an AlMg/AlN composite produced in-situ and processed in a flowing N₂ atmosphere is investigated. Some critical parameters such as the manufacturing process temperature, the percentage of the magnesium consumed, the flowing reactive gas flow and the time for completing the manufacturing are considered as variables for the parametric investigation. Moreover, the effect of different amount of Mg employed has been also investigated, since Mg acts as a catalyst at the surface both for the gas/liquid and solid/liquid systems. Traditional methods were used for the basic characterization of the composite. The microstructure of the composite was investigated by optical and scanning electron microscopy (OM, SEM). SEM analysis was performed in order to observe the microstructural evolution as a function of the Mg content and to identify some reasons of the presence of porosity or any irregularities within the metal matrix. The evolution of mechanical properties, in terms of microhardness, at different percentage of Mg were monitored. By EDS technique the distribution of the elements was obtained. Furthermore, employing an optimization process, uniform dispersion of the strengthening (AlN) particles in the metal matrix with homogeneous properties along the composite material is obtained. Based on the aforementioned statements, it can be concluded that the reactions between Al, Mg and the N₂ atmosphere induce spontaneous infiltration in the metal matrix. The complete mix of properties and experimentally assessed parameters can be used for industrial purpose manufacturing design and development.

Abstract: Ab initio electronic structures for β-Ge₃N₄ are investigated using ultrasoft pseudo-potential method within the generalized gradient approximation functional. The lattice parameters are predicted theoretically, and are compared with available experimental data and the other theoretical results. The elastic constants calculations reveal that the phenacite structure is a stable phase in the pressure range of 020GPa. The high bulk modulus (B=180.2GPa) indicates that β-Ge₃N₄ is a relatively hard material. β-Ge₃N₄ has a direct band gap of 2.94eV, indicating its promising applications as a semiconductor in electronics and optical fibers. On the other hand, the density of states analysis is also included in this paper.* Corresponding author: CHEN Dong

Abstract: In this paper, tribological behaviours for sintering carbides and DLC/nitride film are discussed. During the wear test, two types of hardened steel are setting to sliding against eight series of carbide specimens in order to compare the wear mode and evaluate the wear performance of sintering carbides, which are made by different process parameters. The experiment result shows that a density ratio of sintering carbide between 86% and 99% does not have obviously different effect on wear resistance. Moreover, molybdenum binder with high diffusibility can improve the wear performance of tungsten carbide, but wear performance of titanium carbide is dependent on the amount of nickel/cobalt binder, separately. On the other hand, SAE52100 substrate absorbs the heat of friction and maintains the coated diamond-like carbon film in an excellent wear performance.

Abstract: The thermodynamic analysis shown that oxygen content in master alloy is very low, so other alloy elements content which are balance to oxygen are relatively high. In the amorphous master alloy, deoxidizing capacity of silicon is stronger than boron, and with process of decrease of the temperature, oxygen content decrease. The silicon in the master alloy can also take off the oxygen content below 1 ppm. Denitrification capacity of boron is stronger than silicon, and with process of decrease of the temperature, nitrogen content decrease. The boron in the master alloy can also take off the nitrogen content below 4 ppm. All of the research are based on energy materials and it will be useful for the development for energy saving.

Abstract: Up to now, most of work focused on the grain boundary segregation and the cold shortness caused by non-metallic element of nitrogen had been done. However, it is not clear that the reasons why the nitrogen element can generate the grain boundary segregation and the cold shortness at electron structural level. Therefore, based on the empirical electron theory of solids and molecules(EET), valence electron structures of α-Fe-N, Fe₄N and AlN were calculated, and the cold shortness generated by the nitrogen element as well as the removal mechanism of cold shortness with the help of Al element were analyzed with the phase structure factor n_A. It was found that the phase structure unit of α-Fe-N with bigger n_A firstly segregates on grain boundary，then the Fe₄N with smaller n_A on grain boundary was precipitated from supersaturated solid solution α-Fe-N, resulting in the formation of Fe₄N+α-Fe hybrid followed by the cold short in steel. However, because the value of AlN is larger than that of TiN and VN, the addition of Al element can make the cold shortness starting point decrease distinctly and thus result in the removal of segregation of nitrogen and cold shortness generated by Fe₄N. The results analyzed with the EET were in agreement with experimental fact.

Abstract: Based on the empirical electron theory of solids and molecules (EET), the phase interface electron structure of Fe₄N/a-Fe、AlN/γ-Fe、AlN/γ-Fe-C(Al) are calculated, and the reasons that the cold shortness is resulted from nitrogen as well as the add of Al element is helpful to the removal of cold shortness are analyzed with the use of the interface conjunction factors such as,σ and. The calculated results are as follows. The discontinuous electron density difference of phase interface Fe₄N/a-Fe under the first order approximation results in the remarkable strengthening effect as well as the significant decrease in toughness and ductility, demonstrating the reason that nitrogen can cause cold shortness; as the electron density difference on AlN/γ-Fe、AlN/γ-Fe-C(Al) phase interface is very large and the continuous number of the phase interface is very small, the add of Al can hinder the growth of grain, as a result, the austenite grain is significantly refined and the removal of cold shortness caused by Fe₄N can be achieved.

Abstract: In this study an attempt has been made to produce titanium-aluminium dispersed hard nitride layer on mild steel surfaces by preplacement of 50 % Ti and 50 % Al powder mixture and then melting with TIG torch under nitrogen environment. Parameter such as heat input of the torch was varied between 540, 608 and 675 J/mm and its effect on the resolidified melt pool was studied. Glazing under all energy inputs produced more than 1mm thick resolidified clad layer. The microstructural analysis revealed the clad layer with dispersion of dendrites of Ti-Al nitrides and Ti- Al intermetallic in ferrite matrix. The concentration of dendrites were found to be maximum near the surface and decreased at deeper depths.The maximum hardness of the modified surface layer was found to be 900 Hv compared to180 Hv of the mild steel substrate.

Abstract: Inclusion in steel material plays a decisive role on the purity of steels that becomes more important in the energy critical age. This study was focused on the number and morphology of inclusions with different cooling rate in the continuous casting process. A low carbon steel with 3.36 wt% silicon content was used as test material, which was soaked at 1100°C, 1250°C and 1400°C for 2 hours. The analyzed results of microstructure and chemical compositions showed the inclusions were not dissolved into matrix but formed as compounds like oxide, sulfide, and nitride after reheating at 1100°C. However, the inclusion size and average number possessed increasable trend, compared to as-cast sample. Manganese sulfide began to be dissolved into matrix by reheating at 1250°C. Some evidences showed the dissolution of aluminum nitride under the reheating at 1400°C. The inclusion size varied from 8 μm to 3 μm, and average number decreased with increasing soaking temperature.

Abstract: In this paper, the incorporation of carbide and nitride phases supported on mesoporous materials like SBA type is described in order to obtain a better material than commercial catalysts (NiMoS/Al2O3, Sg=269 m2.gr-1) specifically in the HDS of dibenzothiophene. The XRD patterns exhibit the presence of carbide and nitride phases in each series, respectively. In the nitride materials, the presence of oxide phases was more evident than in the carbide catalysts. The principal product was biphenyl (BF) for all the analyzed series. This behavior suggests that the DBT desulphurization pathway for the carbide materials was similar to that of sulfide catalysts. Bicyclohexyl (BCH) was analyzed as a product, and cyclohexylbenzene traces (CHB) were determined in a single catalyst (NiMoC-2%P/SBA-16). This was attributed to the hydrogenation character of carbide catalyst reported previously.