Papers by Keyword: Nitride

Abstract: It is of great interest to be able to remove residues of impregnating material from the resulting article in order to reduce the cost of manufacturing such parts. To this end, a thermodynamic calculation allows you to obtain the necessary conditions for obtaining high-quality products.

Abstract: In this work, the insulating properties of nitride coatings against the hydrogen penetration into semi-finished or finished products made of VT6 titanium alloy during hydrogenation annealing have been studied. It has been established that an increase of the duration of titanium nitride deposition for more than 30 minutes leads to the formation of pores and cracks in the coating and, as a consequence, to a decrease in the «protective» properties of such coating. It is shown that during linear gradient structure creation, the nitride coating effectively “protects” alloy from penetration of up to 0.5 wt%. of hydrogen.

Abstract: Grain refinement tendency of pure Fe and Fe-X (X=5~10at%Al, 2~10at%Ti) alloys produced by laser powder bed fusion (LPBF) process was investigated. Pure Fe, Al, and Ti powders were dry mixed and cubic samples were built from the mixtures. The microstructure analysis revealed that (1) the microstructure of pure Fe consisted of equiaxed grains having an average diameter of 1.7 μm with fine iron oxide particles. (2) Fe-5 and 10at%Al alloys showed coarse columnar grains. (3) Fe-2at%Ti shows a mixture of fine equiaxed and columnar shape grains. (4) the microstructures of Fe-5at%Ti and 10at%Ti alloys are fully equiaxed, and grain refinement tendency was confirmed with increasing Ti content. Ti(N,O) oxi-nitrides are efficient in reducing the grain size because of the low lattice misfit with the ferrite matrix. Additionally, the effectiveness of Ti(N,O) particles as grain refiners was confirmed by building samples using TiN powder mixed with Fe-10at%Al and Fe-2at%Ti. While these alloys alone are coarse grained, a dispersion of Ti(N,O) particles achieved a fine-grained microstructure.

Abstract: In the present study, seven refractory compounds - TiC, NbC, TaC, WC, Ti (C,N), (Ti,Nb)(C,N) and TiN - have been produced by plasma-chemical synthesis and carbothermal reduction process of a precursor prepared by sol-gel method. The phase composition, crystallite size, morphology and specific surface area of the synthesized powders are investigated by XRD, TEM, SEM and BET respectively. Spark plasma sintering (SPS) method (up to 1850 °C, heating rate of 100 °C/min and dwelling time of 5 min.) are used for investigation of compacting of these compounds. Characteristics of the obtained ceramic materials are provided.

Abstract: High nitrogen stainless steel (HNSS) is becoming an increasingly important engineering material because of its excellent corrosion resistance and good mechanical properties. A hot rolled Cr₁₉Mn₁₉Mo₂N_0.7 HNSS, having a microstructure consisting of banded ferrite and dotted/dendritic nitrides dispersed in the austenite matrix, was solution treated at 1160oC for various times. It is shown that the nitride can be dissolved, and the shape of ferrite can be changed by the solution treatment. The microhardness of both austenite and ferrite decreases with increasing solution treatment time. This is attributed to an increased grain size and a homogeneous distribution of alloying elements. The results are helpful in controlling the thermomechanical processing of HNSSs in commercial practice.

Abstract: Surface modification using fine shot peen (FSP) comparing to and combining to hard film coating TiAlN-PVD on commonly used hardened cold work tool steel are studied in this research for their resistance to adhesive wear. Ball on disk tests were carried out to investigate the performances of those surface modification methods. In comparison to hard thin film coating, PVD-TiAlN coated tool was superior to FSP modified tool for its wear resistance. However, combining FSP and nitriding on TiAlN coated tool had higher wear resistance than that of TiAlN coating alone. Moreover various types of texture obtained from different FSP conditions were also investigated. The average roughness parameter (Ra) which is commonly used is not a good representative to determine the surface required for wear resistance enhancement for FSP. As Ra relates to the magnitude of the roughness profile only. The spacing parameters seem to be more effective. The larger the surface spacing after FSP, the higher is the wear resistance.

Abstract: The mixed gas of nitrogen and hydrogen was used for the plasma nitridation of SiC surface.A small amount of hydrogen was effective to activate the nitridation reaction and suppress the oxidationreaction. The interface properties were improved by using nitride layer as an interfacial bufferlayer of SiC MIS structure.

Abstract: We measured the microwave and millimeter-wave behaviors of ceramics and metal powders as a basis for developing microwave and millimeter-wave heating technology. In this study, nitride powders were subjected to microwave absorption measurements at elevated temperature. These measurements were performed using a system comprising a vector network analyzer, a circular wave-guide fixture, and a vacuum furnace. The sample’s microwave absorbency was evaluated by the change in reflection power from the sample in the circular wave-guide fixture under vacuum heating. Measurements were performed at approximately 24 GHz and at temperature up to approximately 1100°C. Boron nitride (BN) exhibited almost no absorption of microwaves up to 1100°C, similar to the results of a low-loss oxide powder such as alumina. Dichromium mononitride (Cr2N) powder exhibited a rather high absorption of microwaves at room temperature. During vacuum heating, absorbency of Cr2N started to decrease at 300°C, and became almost zero at temperature greater than 600°C, similar to the behavior of iron powder. This result indicated that roughly packed Cr2N powder absorbs microwave radiation; however, during vacuum heating, the compact body was sintered and the whole sample body became a reflector of microwaves. This change was irreversible, and the sample maintained its reflection behavior upon the cooling. When a mixed powder of Cr2N (20 mass%) and Al2O3 was heated under vacuum, the compact sample exhibited microwave absorption that increased with increasing temperature. This change was reversible upon cooling. These results indicated that the mixed powder did not become reflector of microwaves; Cr2N particles were not electrically connected each other because the Al2O3 particles kept the Cr2N particles separate during the vacuum heating process.

Abstract: Thin films of MXN (M stands for early transition metal and X = Si, Ge, Sn) are studied as protective coatings. To extend the knowledge about the formation of nanocomposite films, various MXN systems have been compared. TiSiN, TiGeN, TiSnN, NbSiN, ZrSiN and CrSiN thin films were deposited by reactive magnetron sputtering, from confocal targets in a mixed Ar/N2 atmosphere. The chemical reactivity of germanium and tin with nitrogen is significantly lower than that of Si and Ti. Therefore, the TiGeN and TiSnN systems are different from TiSiN. Important changes in the morphology and structure of MXNfilms are induced by X addition. Nanocrystalline composite films are formed in all these investigated ternary systems.

Abstract: A nitride layer was formed on a SiC surface by plasma nitridation using pure nitrogen as the reaction gas at the temperature from 800°C to 1400°C. The surface was characterized by XPS. The XPS measurement showed that an oxinitride layer was formed on the SiC surface by the plasma nitridation. The high process temperature seemed to be effective to activate the niridation reaction. A SiO₂ film was deposited on the nitridation layer to form SiO₂/nitride/SiC structure. The interface state density of the SiO₂/nitride/SiC structure was lower than that of the SiO₂/SiC structure. This suggested that the nitridation was effective to improve the interface property.