Papers by Keyword: SHS

Abstract: The Al₂O₃ ceramic-lined composite steel pipes were produced by the SHS gravitational separation process (SHS-GS process) from Al, Fe₂O₃ and Cr₂O₃ as the raw materials within different reaction systems. The phase, composition, micro-structure and properties of ceramic coatings were investigated to discuss the strengthening mechanism of the composite steel pipe. The results showed that the phase composition of Al-Fe₂O₃-Cr₂O₃ reaction system could be Al₂O₃ and Fe-Cr alloy compared with the Al₂O₃-Fe-FeAl₂O₄ phases of Al-Fe₂O₃ reaction system, which led to the increase of strength and hardness of ceramic coating. Because the Fe-Cr alloy was formed instead of Fe element, and the addition of Cr₂O₃ reduced the production of erodible FeAl₂O₄. The transition structure consisted of ceramic coating-transition layer-steel pipe was formed, and in its direction the Al and O element contents decreased, the metallic Fe and Cr increased. Therefore, the transitional changes of all the element contents could decrease the stress difference between the layers, and increase the bonding strength of the composite steel pipe.

Abstract: One kind of Al₂O₃ ceramic-lined steel pipe was prepared with the gravitational separation SHS method by using the reaction system of Al-Fe₂O₃-Cr₂O₃. The element line scans of transition structure and the element plane scans of ceramic coating far away from transition layer were analyzed by Scanning Electron Microscopy and Energy Dispersive Spectroscopy, and then they were used to discuss the coating structure and interface bonding mechanism, and investigate the element composition distribution of coating. All of these were closely related to improving the properties of ceramic-lined steel pipe. The results showed that a transition layer was formed between metal pipe and ceramic coating, it was due to the gravitational separation and molecular diffusion motion of the reaction products in molten state; in the transition structure the amount of the reaction elements was gradually transitional from the direction of the coating-transition layer-steel pipe, which could reduce the stress difference between the layers; in the coating far away from the transition layer, only small amount of Fe embedded in the ceramic was left in the form of Fe-Cr alloy, while Cr was uniformly enriched in the Al₂O₃ ceramic, these all have great influence on the anti-corrosion ability of coating.

Abstract: An attempt was made to obtain boron-containing MAX-phase by the process of self-propagating high-temperature synthesis (SHS) of Ti₃AlC₂, replacing some carbon atoms by boron atoms. This was conducted by burning powder mixtures (charges) of the composition 3Ti+2Al+2((1-x)C+xB), where x is the fraction of boron atoms (0.10, 0.15, 0.25, 0.50, 0.75, 0.90), replacing the carbon atoms. X-ray diffraction analysis of the products of combustion have shown that the replacement of carbon with boron to half of the content of carbon atoms in the charge (x=0.10-0.50), does not change the phase composition of the products, including Ti₃AlC₂ and TiC, but leads to a shift of the peaks of these phases in the diffraction pattern in the direction of smaller angles. When replacing more than half of the carbon atoms with the boron (x=0.75 and 0.90), the peaks of titanium carbide and MAX-phase are not observed, and the XRD peaks appear of the titanium borides TiB and TiB₂, and intermetallic compound Al₃Ti. Photomicrographs obtained with an electron microscope show that the SHS products synthesized from the charge with replacing up to half of the carbon atoms with the boron represent plates with a thickness of about 1 μm typical for MAX-phases, but rounded particles of borides and intermetallic compound of titanium appear at a higher boron content. Based on these results, it is concluded that replacement of a part (up to 50%) of the carbon atoms with boron atoms in the SHS charge 3Ti+2Al+2C leads to the synthesis of boron-containing MAX-phase based on the crystal lattice of Ti₃AlC₂.

Abstract: Melt-SHS (Self-propagating High-temperature Synthesis) was used for the preparation of Al–5Ti–1B master alloy. The quality ratio of Ti powder/TiO₂ in initial powder mixture was varied from 0:1 to 1:0. The AES, XRD and SEM were applied to evaluate the microstructure and phase componet. The results showed that the Al-5Ti-1B master alloy could be successful produced by the reaction of Al powder, TiO₂ and H₃BO₃ in Al melt, while the reaction rate was slow. The microstructure mainly presents the TiAl₃ particles with long strip shape. A significant improvement was noted both in reaction rate and in the grain refining efficiency when Ti powder was added to the reactants and the optimized ratio of Ti powder/TiO₂ was 2:3. The TiAl₃ particles were reduced and the grain refining efficiency turned bad when Ti powder was totally used to supply Ti

Abstract: Highly caloric mixtures of metal oxides with reducing agents used in SHS metallurgy can burn at combustion temperatures well above the melting point of final products, which ensures formation of cast products. The data of basic research in the field allowed us to suggest methods for manufacturing new cast nickel aluminides based alloy.

Abstract: Silicon nitride whiskers or rod-like crystals have a wide range application due to its excellent mechanical properties and high temperature performance. Two different silicon powders with different size (mesh 200 and mesh 300, respectively) were chosen to prepare rod-like Si₃N₄ crystals by SHS method and the effects of silicon particle size on the morphology of rod-like Si₃N₄ crystals were investigated. The results indicate that rod-like Si₃N₄ crystals could be formed with either kind of silicon powders when no more than 9wt% extra Y₂O₃ was introduced, which could effectively promote the growth of rod-like Si₃N₄ crystals. The residual free silicon was detected when using coarse silicon powders, while the silicon could be reacted completely with nitrogen gas when using fine silicon powders. The morphology of samples with coarse Si powders as starting materials is more uniform and regular than that of fine Si powders samples. Fine silicon powders are not ideal candidates for forming uniform and regular rod-like Si₃N₄ crystals.

Abstract: A combustion synthesis method has been developed for synthesis of Eu²⁺ doped CaAlSiN₃ phosphor and its photoluminescence properties were investigated. Ca, Al, Si, and Eu₂O₃ powders were used as the Ca, Al, Si and Eu sources. NaN₃ is added as the nitrogen source in the interior part of reactants and also as a reducing agent. While NH₄Cl is added for catalysis of the synthesis reaction. These powders were mixed and pressed into a compact which was then wrapped up with an igniting agent (i.e.,Mg+Fe₃O₄). The compact was ignited by electrical heating under a N₂ pressure of 0.2-1.0MPa. Effects of these experimental parameters on the photoluminescence properties and product yield were investigated. The synthesized CaAlSiN₃:Eu²⁺ phosphor absorbs light in the region of 200-600 nm and shows a broad band emission in the region of 500-800 nm due to the 4f⁶5d¹→4f⁷ transition of Eu²⁺. The peak emission intensity is ~106 % of a commercially available phosphor, YAG:Ce³⁺(P46-Y3), and the peak emission wavelength ranges from 610 to 680 nm depending on the Eu²⁺ concentration upon excitation at 460nm.The synthesized phosphor also shows excellent thermal and chemical stability and thus has a potential application as a red phosphor for white LED lighting.

Abstract: This chapter is devoted to a study of structure, martensitic transformation and shape memory behaviour in TiNi foams produced by self-propagating high-temperature synthesis. The influence of the chemical composition of the Ti+Ni powder mixture as well as pre-heating temperature on the structure and properties of TiNi foams is studied. It is shown that the variation in Ni concentration in the powders mixture allows one to produce a porous TiNi alloy with properties close to the equiatomic cast Ti₅₀Ni₅₀ alloy or Ni-rich cast TiNi alloy. It is shown that the TiNi foams produced from a mixture where the Ni concentration is higher than 45 at.% should be subjected to post-production annealing to decrease the Ni concentration in the TiNi phase. The influence of annealing temperature and duration on the structure and martensitic transformation in TiNi foams produced by SHS is studied. The optimal conditions for annealing of the TiNi foams are found. It is shown that TiNi foams after optimal heat treatment demonstrate good shape memory properties.

Abstract: In this paper, TiC reinforced steel matrix surface composites were prepared by vacuum evaporative casting infiltration process and self-propagating high-temperature synthesis. The effect of original composition, binder types and original coating density on the hardness, wear resistance and microstructure of the coating were also studied. The results showed that the Ti and C content was 80% while added 3% PVA, by pressed at 200MPa pressure leading optimal coating quality. Meanwhile the average hardness was 48HRC and the wear rate was 40%.

Abstract: SHS process in the multilayer nanofoils possesses many unique properties, such as unexpectedly high propagating rate (up to 10² m/s) and extremely short time of reaction and product phase formation (10^-7 – 10^-6 s). Understanding of the mechanism of this process has critical significance not only for the theory of SHS, but also for various applications of the reactive nanofilms, e.g., joining of dissimilar materials and items. An overview of new experimental results shows existence of complex structure of the reaction waves in the multilayer foils and reveals some new “solid-flame” combustion phenomena at macroscopic level. Comparison of these data with the study of the micro- and nano-scale processes by different experimental methods sheds new light on the intrinsic mechanism of the process. The roles of the melts, reactive exothermic dissolution and methastable phases are discussed.