A study of combustion synthesis of Ti-Al intermetallic compounds

The mechanisms involved in the combustion synthesis of Ti-Al intermetallics have been studied by quenching partially transformed pellets to suppress the reaction prior to its completion. The reaction steps leading to the formation of TiAl₃, TiAl or Ti₃Al were found to be similar in all three compositions used for the study. In each case the initial product detected by X-ray diffraction was TiAl₃, while substantial dissolution of Ti into molten Al was found. At the same time the molten Al-Ti liquid adsorbed oxygen, and on quenching the partially transformed pellet, a glass was formed from the liquid. If the combustion synthesis process was completed, the oxygen-rich liquid decomposed, yielding a mixture of oxides and intermetallic compounds.     

Combustion synthesis of TiNi intermetallic compounds

The synthesis of the TiNi intermetallic compound using the thermal explosion mode of the combustion synthesis technique has been used to determine the heat of fusion, ΔH _m (7.77 kcal mol⁻¹), of the TiNi intermetallic and the heat capacity,C _p1 (17.96 cal mol⁻¹ K⁻¹), of the liquid-phase TiNi. The effect of heating rate and degree of dilution of the Ti + Ni powder compact reactants with previously synthesized TiNi on the ignition,T _ig, and combustion,T _c, temperatures in an argon atmosphere have been determined. It was found thatT _c was dependent on heating rate and dilution with TiNi, whereasT _ig remained unchanged with respect to these two process variables.     

Combustion synthesis of TiNi intermetallic compounds

The microstructural characteristics of NiTi intermetallic shape memory compounds produced by combustion synthesis have been investigated. It was found that the microstructure consists mainly of NiTi parent phase and NiTi₂ second phase. The faceted or coarse dendritic NiTi₂ phase, which is produced using a low cooling rate of the synthesized liquid product, can be modified to provide an evenly distributed, fine dendritic structure by increasing the cooling rate. This fine dendritic product can be readily hot-rolled into plate exhibiting the shape memory effect (SME). The initial nickel particle size has an important influence on the microstructure and also on the SME transition temperature. The morphology of the microstructure can also be modified to that of conventionally produced alloy by solution treatment. It is proposed that the synthesis reaction mechanism occurs by two combustion stages, i.e. precombustion and combustion. The particle size plays a key role in the precombustion stage.     

Laser-controlled synthesis of nickel-aluminum intermetallic compounds

Laser-initiated self-propagating high-temperature synthesis (SHS) in a disperse Ni-Al powder composition was studied. The X-ray diffraction measurements reveal the presence of nickel-aluminum intermetallic phases, the relative content of which depends on the regime of laser action. The regimes making possible a laser-controlled SHS of Ni-Al intermetallic compounds are considered.     

Self-propagating combustion synthesis of intermetallic matrix composites in the ISS

Combustion Synthesis experiments have been performed on the ISS (International Space Station) during the Belgian taxi-flight mission ODISSEA in November 2002, in the framework of the ESA-coordinated project COSMIC (Combustion Synthesis under Microgravity Conditions). The main objective of the experiments was to investigate the general physico-chemical mechanisms of combustion synthesis processes and the formation of products microstructure. Within the combustion zone, a number of gravity-dependent phenomena occur, while other phenomena are masked by gravity. Under certain conditions, gravity-dependent secondary processes may also occur in the heat-affected zone after combustion. To study the influence of gravity, a specially dedicated reactor ensemble was designed and used in the Microgravity Science Glovebox (MSG) onboard the ISS. In this work, the experiment design is first discussed in terms of the experimental functionality and reactor ensemble integration in the MSG. To investigate microstructure formation, a sample constituted by a cylindrical portion followed by a conical one, the latter being inserted inside a massive copper block, is used. The experiment focused on the synthesis of intermetallic matrix composites (IMCs) based on the Al-Ti-B system. Depending on the composition, different intermetallic compounds (TiAl and TiAl₃) can be formed as matrix phase while TiB2 represents the reinforcing particulate phase. During the ISS mission, six samples with a relatively high green density of 65%TD have successfully been processed. The influence of the composition on the combustion process will be examined.     

双靶共溅射TiAl系高温耐磨薄膜制备与研究

在同一次双靶共溅射过程中,通过改变基体相对于靶材的位置制备了不同化学成份TiAl系金属间化合物薄膜.采用EDS、XRD、SEM、AFM等手段对薄膜的成分、物相结构和表面形貌进行了表征,并对薄膜的高温摩擦行为进行了分析研究.实验结果表明:薄膜的化学成分、物相结构、表面形貌都随着溅射位置的改变而发生变化,500℃以下时位于双靶中间位置的薄膜具有体系中最佳的性能.     

Mathematical simulation and structural macrokinetics of the high-temperature synthesis of intermetallic compounds

In extending the results of [1], a theoretical study is made of the ignition temperature of a nickel-aluminum powder mixture as a function of the power of the external heating source, the dispersity of the refractory component, and the porosity of the powder mixture in the case of a volume reaction. The initial mixture is modeled by a set of spherical elementary cells whose dimension is determined by the range of nickel particle sizes, the mixture composition, and the porosity.Institute of the Physics of Strength and Material Science, Siberian Branch of the Russian Academy of Sciences, Novosibirsk. Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 65, No. 4, pp. 451–454, October, 1993.     

Effects of the synthesis of intermetallic compounds on the growth and consolidation of detonation diamond nanocrystals

The synthesis of intermetallic compounds belonging to the nickel-aluminum system in the presence of detonation nanodiamond (DND) particles leads to a significant change in the structure of consolidated nanocrystals. The broadening of (111), (220), and (311) X-ray diffraction reflections usually decreases by an order of magnitude, which indicates that the size of nanocrystals increases in approximately the same proportion. This effect significantly depends on the state of the surface of diamond nanoparticles. The X-ray data suggest that aluminum present in the initial metal-diamond mixture actively interacts with oxygen adsorbed on the surface of particles, which leads to the formation of Al₂O₃ oxide. The interaction between particles via cleaned interfaces at high temperatures leads to the activation of recrystallization processes.     

Studies on the oxidation behaviour of intermetallic compounds

The oxidation behaviour of the AB₅ type intermetallic compounds CaNi₅ and LaNi₅ has been studied at different temperatures ranging from 100 to 800° C. The kinetic results indicate that the element A (Ca, La) is first oxidized rapidly followed by slower oxidation of nickel. X-ray diffractograms of the oxidized LaNi₅ show the formation of ternary phases like LaNiO₃ and La₂NiO₄ at temperature as low as 400° C. A comparison between the oxidation behaviour of the two compounds reveals that CaNi₅ is more resistant to oxidation and decomposition than the LaNi₅ system.     

Effect of heating conditions during combustion synthesis on the characteristics of Ni0.5Zn0.5Fe2O4 nanopowders

Ni-Zn ferrite powders were synthesized by combustion reaction. The effect of external conditions of heating on the characteristics of the resulting powders was evaluated. Two synthesis routes were studied. The first involved preheating on a hot plate at 300°C and subsequently heating in a muffle furnace at 700°C (RCPM). In the second route the powders (RCP) were heated directly to 600°C on a hot plate until self-ignition occurred. The resulting RCP products were evaluated before and after attritor milling in order to reduce the size and increase the uniformity of particles and/or agglomerates. The resulting powders were characterized by X-ray diffraction (XRD), BET, scanning electron microscopy (SEM), helium pycnometry, sedimentation and transmission electron microscopy (TEM). The results showed that it was possible to obtain Ni-Zn ferrite powders using both routes and that the second route (RCP) was the most favorable in terms of obtaining powders with high surface area. The efficiency of the grinding was confirmed by the reduction of the size of the particles.     

Effect of carbon sources on the combustion synthesis of TiC

The effect of carbon sources, i.e. graphite and amorphous carbon, on the reaction mechanism, product morphology, and the rate of combustion reaction between Ti and C to form TiC were studied. A reaction mechanism was proposed for each carbon source from the activation energy of combustion reaction. The microstructure and the composition of reaction products were also investigated. It was observed that graphite fissured in a layered form during the combustion reaction and the reaction between graphite and liquid titanium was accomplished mainly on the surface of the thinly fissured layer. Graphite was found to be more reactive with titanium and titanium carbide synthesized with graphite contains less amount of unreacted carbon and is more close to the stoichiometric TiC.     

Effect of aluminum source on the synthesis of AlN powders from combustion synthesis precursors

In the present work, the carbothermal reduction method was employed to fabricate the AlN powders by utilizing the combustion synthesized precursor derived from the mixed solution comprised of an aluminum source (Al(NO₃)₃ or Al₂(SO₄)₃ or AlCl₃), glucose, nitric acid, and urea. Effects of aluminum source on the particle size and morphology of precursors as well as synthesized AlN powders were studied in detail. The size and morphology of precursors, derived from various aluminum sources, had exhibited significant differences. The precursor from Al(NO₃)₃ source had completed the nitridation reaction at 1500 °C in 2 h. However, the nitridation reactions of the precursors from Al₂(SO₄)₃ or AlCl₃ source furnished at increased temperature of 1550 °C in 2 h. Moreover, the AlN powders from various aluminum sources have been synthesized directly from γ-Al₂O₃ without γ-Al₂O₃ to α-Al₂O₃ phase transition. The AlN powders from Al(NO₃)₃, calcined at 1550 °C for 2 h, were comprised of well-distributed spherical particles with an average size of 80 nm. While the AlN powders from AlCl₃ or Al₂(SO₄)₃ consisted of heterogeneously distributed spherical particles ranging from 100 to 200 nm or from 80 to 150 nm, respectively.     

Effect of the type of heating on the rate of destruction of materials

An experimental determination is made of the dependence of the gasification parameter and effective enthalpy on stagnation enthalpy and the fraction of the radiant component of a heat flow.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 50, No. 4, pp. 629–635, April, 1986.     

High work-hardening effect of the pure NiAl intermetallic compound fabricated by the combustion synthesis and hot pressing technique

The pure NiAl intermetallic compound was fabricated by the combustion synthesis and hot pressing technique. Microstructure examination showed that the NiAl intermetallic compound contained fine grains. Analysis of the X-ray diffraction and the HRTEM studies showed that the phase in the intermetallics was the only NiAl phase. The NiAl showed prominent compression properties. The true ultimate compression strength and the fracture strain of the NiAl are 1002_? 94^+ 72 MPa and 21.6_? 1.8^+ 1.8%, respectively. The work-hardening capacity (H_c) is 1.40_? 0.07^+ 0.09 and the Vickers micro-hardness is 360_? 19^+ 15 HV. The finer grains, the high density dislocation and the seriously distorted lattices in the matrix, and the intense interactions between dislocations contribute to the prominent compression properties.     

Effect of fuel type on the aminolysis synthesis of CrN powders from combustion synthesis precursors

CrN nanopowders were synthesized by the aminolysis method by using the low temperature combustion synthesis (LCS) precursor derived from the mixed solution of chromium nitrate and alanine, or urea, or glycine, or citric acid. Effects of fuel type on the particle size and morphology of precursors and their corresponding aminolysis powders were studied in detail. It was found that the use of different types of fuel in solution, had a significant effect on the particle size and morphology of precursors and their corresponding aminolysis powders. Moreover, the optimized fuel type (glycine) yielded the precursor with high specific surface area and reactivity. The characteristics of aminolysis powders were found similar to those of their corresponding precursor. The CrN powders derived from glycine and synthesized at 750?°C for 6?h were comprised of well-distributed spherical particles, exhibiting high specific surface area (32.5?m²/g) with an average size of 30–50?nm.     

Effect of order-disorder transformation modes on the anomalous yield behaviour of Fe3Al intermetallic compounds

Compression tests were performed to clarify the effects of transformation modes on the anomalous yield behaviour of hypo- and hyper-stoichiometric Fe₃Al alloys which show a first- and a second-order transition, respectively. There were great differences in the anomalous yield behaviour depending on the transformation modes. In the first-order transformation alloy, changes in the degree of order played an important role before phase separation, while precipitation of phase had a great influence on the anomalous behaviour after phase separation. In contrast, only the change in the degree of order was a dominant factor in the second-order transformation alloy.     

Reactive processing of nickel-aluminide intermetallic compounds

NiAl have been fabricated by reactive sintering compacts of ball-milled powder mixtures containing Ni and Al. The reaction mechanism, as well as phase and microstructural development, were investigated by analyzing compacts quenched from different temperatures during reactive hot compaction. It was found that the reaction process was strongly affected by pressure, heating rates, heat loss from the sample to the environment. The application of 50 MPa prior to the reaction resulted in the intermetallic-formation reaction initiating at a temperature (480°C) much lower than that (550°C) when no pressure was applied. At high heating rate (50°C/min), when the heat loss is small, the formation of NiAl occurs rapidly via combustion reaction. On the other hand, if the heat loss is significant as in slow heating rate (10°C/min), the reaction process is controlled by solid-state diffusion. The phase formation sequence for the slow solid-state reaction was determined to be: NiAl₃ Ni₂Al₃ NiAl NiAl (Al-rich) + Ni₃Al NiAl.