Combustion characteristics of the Ni3Ti-TiB2 intermetallic matrix composites

Combustion synthesis (SHS) of Ni₃Ti-TiB₂ metal matrix composites (MMCs) was selected to investigate the effect of gravity in a reaction system that produced a light, solid ceramic particle (TiB₂) synthesized in situ in a large volume (>50 pct) of the liquid metallic matrix (Ni₃Ti). The effects of composition, green density of pellets, and nickel particle size on the combustion characteristics are presented. Combustion reaction temperature, wave velocity, and combustion behavior changed drastically with change in reaction parameters. Two types of density effects were observed when different nickel particle sizes were used. The structures of the combustion zones were characterized using temperature profile analysis. The combustion zone can be divided into preflame, reaction, and after-burning zones. The combustion mechanism was studied by quenching the combustion front. It was found that the combustion reactions proceeded in the following sequence: formation of liquid Ni-Ti eutectic at 940 °C → Ni₃Ti+NiTi phases → reduction of NiTi with B→TiB₂+Ni₃Ti.     

Influence of Reaction Temperature and Reaction Time for the Manufacturing of Al–Ti–B (Ti:B?=?5:1, 1:3) Master Alloys and Their Grain Refining Efficiency on Al–7Si Alloys

In the present work, ternary Al?CTi?CB master alloys have been prepared in an induction furnace by the reaction between preheated halide salts (K₂TiF₆ and KBF₄) and liquid molten Al. A number of process parameters such as reaction temperature (800, 900, 1,000?°C), reaction time (45, 60, 75?min.) and compositions (Ti/B ratio: 5/1, 1/3) have been studied. The indigenously prepared master alloys were characterised by chemical analysis, particles size analysis, XRD and SEM/EDX microanalysis. Results of particle size analysis suggest that the sizes of the intermetallic particles [Al₃Ti and TiB₂ in Al?C5Ti?C1B and (Al, Ti)B₂ in Al?C1Ti?C3B] present in various Al?CTi?CB master alloys increases with increase in reaction temperature (800?C1,000?°C) and reaction time (45?C75?min.). The population of the particles decreases with increase in reaction time and temperature. Further, SEM/EDX studies revealed that different morphologies of the intermetallic particles were observed at different reaction temperatures and reaction times. Further, the performances of the above-prepared master alloys were assessed for their grain refining efficiency on Al?C7Si alloy by macroscopy, DAS analysis. Grain refinement studies suggest that, B-rich Al?C1Ti?C3B master alloy shows better grain refinement performance on Al?C7Si alloy when compared to Ti-rich Al?C5Ti?C1B master alloy.     

Extending the compositional limit of combustion-synthesized B4C-TiB2 composites by field activation

Composites of B₄C-TiB₂ with molar ratios B₄C/TiB₂ of up to 8 were synthesized by field activated combustion. The combustion wave velocity depended on this ratio and increased approximately linearly with the applied field. The effect of the field was analyzed and its contribution to the combustion temperature was calculated. X-ray and microscopic analyses showed the synthesis to be a two-step process. Titanium boride forms at or near the leading edge of the combustion zone and B₄C forms at or near the trailing edge.     

Synthesis of TiC–TiB–TiB2 composite powders by solid reaction of powders

In the present work, TiC–TiB–TiB₂ diffusion-layer-coated B₄C composite powders were synthesised via a powder immersion method using Ti and B₄C powders as reactants. The phase compositions and microstructure of the treated powders were characterised by employing X-ray diffraction and scanning electron microscopy. No significant reaction between B₄C and Ti could be detected at 800°C. After treatment at 900°C, the products generated were composed of TiC and TiB. After treatment at 1000°C, the products generated were primarily composed of TiC and TiB, with a small amount of TiB₂. The composition and proportions of the produced phases varied with process temperatures and the composition of the initial powders used. Powder mixtures with a Ti/B₄C molar ratio of 3.5:1 and treated at 1000°C for 14?h were more suitable for synthesis of TiC–TiB–TiB₂-coated B₄C composite powders.     

工艺参数对Ti-C-Ni体系燃烧合成过程的影响

计算研究了Ni含量对Ti-C-Ni三元体系燃烧合成绝热温度的影响,试验研究发现随着Ni含量、稀释剂含量和Ti颗粒尺寸的增加,Ti-C-Ni体系燃烧温度和燃烧速度呈下降趋势。Ni在Ti-C-Ni体系中参与了放热反应。最佳的预制块相对密度为50%～60%,此时Ti-C-Ni体系燃烧速度最快。     

Reaction products of Al/TiC composites fabricated by the pressureless infiltration technique

The interfacial reaction products of the Al-Mg/TiC _p composite fabricated by the pressureless infiltration method were analyzed using scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), and transmission electron microscopy (TEM). During the fabrication of composites, reaction products with various morphologies and sizes were formed in the A1 matrix as well as in the vicinity of the TiC particles by the interfacial reaction between the Al alloy and the TiC particles. From the EDS and selected-area diffraction pattern (SADP) analysis, Al₄C₃, Al₁₈Ti₂Mg₃, Ti₂AlC, Al₃Ti, and TiAl could be identified to form as interfacial reaction products. Both the size and the amount of the reaction products were increased with increasing fabrication temperature as well as fabrication time. Coarse Al₃Ti was barely observed in water-quenched composites, while it was observed at all fabrication temperatures (700 °C to 1000 °C) in furnace-cooled conditions. An erratum to this article is available at .     

Interface characterization of fiber-reinforced Ni3Al matrix composites

The interfacial reaction characteristics of SCS-6, Sigma, and B₄C/B fibers with nickel aluminide (Ni₃Al) matrix have been investigated between 780°C to 980°C for times ranging from 1 to 100 hours. The microstructure and elemental compositions across the reaction zone have been analyzed quantitatively using microscopy and electron probe microanalyses, respectively. The results show that Ni₃Al reacts extensively with SCS-6, Sigma, and B₄C/B fibers to form complex reaction products, and Ni is the dominant diffusing species controlling the extent of reaction. In the SiC/Ni₃Al composite, the C-rich layer on the SiC surface can slow down but cannot stop the inward diffusion of Ni into SiC fiber. When the C-rich layer is depleted, a rapid increase in reaction zone thickness occurs. Diffusion barrier coating on the fibers is required to minimize the interfacial reactions.     

Ti-W-C体系的自蔓延高温合成与反应机理

研究了Ti-W-C体系自蔓延高温合成(SHS)的燃烧温度和燃烧速度与W含量、Ti粉粒度及预热温度的关系。分析了不同W含量和预热温度时SHS产物的相组成,并对体系的SHS反应机理进行了研究。结果表明:W/(Ti+W)≤ 0.3时,基本能合成单相(W/Ti)C;而预热可促进(W,Ti) C的SHS合成;体系的SHS反应过程中存在两种反应机制,即溶解-析出机制和扩散-固溶机制     

Characteristic properties of combustion and structure formation in the Ti-Ta-C system

Macrokinetic characteristics of the combustion of mixtures in the (100% ? X)(Ti + 0.5C) + X(Ta + C) system with a variable mixing parameter X and initial temperature T ₀ of charge heating are considered. For compositions with X = 10 and 30%, an abrupt increase in the velocity U _c and temperature T _c of combustion as a result of passing two parallel chemical reactions of titanium and tantalum carbide formation is established. The U _c (T ₀) and T _c (T ₀) dependencies are linear for the mixture with X = 50%. By hardening the combustion wave, it is revealed that the primary structure formation in the combustion region starts from the selection of submicron grains of nonstoichiometric titanium carbide from the supersaturated titanium melt. In the investigated range of parameter X, synthetic products are single-phase and represent titanium-tantalum carbide. An increase in X results in a decrease in the size and microhardness of (Ti, Ta) C grains and a reduction of the relative density of compact synthetic products. The kinetics of high-temperature oxidation of alloys on the basis of carbide (Ti, Ta) C is studied. Ceramics produced at X = 10% are most heat-resistant.     

Microstructure of TiC–TiN–Ni–(B) cermet systems

Abstract

TiC-TiN-Ni-(B) systems were investigated to understand particle coarsening and morphology changes as a function of sintering time and compositions. In addition, the variations in the C/(C+N) ratios of Ti(C_1-xN_x) solid solutions formed in the system were studied. As expected, the particle size becomes larger with an increase in the duration of sintering. However, added boron significantly reduced the growth of particles. X-ray diffraction analysis shows that the binder phase consists largely of Ni₃B in TiC-TiN-20Ni-1B (in wt-%) system. The presence of boron in the liquid Ni seems to interfere with the dissolution of TiC and TiN and/or transport of Ti, C, and N. The effect of boron decreases as the amount of Ni binder increases. The particle morphology is found to change with variations in the C/(C+N) ratio.     

Internal displacement reactions in multicomponent oxides: Part III. Solid solutions of ternary oxide compounds

In an internal displacement reaction between a reactive metal A and multicomponent oxide (B,C,D,…)O, the noble cation B in the oxide is selectively displaced by reactive metal A, without changing the crystal structure of the oxide. Concurrently, B is precipitated as an internal metal phase in the oxide matrix. The cations (C,D,…) are inert in terms of exchange reaction. The solid-state displacement reaction occurs by the counterdiffusion of A and B inside the reaction zone. The diffusion of “inert” cations and the concentration profile in the product oxide are dependent on the nature of the oxide: (1) “line” compound of narrow homogeneity range or (2) solid solution of wide composition range. These reactions were discussed in previous articles^[1,2] (Parts I and II) along with specific examples. This article is a continuation of studies in Parts I and II and involves the internal displacement reaction between a metal and a quaternary oxide, which is a solid solution of two ternary line compounds. As a model, the reaction between Fe and an ilmenite solid solution of NiTiO₃-MgTiO₃ was studied at 1273 K as a function of time: In ilmenite solid solution (Ni, Fe, Mg) occupy the same cation sublattice, which is different from the Ti sublattice. During the reaction, only Ni cation in the oxide is displaced Fe; Mg and Ti are “inert” in terms of cation exchange. The reaction products consist of internal “Ni” precipitates (Ni-Fe alloy) in a matrix of (Fe, Mg, Ni)TiO₃ solid solution. In particular, the study focuses on cation flux during the reaction and evolution of product oxide composition profile after time t. The three cations in the product oxide that occupy the same sublattice, (Ni, Fe, Mg), show concentration gradients across the reaction zone, even though Mg is inert for cation displacement. The counterdiffusion of Fe and Ni is consistent with their chemical potential gradients. The diffusion of Mg is in the same direction as that of Fe, indicating that, at constant NMgTiO3, the chemical potential for MgTiO₃ is higher in (Mg, Fe)TiO ₃ solid solution than in (Mg, Ni)TiO₃ solid solution. The concentration of Ti, which occupies a different sublattice, remains constant across the reaction zone (i.e., zero diffusional flux for Ti). The ratio, (Fe+Mg+Ni):Ti=1:1, is consistent with the ilmenite structure of the product oxide. The shape of the cation concentration profiles indicates that terms containing cross-coefficients in the general flux equations contribute significantly to cation diffusion during the reaction.     

SHS Technology for Composite Ferroalloys. 2. Synthesis of Ferrosilicon Nitride and Ferrotitanium Boride

The combustion of ferrosilicon in nitrogen is very similar to the combustion of metallic silicon. With increase in silicon content in the initial ferrosilicon, its reaction rate with nitrogen increases, as is clear from the considerably more vigorous combustion. The nitrogen concentration in the combustion products increases here. Over the whole range of initial parameters (nitrogen pressure, grain size of the powder, batch composition), the combustion products consist mainly of β-Si₃N₄. No large quantity of α-Si₃N₄ is observed. In practice, FS75 and FS90 ferrosilicon is optimal for refractory production, while FS65 and FS75 ferrosilicon, with lower impurity content, is best for the production of components used in steel production. The introduction of iron in the Ti–B system (T_ad = 3190 K) considerably restricts the combustion concentration range. A mixture with 16.9% B burns in a narrow Ti:B concentration range close to 0.86. In combustion of the Fe–B + Ti mixture, increase in the initial temperature considerably expands the concentration range for synthesis. In all cases, increase in the initial temperature considerably boosts the combustion rate. Heating to T₀ ≥ 300°C permits the use of mixtures with titanium powder containing larger grains (r_me.Ti ≥ 0.4 mm) in self-propagating high-temperature synthesis (SHS). A wide range of B:Ti ratios may be used. The combustion of such mixtures permits the production of an alloy with 6–14% B and 30–60% Ti. Specialized industrial equipment has been constructed: a series of SHS reactors with working volumes of 0.06, 0.15, and 0.3 m³, permitting the large-scale production of materials based on refractory inorganic compounds for use in metallurgy. The industrial production of composites based on oxygen-free compounds by self-propagating hightemperature synthesis has been introduced.     

热爆法制备多孔NiTi形状记忆合金

Porous NiTi shape memory alloys (SMAs) havebeen widely used in medical fields such as hard tis-sue implant and medical instrument because of itsspecial pseudoelasticty, which can accommodate thedeformation of hard tissue, and its attractive combi-nation of properties such as excellent mechanicalproperties, good corrosion resistance, biocompati-bility and unique shape memory effect[1,2]. Moreo-ver, its porous structure allows the ingrowths of newtissue along with the transport of body fluids, …     

Adhesion Behaviour,Nanohardness and Surface Roughness of Ti–6Al–4V–6B<Subscript>4</Subscript>C Thin Films Grown on AISI 1040 Steel

The nanohardness of Ti–6Al–4V–6B₄C thin film coated AISI 1040 steel were investigated using nanoindentation based on an AFM measurement technique. Thin films of Ti–6Al–4V–6B₄C were grown by the magnetron sputtering deposition method. X-ray diffraction analysis revealed that the deposited thin films were highly purified. The nanohardness of 18, 14 and 11.3 GPa were obtained for the coating of Ti–6Al–4V–6B₄C, Ti–6Al–4V, and bare substrate respectively. The surface roughness (R_a) of 0.5 and 1 h coating were 3.39 and 15.74 nm respectively. The results showed that the B₄C particles had a significant effect on the microstructural and mechanical properties of the coatings. The Ti–6Al–4V–6B₄C coating was obtained for a coating thickness of 40 and 100 nm for 0.5 and 1 h coating time respectively. In the meantime, the respective coating thickness of Ti–6Al–4V was obtained as 30 and 80 nm for 0.5 and 1 h coating time respectively. Strong adhesion was observed between the Ti–6Al–4V–6B₄C coating and AISI 1040 steel substrate than Ti–6Al–4V samples. The adhesion mechanism between the Ti–6Al–4V–6B₄C coating, AISI 1040 steel substrate, and the interfacial structure were studied by using scanning electron microscope (SEM). The use of Ti–6Al–4V–6B₄C coating could be a novel technique for developing high-performance applications due to excellent adhesion and nanohardness.     

Present Technology of Hard and Soft Ferrites

Abstract

In order to improve the mechanical properties of cemented carbides, Ti(C,N)–Ni–Mo alloys, in which carbon in the titanium carbide is replaced by nitrogen, are of potential interest from the viewpoint of grain size control. Since grain size control by nitrogen was also observed in Ti(C,N)–Ni alloys containing no molybdenum, the effect of nitrogen on grain growth of Ti(C,N)–Ni alloys was investigated by comparing TiC–Ni and TiN–Ni alloys. The grain growth rate of Ti(C,N)–Ni alloys showed a minimum value at the carbon content C/C+N = 0·5. From the results of chemical and grain size analyses, it is considered that the growth rate depends on the solubility of Ti(C,N) in the nickel solid solution and the degree of coalescence because the solubility decreases with decreasing carbon content. With nitride, the amount of liquid increases by denitrification of TiN, owing to the formation of the nickel solid solution or TiNi₃ phases, and growth of TiN grains by Ostwald ripening is observed. The apparent activation energy for the growth of TiC and TiN grains is calculated to be ～4·4×10⁵ and 1·9 × 10⁵ J mol^?1 respectively. PM/0201     

Effects of Si and Ni powder refining on the formation mechanism of nickel silicides induced by mechanical alloying

The synthesis of the Ni₂Si, Ni₅Si₂, and NiSi phases has been investigated by mechanical alloying (MA) of Ni-33.3 at. pct Si, Ni-28.6 at. pct Si, and Ni-50 at. pct Si powder mixtures. As-received and 60-minute premilled elemental powders were subjected to MA. The average surface area of the premilled Ni powder particles, which had a flaky shape, was 3.5 times larger than that of the as-received Ni powder particles, which had a spherical shape. The as-received Si powder was angular in shape and the mean particle size was 19.1 μm, whereas the mean particle size of the premilled Si powder was 10 μm. A self-propagating high-temperature synthesis (SHS) reaction, followed by a slow solid-state diffusion reaction, was observed to produce Ni silicide phases during MA of the elemental powders. The reactants and the product, however, coexisted for a long period of MA time. On the other hand, only the SHS reaction was observed to produce Ni silicides during MA of the premilled elemental powders, indicating that Ni silicides formed rather abruptly in a short period of MA time. The mechanisms and reaction rates for the formation of Ni silicides via MA appeared to be influenced by the elemental powder particle size and shape as well as the heat of formation of the products.     

Research on preparation optimization of nano CeB6 powder and its high temperature stability

High temperature self-propagating synthesis (SHS) process is very rapid, the reaction process becomes un-controlled after the SHS reaction is ignited. So the initial reaction conditions will have great effects on phase compositions and microstructures of reaction products. In this paper, the effects of the proportioning amount of Mg on the yield ratio and particle sizes of CeB6 were studied. The SHS reaction products and leached products were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The results indicated that the SHS products consisted of MgO, CeB6 and little Mg3B2O6. The single CeB6 phase was contained after the SHS reaction products were leached. The purity of CeB6 was higher than 99.0 mass%, and the minimum particle sizes of CeB6 were within 30-70 nm. When the proportioning amount of Mg was 25% more than the theoretic amount, the yield of CeB?6 was 68.68%. The antioxidant ability of CeB6 was rather stronger, which was oxidized step by step, and the initial oxidation temperature was 750 oC, which indicated that it had good high temperature stability. The apparent activation energies of oxidation reactions of CeB6 were 200.09 and 312.10 kJ/mol, respectively, and reaction orders were 0.69 and 0.40, respectively.     

On sintering of Ti–Ni (–TiB2) alloys to near full density

Abstract

Using a combination of mixed elemental powders and TiB₂, a series of Ti–Ni and Ti–Ni–B alloys were optimised for sintering by varying the nickel and boron contents, the particle size of the elemental powders and the compaction pressure. The sintering temperature was maintained at 1200°C to limit the costs of a potential commercial sintering operation. For Ti–Ni alloys, a density of 99% was attained in Ti–7Ni made using fine Ti and Ni powders sintered in the solid state, and from liquid phase sintering of Ti–8Ni made using coarser powders. Porosity was almost eliminated from Ti–7Ni–xB alloys made by adding 1–3%TiB₂ to the coarser Ti and Ni powders. The action of TiB₂ as a sintering aid is possibly owing to a combination of the formation of a small amount of liquid at the sintering temperature and the restriction of grain growth owing to the presence of TiB particles.     

Cryomilling for the fabrication of a particulate B4C reinforced Al nanocomposite: Part I. Effects of process conditions on structure

Metal matrix composites (MMCs) are a relatively new category of engineering materials, which provide tailorable properties to meet specific needs. Cryomilling, mechanical milling at cryogenic temperatures, was employed in this study to fabricate nanostructured metal matrix composite powder with nanocrystalline aluminum alloys as the matrix and particulate B₄C as the reinforcement. Cryomilling provided an extremely low temperature for the processing of this composite, which prevented the formation of secondary phases that are detrimental to mechanical properties. A uniform distribution of B₄C in the Al and a clean strong interface between them were achieved. The contamination that results from cryomilling was analyzed. The effects of the B₄C addition and the process control agent (PCA) on the microstructure of the composite powder were investigated. Results indicate that these additives had significant, yet opposing, effects on powder yield; a slight effect on contamination, particle size, and particle morphology; and no detectable effect on grain size refinement in the matrix.     

Calciothermic co-reduction of TiO2-Cr2O3 oxides in molten CaCl2: Effect of particle size of starting materials

In this research, the effect of particle size of starting materials (TiO₂ and Cr₂O₃) was investigated on calciothermic co-reduction of oxides and in-situ dissolution of the CaO by-product in molten CaCl₂. The particle size of starting oxides, molar ratio of molten salt and holding time of reaction at elevated temperature affected the progress of reduction reactions and the remaining oxygen. In the best optimized condition, the remaining oxygen in the obtained TiCr₂ was 1020 and 802 ppm using 388 and 120 nm particle sizes of starting oxides, respectively. The formation of TiCr₂ in calciothermic co-reduction process was considered to be mutual diffusion phenomena. Also, the kinetics of hydrogen adsorption for the co-reduced sample was better than that of the arc-melted sample. Particle sizes of the obtained products decreased with-the decrease of the particle sizes of the starting oxides.