Dual-solution-precipitation mechanism of combustion synthesis of TiC-Fe cermet with fine Ti powder

A Ti-C-Fe powder mixture with a finer Ti powder was used for a combustion front quenching test to investigate the effect of titanium particle size on the mechanism of the combustion reaction, and the microstructural evolution in the quenched specimen was then observed with scanning electron microscopy, and the combustion temperature was also measured. The results showed that the nature of the combustion reaction could be described with a dual-solution-precipitation mechanism and a correspondent model. The melting of the finer Ti particle prior to its reaction was attributed to a combined effect of two factors: a decrease of its size-controlled melting point, and a decrease of its composition-controlled melting point. The use of the finer Ti powder led to a more complete combustion reaction and hence a higher combustion temperature. As a result, the combustion-synthesized TiC-Fe cermet had a greater average size of TiC particles and layer-shaped pores that was confirmed to be a consequence of gathering of the evolved gases into the combustion wavefront.     

原料组份、粒度对Ti-C-Fe体系自蔓延高温合成的影响

本文探讨了Fe含量、碳源及Ti、C颗粒大小对Ti－C－Fe体系自蔓延高温合成过程及产物结构特征的影响．结果表明：Fe含量增高,燃烧温度降低,产物颗粒变细,而燃烧波速度在10wt％Fe时出现极大值,反映了Fe液相的作用．石墨作碳源燃烧合成的TiC更接近于化学计量的TiC,且TiC颗粒较粗,燃烧温度、燃烧波速度均较高,反映了碳源结构差异对燃烧合成的影响．Ti、C颗粒越细,越有利燃烧反应合成．随着Fe含量增高,Ti－C－Fe体系燃烧方式由稳态变为振荡式及螺旋式燃烧．Fe含量＞60wt％;反应则不能自持．     

Ti-C-xFe体系自蔓延高温合成及机理

采用自蔓延高温合成新技术合成ＴｉＣ／Ｆｅ复合材料,研究了原料组份、粒度对合成过程及产物特征的影响。探讨了燃烧反应及结构形成机理。结果表明,随Ｆｅ含量的增大,燃烧合成温度降低,合成ＴｉＣ粒度变细,燃烧波速度在Ｆｅ含量为１０％（质量分数）时出现极大值。与碳黑作碳源对比,细粒石墨在反应合成过程中表现出更大的活性。用铜楔块燃烧波淬息法研究了合成过程。整个合成过程经历了金属的熔融、碳向熔融体中的溶解扩散、大团聚的形成、小的ＴｉＣｘ颗粒生长及ＴｉＣ长大等阶段。     

Synthesis and Deposition of TiC-Fe Coatings by Oxygen-acetylene Flame Spraying

A simpler and more convenient method for producing wear-resistant, TiC-reinforced coatings were investigated in this study. It consists of the simultaneous synthesis and deposition of TiC-Fe materials by oxyacetylene flame spraying. Solid reagents bound together to form a single particle are injected into the flame stream where an in-situ reaction occurs. The reaction products are propelled onto a substrate to form a coating. Microstructural analyses reveal that TiC and Fe are the dominant phases in the coatings. The reaction between Ti and C happens step by step along with the reactive spray powder flight, and TiC-Fe materials were mainly synthesized where the spray distanceis 125～170 mm. The TiC-Fe coatings are composed of alternate TiC-rich and TiC-poor lamellae with different microhardness of 11.9～13.7 and 3.0～6.0 GPa, respectively. Submicron and round TiC particles are dispersed within a ductile metal matrix. The peculiar microstructure is thought to be responsible for its good wear resistance, which is better nearly five times than WC-reinforced cermet coatings obtained by traditional oxyacetylene flame spray.     

Micrometer size grains of hot isostatically pressed alumina and its characterization

Alumina samples were prepared from two different particle size powders. Finer particle compacts when heated along with coarser particle compacts at same processing temperatures produce bigger grain microstructures due to higher grain growth. An unconventional method of etching by molten V₂O₅ was adopted to look at the microstructure for accuracy in reported data. On an average starting with finer particles give microstructure with a grain size of 5.5 μm and starting with coarser particles, give microstructure with 2.2 μm average grain size. The flexural strength is around 400 MPa for alumina samples prepared from finer powder in comparison with about 550 MPa for alumina samples prepared from coarser powder. The Vickers hardness in 5.5 μm grain microstructure is around 20 GPa in comparison to about 18 GPa in microstructure with smaller grains of 2.2 μm size.     

Synthesis and structural control of Fe-based porous layer on Fe substrate for joining with resin parts using combustion reaction

A porous Fe/TiB₂ composite layer was synthesized on an Fe substrate by a powder metallurgy process using combustion reactions among Fe, Ti, and B to achieve Fe/resin joints through interpenetrating phase layers. The effects of Fe particle size and the blending ratio of the raw powder mixture on the porous structure, roughness of the top surface of the porous layer, and adhesiveness between the porous layer and Fe substrate were investigated. The peak temperature measured with a thermocouple increased with increasing Fe particle size and blending ratio of Ti and B. An increase in the peak temperature does not affect the porosity of the porous layer. Higher peak temperatures increase the pore size and change the pore morphology from open to semi-closed (although pores are not completely isolated). The change in pore morphology prevents the exposure of pores on the top surface of the porous layer, resulting in decreasing surface roughness. Moreover, an increase in the maximum temperature promotes bonding between the Fe substrate and porous layer. These results are discussed in view of the thermodynamic assessment using the calculated equilibrium phase diagram.     

Powder Microstructure and Overlay Coating Property ofNiCrAlY Alloy

The microstructural features of NiCrAlY alloy powders with different particle size fractions and their effects on the overlay coating property have been investigated. It is shown that the finer (20~30 μm) powder particles experience rapid recalescence and heat extraction to the surroundings resulting in microcellular structure, whereas the coarser (40~50μm) powder particles exhibit a coarse cellular and dendritic mixed structure because of recalescence followed by slow cooling.In addition, it is also indicated that the finer the powder particle sizes, the higher the mechanical property and the metallurgical thermal stability of the overlay coatings deposited by as-atomized powders, which is presumably attributed to the formation of dense fine grain Structure and oxide layer for the fine size fraction of the powders.     

Mechanism of combustion synthesis of TiC–Fe cermet

To investigate the mechanism of combustion synthesis of TiC–Fe cermet, a mixture of (Ti+C)+30 wt% Fe was used for a combustion front quenching test, and the microstructural evolution in the quenched sample was analyzed by scanning electron microscopy and energy dispersive spectrometry. The temperature-time profile of the combustion was measured, and the phase constituents of the product were inspected by X-ray diffraction. Based on these results, the mechanism of the combustion synthesis was analyzed, and a ternary-reaction-diffusion/solution-precipitation model was proposed. Asynchronism and incompleteness of the combustion are discussed also.     

反应物量对燃烧合成Ni-Zn铁氧体粉的影响

为探讨燃烧合成法制备Ni0.4Zn0.6Fe2O4粉末工业化放大合成的可行性,研究不同反应物量对燃烧合成制备的Ni0.4Zn0.6Fe2O4粉体及烧结后产物的物相、微观形貌及磁性能的影响,对终产物进行XRD、SEM和EDS分析,对样品经行磁性能测试.结果表明:Fe-Fe2O3-Zn O-Ni O体系燃烧合成过程是以扩散-溶解-析出机制进行的,燃烧反应在非平衡条件下进行,燃烧产物的主要物相为Ni-Zn铁氧体,其中存在Zn O及一些铁的氧化物的杂质,产物经热处理后物相全部转变为尖晶石结构;随着反应物量的增加,产物颗粒尺寸增大,均匀度增加,反应物量的增加对产物的磁性能影响不大;随着反应物量的增加,饱和磁化强度逐渐增加,矫顽力基本不变,反应物量为1 500 g时制备的产品磁性能最佳,具有较高的饱和磁化强度Ms=63.72 emu/g和较低的矫顽力Hc=15.61 Oe.     

Mixture of fuels approach for the solution combustion synthesis of Al2O3-ZrO2 nanocomposite

A modified solution combustion approach was used for the first time in the preparation of nanosize zirconia toughened alumina (ZTA) composite. ZTA-1 with an average particle size of ∼37 nm was prepared using corresponding metal nitrates and urea. ZTA-2 with an average particle size of <10 nm was prepared by using mixture of fuels such as ammonium acetate, urea and glycine. The products formed were characterised by powder X-ray diffractometry, Transmission electron microscopy and BET surface area analysis. By using mixture of fuels, the energetics of the combustion reaction and eventually the properties of the combustion product have been changed. A series of combustion reactions were carried out to optimise the fuel ratio combinations required to obtain <10 nm ZTA particles. The microstructure of ZTA consisted of crystallites of Al₂O₃ and ZrO₂ both of which were nanocrystalline as evident from TEM.     

燃烧合成MgB2超导材料

采用自蔓延及热爆两种燃烧模式合成了较纯的MgB2金属间化合物。用XRD和SEM对Mg-B体系燃烧合成产物进行了研究,结果表明,压坯压力越大合成产物越致密,孔隙明显减少,产物更加均匀,但过大的压坯压力,降低了体系的燃烧温度,影响Mg、B间的反应程度;而对于细小的Mg粒,Mg-B间充分反应产生较高的燃烧温度,导致MgB2分解出现MgB4,影响合成产物纯度。     

Reaction synthesis of TiC–TiB<Subscript>2</Subscript>/Al composites from an Al–Ti–B<Subscript>4</Subscript>C system

The TiC–TiB₂/Al composites were fabricated by self-propagating high-temperature synthesis (SHS) from Al–Ti–B₄C compacts. The addition of Al to the Ti–B₄C reactants facilitates the ignition occurrence, lowers the reaction exothermicity, and modifies the resultant microstructure. The maximum combustion temperature and combustion wave velocity decrease with the increase in the Al amount. The B₄C particle size exerts a significant effect on the combustion wave velocity and the extent of the reaction, while that of Ti has only a limited influence. The reaction products are primarily dependent on the B₄C particle size and the Al content in the reactants. Desired products consisting of only the TiC, TiB₂, and Al phases could be obtained by a cooperative control of the B₄C particle size and the Al content.     

Fe-Ti-C 熔体在大气条件下原位合成TiCP/Fe 复合材料的研究

为了在大气条件下利用Fe-Ti-C 熔体中T iC 的合成反应制备原位( in situ) TiC_P/Fe 复合材料, 研究了三种覆盖剂对熔体中T i 元素氧化烧损率的影响, 并分析了所得复合材料的组织和性能。结果表明: 采用所开发的混合盐型覆盖剂能在大气条件下制备出原位TiC_P/Fe 复合材料, 且原位合成的T iC 颗粒尺寸细小、分布均匀, 从而使制备的复合材料特别是经淬火处理后的复合材料具有较高的力学性能。      

化学液相法制备BaPbO3导电陶瓷

采用化学液相法制备了ＢａＰｂＯ３陶瓷，通过Ｘ射线衍射、扫描电镜等手段分析了合成条件对粉末纯度的影响，了烧结条件对ＢａＰｂＯ３陶瓷组织结构及室温电阻率的影响。实验结果表明，２化学液相法制备的ＢａＰｂＯ３粉末纯度高、粒度细，由此粉末制备的ＢａＰｂＯ３陶瓷的室温电阻率达６．２８×１０＾－４Ω·ｃｍ，是一种很有前途的导电陶瓷材料     

Investigation of joining Al–C–Ti cermets and Ti6Al4V by combustion synthesis

The paper has addressed a route for the welding of titanium alloy (Ti6Al4V) and Al–C–Ti powders by the combustion synthesis (CS) method. Al–C–Ti powders were compressed in the titanium alloy pipes with relative densities of 65%, and then the powder compact was sintered by two reaction mode at the same time as the annulus of titanium alloy and the synthesized product were joined. The paper has studied the effects of reaction mode and Al content in starting powders on the structure and property of the welded joints. And it has also discussed the microstructure of welded joints by laser-induced combustion synthesis (LCS). The mechanical properties of the welding seam have been also tested. The results show that LCS welding has realized fusion welding and the welding seam has good mechanical properties. Furthermore, SEM analysis has indicated that nano-size grains of TiC were formed in the joint layer.     

Effect of reactant Ti/B4C ratio on the stoichiometry and mechanical properties of h-BN-Ti(C,N) prepared by combustion synthesis

h-BN-Ti(C,N) ceramic composites were prepared by combustion synthesis from B₄C-Ti powder compacts ignited under high gaseous nitrogen pressure. The influences of Ti/B₄C ratio in reactant on the combustion temperature and velocity, phase composition and N content in Ti(C,N) phase were analyzed through theoretical and experimental studies. Experimental results show that combustion temperature and velocity increased with the increase of Ti/B₄C ratio in reactant. TiN is the preferential formation phase under high nitrogen pressure, which resulted in higher N content in Ti(C,N) phase. Mechanical properties of the composites increased with the increase of Ti/B₄C ratio because of higher Ti(C,N) content in products.     

Effect of heating rate on the combustion synthesis of Ti-Al intermetallic compounds

Titanium aluminide compounds were synthesized by the thermal explosion mode of self-propagating high-temperature synthesis (SHS). The effects of heating rate on the combustion characteristics and the microstructures of the products were studied. It was found that the low density of the reacted sample was due to the outgassing of water vapour and other gases, which were released by dissociation of hydrated aluminium oxides. Higher heating rates resulted in a product of higher density and single-phase microstructure. At lower heating rates, the reaction product was a mixture of phases for TiAl and Ti₃Al reactions. A liquid (Al)-solid (Ti) reaction mechanism is predicted for slow heating while a solid-solid mechanism is expected for high heating rates. The origin of porosity in the product is also discussed.     

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.     

Self-propagating high-temperature synthesis of ultrafine and nanometer-sized TiC particles

The feasibility of preparing ultrafine and nanometer-sized titanium carbide particles by self-propagating high-temperature synthesis (SHS) has been studied. Data are presented on the structure formation of TiC powders during SHS with a reduction step. Basic to this process is an exothermic reaction between titanium dioxide, magnesium metal, and carbon. The effects of the composition of the starting mixture, relationship between its components, and the morphology and particle size of the starting TiO₂ powder on the particle size of the forming material have been investigated. The TiC powder was recovered from the sinter cake by chemical dispersion, a chemothermal treatment of the synthesis product in different solutions. The results demonstrate that treatment of the sinter cake with appropriate solutions removes impurities and causes imperfect intergranular layers to dissolve. As a result, the cake breaks down into homogeneous single-crystal particles. Subsequent treatment in different solutions further reduces the particle size of the powder. The effect of the composition of the dispersing solution on the particle size of the TiC powder has been studied. Our results made it possible to identify conditions for the preparation of titanium carbide powders containing up to 70% of particles less than 0.3 μm in size by SHS followed by chemical dispersion.