Thermodynamic analysis of the formation of <Emphasis Type="Italic">In-situ</Emphasis> reinforced phases in cast Al-4.5Cu alloy

The thermodynamic analysis of the formation of in-situ reinforced phases in （TiB2＋Al3Ti）/Al-4.5Cu composites prepared by mixed salts reaction was conducted, and heat changes of mixed salts system were analyzed by differential thermal analysis（DTA）.The results show that although TiB2 possesses the strongest formation ability in Al-Ti-B ternary system, [Ti] is relatively excessive in the in-situ reaction and it combines with Al to form AlaTi phase. The reinforced phases are TiB2 and AlaTi in the produced composites due to the reaction taking place to form reinforced phase with the addition of mixed salts into Al-4.5Cu melt between 900 ℃ and 1 032 ℃.     

Dissolution-precipitation mechanism of self-propagating high-temperature synthesis of TiC-Cu cermets

The mechanism of self-propagating high-temperature synthesis (SHS) of TiC-Cu cermets was studied using a combustion front quenching method. Microstructural evolution in the quenched sample was observed using scanning electron microscope (SEM) with energy dispersive X-ray (EDX) spectrometry, and the combustion temperature was measured. The results showed that the com- bustion reaction started with local formation of Ti-Cu melt and could be described with the dissolution-precipitation mechanism, namely, Ti, Cu, and C particles dissolved into the Ti-Cu solution and TiC particles precipitated in the saturated Ti-Cu-C liquid solu- tion. The local formation of Ti-Cu melt resulted from the solid diffusion between Ti and Cu particles.     

Reaction dynamics in the combustion synthesis system of Al-CrO3-Al2O3-NaF-N2-O2

A new material with heat-resistant and adiabatic characteristics and high strength was prepared using the combustion synthesis method by mixed powders of CrO3, Al, Al2O3, and NaF in atmospheric gas. The reaction dynamic process of the Al-CrO3-NaF-Al2O3-N2-O2 new material system by the combustion synthesis method was discussed based on the observation results by SEM, EDS, and XRD in combination with the combustion front quenching method （CFQM） and the relation curves between reaction free enthalpies and the corresponding temperatures. The combustion synthesis mechanism and the formation reasons of the phase in the combustion product were analyzed.     

Microstructural evolution during self-propagating high-temperature synthesis of Ti-Al system

In order to investigate the microstructural evolution during self-propagating high-temperature synthesis （SHS） of Ti-Al powder mixture with an atomic ratio of Ti： Al=1：1, a combustion front quenching method （CFQM） was used for extinguishing the propagating combustion wave, and the microstructures on the quenched sample were observed with scanning electron microscope （SEM） and analyzed with energy dispersive spectrometry （EDS）. In addition, the combustion temperature of the reaction was measured, and the phase constituent of the synthesized product was inspected by X-ray diffraction （XRD）. The results showed that the combustion reaction started from melting of the Al particles, and the melting resulted in dissolving of the Ti particles and forming of Al3Ti grains. As the Al liquid was depleted, the combustion reaction proceeded through solid-state diffusion between the solid Al3Ti and the solid Ti. This led to the forming of TiAl and Ti3Al diffusing layers. In addition, the combustion reaction is incomplete besides TiAl, there are a large amount of Ti3Al and TiAl3 and a small amount of Ti in the final product. This incompleteness chiefly results from the using of coarser Ti powder.     

Materials,Metallurgy, Chemistry and Chemical Engineering Microstructure and phase forming process of Al-3Ti-0.2C-1RE grain refiner简

An Al-3Ti-0.2C-1RE grain refiner was prepared by in-situ reaction method. The microstructure was investigated by optical microscopy （OM）, scanning electron microscopy （SEM） equipped with energy-dispersive spectrometry （EDS） and X-ray diffraction （XRD）. The results show that the Al-3Ti-0.2C-1RE grain refiner is composed of α-Al, TiAl3, TiC and Ti2Al20Ce phases. Compared with Al-3Ti-0.2C refiner, the morphology of TiAl3 phase is changed and Ti2Al20Ce phases form with the addition of RE. Accordingly, the refining performance is improved. The phase forming process of the refiner is as follows： Blocky Ti2Al20Ce and fine blocky TiAl3 form in the melt at the initial stage of reaction, then the fine blocky TiAl3 gradually disappears, and the blocky Ti2Al20Ce grows bigger with the increase of holding time. The predominant mechanism to synthesize TiC particles is the reaction between high concentration of solute Ti atoms and graphite particles.     

Crystallography of Zr poisoning of Al-Ti-B grain refinement using edge-to-edge matching model

The mechanism of zirconium poisoning on the grain-refining efficiency of an Al-Ti-B based grain refiner was studied. The experiment was conducted by melting Al-5Ti-1B and Al-3Zr master alloys together. The edge-to-edge matching model was used to investigate and compare the orientation relationships between the binary intermetallic compounds present in the Al-Ti-B-Zr system. The results show that the poisoning effect probably results from the combination of Al3 Zr with Al3 Ti and the decreased amount of Ti solute, for Al3 Ti particles have good crystallographic relationships with Al3 Zr. Totally six orientation relationships may present between them, while they play vital roles in grain refinement. TiB2 particles appear to remain unchanged because of a bit large misfit. Only one orientation relationship may present between them to prevent Al3 Zr phase from forming on the surface of TiB2, though TiB2 is agglomerated. The theoretical calculation agrees well with the experimental results. The edge-to-edge matching model is proved to be a useful tool for discovering the orientation relationships between phases.     

Synthesis of Ti3SiC2/TiB2 Composite by In-situ Hot Pressing （HP） Method

Ti3SiC2/TiB2 composite was successfully obtained by hot pressing Ti/TiC/Si/B4C power mixtures.Volume fraction of TiB2 in Ti3SiC2/TiB2 composite can not exceed 10%.Incorporation of excessive TiB2 will affect the reactions process.TiC and Ti5Si3 were two important intermediate phases during the whole reactions.The microstructure characteristics of the Ti3SiC2/TiB2 composites were analyzed using scanning electron microscopy （SEM） and transmission electron microscopy （TEM）.The experimental results show that the grains of Ti3SiC2/TiB2 composite are structured in a layered form,and the formation of TiB2 particles as reinforcements with elongated or equiaxed shape distributes in Ti3SiC2 matrix.     

Instability of TiC and TiAl3 compounds in Al-10Mg and Al-5Cu alloys by addition of Al-Ti-C master alloy

The performance of Al-Ti-C master alloy in refining Al-10Mg and Al-5Cu alloys was studied by using electron probe micro-analyzer （EPMA） and X-ray diffractometer （XRD） analysis. The results indicate that there are obvious fading phenomena in both Al-10Mg and Al-5Cu alloys with the addition of Al-5Ti-0.4C refiner which contains TiC and TiAl3 compounds. Mg element has no influence on the stability of TiC and TiAl3, while TiC particles in Al-10Mg alloy react with Al to form Al4C3 particles, resulting in the refinement fading. However, TiC particles are relatively stable in Al-5Cu alloy, while TiAl3 phase reacts with Al2Cu to produce a new phase Ti（Al, Cu）2, which is responsible for the refinement fading in Al-5Cu alloy. These indicate that the refinement fading will not occur only when both the TiC particles and TiAl3 compound of Al-Ti-C refiner are stable in Al alloys.     

Combustion Synthesis and Densification of NiAl/TiB_2 Composites

A suitable combustion synthesis and densification process was designed to fabricate dense NiAl/ TiB2 composites from Ni-Al- Ti-B system. Combustion synthesis processing and microstructure characteristics of products were studied in detail. The results show that the amount of TiB2 ceramics has a great influence on the combustion synthesis processing and microstructure; with the increase of the amount of TiB2 ceramics, the combustion temperature and combustion velocity increase rapidly. The volume of synthesized products and the grain size of ceramics particle size are also affected by the amount of TiB2 ceramics. TiB2 ceramics fiber can be produced in this synthesis system. The dense NiAl/ TiB2 composites with residual porosity of no more than 1% are fabricated by the combustion synthesis and hot pressing, the mechanical properties of the dense NiAl/ TiB2 composites increase with increase of the amount of TiB2 ceramics.     

Preparation of Fe-Al Intermetallie /TiC-Al2O3 Ceramie Composites from llmenite by SHS

Fe-Al intermetallic/TiC-Al2O3 ceramic composites were successfully prepared by selfpropagating high-temperature synthesis （SHS） from natural ilmenite, aluminium and carbon as the raw materials. The effects of carbon sources, preheating time and heat treatment temperature on synthesis process and products were investigated in detail, and the reaction process of the FeTiO3-Al-C system was also discussed. It is shown that the temperature and velocity of the combustion wave are higher when graphite is used as the carbon source, which can reflect the effect of the carbon source structure on the combustion synthesis; Prolonging the preheating time or heat treatment temperature is beneficial to the formation of the ordered intermetallics; The temperature and velocity of the combustion wave are improved, but the disordered alloys are difficult to eliminate with the preheating time prolonged. The compound powders mainly containing ordered Fe3Al intermetallic can be prepared through heat treatment at 750 ℃.     

B4C/TiO2/Al复合材料制备及其性能

采用热压法制备了B4C/TiO2/Al复合陶瓷材料，试验结果表明，TiO2和Al的加入，使得B4C/TiO2/Al复合材料的硬度、抗弯强度和断裂韧性比纯B4C陶瓷材料有较大程度的提高；而且，添加相促进了复合材料的烧结.利用热力学和X射线衍射分析研究烧结过程中的化学反应，分析结果表明，复合材料中没有发现TiO2，Al，Al2O3；同时在复合材料中出现了TiB2，因为在热压过程中TiO2与B4C反应生成TiB2.分析了B4C/TiO2/Al复合陶瓷材料的微观结构和增韧机理.     

Combustion Synthesis of TiB_2 Ceramics Powder from B_2O_3-TiO_2-Mg System in Air Atmosphere

1Introduction Titaniumdiborideisanincreasingimportantceramic materialbecauseofitschemicalstability,highwearresis tance,andsuperiorelectricalandthermalconductivities,whichmakeTiB2ceramicsidealforapplicationsincutting tools,armormaterials,wearresistantcoati…     

Ti3SiC2/TiB2复合材料的制备及其组织和力学性能

以2TiC／Ti／Si／0．2Al／TiB2粉为原料，采用热压烧结工艺成功制备了Ti3SiC2／TiB2复合材料。结果表明：不同TiB2含量的试样中主晶相为Ti3siC2与TiB2两相，没有发现其它杂质相；当复合材料中TiB2的体积分数为10％时，其硬度、抗压强度、弯曲强度、断裂韧性都有显著的提高。经热处理后，Ti3SiC2／10％TiB2复合材料的弯曲强度由367．5MPa     

Thermodynamic Study on Self-propagating High Temperature Synthesis of TiB_2/Fe Composites

Based on the experimental analysis and theoretical calculation, the self-propagating high temperature synthesis of TiB_2/Fe composite was studied. The experimental results show that the interfacial between TiB_2 and Fe was smooth and clear, and the composite bending strength increased with the addition of Fe, however, the hardness decreased accordingly. The thermodynamics of the composites preparation process was calculated. The calculation results show that the primary chemical reaction was the reaction between Ti and B. The extra B can react with Fe, producing the brittle phase Fe_2 B. By increasing Ti, the production of Fe_2B will decrease and a few of Ti-Fe intermetallic compound will be produced by the reaction between Ti and Fe in the composites. Finally, according to the Merzhanov condition of the adiabatic system, it is concluded that the Fe content must be selected between 16.3% and 54.3% by the thermodynamics temperature of reaction calculation.     

以TiB2作为硼源制备硼酸铝晶须的合成机理

以TiB2作为硼源制备了硼酸铝晶须，对反应过程中的相转变以及晶须的生长机理进行了分析。结果表明，（NH4）2SO4分解释放活性[O]使TiB2氧化生成B2O3，为硼酸铝晶须的生长提供硼源。砧／B的配比对晶须的形态影响较大。在晶须的生长过程中，过量的液态B2O3作为一个载体可以把Al2O3输运到晶核的附近促进晶须的生长。     

自蔓延高温反应合成NiCuZn铁氧体粉料的研究

以碳粉作为SHS反应的燃料合成(Ni0.2Cu0.2Zn0.6O)1.02(Fe2O3)0.98铁氧体粉料,通过XRD、SEM和VSM等检测手段,研究了C粉含量和氧气压力对NiCuZn铁氧体烧结样品的物相、形貌及磁性能的关系.研究表明,当氧气压力为0.2 MPa时,C质量分数为5%时,可获得铁氧体化较完全的铁氧体料粉,其饱和磁化强度为45.5 Am2/kg;随着C含量增加,产物中有ZnO相的出现,饱和磁化强度降低.当C质量分数为15%时,随着氧气压力的增大,铁氧体尖晶石相的衍射峰逐渐变锐,晶形转变趋于完整.     

Effect of Electric Current on Diffusion of Aluminum in Ti_3AlC_2 into Zirconium Alloy

The spark plasma sintering(SPS) method was used to study the mechanism of reaction interface between Zr and Ti_3AlC_2 with electric current going through it. It was found that electric current greatly reduced the bonding temperature of Zr and Ti_3AlC_2. By the micro-structure analysis of the interface through SEM/EDS, it was found that Al atoms diffused from the Ti_3AlC_2 substrate into the Zr side and reacted with Zr to form the Zr-Al compounds at the interface, which is the strengthening mechanism of Ti_3AlC_2-Zr bonding. The thickness of reaction layers(Zr-Al alloy) was from 0.879 to 13.945 mm depending on different sintering condition. Current direction, heating rate, soaking time, pulse patterns all influenced the diffusion of Al atoms which affected the joining quality of Zr and Ti_3AlC_2.     

Effect of Cu-Ti-C Reaction Composition on Reinforcing Particles Size of TiC_x/Cu Composites

TiC_x/Cu composites were fabricated by combustion synthesis and hot press technology. Using XRD, SEM, EDS, FESEM analysis methods, the effects of various carbon sources and different Cu contents on the microstructures of TiC_x/Cu composites and the size of TiC_x particles were investigated. Results showed that TiC_x reinforcing particles size increases with decreasing Cu content in Cu-Ti-C reaction system. With carbon nanotubes(carbon black) serving as carbon source, the generated TiC_x particles size transits from nanometer to submicron when Cu content corresponding to the reaction system is reduced to 60 vol%(70 vol%); while graphite serves as carbon source, there is no clear limiting concentration. C particles with smaller size, larger specific surface area and better distribution result in finer TiC_x particles, which is more beneficial to generating nano-sized TiC_x/Cu composites.