Ti3SiC2及Ti3SiC2基复合材料的研究现状及发展

介绍了Ti3SiC2陶瓷材料的微观结构与性能，认为该材料良好的综合性能有望解决陶瓷材料的脆性问题．并概述了Ti3SiC2及Ti3SiC2基复合材料各种制备方法的特点和研究状况、应用前景和发展趋势．     

Al2O3对3Ti/Si/2C体系自蔓延高温合成Ti3SiC2的影响

以3Ti/Si/2C粉体为原料,通过自蔓延高温合成技术合成了Ti3SiC2材料。研究了Al2O3助剂对自蔓延高温合成Ti3SiC2的影响。研究结果表明,3Ti/Si/2C粉体会发生自蔓延反应,产物的组成相为TiC、Ti3SiC2和Ti5Si3,产物中Ti3SiC2含量约为23%。添加适量的细粒度Al2O3可显著促进反应合成Ti3SiC2,3Ti/Si/2C/0.1Al2O3原料反应后得到的产物中Ti3SiC2含量达64%。     

层状三元碳化物Ti3SiC2及其制备研究

三元碳化物Ti3SiC2属于层状六方晶体结构，空间群为P63／mmC；它同时具有金属和陶瓷的优良性能，有良好的导电和导热能力，在室温下可切削加工，在高温下有良好的热稳定性和塑性变形能力，还具有优异的抗氧化性能，抗热震等；应用CVD、SHS、HP／HIP等方法可制备该化合物，用HIP方法能制备高纯、致密的Ti3SiC2陶瓷。最近，以元素单质粉为原料，采用放电等离子烧结工艺成功制备了高纯Ti3SiC2材料。     

Corrosion behaviors of NdFeB magnets prepared by spark plasma sintering

The spark plasma sintering (SPS) technique was introduced into the field of NdFeB preparation due to its own advantages. High property NdFeB magnets with fine grains were prepared by SPS method. The corrosion behaviors of SPS NdFeB were studied by electrochemical measurements and 92% RH hyther tests at 353 K. The results were compared with those of the traditional sintered NdFeB magnets. It shows that both the SPS NdFeB and the traditional sintered NdFeB have good corrosion resistance in alkaline environment due to surface passivation; while, the fine grain microstructure of SPS NdFeB results in a more homogeneous phase com-position distribution and thus reduces the electrochemical inhomogenity between the ferromagnetic phase and the Nd-rich inter-granular phase in the magnet. Therefore, the SPS NdFeB exhibits better corrosion resistance than the traditional sintered NdFeB in neutral and weak acidic environment.     

Effects of different atmospheres on the arc erosion behaviors of Ti3SiC2 cathodes

The effects of ambient atmospheres on the arc erosion behaviors of Ti_3SiC_2 cathodes were investigated at 5.5 kV in argon,nitrogen, air, and oxygen. The mass loss of the cathodes increased in the order of argon, nitrogen, air, and oxygen and the morphologies were measured by 3D laser scanning confocal microscope with a gradual blooming phenomenon. Raman spectroscopy, X-ray diffraction, and X-ray photoelectron spectroscopy were employed to detect the components of erosion regions.The erosion-chemical products mainly consisted of TiN_x in nitrogen, TiN_x, TiO_2 and SiO_2 in air, TiO_2 and SiO_2 in oxygen. The arc energy was responsible for the arc erosion characteristics in different atmospheres.     

热压烧结Ti3SiC2材料的性能

热压烧结n(TiC)∶n(Ti)∶n(Si)∶n(Al)=2∶1∶1∶0.2的混合粉末制备了含铝Ti3SiC2材料并研究了它的力学性能、电性能、热性能和高温氧化性能。该试样的抗压强度、弯曲强度、断裂韧性和维氏硬度分别为854MPa、420MPa、5.8MPa·m1/2和3.5～5.0GPa;25℃和800℃时的电导率分别为4.3×106S/m和1.0×106S/m;热膨胀系数为9.0×10-6/K。固溶在基体中的Al改变了材料的氧化机理,氧化过程中Al的向外扩散代替了Ti的向外扩散,并在表面形成致密以αAl2O3为主要成分的氧化膜,提高了材料的抗氧化性能。     

烧结法制备四钛酸钾晶须的研究

根据K2O／TiO2相图，结合TiO2和K2CO3混合粉末的差热分析以及不回温度不同时间的合成样品XRD图谱，确定烧结法制备四钛酸钾最佳合成工艺条件为TiO2／K2CO3的摩尔比为3、反应温度940℃、反应时间为3．5h，且通过SEM表征可以看出合成的四钛酸钾为短棒状，晶须长8～12μm，直径0．5～1．5μm，长径比为5～30．初步讨论了四钛酸钾晶须的LS生长机理．     

烧结法制备四钛酸钾晶须的研究

根据K2O/TiO2相图,结合TiO2和K2CO3混合粉末的差热分析以及不同温度不同时间的合成样品XRD图谱,确定烧结法制备四钛酸钾最佳合成工艺条件为TiO2/K2CO3的摩尔比为3、反应温度940 ℃、反应时间为3.5 h,且通过SEM表征可以看出合成的四钛酸钾为短棒状,晶须长8～12 μm,直径0.5～1.5 μm,长径比为5～30.初步讨论了四钛酸钾晶须的LS生长机理.     

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.     

Si对热压法制备Ti3SiC2/SiC复合材料的影响

通过热压法制备了Ti3SiC2／SiC复合材料,并通过扩散偶实验及组织观察,探讨了Si元素对热压制备Ti3SiC2／SiC复合材料的反应过程及组织的影响．结果表明,Si元素在反应过程中起主要作用,决定着反应进行的速度与方向．而且随着反应物中Si量的增加,更有利于Ti3SiC2／SiC复合材料的形成．     

放电等离子烧结含铝Ti3SiC2相的形成规律研究

用放电等离子烧结工艺以元素粉为原料制各Ti3SiC2材料时，掺入适量铝能改善Ti3SiC2的反应合成。应用X--射线衍射和扫描电子显微镜研究不同烧结温度下材料的相组成和显微结构特征。结果表明：含铝Ti3SiC2相在1100℃开始大量形成，经1150一1250℃烧结，能制备纯净致密含铝Ti3SiC2固溶体材料。铝的固溶降低了Ti3SiC2的化学热稳定性．使其分解温度降低至1300℃。     

Ti_3SiC_2陶瓷的制备、性能与应用

三元化合物Ti3SiC2兼具金属和陶瓷材料的一些优异特性,综合评述了其晶体结构、基本特性、合成与制备方法、性能以及应用,并提出了今后研究的方向.     

Gradient Structure of Ti-Al-C Ternary Carbide Prepared by Hot-pressing Sintering

X-ray diffraction ( XRD ) analysis on different polished surfaces normal to the hot pressing direction reveals that the phase compositions of the polished surfaces from the outside to the inside are pure TiC,Ti3 AlC2 TiC, pure Ti3 AlC2 and Ti2 AlC Ti3 AlC2 , no matter elemental powder or TiC is used as raw materials, It is found that ternary-la2ered carbide Ti2 AlC samples synthesized at 1500℃ by hot-pressing sintering are inhomogeneous and have a gradient structure. Electron probe X-ray micro-analysis ( EPMA ) indicates that the Al content along the hot pressing axis is parabolic, it is the highest in the center and the lowest at the both ends,while the Ti content is constant along the axis. The experimental result reveals that the evaporation of Al in samples in an open ,system during hot pressing sintering results in a gradient structure.     

Si和Al对机械合金化合成Ti3SiC2的影响

采用3Ti／Si／2C单质粉体为原料,进行机械合金化,以合成Ti3SiC2粉体。研究了Al和过量Si对机械合金化合成Ti3SiC2的影响。研究结果表明,机械合金化单质混合粉体,会诱发自蔓延反应。反应后产生大量坚硬的颗粒状产物。机械合金化3Ti／Si／2C粉体,会产生组成相为TiC、Ti3SiC2、TiSi2和Ti5Si3的粉体与颗粒产物。添过量Si并不会促进机械合金化反应合成Ti3SiC2。添适量Al可消除硅化物,明显促进反应合成Ti3SiC2。采用3Ti／Si／2C／0．15Al粉体作原料时,颗粒产物中Ti3SiC2含量最高,为92．8wt％;而采用3Ti／Si／2C／0．20Al粉体作原料时,粉体产物中Ti3SiC2含量最高,为61．9wt％。     

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     

Synthesis of high pure Ti3AlC2 and Ti2AlC powders from TiH2 powders as Ti source by tube furnace

Titanium aluminum carbide (Ti₃AlC₂ and Ti₂AlC) powders were synthesized from TiH₂ powders instead of Ti powders as Ti source by a tube furnace under argon atmosphere without preliminary dehydrogenation. 95 wt% pure Ti₃AlC₂ powders were synthesized from TiH₂/1.1Al/2TiC at 1 450 °C for 120 min. High-purity Ti₂AlC powders were also prepared from 3TiH₂/1.5Al/C and 2TiH₂/1.5Al/TiC powders at 1 400 °C for 120 min. The as-synthesized samples were porous and easy to be ground into powders. Sn or Si additives in starting materials increased the purity of synthesized Ti₃AlC₂ obviously and expanded the temperature range for the synthesis of Ti₃AlC₂. With Si or Sn as additives, high pure Ti₃AlC₂ was synthesized at 1 200 °C for 60 min from TiH₂/x Si/Al/2TiC and TiH₂/x Sn/Al/2TiC (x = 0.1, 0.2), respectively.     

Microstructure and mechanical properties of submicron-grained NiAl-Al2O3 composite prepared by pulse current auxiliary sintering

Dense and submicron-grained NiAl-Al2O3 composite was fabricated by pulse current auxiliary sintering(PCAS).Its microstructure was analyzed by XRD,SEM and TEM,and its mechanical behavior was evaluated through compression test and fracture toughness test.The average grain sizes of NiAl and Al2O3 are about 200 nm and 100 nm respectively.The Al2O3 particles dispersed in NiAl matrix,forming intergranular structure and intragranular structure.During sintering,Al2O3 particles were remarkably spherized due to the unique sintering mechanism of PCAS,which is beneficial to the improvement of toughness.The NiAl-Al2O3 composite exhibits high compressive yield strength,whether at room temperature or elevated temperature.Its room-temperature(23 ℃) and elevated-temperature(1 200 ℃) compressive yield strength are up to 2 050 MPa and 140 MPa,respectively.Meanwhile,its fracture toughness is significantly enhanced,which is up to 8.2 MPa?m1/2.It is suggested that the main strengthening-toughening mechanisms are grain refinement strengthening and Al2O3 dispersion strengthening.The fracture of larger NiAl grain is the transgranular cleavage and this is induced by crack tip deflection and grain boundary weakening which are caused by intergranular and intragranular Al2O3 particles,respectively.     

Electronic Structure and Chemical Bond of Ti3SiC2 and Adding Al Element

The relation among electronic structure, chemical bond and property of Ti3SiC2 and Al-doped was studied by density function and discrete variation （ DFT- DVM） method. When Al element is added into Ti3 SiC2 , there is a less difference of ionic bond, which does not play a leading role to influent the properties. After adding Al, the covalent bond of Al and the near Ti becomes somewhat weaker, but the covalent bond of Al and the Si in the same layer is obviously stronger than that of Si and Si before adding. Therefore, in preparation of Ti3 SiC2 , adding a proper quantity of Al can promote the formation of Ti3 SiC2 . The density of stnte shows that there is a mixed conductor character in both of Ti3 SiC2 and adding Al element. Ti3 SiC2 is with more tendencies to form a semiconductor. The total density of state near Fermi lever after adding Al is larger than that before adding, so the electric conductivity may increase after adding Al.     

High-temperature dielectric and microwave absorption performances of TiB_2/Al_2O_3 ceramics prepared by spark plasma sintering

TiB_2/Al_2O_3 ceramics reinforced with Mg O are prepared by spark plasma sintering (SPS).The dielectric and microwave (MW)absorption properties are discussed.The results indicate that both the commercial TiB_2(C-TiB_2) content and preparing temperature play important roles in the dielectric properties.Simultaneously,TiB_2/Al_2O_3 composite shows the best MW absorption property when the C-TiB_2 content and preparing temperature are 9 wt% and 1400°C.To further improve the MW absorption properties,the composite containing 9 wt% synthesized TiB_2(S-TiB_2) has been sintered at 1400°C.Its high-temperature complex permittivity is greater than that of TiB_2/Al_2O_3 composite with 9 wt% C-TiB_2 sintered at 1400°C and is directly proportional to the temperature.Besides,TiB_2/Al_2O_3 composite with 9 wt% S-TiB_2 possesses a better MW absorption at 25–500°C,its effective absorption bandwidth (RL-5 dB) can reach 4.2 GHz at 25–500°C.And the minimum reflection loss (RL_(min)) value reaches-43.41 dB at the temperature of 800°C with a thickness of 1.45 mm for TiB_2/Al_2O_3 composite with 9 wt% C-TiB_2.Consequently,the satisfying absorbing layer (d1.75 mm),flexural strength,heat stability and considerable high-temperature MW absorption ability grant TiB_2/Al_2O_3 ceramics practical applications as high-temperature microwave absorption materials (MAMs).     

Properties of CNTs/MoSi_2 composites prepared by spark plasma sintering

Molybdenum disilicide(MoSi_2) based composites with various contents of carbon nanotubes(CNTs) were fabricated by spark plasma sintering(SPS) in vacuum under a pressure of 25 MPa.The composites obtained under a sintering temperature of 1500 °C and time of 10 min exhibited optimum mechanical properties at room temperature in terms of fracture toughness and transverse rupture strength.MoSi_2 based composite with 6.0% CNTs(volume fraction) had the highest fracture toughness,transverse rupture strength and hardness,which were improved by about 25.7%,51.5% and 24.4% respectively,as compared with pure MoSi_2.A Mo_(4.8)Si_3C_(0.6) phase was detected in CNTs/MoSi_2 composites by both X-ray diffraction(XRD) method and microstructure analysis with scanning electron microscopy(SEM).It is believed that the fine grains and well dispersed small Mo_(4.8)Si_3C_(0.6) particles had led to a higher hardness and strength of CNTs/MoSi_2 composites because of their particle pullout,crack deflection and micro-bridging effects.