TiC/Ti-Al基复合材料的燃烧合成

为了改善Ti-Al金属间化合物的脆性,利用SHS/PHIP工艺制备了TiC/Ti-Al基复合材料.理论分析表明,绝热温度随C质量分数的增加而呈升高趋势,当体系中碳的质量分数≥2%时,该体系能完成自蔓延过程.采用电子扫描显微镜,X射线衍射仪对合成产物进行了分析.结果表明,合成产物中除存在基体相Ti3Al和TiAl和增强相TiC外,还存在许多三元相Ti3AlC和Ti2AlC相;随着Al质量分数的增加,增强相的形貌由颗粒状逐渐变成棒状或片状;复合材料的硬度和压缩强度随C质量分数的增加逐渐增加,但密度及相对密度随C质量分数的增加呈先增加后降低的趋势.当C的质量分数达到4%时,其实际密度和相对密度均达到最大.     

Effects of HIPing pressure on microstructures and properties of TiAl alloy

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机械诱发自蔓延反应合成Ti3AlC2的机理研究

以3Ti／Al／2C粉体为原料,采用机械合金化的方法以合成Ti3AlC2材料。研究结果表明,在机械合金化过程中诱发自蔓延反应,反应会产生大量坚硬的小块体颗粒,大小约为0．2-11mm。粉体的组成相为TiC、Ti3AlC2、Ti2AlC,而块体仅含有TiC和Ti3AlC2。获得的粉体和块体产物中Ti3AlC2含量分别约为63wt％和84．8wt％。提出了一个机械诱发自蔓延反应合成Ti3AlC2的反应机制,即Ti3AlC2是从固相TiC与Ti-Al液相中形核并长大。     

Fabrication of High-purity Ternary Carbide Ti3AlC2 by Spark Plasma Sintering （SPS） Technique

The effect of silicon on synthesis of Ti3AlC2 by spark plasma sintering （SPS） from TiC/Ti/Al powders was investigated. X-ray diffraction （XRD） and scanning electron microscope （SEM） were used for phase identification and microstructure evaluation. The results show that addition of silicon can considerably accelerate the synthesis reaction of Ti3AlC2 and fully dense, essentially single-phase （purity 〉98%） polycrystalline Ti3AlC2 could be successfully obtained by sintering 2TiC/lTi/lAl/0.2Si powders at 1 200- 1 250 ℃ under a pressure of 30 MPa. SEM photographs show that the obtained Ti3AlC2 samples from mixtures powders are in plane-shape with a size of about 2-5 μm and 10-25 μm in the thickness dimension and elongated dimension, respectively.     

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.     

Study on the isothermal oxidation behavior in air of Ti_3AlC_2 sintered by hot pressing

The isothermal oxidation behavior at 900―1300℃ for 20 h in air of bulk Ti3AlC2 with 2.8 wt% TiC sintered by means of hot pressing was investigated in the work. The isothermal oxidation behavior generally followed a parabolic rate law. The parabolic rate constants increased from 1.39×10-10 kg2·m-4·s-1 at 900℃ to 5.56×10-9 kg2·m-4·s-1 at 1300℃. The calculated activation energy was 136.45 kJ/mol. It was demonstrated that Ti3AlC2 had excellent oxidation resistance due to the continuous, dense and adhesive protect scales consisted of a mass of α-Al2O3 and a little of TiO2 and/or Al2TiO5. In principle, the oxide scale was grown by the inward diffusion of O2- and the outward diffusion of Ti4 and Al3 . The rapid outward diffusion of cations usually resulted in the formation of cracks, gaps, and holes.     

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.     

Preparation of TiAl/Ti2AlC Composites with Ti/Al/C Powders by In-situ Hot Pressing

TiAl/Ti2AlC composites were prepared by in-situ hot pressing of TilAl/C powders mixtures and sintered at different temperatures were investigated by X- ray diffraction （ XRD ） of samples. The reaction procedure of Ti-Al-C system could be divided into three stnges. Below 900℃ , Ti reacts with Al to form TiAl intermetallics ; above 900 ℃ , C reacts with remain Ti to form TiC triggered by the exothermal reaction of Ti and Al ; TiAl reacts with TiC to produce dense TiAl/Ti2AlC compasites.In the holding stage, ternary Ti2AlC develops to layered polycrystal and composites pyknosis in the meanwhile. The mechanism of synthesis and microstructure was especially discussed.     

Kinetics of Combustion Synthesis in Ti-C-3Ni-Al System

The Kinetics and mechanisms of the combustion reaction in theTi-C-3Ni-Al system were studied. Samples were prepared by igniting compacts of elemental Ti, C, Ni and Al powders with a heating tungsten coil under an inert argon atmosphere. The activation energies of Ti+C+50wt%(3Ni+Al)→TiC+50%Ni3Al and Ti+C+80wt%(3Ni+Al) →TiC+80%Ni3Al exothermic reactions were determined by measuring the combustion wave velocity and the combustion temperature, which are 129kJ.mol-1 and 79kJ*mol-1, respectively. The mechanism of formation of products for Ti-C-3Ni-Al system was found:metal phases (Ti-3Ni-Al) are melted in combustion process,and carbon dissolves into the liquid metal and TiC is subsequently precipitated out of solution, and Ni3Al is crystallized during the cooling process. The mechanism is fairly similar with that of Ti+C→TiC and Ti+C+Ni→TiC+Ni. There are two reactions (Ti+C→TiC, 3Ni+Al→Ni3Al) in the Ti+C+3Ni+Al system, and the wave velocity is mainly controlled by the velocity of Ti + C→TiC, but the velosity of 3Ni+Al→Ni3Al may play a significant role when Ni3Al contents are higher than 70wt%.     

Fabrication of Ti_2AlC by Spark Plasma Sintering from Elemental Powders and Thermodynamics Analysis of Ti-Al-C System

A ternary-layered carbide Ti 2 AlC material could be synthesized by spark plasma sintering(SPS)technology using elemental powder mixture of Ti,Al and active carbon.By means of XRD and SEM,phases were identified and microscopically evaluated.The experimental results show that the main phase in the product was fully crystallized Ti 2 AlC with small particle size when sintered at 1200 C.The syn-thesis temperature of SPS was 200-400 C lower than that of hot pressing(HP)or hot isostatic pressing(HIP). Through thermodynamics calculations,the mechanism of Ti 2 AlC was studied by calculating changes of Gibbs free energy of reactions.     

TiO2原位反应合成MgO-TiC颗粒增强的铜基复合材料

利用TiO₂镁热碳热原位还原技术制备MgO-TiC增强的铜基复合材料,通过XRD、SEM和力学性能检测方法研究TiO₂原位合成对MgO-TiC增强铜基复合材料的相、组织和力学性能的影响。结果显示:在烧结过程中TiO₂、Mg和C粉发生了原位合成反应,生成了MgO和TiC相,并产生了少量的MgTiO₃;材料的组织与增强相含量有着密切的关系,当增强相含量较小时,MgO-TiC颗粒弥散分布在铜基体上,随着增强相含量的增加,材料的组织中出现了MgO-TiC颗粒聚集分布的组织;材料的尺寸变化在烧结过程中主要以收缩为主,随着保温时间的延长或温度的升高,增强相含量为5%的材料的相对密度和硬度逐渐增大,增强相含量为10%的材料的相对密度和硬度逐渐降低。     

石墨配比对钨极氩弧熔敷层TiC增强相含量及分布形态的影响

利用钨极氩弧熔敷预涂在碳钢表面的钛铁和石墨粉末能够在碳钢表面获得性能优异的TiC增强涂层.预涂粉末Ti、C元素配比及含量对增强相的数量、形态和分布方式有重要影响：一方面,随着预涂粉末中含碳量的增加,熔敷层中Fe2Ti有害相降低,但出现了极少量的石墨相;另一方面,熔敷层中原位合成TiC增强相的含量增加,颗粒尺寸也随之增加,TiC颗粒的树枝状分布形态也由细枝状向粗枝状转化.     

Electronic Structures and Bonding Properties of Ti_2AlC and Ti_3AlC_2

The relation among electronic structure, chemical bond and property of Ti2AlC, Ti3AlC2 and doping Si into Ti2AlC was studied by density function and the discrete variation (DFT-DVM) method. After adding Si into Ti2AlC, the interaction between Si and Ti is weaker than that between Al and Ti, and the strengths of ionic and covalent bonds decrease both. The ionic and covalent bonds in Ti3AlC2, especially in Ti-Al, are stronger than those in Ti2AlC. Therefore, in synthesis of Ti2AlC, the addition of Si enhances the Ti3AlC2 content instead of Ti2AlC. The density of state (DOS) shows that there is mixed conductor characteristic in Ti2AlC and Ti3AlC2. The DOS of Ti3AlC2 is much like that of Ti2AlC. Ti2SixAl1-xC has more obvious tendency to form a semiconductor than Ti2AlC, which is seen from the obvious difference of partial DOS between Si and Al 3p.     

B、Ti联合作用下堆焊层显微组织和生长机制

为了探究B、Ti联合作用下堆焊层的显微组织和生长机制,采用自行研制的铁基耐磨药芯焊丝,利用自保护明弧堆焊法制备了Fe-Cr-C-B-Ti堆焊合金.利用光学显微镜、扫描电子显微镜和X射线衍射仪对堆焊层的显微组织和生长机制进行了分析.结果表明,堆焊层中原位合成了Ti C和M_(23)(C,B)_6相.随着Ti元素含量的增加,显微组织中TiC相的数量逐渐增加并主要沿晶界分布.B元素含量的提高导致显微组织中Ti C相的数量变得不稳定.作为形核衬底的Ti C相可为M_(23)(C,B)_6相的附生生长提供条件.通过原位合成Ti C和M_(23)(C,B)_6硬质相可以提高堆焊层的综合性能.     

Precipitation characteristic of high strength steels microalloyed with titanium produced by compact strip production

Transmission electron microscopy (TEM) and physics-chemical phase analysis were employed to investigate the precipitates in high strength steels microalloyed with Ti produced by compact strip production (CSP). It was seen that precipitates in Ti microalloyed steels mainly included TiN, Ti4C2S2, and TiC. The size of TiN particles varied from 50 to 500 nm, and they could precipitate during or before soaking. The Ti4C2S2 with the size of 40-100 nm might precipitate before rolling, and the TiC particles with the size of 5-50 nm precipitated heterogeneously. High Ti content would lead to the presence of bigger TiC particles that precipitated in austenite, and by contrast, TiC particles that precipitated in ferrite and the transformation of austenite to ferrite was smaller. They were less than 30 nm and mainly responsible for precipitate strengthening. It should be noted that the TiC particles in higher Ti content were generally smaller than those in the steel with a lower Ti content.     

Ti-C-Al-Fe_2O_3反应体系的热力学及形成产物的分析

针对Ti-C-Al-Fe2O3体系进行了热力学计算,并结合DSC及XRD分析,为研究该体系反应合成TiC,Al2O3提供了理论依据.计算结果表明：该体系在发生SHS反应时,可以生成TiC,Al2O3,Fe2Ti,TiAl3,Fe3C和Al4C3等产物,但TiC,Al2O3的热力学稳定性要远远大于Fe2Ti,TiAl3,Fe3C和Al4C3等相,因此,在1600℃的钢液引燃的SHS反应过程中,只能生成TiC,Al2O3两种产物.通过XRD分析也证明了在反应产物中只有TiC,Al2O3两种物质形成.     

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.     

原位自生TiC和（TiW）C增强Fe基复合材料的研究

利用块体原材料原位合成10vol%TiC-Fe和(TiW)C-Fe两种复合材料,采用扫描电镜分析了复合材料的微观结构,利用X射线分析了相组成。结果表明,在TiC-Fe复合材料中,TiC作为唯一的第二相呈现粒状和条状两种形态。分析认为,粒状相为亚共晶相,而条状第二相为共晶相。通过用W替代部分Ti,成功地制备了10vol%(TiW)C-Fe复合材料,其中,(TiW)C作为唯一的第二相比较均匀地分布在Fe基体中,其形态大部分呈粒状,条状相较少。在粒状(TiW)C相中,中心富Fe,而边缘W、Ti和C元素的分布是均匀的。与TiC相比,(TiW)C的密度与Fe更为接近,它更适合作为大型铸件的增强相。     

Fe-C-Ti-Mn合金系中TiC原位生成反应的热力学分析

根据溶液热力学理论对Fe C Ti Mn体系中TiC增强体的原位合成进行了热力学分析。计算表明,体系中TiC优先于Fe3C和Fe2Ti形成,且在热力学上比Fe3C和Fe2Ti稳定。多数情况下,TiC基体合金在液态未凝固时即可形成,而Fe3C和Fe2Ti则是在合金凝固和冷却过程中才有可能析出。随C含量增加,形成TiC和Fe3C的可能性增大;随Ti含量增加,形成Fe2Ti的可能性增大,而形成Fe3C的可能性减小;高Ti高C时,有利于形成TiC,高Ti低C时有利于形成Fe2Ti;高C低Ti时有利于形成Fe3C;添加适量的Mn既可有效抑制Fe3C的形成,又明显降低TiC的合成温度,使大多数TiC的合成反应发生在合金熔体充满铸型后的冷却、凝固过程中,可能解决TiC过早析出、熔体粘度增大、充型困难等问题。     

Fabrication of Ti2AlC by Spark Plasma Sintcring from Elemental Powders and Thermodynamics Analysis of Ti-M-C System

A ternary-layered carbide Ti2AlC material could be synthesized by spark plasma sintering（SPS） technology using elemental powder mixture of Ti, Al and active carbon. By means of XRD and SEM, phases were identified and microscopically evaluated. The experimental results show that the main phase in the product was fully crystallized Ti2AlC with small particle size when sintered at 1200℃. The synthesis temperature of SPS was 200-400℃ lower than that of hot pressing （HP） or hot isostatic pressing （HIP）. Through thermodynamics calculations, the mechanism of Ti2AlC was studied by calculating changes of Gibbs free energy of reactions.