Preparation of porous silicon carbide by combustion synthesis

Porous silicon carbide ceramics were prepared by combustion synthesis technique. SiC/TiC composite was gained by combustion reaction of Si, C and Ti. Thermodynamics analysis of Si-C-Ti system indicates that the content of TiC in products should be larger than 30%. The experimental results show that the content of Ti C should be larger than 25% to achieve a complete combustion reaction. The X-ray diffractometry results show that the final products with a relative density of 45%-64% are composed of a-SiC,β-SiC, TiC and a small quantity of Si. The images of scanning electron microscopy show that the structures of grain in SiC based porous ceramics consist of particles with a few microns in size.     

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%。     

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％。     

Microstructural evolution of titanium matrix composite coatings reinforced by in situ synthesized TiB and TiC by laser cladding

Titanium-based composite coatings reinforced by in situ synthesized TiB and TiC particles were successfully fabricated on Ti6Al4V by laser cladding using Ti-B_4C-Al or Ti-B_4C-C-Al powders as the precursor materials.The microstructural and metallographic analyses were made by X-ray diffraction(XRD),optical microscope(OM),scanning electron microscopy(SEM),and electron probe microanalysis (EPMA).The results show that the coatings are mainly composed ofα-Ti cellular dendrites and a eutectic transformation p...     

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.     

激光熔覆钛基复合涂层的显微组织和硬度分析

采用激光熔覆快速非平衡合成方法制备了原位反应合成TiB增强钛基复合材料.用Y2O3、Ti和B的混合粉末在Ti-6Al-4V基体表面激光熔覆制得TiB/Ti复合涂层.采用X线衍射仪(XRD)、扫描电子显微镜(SEM)、能量散射光谱仪(EDS)和硬度测试等方法,研究了原位合成TiB/Ti复合涂层的显微结构和显微硬度.结果显示:激光熔覆层的相结构主要为α-Ti和TiB两相,TiB增强相均匀地分布于复合涂层中,熔覆层的硬度值高于基体Ti合金的硬度值1倍以上,Y2O3含量(质量分数w,全文同)为1％的激光熔覆涂层内部的增强相组织最为均匀、细小,且硬度值也最高,平均硬度(HV)值约为830.     

Self-Propagating High-Temperature Reductive Synthesis of TiB_2-Al_2O_3 Composite Powders

TiB2-Al2O3 composite powders were produced by self-propagating high-temperature synthesis(SHS) method with reductive process from B2O3-TiO2-Al system. X-ray diffraction(XRD) and scanning electron microscopy(SEM) analyses show the presence of TiB2 and Al2O3 only in the composite powders produced by SHS. The powders are uniform and free-agglomerate. Transmission electron microscopy (TEM) and high resolution electron microscopy (HREM) observation of microstructure of the composite powders indicate that the interfaces of the TiB2-Al2O3 bond well, without any interfacial reaction products. It is proposed that the good interfacial bonding of the composite powders can be resulted from the TiB2 particles crystallizing and growing on the Al2O3 particles surface with surface defects acting as nucleation centers.     

(TiB_2+SiC_p)/ZL101复合材料组份优化及其力学性能

为了确定(TiB2+SiCp)/ZL101复合材料的最佳成分,通过采用正交实验分析方法,研究复合材料的制备工艺,测试了复合材料的力学性能,并对该材料进行了显微金相分析和透射电子显微分析.结果表明,复合材料经过热处理后,抗拉强度、布氏硬度分别较基体合金ZL101提高了21.4%、49.3%;热膨胀系数较基体合金降低了14.1%;热处理后,复合材料中的共晶硅以粒状形态均匀分布于基体中;复合材料中增强相TiB2为粒状,SiC粒子为多边形尖角块状,两相较均匀分布于基体晶粒内部,且与-αAl的界面结合良好.     

金属硅化物熔体中不同形貌SiC晶体的生长

以过渡族金属硅化物为溶剂，采用自发熔渗法和溶液法来研究不同形貌SiC晶体在金属硅化物熔体中的生长情况.利用光学显微镜（OM）、扫描电镜（SEM）、体视显微镜等对熔渗试样和采用溶液法生长的单晶和晶须的形貌结构进行了观察和表征，利用X射线衍射仪（XRD）对采用溶液法生长的晶体和晶须进行了相组成和晶型的表征，并讨论了SiC晶须和SiC单晶的生长机理.结果表明，Fe5Si3、CoSi、Co4.5CrSi4.5、Ti2.3Si7.7等熔体适合生长SiC单晶，FeSi、FeSi2等熔体适合生长SiC晶须，而当Fe3Si熔体渗入SiC预制件后，仅有石墨相析出.     

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.     

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     

Microstructure and mechanical properties of an in situ synthesized TiB and TiC reinforced titanium matrix composite coating

A titanium-based composite coating reinforced by in situ synthesized TiB and TiC particles was fabricated on Ti6Al4V by laser cladding. The microstructure and mechanical properties were investigated. The coating was mainly composed of β-Ti cellular dendrites and an eutectic in which a large number of rod/needle-shaped TiB and a few equiaxial TiC particles were homogeneously embedded. The microstructural evolution could be divided into four stages: precipitation and growth of primary β-Ti phase, formation of the binary eutectic β-Ti+TiB, formation of the ternary eutectic β-Ti+TiB+TiC, and solid transformation from β-Ti to β-Ti. Microhardness of the coating showed a gradient variation from the surface (about HV0.2 876) to the bottom (about HV0.2 660) and was prominently improved in comparison with that of the substrate. Fracture toughness of the coating also exhibited a gradient variation from the surface (6.3 MPa·m1/2) to the interface (11.9 MPa·m1/2). Wear resistance of the coating was significantly superior to that of Ti6Al4V.     

Thermodynamic Stability of the Molding Materials for Casting Ti-6Al-4V Alloy

omoxForitShighstrength-to-weightratio,excellentcorm-sionresisboceandappropriatehightemperatureproPer-ties,Ti-6Al-4VcastingsarewidelyusedasimportantstIUctUralcOrnpoentSforaerospaceaPplications.ButthetuterachonofmoltentitaniurnanoywithmoldingmaterialsmayresultinreducedqUalihesandflexundandfatigUestrengthofthecashngS['J.Thereasoishighchendcalre-activityofmoltentitaniumleadstofowredchedricalsta-bilityofmodingmaterialsincontactandsutheeconed-nationcauseshaIdeningofcasting['1.fomereseareherstr…     

(TiB+TiC)/Ti复合材料的高温蠕变机制

对原位合成非连续增强体积分数为5%的(TiB+TiC)/Ti复合材料和纯Ti在500~700℃温度范围内的蠕变变形机制进行了研究.结果表明,复合材料在实验温度范围内其应力指数为5.80~6.43,与扩散型变形机制的应力指数相近,激活能为284 kJ/mol;Ti的蠕变机制随温度的提高发生了变化,在500℃和600℃温度的下应力指数为4.30、4.03,与位错型蠕变变形机制应力指数相近,其激活能为228 kJ/mol;而在700℃时Ti的蠕变机制为扩散型变形机制,应力指数为5.91.在700℃时纯钛和复合材料的蠕变速率和应力指数n较接近,这说明在此温度下由于增强相与基体传递载荷的能力下降,导致了增强效果的下降.     

TiB2/Cu复合材料组织与性能的研究

以Ti、B和Cu的单质粉末为原料,经混粉-冷压成形-真空烧结,制备出原位自生TiB2陶瓷颗粒增强铜基复合材料.并借助热分析方法和X射线衍射对增强颗粒进行分析,同时通过扫描电子显微镜对复合材料组织进行观察,进一步测定复合材料的力学性能.结果表明,在Ti-B-Cu体系中,通过原位反应生成增强相是TiB2.随着B粉和Ti粉含...     

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。     

Effect of Y2O3 on cracking susceptibility of laser-clad Ti-based composites coatings

Ti-based composite coatings reinforced by in situ synthesized TiB and TiC were deposited on Ti6AlaV substrates by laser cladding. The effects of Y2O3 on the microstructure and cracking susceptibility of the coatings were investigated in details. It is shown that a small amount of Y2O3 addition can significantly refine the microstructure of the coatings by hastening spheroidization of the primary phase structure. The maximum refinement in microstructure was obtained with the optimum （2 wt%） addition of Y2O3. Moreover, it can increase the volume fraction of TiC and reduce the residual stress of the coatings due to the decrease in lattice distortion of the α（Ti） matrix. All of these factors lead to the reduction in cracking susceptibility of the coatings containing Y2O3 on the premise that the hardness of the coatings is improved. The fracture toughness of the coatings without and with Y2O3 （2 wt%） is 8.32 and 17.36 MPa.m1/2, respectively. Scanning electron microscope examination reveals a transition of the fractured surfaces from cleavage fracture to quasi-cleavage fracture resulting from the Y2O3 addition.     

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.     

TiB_2/SiC陶瓷复合材料制备工艺的研究

以TiO2、B4C和C为原料,基于原位合成法在SiC基体中生成TiB2颗粒,并采用无压烧结法制备出TiB2/SiC复合陶瓷.通过对复合材料制备工艺的研究,发现：高于1 300℃的预烧结能形成TiB2/SiC复合陶瓷坯体.C含量、烧结温度和保温时间对复合材料的相对密度均有影响.当C含量（质量分数）为4%时、在1 400℃×60 min＋2000℃×30 min的烧结工艺下能够制备出致密的TiB2/SiC陶瓷复合材料.微米级TiO2粉比纳米级TiO2粉更有利于形成较致密的烧结复合材料.随着生成TiB2体积分数的增加（5%～20%）,复合材料中TiB2颗粒逐渐粗化,间距逐渐变小.对复合材料的烧结机理还进行了分析.     

Microstructures and Properties of SiC／Al2O3 ／Al- Si Composites Prepared by Reactive Penetration

The composition, microstructures and properties of SiC/Al2O3/Al-Si composites formed by reactive penetration of the molten aluminum into the preforms of SiO2 and SiC were investigated. The composition of the composites was measured by X-ray diffraction ( XRD ). The microstructures of the composites were also measured by scanning electron microscopy (SEM) and optical microscopy. In addition, the factors affecting the properties of the composites were discussed. The experiments show that the mechanical properties of the composites depend on their relative densities and the sizes of the fillers“ SiC gains“. The denser the SiC/Al2O3/Al-Si composites, the higher their bending strength. As the filler “SiC gains“ become fine, the bending strength of the composites increases.