原位反应渗透法TiCp/Mg复合材料的制备和性能

利用Ti和C元素粉末间的原位放热反应合成TiCp,结合Mg熔体的自发渗透技术制备了TiCp/Mg以及TiCp/AZ91D两种镁基复合材料,观测了复合材料的相组成和原位反应生成物TiCp的形貌,研究了这两种镁基复合材料的常温压缩性能.结果表明,原位反应自发渗透技术制备的Mg基复合材料组织致密,增强相呈细小的颗粒状和互穿网片状,分布均匀.这是材料的压缩强度得到提高的原因.在常温以及应变速率为0.01 s-1的条件下,TiCp/Mg和TiCp/AZ91D镁基复合材料的压缩强度分别达到598和650 MPa.     

Processing and Characterization of In Situ (TiC–TiB2)p/AZ91D Magnesium Matrix Composites

In this paper, a practical and cost‐effective processing route, in situ reactive infiltration technique, was utilized to fabricate magnesium matrix composites reinforced with a network of TiC–TiB₂ particulates. These ceramic reinforcement phases were synthesized in situ from Ti and B₄C powders without any addition of a third metal powder such as Al. The molten Mg alloy infiltrates the preform of (Ti_p + B₄C_p) by capillary forces. The microstructure of the composites was investigated using scanning electron microscope (SEM)/energy dispersive X‐ray spectroscopy (EDS). The compression behavior of the composites processed at different conditions was investigated. Also, the flexural strength behavior was assessed through the four‐point‐bending test at room temperature. Microstructural characterization of the (TiB₂–TiC)/AZ91D composite processed at 900 °C for 1.5 h shows a relatively uniform distribution of TiB₂ and TiC particulates in the matrix material resulting in the highest compressive strength and Young's modulus. Compared with those of the unreinforced AZ91D Mg alloy, the elastic modulus, flexural and compressive strengths of the composite are greatly improved. In contrast, the ductility is lower than that of the unreinforced AZ91D Mg alloy. However, this lower ductility was improved by the addition of MgH₂ powder in the preform. Secondary scanning electron microscopy was used to investigate the fracture surfaces after the flexural strength test. The composites show signs of mixed fracture; cleavage regions and some dimpling. In addition, microcracks observed in the matrix show that the failure might have initiated in the matrix rather than from the reinforcing particulates.     

A developed method for producing in situ TiC/Al composites by using quick preheating treatment and ultrasonic vibration

Quick preheating treatment of Al–Ti–C was introduced in the fabrication of in situ TiC/Al metal matrix composites in our research. Al–Ti–C pellets were preheated in the furnace at 750 °C, in which the pure aluminum was melted. After adding the preheated pellets into the molten aluminum, the thermal explosion reaction of Al–Ti–C took place in a short time. In situ TiC particles synthesized in the pure molten aluminum were spherical in morphology and most of which were smaller than 1 μm in size. The synthesizing temperature of in situ TiC/Al composites was decreased significantly by using the quick preheating treatment, at least 150 °C lower than those used in the conventional methods. In addition, high-intensity ultrasonic vibration was applied into the melt to disperse TiC particle-reinforcement into the matrix and degas the melt as well. In situ TiC particles were distributed uniformly in the matrix, and the porosity in the composites was below 1% due to the effect of ultrasonic vibration. Furthermore, the microhardness test indicated that a homogeneous microstructure of in situ TiC/Al composite was obtained.     

Processing of B4C Particulate-reinforced Magnesium-matrix Composites by Metal-assisted Melt Infiltration Technique

In fabricating magnesium-matrix composites, an easy and cost-effective route is to infiltrate the ceramic preform with molten Mg without any external pressure. However, a rather well wettability of molten Mg with ceramic reinforcement is needed for this process. In order to improve the wettability of the metal melt with ceramic preform during fabricating composites by metal melt infiltration, a simple and viable method has been proposed in this paper where a small amount of metal powder with higher melting point is added to the ceramic preform such that the surface tension of the Mg melt and the liquid-solid interfacial tension could be reduced. By using this method, boron carbide particulate-reinforced magnesium-matrix composites （B4C/Mg） have been successfully fabricated where Ti powder immiscible with magnesium melt was introduced into B4C preform as infiltration inducer. The infiltration ability of molten Mg to the ceramic preform was further studied in association with the processing conditions and the mechanism involved in this process was also analyzed.     

Understanding the reaction mechanism of in-situ synthesized (TiC–TiB2)/AZ91 magnesium matrix composites

Magnesium matrix composites reinforced with a network of TiC and TiB₂ compounds have been successfully synthesized via an in-situ reactive infiltration technique. In this process, the ceramic reinforcing phases, TiC and TiB₂, were synthesized in-situ from the starting powders of Ti and B₄C without any addition of a third metal powder such as Al. The molten AZ91 magnesium alloy infiltrates the preform of 3Ti–B₄C by capillary forces. Furthermore, adding different weight percentages of MgH₂ powder to the 3Ti–B₄C preforms was used in an attempt to increase the Mg content in the fabricated composites. The results reveal a relatively uniform distribution of the reinforcing phases in the magnesium matrix with very small amounts of residual Ti, boron carbide and intermediate phases when they are fabricated at 900 °C for 1.5 h using a 3Ti–B₄C preform with 70% relative density. On the other hand, after adding MgH₂ to the 3Ti–B₄C preform, TiC_x and TiB₂ formed completely without any residual intermediate phases with the formation of the ternary compound (Ti₂AlC) at the expense of TiC. The percentage of reinforcing phases can be tailored by controlling the weight percentages of MgH₂ powder added to the 3Ti–B₄C preform. The results of the in-situ reaction mechanism investigation of the Ti–B₄C and Mg–B₄C systems show that the molten magnesium not only infiltrates through the 3Ti–B₄C preform and thus densifies the fabricated composite as a matrix metal, but also acts as an intermediary making the reaction possible at a lower temperature than that required for solid-state reaction between Ti and B₄C and accelerates the reaction rate. The investigation of the in-situ reaction mechanism with or without the addition of MgH₂ powder to the 3Ti–B₄C preforms reveals similar mechanisms. However, the presence of the MgH₂ in the preform accelerates the reaction resulting in a shorter processing time for the same temperatures.     

Fabrication and Microstructure of C/Cu Composites

C/Cu composites were prepared by a melting infiltration technique in vacuum. In order to improve the wettability between Cu and carbon fibers, Ti (8 wt.‐%) and Cr (1 wt.‐%) were added to the Cu alloy. Microstructures of the composites and interface between C and Cu were investigated by XRD, SEM, EDS and HRTEM. The results show that the Ti and Cr improved the wettability between Cu and C? C preform and the infiltration ability of Cu into C? C preform greatly. The prepared C/Cu composites are characterized as having good interface bonding and high density. In the process of infiltration, Ti and Cr concentrate on the boundary of carbon fiber. Formation of TiC results from the reaction of Ti and C between Cu and carbon fiber.     

Effect of compact density and preheating temperature of the Al–Ti–C preform on the fabrication of in situ Mg–TiC composites

Magnesium reinforced in situ TiC particulates was successfully synthesized by utilizing the self-propagating high temperature synthesis (SHS) process. The result showed that preform temperature and compact density have effects on the SHS reaction. It is observed that when the compact density was below 68% of the theoretical density, no SHS reaction occurred. However, with an increase in density from 68 to 72%, the successful thermal explosion reaction was observed in the Mg melt. Besides this, the effect of preheat temperature on the fabrication of Mg/TiC composite was extensively studied and found that the preheat temperature below 300 °C failed to give rise to SHS reaction. However, the preheat temperature of 450, 500, and 550 °C favors the reaction inside the liquid melt, but the temperature of 600 °C leads to the ignition reaction in the preheating furnace itself. SEM and EDX study confirms fine distribution of TiC in the matrix.     

Microstructure and Mechanical Property of in-situ Al-Cu/TiC Composites

An approach named direct reaction synthesis (DRS) has been developed to fabricate particulate composites with an extremely fine reinforcement size. ID situ Al matrix composites were fabri-cated by DRS. Extensive analysis of the composites microstructure using SEM and TEM identify that the reinforcement formed during the DRS process is Ti carbide (TiC) particle, generally less than 1.0 μm. The reacted, semisolid extruded samples exhibit a homogeneous distribution of fine TiC particles in Al-Cu matrix, Mechanical property evaluation of the composites has revealed a very high tensile strength relative to the matrix alloy. Fractographic analysis indicates ductile failure although the ductility and strength are limited by the presence of coarse titanium aluminides (Al3Ti).     

In situ synthesis of Al–TiC in aluminum melt

In situ technology for the preparation of Al–TiC composite by self-propagating high-temperature synthesis is considered in this paper. It involves the synthesis of the reinforcement phase TiC from elemental powders directly in aluminum melt. Based on thermodynamic calculations, the composition and molar ratio of powders were chosen for the experiments. The effects of initial melt temperature and fluxes on the character of SHS reaction and TiC recovery were studied. The synthesis was shown to result in the formation of Al and TiC phases. The composites Al–TiC with the uncontaminated macrofracture, with the best TiC recovery and with the smallest TiC particles, can be produced at 1000 °C with fluxes.     

液硅渗透法制备Ti3SiC2改性C/CSiC复合材料

采用浆料浸渗结合液硅渗透法原位生成高韧性Ti₃SiC₂基体, 制备Ti₃SiC₂改性C/C-SiC复合材料。研究了TiC颗粒的引入对熔融Si浸渗效果的影响, 分析了Ti₃SiC₂改性C/C-SiC复合材料的微结构和力学性能。实验结果表明: TiC与熔融Si反应生成Ti₃SiC₂是可行的, 而且C的存在更有利于生成Ti₃SiC₂; 在含TiC颗粒的C/C预制体孔隙(平均孔径22.3 μm)内, 熔融Si的渗透深度1 min内可达10.8 cm; Ti₃SiC₂取代残余Si后提高了 C/C-SiC复合材料的力学性能, C/C-SiC-Ti₃SiC₂复合材料的弯曲强度达203 MPa, 断裂韧性达到8.8 MPa·m1/2; 对于厚度为20 mm的试样, 不同渗透深度处材料均具有相近的相成分、 密度和力学性能, 无明显微结构梯度存在, 表明所采用的浆料浸渗结合液硅渗透工艺适用于制备厚壁Ti₃SiC₂改性C/C-SiC复合材料构件。      

原位自生Ti3 Al金属间化合物基复合材料的微观结构

采用原位自生（XD）法制备Ti3Al金属间化合物基复合材料,对复合材料的XRD,OM和SEM的分析结果表明,Ti-17Al-0.5C复合材料的基体为Ti3Al,增强相为Ti3AlC,且增强相在基体中按一定的方位排列,Ti-17Al-1.5(2.0)C复合材料的基体为Ti3Al,增强相由心部TiC矣包覆层Ti3AlC双层组成,随着含C量的增加,增强相由不发达的树脂晶变为等轴晶,对合金进行微力学探针测试表明,增强相TiC和Ti3AlC的显微硬度和弹性模量均大于基体Ti3Al,随着C含量的增加,合金中增强相和基体的显微硬度和弹性模量无明显变化。     

原位自生Al_2O_3-TiC_p/Al基复合材料的热力学分析

采用熔铸法制备了原位自生Al2O3-TiCp/Al基复合材料。借助差示扫描量热仪(DSC)、扫描电子显微镜(SEM)、能谱分析仪(EDS)、X射线衍射仪(XRD)等测试技术,对Al-TiO2-C体系的热力学进行了详尽的分析,讨论了过量铝对Al-TiO2-C体系反应的影响。结果表明,通过控制反应温度等工艺参数完全可以获得原位自生Al2O3-TiCp/Al基复合材料,避免副产物Al3Ti和Al4C3的产生。Al-TiO2-C体系原位合成Al2O3-TiCp/Al基复合材料存在着复杂的化学反应。首先在无过量铝的情况下,Al与TiO2发生置换反应,生成了Al2O3和游离态[Ti],而后游离态[Ti]与C结合生成TiC;而存在过量铝的情况下,首先发生铝热反应生成Al3Ti,进而Al3Ti与C结合生成TiC。最终完全获得Al2O3-TiCp/Al复合材料。随着过量Al含量由0增加至70%,Al与TiO2反应生成Al2O3的反应起始温度不断降低。     

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。      

熔融渗透工艺制备SiC-TiSi2复相陶瓷的反应机理

熔融Si渗透过程伴随着复杂的化学反应及多组分扩散,对该过程进行研究有助于更好地理解熔渗反应机理。本工作采用熔融渗透工艺制备SiC-TiSi2复相陶瓷,在生成SiC基体的同时原位生成TiSi2。通过扫描电子显微镜(SEM)、X射线能谱分析(EDS)和微区X射线衍射(micro-beam XRD)分别对熔融硅区域、Si/SiC界面以及SiC基体的微观结构和相组成进行表征和分析,研究了熔渗工艺制备SiC-TiSi2的反应机理。结果表明:高温下液Si渗入C-TiC预制体,发生化学反应生成SiC、TiSi2以及少量副产物Ti5Si3,其中Ti5Si3主要集中于Si/SiC界面处。随着反应进行,液Si与TiSi2形成液态Ti-Si共晶。该液态共晶通过流动扩散在Si区域中析出TiSi2。而预制体中的少量固态C在液Si中溶解、扩散,并在Si区域生成均匀分布的孤立SiC颗粒。     

原位合成TiC颗粒增强铁基复合材料的微观结构研究

采用不同化学成分基体制备了原位合成ＴｉＣ颗粒增强铁基复合材料,并以透射电镜为手段对其微观结构进行了分析研究,结果表明,ＴｉＣ增强相周围基体组织与基体含碳量有关,基体中较高的含碳量有助于抑制Ｆｅ２Ｔｉ相的形成,在含钼基体中ＴｉＣ增强相与基体之间存在一富钼的包覆层,进一步改善了基体对碳化钛的润湿性,有利于增强体在基体中的均匀分布。     

Synthesis of TiC/Ti–Cu composites by pressureless reactive infiltration of TiCu alloy into carbon preforms fabricated by 3D-printing

The microstructure of dense TiC/Ti–Cu composites fabricated by pressureless infiltration of TiCu alloy into porous starch derived carbon preform produced by 3D-printing has been studied. The reactive melt infiltration was carried out at 1100 °C in a flowing Ar atmosphere and resulted in formation of a composite comprised predominantly of substoichiometric TiC_x (x=0.78), binary intermetallic Ti–Cu phases and residual carbon. SEM analyses revealed a microstructure consisting of a dispersed fine-grained TiC_0.78 (∼7 μm) in a Ti–Cu matrix.     

In situ synthesis of TiC from nanopowders in a molten magnesium alloy

The synthesis of in situ formed TiC/Mg(ZM5) composite utilizing the exothermic reaction of the preforms consisting of Al, C and Ti powders in molten magnesium was investigated. The result showed that the reactant particle size has a great effect on the reaction. For a nano-size Al and C, and micron-size Ti powders system, in situ TiC/Mg(ZM5) composite was fabricated successfully.     

Assessment of Microwave Heating for Sintering of Al/SiC and for in‐situ Synthesis of TiC

This work describes sintering of SiC‐reinforced Al‐matrix composites and in‐situ synthesis of TiC in a powder mixture of Ti and C. In the first case, microwave energy is absorbed by SiC grains, heating the metal matrix to sintering and even melting temperature. The composite is processed at <1 kW microwave power. Microwave absorption and the heating rate increase with decreasing SiC particle size. Composites with high SiC content (70 vol.‐%) are processed at 650 °C/1 h in the microwave furnace, whereas conventional resistive heating at the same temperature did not allow sintering of the sample. In the second case, radiative energy allowed the heating of Ti/C samples up to 950 °C, and microwave assistance enhanced the reaction sintering of Ti/C powder mixtures forming TiC at the border of the Ti particles. The results are compared with conventional processing. Optical images and XRD patterns confirmed the formation of TiC for both techniques.     

Microstructural evolution of reinforcements in the remelting in situ TiC/Al-12Si composites treated by ultrasonic vibration

Clusters of reinforced particles and long rod-like Al₃Ti particles are usually present in the matrix of in situ TiC/Al alloy composites fabricated via SHS reaction of the Al-Ti-C system in the molten aluminum alloys. In order to improve the properties of the composites, the above issues should be solved effectively. In our research, high-intensity ultrasonic vibration was introduced into the remelting TiC/Al-12Si composites containing clusters of TiC particles and long rod-like Al₃Ti phase to optimize the microstructure of the composites. The results of SEM showed that long rod-like Al₃Ti particles were turned into small blocky ones and large clusters were broken up into small ones. In the meantime, individual TiC particles could be peeled off from the clusters and distributed uniformly in the matrix. An in situ TiC/Al-12Si composite with a homogeneous microstructure was attained successfully. The evolution of the morphology of Al₃Ti phase and the clusters in the ultrasonic field was also discussed.     

石墨添加对原位合成钛基复合材料高温力学性能的影响

利用钛与碳化硼及石墨之间的自蔓延高温合成反应经普通的熔铸工艺原位合成制备了不同摩尔比值TiB和TiC增强的钛基复合材料。测定了原位合成钛基复合材料的高温力学性能。结果表明:由于增强体的原位合成,复合材料的高温拉伸性能与基体合金比较有了明显的提高。高温拉伸断裂与温度有关,温度较低时,增强体断裂是材料失效的主要原因;而随着温度的提高,增强体与基体合金界面脱粘成为材料失效的主要原因。高温拉伸时裂纹容易在短纤维状增强体TiB的端面处形核与长大从而使增强体与基体合金脱粘导致材料失效,因此加入石墨形成更多的TiC粒子有利于提高复合材料的高温力学性能。