Microstructure and mechanical properties characterization of AA6061/TiC aluminum matrix composites synthesized by in situ reaction of silicon carbide and potassium fluotitanate

Aluminum alloys AA6061 reinforced with various amounts （0, 2.5% and 5%, mass fraction） of TiC particles were synthesized by the in situ reaction of inorganic salt K2TiF6 and ceramic particle SiC with molten aluminum. The casting was carried out at an elevated temperature and held for a longer duration to decompose SiC to release carbon atoms. X-ray diffraction patterns of the prepared AMCs clearly revealed the formation of TiC particles without the occurrence of any other intermetallic compounds. The microstructure of the prepared AA6061/TiC AMCs was studied using field emission scanning electron microscope （FESEM） and electron backscatter diffraction （EBSD）. The in situ formed TiC particles were characterized with homogeneous distribution, clear interface, good bonding and various shapes such as cubic, spherical and hexagonal. EBSD maps showed the grain refinement action of TiC particles on the produced composites. The formation of TiC particles boosted the microhardness and ultimate tensile strength （UTS） of the AMCs.

FATIGUE CRACK GROWTH FEATURE OF Fe-Cr-Ni MATRIX COMPOSITE REINFORCED BY TITANIUM CARBIDE PARTICULATE AT 1023K

The initiation and propagation of the short fatigue crack in a 10vol% titanium carbide particulate reichreed cast Fe-26Cr-14Ni mathe coopsite at 1023K were investigated.It is shown that the titanium carbide particulate may hinder the crack propagation and fatigue fracture of the composite. The relationships between fatigue crack propagation rate and stress intensity factor are da/dN=4.2×10-c(△K)4 for the matrix alloy and da/dN=1.4×10-19(△K)c for the composite. The fatigue thresholds of the composite and mathe alloy are 78 and 3.2MPa.m1/2, respectively. Microcracks initiate at the intedece between titanium carbide particulate and austenite and then propagate in carkide particles. The fracture sudece of the composite shows a distinct transition from wavy and serated cleavage near the threshold regime to striation-type splitting in the stable fatigue crack propagation stage and to a veined morphology characteristic in unstable rapid region.

Ballistic performance of titanium-based layered composites made using blended elemental powder metallurgy and hot isostatic pressing

Metal matrix composites tiles based on Ti-6Al-4V(Ti64)alloy,reinforced with 10,20,and 40(vol%)of either TiC or TiB particles were made using press-and-sinter blended elemental powder metallurgy(BEPM)and then bonded together into 3-layer laminated plates using hot isostatic pressing(HIP).The laminates were ballistically tested and demonstrated superior performance.The microstructure and properties of the laminates were analyzed to determine the effect of the BEPM and HIP processing on the ballistic properties of the layered plates.The effect of porosity in sintered composites on further diffusion bonding of the plates during HIP is analyzed to understand the bonding features at the interfaces between different adjacent layers in the laminate.Exceptional ballistic performance of fabricated structures was explained by a significant reduction in the residual porosity of the BEPM products by their additional processing using HIP,which provides an unprecedented increase in the hardness of the layered composites.It is argued that the combination of the used two technologies,BEPM and HIP is principally complimentary for the materials in question with the abilities to solve the essential problems of each used individually.

Corrosion Behaviour of TiC-Reinforced Hadfield Manganese Austenitic Steel Matrix In-Situ Composites

The corrosion behaviour of Hadfield manganese austenitic steel matrix composite reinforced with the varying amount of TiC and unreinforced Hadfield manganese austenitic steel matrix alloy has been evaluated in 3.5% NaCl aqueous solution with the pH value of 6 by the potentiodynamic polarization curves and linear polarization resistance measurements at a scan rate of 1 mV/s at room temperature (25°C ± 2°C). The corrosion rate of the composites is higher than that of their unreinforced matrix alloy and it increases with the increasing volume fraction of TiC. The poor corrosion resistance of the composites can be attributed to the galvanic effects between the matrix and reinforcement.

Interconnected microstructure and flexural behavior of Ti_(2)C-Ti composites with superior Young’s modulus

To enhance the Young’s modulus(E)and strength of titanium alloys,we designed titanium matrix composites with intercon-nected microstructure based on the Hashin-Shtrikman theory.According to the results,the in-situ reaction yielded an interconnected microstructure composed of Ti_(2)C particles when the Ti_(2)C content reached 50vol%.With widths of 10 and 230 nm,the intraparticle Ti lamellae in the prepared composite exhibited a bimodal size distribution due to precipitation and the unreacted Ti phase within the grown Ti_(2)C particles.The composites with interconnected microstructure attained superior properties,including E of 174.3 GPa and ultimate flexural strength of 1014 GPa.Compared with that of pure Ti,the E of the composite was increased by 55% due to the high Ti_(2)C content and interconnected microstructure.The outstanding strength resulted from the strong interfacial bonding,load-bearing capacity of interconnected Ti_(2)C particles,and bimodal intraparticle Ti lamellae,which minimized the average crack driving force.Interrupted flexural tests revealed preferential crack initiation along the{001}cleavage plane and grain boundary of Ti_(2)C in the region with the highest tensile stress.In addition,the propagation can be efficiently inhibited by interparticle Ti grains,which prevented the brittle fracture of the composites.

INVESTIGATION ON THE FORMATION MECHANISM OF TITANIUM CARBIDE PREPARED BY IN SITU REACTION IN MOLTEN ALUMINUM

A novel technique in which TiC particulate are prepared by an in situ reaction in molten aluminum was introduced for producing TiC/Al composite. In order to reveal the characteristics of the technique, the formation mechanism of TiC particulate prepared by this method was studied. Both theoretical and experimental results show that the TiC particulate is formed by a diffusion mechanism when the molar fraction of aluminum in the preforms is higher than 20.02%. On the contrary, the TiC particulate is formed by a solution-precipitation mechanism when the fraction of aluminum in the preforms is lower than 20.02%.

Pseudo-in-situ stir casting: a new method for production of aluminum matrix composites with bimodal-sized B_4C reinforcement

A new method was applied to produce an Al-0.5wt%Ti-0.3wt%Zr/5vol%B_4C composite via stir casting with the aim of characterizing the microstructure of the resulting composite. For the production of the composite, large B4 C particles（larger than 75 μm） with no pre-heating were added to the stirred melt. Reflected-light microscopy, X-ray diffraction, scanning electron microscopy, field-emission scanning electron microscopy, laser particle size analysis, and image analysis using the Clemex software were performed on the cast samples for microstructural analysis and phase detection. The results revealed that as a consequence of thermal shock, B_4 C particle breakage occurred in the melt. The mechanism proposed for this phenomenon is that the exerted thermal shock in combination with the low thermal shock resistance of B_4 C and large size of the added B_4 C particles were the three key parameters responsible for B_4 C particle breakage. This breakage introduced small particles with sizes less than 10 μm and with no contamination on their surfaces into the melt. The mean particle distance measured via image analysis was approximately 60 μm. The coefficient of variation index, which was used as a measure of particle distribution homogeneity, showed some variations, indicating a relatively homogeneous distribution.

Analysis of in situ Reaction and Pressureless Infiltration Process in Fabricating TiC/Mg Composites

An innovative processing route, in situ reaction combined with pressureless infiltration, was adopted to fabricate magnesium matrix composites, where the reinforcement TiC formed in situ from elemental Ti and C powders and molten Mg spontaneously infiltrated the preform of Ti and C. The influences of primarily elemental particle sizes, synthesizing temperature, holding time etc on in situ reactive infiltration for Mg-Ti-C system were systematically investigated in order to explore the mechanism of this process. In fabricating TiC/Mg composites, Mg can not only spontaneously infiltrate the preform of reinforcement and thus densify the as fabricated composites as matrix metal, but also it can accelerate the in situ reaction process and lower the synthesizing temperature of Ti and C as well. In situ reaction of Ti and C and Mg infiltration processes are essentially overlapping and interacting during fabrication of TiC/Mg composites. The mechanism proposed in this paper can be used to explain the formation and morphologies of the reinforcement phase TiC.

Comparison of wear behaviour of LM13 Al−Si alloy based composites reinforced with synthetic(B_(4)C)and natural(ilmenite)ceramic particles

Dry sliding wear behaviour of stir-cast aluminium matrix composites(AMCs)containing LM13 alloy as matrix and ceramic particles as reinforcement was investigated.Two different ceramic particle reinforcements were used separately:synthetic ceramic particles(B_(4)C),and natural ceramic particles(ilmenite).Optical micrographs showed uniform dispersion of reinforced particles in the matrix material.Reinforced particles refined the grain size of eutectic silicon and changed its morphology to globular type.B_(4)C reinforced composites(BRCs)showed maximum improvement in hardness of AMCs.Ilmenite reinforced composites(IRCs)showed maximum reduction in coefficient of friction values due to strong matrix−reinforcement interfacial bonding caused by the formation of interfacial compounds.Dry sliding wear behaviour of composites was significantly improved as compared to base alloy.The low density and high hardness of B_(4)C particles resulted in high dislocation density around filler particles in BRCs.On the other hand,the low thermal conductivity of ilmenite particles resulted in early oxidation and formation of a tribo-layer on surface of IRCs.So,both types of reinforcements led to the improvement in wear properties of AMCs,though the mechanisms involved were very different.Thus,the low-cost ilmenite particles can be used as alternative fillers to the high-cost B_(4)C particles for processing of wear resistant composites.

Microstructure and high-temperature wear properties of in situ TiC composite coatings by plasma transferred arc surface alloying on gray cast iron

In this work, an in situ synthesized TiC-reinforced metal matrix composite （MMC） coating of approximately 350-400μm thickness was fabricated on a gray cast iron （GCI） substrate by plasma transferred arc （PTA） surface alloying of Ti-Fe alloy powder. Microhard- ness tests showed that the surface hardness increased approximately four-fold after the alloying treatment. The microstructure of the MMC coating was mainly composed of residual austenite, acicular martensite, and eutectic ledeburite. Scanning electron microscopy （SEM） and X-ray diffraction analyzes revealed that the in situ TiC particles, which were formed by direct reaction of Ti with carbon originally contained in the GCI, was uniformly distributed at the boundary of residual anstenite in the alloying zone. Pin-on-disc high-temperature wear tests were performed on samples both with and without the MMC coating at room temperature and at elevated temperatures （473 K and 623 K）, and the wear behavior and mechanism were investigated. The results showed that, after the PTA alloying treatment, the wear resistance of the sam- ples improved significantly. On the basis of our analysis of the composite coatings by optical microscopy, SEM with energy-dispersive X-ray spectroscopy, and microhardness measurements, we attributed this improvement of wear resistance to the transformation of the microstruc- ture and to the presence of TiC particles.

Effect of molybdenum on interfacial properties of titanium carbide reinforced Fe composite

This study shows that the mechanical strength of the composite of Fe matrix and titanium carbide(Ti C)ceramic particles is significantly enhanced with addition of molybdenum(Mo) atoms. Ti C reinforced Fe(Fe-0.2C-7Mn) composites with and without Mo were fabricated by a liquid pressing infiltration(LPI)process and the effect of Mo on interfacial properties of TiC–Fe composite was investigated using atomic probe tomography(APT) analysis, molecular dynamics(MD) simulations, first-principle density functional theory(DFT), and thermodynamic calculations. First, DFT calculations showed that total energies of the Mo-doped Ti C–Fe superlattices strongly depend on the position of Mo defects, and are minimized when the Mo atom is located at the TiC/Fe interface, supporting the probable formation of MoC-like interphase at the TiC/Fe interface region. Then, APT analysis confirmed the DFT predictions by finding that about6.5 wt.% Mo is incorporated in the Ti C–Fe(Mo) composite and that sub-micrometer thick(Ti,Mo)C interphase is indeed formed near the interface. The MD simulations show that Mo atoms migrate to the Mo-free TiC–Fe interface at elevated temperatures and the mechanical strength of the interface is considerably enhanced, which is in good agreement with experimental observations.

常见结构材料低温性能研究进展

随着深空探测、极地科考、低温贮运等低温领域的快速发展,对低温材料的要求越来越高,低温材料逐渐成为目前国内外的研究热点。本文综述低温钢、铝合金、钛合金、铝基复合材料以及树脂基复合材料等常见结构材料的低温性能,归纳不同晶体结构、合金种类、合金元素等因素对结构材料的低温强度、塑性与韧性等力学性能的影响及低温变形和强韧化机理,介绍不同种类低温结构材料在国内外重要领域的应用,提出了低温材料未来的研究展望。

TiC和ZrC颗粒增强钨基复合材料

用粉末冶金热压法制备ＴｉＣＰ／Ｗ和ＺｒＣＰ／Ｗ两种钨基复合材料，对其高温强度进行了研究，结果表明：随着温度提高，两种复合材料的抗弯强度开始时逐渐提高；当ＴｉＣＰ／Ｗ复合材料达到１０００℃时有最大值１１５５ＭＰａ，ＺｒＣＰ／Ｗ复合材料在８００℃时有最大值８２９ＭＰａ，分别比各自的室温强度提高５７％和１７％。而后，随温度的进一步提高，复合材料的强度又下降。分析了复合材料高温增强的机理。

钛铁矿资源综合利用现状与发展

钛铁矿资源储量大,分布广。目前,每年开采的含钛矿石约有90％用于制取钛白,5％左右用于生产海绵钛,其余部分用于其它。概括了钛铁矿资源利用现状,指出了存在的问题,介绍了钛铁矿综合利用的最新研究动向。节能降耗,减少环境污染,综合利用铁、钛两种组分是钛铁矿利用发展的必然趋势。

碳化钨颗粒增强钢基复合材料的冲蚀磨损性能研究

以直径为188～250um的石英砂为磨料，在自制颗粒冲蚀磨损试验机上对WC颗粒增强ZG45钢基表层复合材料的气-固两相冲蚀磨损性能进行研究，采用扫描电子显微镜观察其磨损表面形貌．结果表明，在相同冲蚀角条件下，增强相WC颗粒的直径越大，复合材料的耐磨性越差，复合材料在冲蚀角为45°时的冲蚀磨损率最大；而ZG45钢在冲蚀角为15°～30°范围内的冲蚀磨损率达到最大值，此后随着冲蚀角增加而减小；复合材料抗冲蚀磨损性能在较小冲蚀角（15°左右）下优于ZG45钢，在较大冲蚀角（≥30°）时劣于ZG45钢．

WC/钢基合金不同热处理状态的微观特征

对ＷＣ／钢基复合材料进行了比较细致的微观分析，揭示了这种材料具有与相近基体成分的钢材明显不同的微观特征。其退火组织典型的”白区”与”暗区”分别由大块硬质相与基体上细小碳化物的密集分布区相间而成。在９６０℃～１１００℃宽范围内加热淬火后均可得到细马氏体组织（奥氏体晶粒度为ＡＳＴＭ１１～１２．５级）。此材料具有大、中、小三种不同尺寸的碳化物分布；大块硬质相中棱角状碳化物与团块状碳化物的性质与物理状态均不相同。本工作还测试分析了合金微观组成单元的显微硬度及与宏观洛氏硬度的对应关系。

WC/钢基合金的强韧化因素分析

基于力学性能试验、断裂韧性试验及微观分析 ,对碳化钨增强钢基颗粒复合材料的强化与韧化因素作了较全面的综合分析 ,得出此类材料的主要强韧化机理为高强韧的马氏体、大量超硬碳化物的复合强化、超细晶粒强韧化、界面强韧化以及硬质相与基体交互作用带来的强韧化效果 .

碳化钨增强钢铁基耐磨复合材料的研究和应用

评述了制备复合材料的铸渗法、粉末烧结法、堆焊法、电渣熔铸法等工艺方法,以及碳化钨和钢铁基体的选择、界面反应和强度、复合材料的性能和应用现状。重点介绍了粘结剂、其他添加剂、碳化钨颗粒形状、粒度及其分布、浇注温度等对铸渗工艺及其表面复合材料的影响。阐明铸渗法是一种有前途的制备工艺,自蔓延工艺和铸造工艺的组合有可能取得新的成效。指出复合层厚度在10mm以上的铸渗工艺,工程化和产业化关键技术以及复合工艺的稳定化是今后的研发重点,表面耐磨复合材料较适用于零部件的局部磨损和低角度的冲蚀磨损,应据磨损工况来选择制备工艺及其复合材料。

电冶熔铸WC-Co/钢复合材料组织和性能的研究

用回收的废WC Co硬质合金作原料,采用电冶熔铸法制备了新型的WC/钢基复合材料。借助金相分析、扫描电镜及X射线衍射等方法研究了该材料铸造原始态和退火态的微观组织结构,还测试了主要力学性能。材料中的硬质相和钢基体相的相互溶解,使两相实现了冶金结合,形成含W和Co的碳化物,但形态不佳。增加电磁搅拌可使枝晶"破碎";经退火处理和锻造可以改善材料中的不良组织,使硬质相碳化物粒子均匀地分布在钢基体中,冲击韧度也得到提高。

激光熔覆制备原位自生TiC颗粒强化Ni基合金复合涂层的研究

为了在碳钢表面获得耐磨、耐蚀、抗热疲劳等综合性能优良的TiC颗粒强化Ni基合金复合涂层 ,利用3kW连续波快速轴流CO2 激光器进行了一系列的激光表面熔覆实验研究 ,光斑直径 3 5mm ,扫描速度 3 10mm/s,送粉速率 3 2 6 g/min。实验结果表明 :利用送粉式激光表面熔覆技术 ,可以在碳钢表面直接原位合成TiC颗粒增强的Ni基合金复合涂层 ,涂层与基体呈良好的冶金结合 ,涂层宏观质量完好 ,无裂纹 ,但有少量的气孔。涂层组织由γ 奥氏体枝晶、CrB、TiB2 、M2 3 C6和TiC组成。经激光表面重熔后 ,涂层显微硬度达HV0 2 110 0 ,是基材显微硬度的 4