Reaction procedure of a graphite fiber reinforced Ti-Al composite produced by squeeze casting-<Emphasis Type=Italic>in situ</Emphasis> reaction

The in situ reaction procedure and microstructure evolution of a graphite fiber reinforced Ti-Al composite (Grf/Ti-Al) was investigated, and the stability of TiAl_3 at high temperature was discussed. As-cast material was prepared by pressing molten pure aluminum into a preform, which was composed of titanium particles and graphite fibers. The in sire reaction procedure of the as-cast material was investigated by dif-ferential scanning calorimetry (DSC), and phases in the products were detected by X-ray diffraction (XRD). Experimental results showed that TiAl_3 was formed first. With an increase in temperature, TiC and Al_4C_3 were observed, but TiAl_3 decreased. In the final product, Al_2O_3 and TiO_2 were observed. It was considered that the previous forming TiAl_3 decomposed, then TiC precipitated, and subsequently, oxidation resulted in the formation of Al_2O_3 and TiO_2.     

Reaction diffusion in continuous SiC fiber reinforced Ti matrix composite

SiC continuous fiber-reinforced pure Ti(TA1)matrix composites were fabricated by a vacuum hot pressing(VHP)methodand then heat-treated in vacuum under different conditions.The interfacial reaction and the formation of interfacial phases werestudied by using SEM,EDS and XRD.The results show that there exists reaction diffusion at the interface of SiC fibers and Timatrix,and the concentration fluctuation of reaction elements such as C,Ti and Si appears in interfacial reaction layer.The interfacialreaction products are identified as Ti3SiC2,TiCx and Ti5Si3Cx.At the beginning of interfacial reaction,the interfacial reactionproducts are TiCx and Ti5Si3Cx.Along with the interfacial reaction diffusion,Ti3SiC2 and Ti5Si3Cx single-phase zones come forth inturn adjacent to SiC fibers,and the TiC Ti5Si3Cx double-phase zone appears adjacent to Ti matrix,which forms discontinuousconcentric rings by turns around the fibers.The formed interfacial phases are to be Ti3SiC2,Ti5Si3Cx and TiCx Ti5Si3Cx from SiCfiber to Ti matrix.The interfacial reaction layer growth is controlled by diffusion and follows a role of parabolic rate,and theactivation energy(Qk)and(k0)of SiC/TA1 are 252.163 kJ/mol and 7.34×10?3m/s1/2,respectively.     

激光熔覆高铌Ti-Al金属间化合物复合涂层的原位反应机制及其微结构特征

通过激光熔覆增技术在BT3-1钛合金表面制备了高铌Ti-Al金属间化合物复合涂层。根据差热(DTA)和热重(TG)曲线,探讨了氩气和氮气保护下Ti、Al、Nb三种元素混合粉末之间的激光原位合成反应机制。借助X射线衍射(XRD)和扫描电镜(SEM)分析了复合涂层的物相结构和微观形貌。结果表明：复合涂层主要由单质Nb、金属间化合物γ-TiAl、α₂-Ti₃Al和Ti₃Al₂等物相组成,Nb只有部分发生了原位反应。N₂能够降低Ti-Al二元反应之间的反应温度,提高反应速率,对Ti-Al二元反应起催化作用。复合涂层中没出现通常激光熔覆所具有的外延生长柱状晶组织,而是形成了细小的等轴晶组织。     

Characterization of in situ synthesized TiC particle reinforced Fe-based composite coatings produced by multi-pass overlapping GTAW melting process

In this paper, in situ synthesized TiC particles reinforced Fe-based surface composite coatings by multi-pass overlapping gas tungsten arc welding (GTAW) melting process employing a proper amount of graphite and ferrotitanium (FeTi) on AISI 1020 steel substrate was produced. The microstructure and wear properties of the composite coatings were investigated by means of an electron microprobe microanalysis (EPMA), X-ray diffractometer and wear tester. The results showed that the multi-pass overlapping GTAW melting surface composite coatings can be obtained under suitable welding parameters, and no crack and porosity are found in the tracks. The X-ray and EPMA results confirm that TiC particles can be formed via reaction of FeTi and graphite during multi-pass overlapping GTAW melting process. TiC particles present cubic and dendrite shape in the non-overlapping zone. It is found that there occurred TiC particles coarsening at the overlap regions, which can lead to detrimental effects on the hardness and wear performance. Composite coatings give a high hardness and excellent wear resistance; and the wear friction coefficient of the coating is less than that of the 1020 steel. As a result, multi-pass overlapping GTAW melting process can be used effectively for producing surface composite coatings with a pre-placed powder to improve wear resistance of the AISI 1020 steel.     

Properties of copper/graphite/carbon nanotubes composite reinforced by carbon nanotubes

Electroless Cu plating was used for flake G powder and CNTs, Cu-G-CNTs (copper/graphite/carbon nanotubes) composites were manufactured by means of powder metallurgical method. The influences of CNTs on the mechanical properties, conductivity properties, friction, and wear performance of the composite were examined. The results indicate that adding a small amount of CNTs can improve comprehensive property of the composites, especially mechanical property. However, excessive CNT, which is easily winding reunion and grain boundary segregation, results in performances degradation.     

Solidification microstructures in a short fiber reinforced alloy composite containing different fiber fractions

Al2O3 short fiber reinforced aluminium alloy has a lot ofsuperior properties, including low weight, low thermalexpansioncoefficient,highstrength-to-weightandstiffness-to-weight ratio, high-temperature resistance, high corrosionresistance and so on. All these excellent propertiespromise the material a good application perspective in theaerospace automotive, and mechanical engineering areas.Despite the widespread application of the material,however, there have, as yet, been few reports available…     

柔性三元碳化物增强Ti-Al系金属间化合物的研究进展

Ti-Al系金属间化合物被认为是极具发展潜力的高温轻合金,但是室温塑性差和脆性大,超过850 ℃氧化抗力不足等问题严重阻碍了其实用化进程。复合化技术作为一种高效手段被广泛用于制备Ti-Al基金属间化合物,此时增强相的类型影响着产物的性能。与大多数脆性硬质陶瓷相相比,柔性层状三元化合物M_n+1AX_n（简称MAX）兼具金属和陶瓷的双重优异特性,是Ti-Al系金属间化合物最为理想的增强相。本文主要介绍了国内外关于MAX相增强Ti-Al系金属间化合物的研究现状,以期为其他研究者提供一种思路,进一步推动高性能Ti-Al系金属间化合物的发展。     

氩弧原位合成TiC颗粒增强Fe基复合层

通过在Fe基自熔合金粉末中添加一定比率的强碳化物形成元素Ti及石墨,采用氩弧熔敷法在中碳钢基体上制备原位形成的TiC颗粒增强Fe基合金复合涂层.利用扫描电镜、电子探针、X射线衍射和图像分析系统,对熔敷层显微组织及其影响因素进行了观察与分析.研究结果表明,利用氩弧熔敷技术,可以原位形成细小、弥散分布的TiC颗粒;TiC颗粒沿熔敷层深度呈梯度分布.通过调整预置涂层的厚度、熔敷工艺参数以及石墨的加入量,可以调整控制熔敷层的成形及组织与性能.     

等离子原位合成陶瓷相增强铁基堆焊层

采用等离子堆焊技术,在碳钢基体表面预涂一定混合比例的高碳铬铁、钒铁和石墨,制备原位自生陶瓷相增强铁基堆焊层,并对堆焊层的组织和性能进行测试.结果表明:堆焊层与基体之间形成良好的冶金结合,堆焊层微观组织由马氏体、少量残余奥氏体、(Fe,Cr,V)7C3和VC构成.初生(Fe,Cr,V)7C3呈六边形,晶粒尺寸较大,均匀弥散分布在熔覆层中,VC颗粒呈团聚状或球状,晶粒较细小.堆焊层硬度从基体到表面呈合理的梯度分布,使材料具有较好的耐磨性.     

Microstructural and abrasive wear properties of SiC reinforced aluminum-based composite produced by compocasting

The effect of SiC particles reinforcement with average size of 1, 5, 20 and 50 μm and volume fraction of 5%, 10% and 15% on the microstructure and tribological properties of Al-based composite was investigated. Composites were produced by applying compocasting process. Tribological properties of the unreinforced alloy and composites were studied using pin-on-disc wear tester, under dry sliding conditions at different specific loads. The influence of secondary mechanical processing with different rolling reductions on the dry sliding wear characteristics of Al matrix composites was also assessed. Hardness measurement and scanning electron microscopy were used for microstructural characterization and investigation of worn surfaces and wear debris. The proper selection of process parameter such as pouring temperature, stirring speed, stirring time, pre-heated temperature of reinforcement can all influence the quality of the fabricated composites. The porosity level of composite should be minimized and the chemical reaction between the reinforcement and matrix should be avoided.     

原位冶金反应碳化钨增强铁基复合材料

利用自耗电极直流电弧原位冶金的方法,获得了碳化钨增强铁基复合材料.采用SEM、EDS、XRD等研究了复合材料的组织,利用显微硬度计测试了其显微硬度.结果表明:W在富C的过热液相中混合扩散,发生原位冶金反应生成WCp.WCp和鱼骨状(Fe,W)6C组织弥散分布在由Fe、Cr、Ni、Mn、C等元素组成的粘结相中,这种强硬质相、辅助硬质相与基体的弥散分布和交叠组合是获得良好力学性能的基础.     

浸渗-反应合成Cf/Ti-Al复合材料的反应机理

以Ti粉、纯Al和碳纤维为原料,采用浸渗-反应合成法研制了Cf/Ti-Al复合材料,根据DSC测试结果确定反应合成温度.结果表明:在后期加热过程中,随着反应温度的升高,TiAl3的含量先增多后减少,碳纤维与Al的界面反应逐渐增强,Al4C3和TiC逐渐增多,在高温阶段,氧参与反应,复合材料中有Al2O3生成.通过SEM和XRD测试分析了复合材料内部的显微组织及相组成,同时探讨了Cf/Ti-Al复合材料中各物相形成过程的反应机理.     

Fabrication of Ti-Al composite coatings by the mechanical alloying method

The method of mechanical alloying (MA) allows one to fabricate sufficiently thick and dense composite coatings using short-time treatments at room temperature. The method is very simple and requires no special atmosphere. It was used to synthesize coatings of Ti-Al, Ti-Al-W-C, and Ti-Al-Si on the titanium surface. During the heating of Ti-Al composite coatings in a temperature range of 600–1000°C, Ti-Al intermetallic phases are formed on the titanium surface. In Ti-Al-Si coatings annealed at 900–1000°C, Ti-Al intermetallic and silicide phases are the basis of the coatings. The temperature ranges of phase and structural transformations in the coatings depend on the initial chemical composition. For the thermal stabilization of Ti-Al intermetallic phases, additions of alloying elements retarding diffusion in the Ti-Al system can be used.     

Sliding wear resistance of TiCp reinforced titanium composite coating produced by laser cladding

Titanium metal matrix composite coatings (MMC) are considered to be important candidates for high wear resistance applications. Laser cladding (LC) by coaxial powder feeding is an advanced coating manufacturing process, which involves laser processing fine powders into components directly from computer aided design (CAD) model.In this study, the LC process was employed to fabricate TiC particle reinforced Ti6Al4V MMC coatings on Ti6Al4V hot rolled samples.The experimental results show that during LC process, TiC particles are partially dissolved into melted Ti-base alloy and precipitated in the form of TiC dendrites during cooling.Dry sliding wear properties of these MMC layers have been compared with substrate materials wear. The observed wear mechanisms are summarized and related to detailed microstructural observations. The layers have been found to show improved tribological properties connected with the TiC_p addition and the LC process parameters.     

机械合金化Ti-Al复合粉末的结构及显微形貌(英文)

研究了不同球磨时间内Ti-Al复合粉末显微结构及成分的演变。随着球磨时间的延长,原始粉末的形貌发生了一系列变化,从球磨2h的扁平状变为球磨6h的细小的等轴状。球磨8h后粉末的晶粒尺寸达到纳米级,平均约为17nm。对钛铝复合粉末的演化机理进行了分析。在球磨过程中,铝逐渐融入钛晶格形成钛的固溶体。球磨不同时间的粉末中钛铝反应的起始温度的差热分析表明,机械合金化细化了复合粉末,显著降低了钛、铝反应的起始温度。     

Tribological properties of Ti-aluminide reinforced Al-based in situ metal matrix composite

For structural application of moving components, the tribological properties (friction and wear) are considered to be one of the major factors controlling the performance. In recent years, lightweight metal matrix composites (MMC) have received wider attention for their technological application, such as automotive parts etc. This paper reports the tribological behavior of Al based composites reinforced with in situ Ti_xAl_y and Al₂O₃ particles. The wear experiments were performed on a newly designed fretting tribometer to evaluate the role of intermetallic particulates on the wear performance of in situ composites against bearing steel under the ambient conditions of temperature (22–25 °C) and humidity (50–55% RH). Based on the topographical observation of the worn surfaces the plausible wear mechanisms are discussed. An important result is that Al-based composites with 20 vol% reinforcement exhibit an extremely low coefficient of friction of 0.2 under unlubricated conditions. Also, around five times lower wear volume is measured with 20 vol% composites when compared to unreinforced Al.     

Effect of graphite intercalation compounds in the interfacial zone on the mechanical and thermal properties of unidirectional carbon fiber reinforced spodumene composite

The interface in unidirectional carbon-fiber-reinforced β-spodumene matrix composite (UD-Cf/β-spodumene) significantly affected the thermal conductivity characteristics and mechanical properties due to the presence of a multi-layer interface. The mechanical and thermal properties of UD-Cf/β-spodumene composites with and without a multi-layer interface have been studied. The measured thermal conductivities, flexural strength and fracture toughness of composites with a multi-layer interface were much better than those composites with a clear interface. Interfacial layers with a multi-layer morphology originated from the diffusion of lithium from the β-spodumene matrix to the surface of the carbon fiber, which led to the formation of graphite intercalation compounds. The mechanical properties and thermal conductivity of UD-Cf/β-spodumene hot pressed at 1350 and 1400 °C were enhanced due to the textured interfacial microstructure and high thermal conductivity of graphite intercalation compounds. The textured interface decomposed at 1450 °C, resulting in the formation of a “strong” interface. Inevitably, the mechanical properties and thermal conductivity decreased.     

激光熔覆原位自生TiC-VC颗粒增强Fe基金属陶瓷涂层

采用钛铁、钒铁、石墨等组分,利用5 kW横流CO2激光器,氩气保护在低碳钢板上制备了致密、无孔隙与基体呈冶金结合的原位自生TiC-VC复合碳化物颗粒增强Fe基熔覆层.利用金相显微镜、X射线衍射、电子探针及显微硬度计,研究了熔覆层的显微组织及性能.结果表明,钛铁、钒铁与石墨通过激光熔覆的反应,所得细小的TiC-VC复合碳化物增强相弥散分布Fe基体之中,熔覆层硬度从基体到表面呈梯度分布,较基体有显著提高.     

Size effects in micro drilling of carbon fiber reinforced plastic composite

The contribution presents investigations regarding the size effects on cutting forces in micro drilling of carbon fiber reinforced plastic composite. Generally, size effect is described as non-linear increase of specific cutting force with decreasing chip thickness. Specific cutting forces are determined by dividing cutting force components by chip area. In a mathematical model, specific cutting force is expressed as a function of the ratio of undeformed chip thickness to cutting edge radius. The coefficients of the model are determined by regression analysis using experimental results. Non-linear increase of specific cutting force is observed when the ratio decreases, especially when the ratio is less than unity.     

Mechanical properties of tungsten fiber reinforced ZrAlNiCuSi metallic glass matrix composite

Tungsten fiber reinforced (Zr₅₅Al₁₀Ni₅Cu₃₀)_98.5Si_1.5 metallic glass composites were fabricated and characterized. The mechanical properties of the composite under compression and tension were investigated. Tungsten reinforcement greatly increased compressive strain to failure compared to the unreinforced (Zr₅₅Al₁₀Ni₅Cu₃₀)_98.5Si_1.5 metallic glass. The compressive failure mode changed from a single shear band to multiple shear bands and to localized fiber buckling and tilting as the volume fraction of tungsten fiber increased. The maximum tensile strength and strain to failure of each of the composites were lower than those of unreinforced material due to the lack of substantial shear bands. Tensile toughness changed to some extent due to different interface reactions. The reason for the improved mechanical properties is discussed.