Carbon Fiber Breakage Mechanism in Aluminum(Al)/Carbon Fibers(CFs) Composite Sheet during Accumulative Roll Bonding(ARB) Process

We put forward a method of fabricating Aluminum(Al)/carbon fibers(CFs) composite sheets by the accumulative roll bonding(ARB) method. The finished Al/CFs composite sheet has CFs and pure Al sheets as sandwich and surface layers. After cross-section observation of the Al/CFs composite sheet, we found that the CFs discretely distributed within the sandwich layer. Besides, the tensile test showed that the contribution of the sandwich CFs layer to tensile strength was less than 11% compared with annealed pure Al sheet. With ex-situ observation of the CFs breakage evolution with-16%,-32%, and-45% rolling reduction during the ARB process, the plastic instability of the Al layer was found to bring shear damages to the CFs. At last, the bridging strengthening mechanism introduced by CFs was sacrificed. We provide new insight into and instruction on Al/CFs composite sheet preparation method and processing parameters.

Microstructure,interfacial reaction behavior,and mechanical properties of Ti_3AlC_(2)reinforced Al6061 composites

The interfacial reaction behavior of Al and Ti_3AlC_(2)at different pouring temperatures and its effect on the microstructure and mechanical properties of the composites were investigated.The results show that the addition of3.0 wt.%Ti_3AlC_(2)refines the average grain size ofα(Al)in the composite by 50.1%compared to Al6061 alloy.Morphological analyses indicate that an in-situ Al_(3Ti)transition layer of-180 nm in thickness is generated around the edge of Ti_3AlC_(2)at 720℃,forming a well-bonded Al-Al_(3Ti)interface.At this processing temperature,the ultimate tensile strength of A16061-3.0 wt.%Ti_3AlC_(2)composite is 199.2 MPa,an improvement of 41.5%over the Al6061 matrix.Mechanism analyses further elucidate that 720℃is favourable for forming the nano-sized transition layer at the Ti_3AlC_(2)edges.And,the thermal mismatch strengthening plays a dominant role in this state,with a strengthening contribution of about 74.8%.

Effect of HEA/Al composite interlayer on microstructure and mechanical property of Ti/Mg bimetal composite by solid-liquid compound casting

In this study,HEA/AI composite interlayer was used to fabricate Ti/Mg bimetal composites by solidliquid compound casting process.The Al layer was prepared on the surface of TC4 alloy by hot dipping,and the FeCoNiCr HEA layer was prepared by magnetron sputtering onto the Al layer.The influence of the HEA layer thickness and pouring temperature on interface evolution was investigated based on SEM observation and thermodynamic analysis.Results indicate that the sluggish diffusion effect of HEA can effectively inhibit the interfacial diffusion between Al and Mg,which is conducive to the formation of solid solution,especially when the thickness of HEA is 800 nm.With the increase of casting temperature from 720 ℃ to 730 ℃,740℃,and 750 ℃,α-Al(Mg),α-Al(Mg)+Al3Mg2,Al3Mg2+Al12Mg17,and Al12Mg17+δ-Mg are formed at the interface of Ti/Mg bimetal,respectively.When the thickness of the HEA layer is 800 nm and the pouring temperature is 720 ℃,the bonding strength of the Ti/Mg bimetal can reach the maximum of 93.6 MPa.

Effect of Hot Processing Technology on Mechanical Properties and Structure of Interface of Ti/Steel Composite Sheet

研究了热加工工艺对钛-钢复合板界面力学性能和显微组织的影响。测试了在A，B，C，D4种温度下热轧复合板界面的力学性能，用金相显微镜及扫描电镜观察了界面显微组织并分析了界面的成分。结果表明，在A，B2种温度下轧制的钛-钢复合板界面机械性能良好，延伸率高，其剪切强度不但可保持坯料原有的水平，甚至还略有增加。在C，D2种温度下轧制的钛-钢复合板界面机械性能相对较低，延伸率较高，但剪切强度要比爆炸复合坯料低，尤其是D加热温度，轧制后界面剪切强度急剧下降。热轧的终轧温度也是影响钛-钢复合板界面结合性能的重要因素。在低于相转变温度的合适温区热轧，且终轧温度合适，获得的钛-钢复合板结合界面无爆炸波纹，没有污染，生产的脆性化合物极细小，组织类同于钛材完全退火的等轴组织。

粉末套管法Ti/Al/Ti复合板的界面结合性能

采用粉末套管法,通过“热轧+中间退火+进一步冷轧”工艺制备Ti/Al/Ti复合板。利用扫描电镜、电子探针、能谱仪、XRD分析以及万能实验机,研究不同制备参数下Ti/Al/Ti复合带材的界面形貌、元素分布、物相种类和界面结合强度。结果表明,单一脆性金属间化合物TiAl_(3)的产生会阻碍Ti/Al元素的扩散,扩散层厚度发生减薄。500℃退火,扩散层主要是由扩散形成的冶金结合层,局部区域有少量的金属间化合物TiAl_(3)生成,界面结合强度受冶金结合强度与机械结合强度的动态变化影响,随着压下率升高,结合强度先降低后升高再降低;550℃退火,界面反应增强,TiAl_(3)相逐渐增多,扩散层强度增加,冶金结合强度提高,由14.3 N/mm(500℃)增加至35.1 N/mm(550℃),随着压下率的增大,化合物层破碎程度增加,界面结合强度逐渐降低。

熔体压力对水平双辊铸轧Ti/Al复合板界面结合强度的影响

除了铸轧速度和熔体浇铸温度外,铸轧区内的熔体压力也是影响水平双辊铸轧Ti/Al复合板工艺稳定性和界面结合强度的重要因素。本工作在铸轧复合过程中通过调节前箱内熔体的液面高度,获得了在不同铸轧区熔体压力下制备的Ti/Al复合板。通过金相、扫描电镜、显微硬度、室温拉伸实验、T型剥离实验等手段对复合板的显微组织和界面结合性能进行表征和测试。结果表明,当熔体压力较高时,可以生产出充盈饱满、板型良好、结合强度高的复合板,但熔体压力过高会影响铸轧复合过程的稳定性。当熔体压力过低时,熔体的横向流动能力减弱,铸轧区内不能完全被熔体填充满,板材出现热带、褶皱等缺陷,同时,在Ti/Al上出现了部分微孔和微裂缝。在较高熔体压力下,固/液接触距离更长,带材表面与熔体的润湿更加充分,熔体分布更加均匀,固/液扩散更加充分。因此,当熔体压力较高时,复合板具有更高的结合强度,界面结合强度达到20.1 N/mm。

固溶时间对Ti@(Al-Si-Ti)_(p)/A356复合材料组织及力学性能的影响

采用粉末触变成形技术制备了原位自生心-壳结构增强A356铝基复合材料,并研究了固溶时间对Ti@(Al-Si-Ti)_(p)/A356复合材料显微其组织及力学性能的影响。结果表明,随着固溶时间增加,初生α-Al相颗粒粗化长大;共晶Si相不断溶解,晶界上残余的共晶Si粗化、球状化;Al基体、Ti心部继续反应,增强体颗粒壳层发生相转变。复合材料在545℃固溶处理1 h时,力学性能达到峰值,其抗拉强度、屈服强度和伸长率分别为263.9 MPa、175.1 MPa、20%,比制备态复合材料分别提高了7.3%、21.4%和12.4%,维氏硬度也从59.3 HV提高到72.8 HV。

轧制工艺对铸轧Ti-Al复合板界面组织与性能的影响

除热处理工艺外,轧制工艺也是影响铸轧Ti/Al复合板工艺稳定性和界面结合强度的重要因素。通过改变铸轧复合过程中的轧制温度和轧制变形量,获得了不同的Ti/Al复合板。利用SEM、EBSD、XRD等手段对复合板的显微组织和界面结合性能进行了表征和测试。结果表明,在不同温度下进行50%变形量的轧制时,复合板发生不同程度翘曲。当轧制温度为470℃时,复合界面在高倍扫描电镜下为锯齿状界面;而在轧制温度为500和530℃时,复合界面为波浪状界面。随着轧制温度的升高,复合板的结合强度也有所提高。在温度一定、变形量改变的轧制过程中,当变形量小于50%时,复合板的平均结合强度随着变形量的增大而增加。当变形量为75%时,由于钛层金属太薄,且变化不平均,导致钛层出现破裂使复合板失效。综上所述,在温度为500℃,轧制变形量为50%时,复合板的平均结合强度最好。

Preparation of Al-Al_3Ti in situ composites by direct reaction method

Al-Al3Ti composites were prepared by a direct reaction method, in which Al3Ti was formed by the reaction of Ti and Al in aluminum alloy melt. The morphology of Al3Ti changes apparently from the fine particle, needle-like to large block with the increase of Al3Ti content. The addition of magnesium can markedly change the morphology of Al3Ti and reduce their size. Short rod-like Al3Ti was formed and homogeneous distribution was obtained with the addition of 3 wt.% Mg. The effect of Al3Ti and Mg on the microstructure of Al-Al3Ti composites and the mechanism were also discussed.

Microstructure and mechanical properties of a hot-extruded Al-based composite reinforced with core–shell-structured Ti/Al3Ti

An Al-based composite reinforced with core–shell-structured Ti/Al_3Ti was fabricated through a powder metallurgy route followed by hot extrusion and was found to exhibit promising mechanical properties. The ultimate tensile strength and elongation of the composite sintered at 620°C for 5 h and extruded at a mass ratio of 12.75:1 reached 304 MPa and 14%, respectively, and its compressive deformation reached 60%. The promising mechanical properties are due to the core–shell-structured reinforcement, which is mainly composed of Al_3Ti and Ti and is bonded strongly with the Al matrix, and to the reduced crack sensitivity of Al_3Ti. The refined grains after hot extrusion also contribute to the mechanical properties of this composite. The mechanical properties might be further improved through regulating the relative thickness of Al–Ti intermetallics and Ti metal layers by adjusting the sintering time and the subsequent extrusion process.

Microstructure,hardness and corrosion properties of laser processed Ti6Al4V-based composites

Nb and Ti-13 Nb powders were used for improving the surface of Ti6Al4 V alloy.The deposition of the powders was carried out at various laser powers.The scanning electron microscopy（SEM）-EDS and optical microscopy were used for characterization.X-ray diffractometer（XRD） was used for analyzing the elemental composition and phase constituents.The hardness,wear and corrosion properties were achieved.The corrosion and the wear behaviours of the deposited layers were studied in a Hanks solution（simulated body fluid,SBF）.The microstructures of Nb coatings reveal the presence of orthorhombic,dendritic α″ and metastable β-Nb phases which produce uneven hardness with an average of HV 364.For Ti-13 Nb coatings,martensitic α′ and metastable β-Nb phases with an average hardness of HV 423 were observed.The resistance of wear on dry sliding of Ti-13 Nb coating is attributed to the increase in hardness.Experimental results indicate that deposition of Nb and Ti-13 Nb on Ti6Al4 V grossly reduces the mass fractions of Al and V in all coatings.In SBF,Nb reinforcement produces the best coating that reveals the best wear and corrosion resistances as compared with the substrate.Hence,this coating will perform best for orthopaedic implant material enhancement.

Formation mechanism and growth kinetics of TiAl_(3) phase in cold-rolled Ti/Al laminated composites during annealing

Cold-rolled Ti/Al laminated composites were annealed at 525−625℃for 0−128 h,and the interfacial microstructure evolution was investigated.The results indicate that only the TiAl_(3) phase was formed at the Ti/Al interface;most of TiAl_(3) grains were fine equiaxed with average sizes ranging from hundreds of nanometers to several microns and the TiAl_(3) grain size increased with increasing annealing time and/or temperature,but the effect of annealing temperature on the TiAl_(3) grain size was far greater than that of annealing time.The growth of the TiAl_(3) phase consisted of two stages.The initial stage was governed by chemical reaction with a reaction activation energy of 195.75 kJ/mol,and the reaction rate constant of the TiAl_(3) phase was larger as the Ti/Al interface was bonded with fresh surfaces.At the second stage,the growth was governed by diffusion,the diffusion activation energy was 33.69 kJ/mol,and the diffusion growth rate constant of the TiAl_(3) phase was mainly determined by the grain boundary diffusion owing to the smaller TiAl_(3) grain size.

Effect of Ti/B Additions on the Formation of Al_3 Ti of in situ TiB_2/Al Composites

A novel technique for fabricating TiB_2/Al composites in molten aluminum was introduced. The formation mechanism of brittleAl,Ti particulates up to 30 m in size produced in the composites was studied and a method of eliminating them was proposed. The resultsshow that (l) the brittle Al,Ti particulates are always present in the composites when the molar ratio of Ti to B 'T,:nB is l:2; and (2) theformation of the brittle Al,Ti phase can be avoided entirely from the final product by using a proper 'T,:nB of l:4 in the Ti-B-Al preforms.In the former case, the tensile elongation of the composite is only 4%, much lower than the value of pure aluminum (20%). In the latercase, the tensile elongation of this composite is 10%, higher than the value of the composite with a lot ofAl,Ti (4%), whereas the ultimatetensile stfength of the former is nearly that of the later.

The Role of Ti in the Preparation of SiC/7075 Aluminum Matrix Composite

SiC/7075 aluminum matrix composites were prepared by a liquid stirring method.The role of Ti facilitating the preparation of SiC/7075 aluminum matrix were studied by means of direct-reading spectrometer,scanning electron microscope,energy dispersive spectrometer,X-ray diffraction and the sessile drop method.The results show that the SiC content in the SiC/7075 composite increases with an increase of Ti addition.The addition of Ti can significantly improve the wettability of SiC/Al system,there is a critical value of above 0.5%of Ti content in improving the wettability of the Al/SiC system at 1173K.The temperature of the"non wetting-wetting"transition for the(Al-2Ti)/SiC system is about 1123K,the contact angle decreases to 88°at 200 seconds and reaches a stable contact angle of 28°at 2100 seconds.

IN SITU PROCESSING OF Al_(2)O_(3) WHISKERS REINFORCED Ti-Al INTERMETALLIC COMPOSITES

In situ Al2O3 whiskers reinforced Ti-Al intermetallic composites were fabricated at ~1200℃ by reaction sintering of cold-consolidated fillets consisting mainly of Ti, Al, and different additives. The phases and microstructures of the sintered composites were characterized using X-ray diffraction (XRD) and scanning electron microscopy (SEM) coupled with energy dispersive spectroscopy (EDS). The process of synthesis was investigated using differential thermal analysis (DTA). The effects of processing parameters and additives on the microstructures of the composites and the development of whisker were examined. It is found that the morphology of the whisker is strongly influenced by the additives, the exothermal reaction process, and the processing parameters.

Microstructure and abrasive wear behaviour of anodizing composite films containing Si C nanoparticles on Ti6Al4V alloy

Anodized composite films containing Si C nanoparticles were synthesized on Ti6Al4 V alloy by anodic oxidation procedure in C4O6H4Na2 electrolyte. Scanning electron microscopy(SEM), energy dispersive spectroscopy(EDS) and X-ray photoelectron spectroscopy(XPS) were employed to characterize the morphology and composition of the films fabricated in the electrolytes with and without addition of Si C nanoparticles. Results show that Si C particles can be successfully incorporated into the oxide film during the anodizing process and preferentially concentrate within internal cavities and micro-cracks. The ball-on-disk sliding tests indicate that Si C-containing oxide films register much lower wear rate than the oxide films without Si C under dry sliding condition. Si C particles are likely to melt and then are oxidized by frictional heat during sliding tests. Potentiodynamic polarization behavior reveals that the anodized alloy with Si C nanoparticles results in a reduction in passive current density to about 1.54×10-8 A/cm2, which is more than two times lower than that of the Ti O2 film(3.73×10-8 A/cm2). The synthesized composite film has good anti-wear and anti-corrosion properties and the growth mechanism of nanocomposite film is also discussed.

Compositing Soft Coated Ti-Fiber Reinforced Ti-Al Matrix Composites

It is showed that there are Ti 3Al, Ti 2Cu and β phase in the interface of Ti/Ti Al composites reinforced with Y 2O 3 Cr composite soft coated Ti fiber, and that interface bonding is intact. Bending strength of the composites can be increased by 26%, to 709 MPa, and bending deflection increased slightly compared with the Ti/Ti Al composites reinforced by Ti fibers coated with Y 2O 3.

PREPARATION OF Ti-Al BASED NANOPHASE COMPOSITE POWDER BY MECHANICAL ALLOYING

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Effect of Nb on the Mechanical Properties of Ti/Al_2O_3 Composite

Ti/Al 2O 3 composite with improved mechanical properties was synthesized by th e spark plasma sintering. The effect of Nb on the microstructure of the composit e was analyzed by TEM, SEM and so on. The experimental results indicate that the bending strength, fracture toughness, micro-hardness and relative density of t he composite are 897.29MPa, 17.38MPa·m 1/2, 17.13GPa and 99.24% respec tively when adding 1.5vol%Nb. The bending strength is improved by reason of form ing dislocation ring and transfering fracture mode from intergranular to mixture fracture of intergranular and transgranular. The crack propagating is mainly th e deflection bridging. It indicates a reduction of crack driving force and an in crease in crack growth resistance,which results in toughness enhanced.

Intermetallic growth behavior during post deformation annealing in multilayer Ti/Al/Nb composite interfaces

The tri-metal Ti-Al-Nb composites were processed through three procedures:hot pressing,rolling,and hot pressing,followed by subsequent rolling.The fabricated composites were then subjected to annealing at 600,625,and 650℃ temperatures at different times.Microstructure observation at the interfaces reveals that the increase in plastic deformation strain significantly affects TiAl_(3) intermetallic layers’evolution and accelerates the layers’growth.On the contrary,the amount of applied strain does not significantly affect the evolution of the NbAl_(3) intermetallic layer thickness.It was also found that Al and Ti atoms’diffusion has occurred throughout the TiAl_(3) layer,but only Al atoms diffuse through the NbAl_(3) layer.The slow growth rate of the NbAl_(3) intermetallic layer is due to the lack of diffusion of Nb atoms and the high activation energy of Al atoms’reaction with Nb atoms.