Nickel particle embedded aluminium matrix composite with high ductility

Nickel particulate reinforced aluminium matrix composite was processed without formation of deleterious Al₃Ni intermetallic by friction stir processing (FSP). FSP resulted in uniform dispersion of nickel particles in the aluminium matrix with excellent interfacial bonding and also lead to grain refinement of the matrix. The composite exhibited a threefold increase in the yield stress (0.2% proof stress). The most novel feature of the composite is that an appreciable amount of ductility is retained while the strength increases significantly. The microstructure evolution was studied by transmission electron microscopy and electron backscattered diffraction analysis. EBSD analysis showed a dynamically recrystallized equiaxed microstructure having a considerable fraction of low-angle boundaries. TEM observations revealed that these low-angle boundaries are essentially subgrain boundaries formed by dislocation rearrangement and absorption during friction stir processing.     

Effect of friction stir processing and hybrid reinforcements on copper

In this research, a copper based surface composite was fabricated through dispersing hybrid composite particles onto its surface through friction stir processing (FSP) technique. Optical micrographs and scanning electron microscopy images indicates finer refinement of grains and particles dispersion into matrix along with its bonding and particle separation. As per the outcomes of microhardness analysis, hardness of the developed surface composite shows increment with increase in dispersion of volume fraction of hybrid particles. Strength of the developed copper surface composite exhibited a positive trend with introduction of hybrid reinforcement particle onto the surface of the composite but yet again ductility reduced. Wear resistance of the composite increased with reinforcement addition and the same was supported through worn out surface morphology. Fluctuations in friction coefficient value reduced with increase in particles, as for the presence in BN particles while the average frictional coefficient value was observed increasing. A reduction in corrosion rate was observed with increase in reinforcement particle dispersion onto copper matrix through FSP.     

Microstructure evolution and mechanical properties in ultrafine grained Al/TiC composite fabricated by accumulative roll bonding

In this study, the influence of nano-TiC particle on microstructure development and mechanical properties of Al/TiC composite fabricated by accumulative roll bonding (ARB) was considered to investigate. Microstructural characterization by electron backscatter diffraction (EBSD) system proved that the grain size decreased to around 200 nm and the TiC reinforcement particles were uniformly distributed in the Al matrix by 7-cycle of the ARB process. It is also found that presence of the TiC particles could accelerate grain refinement. Uniaxial tensile test exhibited that yield and ultimate tensile strength significantly improved more than four times in the 7-cycle ARB processed Al/TiC composite compared with the annealed aluminum specimen which used as the starting material. In addition, the obtained results demonstrated that adding the TiC reinforcement particles could improve the yield strength of the 7-cycle ARB processed Al sheet about 40 percentage.     

搅拌摩擦加工制备颗粒增强铝基复合材料的研究现状及展望

铝合金作为现代工程和高新技术领域发展的关键材料之一,具有密度小、比强度和比刚度高、耐蚀性好等特点。通过在铝基体中添加增强相颗粒,制备得到的颗粒增强铝基复合材料既有铝合金良好的强度、韧性、易成形性等特点,又有颗粒的高强、高模等优点,是近年来应用最广的一类金属基复合材料。 目前,制备铝基复合材料的方法主要有粉末冶金法、铸造以及超声波法等,但这些方法在制备过程中需要较高的温度,颗粒与金属基体容易发生不良的界面反应,从而影响界面结合效果,降低复合材料的性能。搅拌摩擦加工(FSP)作为一种新型的固相加工技术,可同时实现材料微观组织的细化、致密化和均匀化。目前,FSP直接法已在铝基复合材料制备方面取得应用,主要是将增强相颗粒通过打盲孔或开槽的方式预置在金属基体内再进行FSP,进而制备出高致密度的颗粒增强铝基复合材料。因为FSP过程的温度低,颗粒与铝基体不会发生界面反应,所以该方法也被用于制备具有形状记忆效应(SME)的铝基功能复合材料。 近年研究结果表明,颗粒相对FSP制备的铝基复合材料晶粒细化起到显著作用,这有助于提高复合材料的拉伸强度、显微硬度及疲劳强度等力学性能。随着颗粒含量的增加和颗粒尺寸的减小,复合材料的力学性能得以增强。再者,减小颗粒尺寸有利于改善颗粒与基体之间的结合。另外,通过优化搅拌头的结构、形状和尺寸,以及FSP工艺参数,已经可以实现加工后颗粒相在基体中的均匀分布。 鉴于搅拌摩擦加工(FSP)直接法在制备颗粒增强铝基复合材料方面所具备的短流程、高效能以及基体与增强相颗粒界面无杂质等优势,本文对目前FSP直接法制备颗粒增强铝基复合材料的最新研究现状进行了总结。主要综述了FSP制备颗粒增强铝基复合材料过程中颗粒的含量、类型及尺寸对复合材料组织与力学性能的影响,并对颗粒分布均匀性以及颗粒与铝基体的界面问题做了阐述。文章最后深入分析了当前研究中的不足之处并展望了未来的研究方向。     

Influence of carbide reinforcements on accumulative roll bonded Al 8011 composites

Numerous methods are available to produce ultrafine grained material in severe plastic deformation (SPD) techniques. Accumulative roll bonding (ARB) is the most effective techniques to produce ultrafine grained composites with superior properties. The present investigation deals with the fabrication and comparison of Al 8011 composite by introducing various reinforcements such as Titanium carbide (TiC), Tungsten carbide (WC), Boron carbide (B4C) and Zirconium carbide (ZrC) through ARB technique by deforming plastically. Here, four specimens were prepared by incorporating 8 wt.% each of aforementioned carbide particles in Al matrix and compared with each other and characterized through advanced microscopic techniques such as SEM, EDAX, EBSD and TEM besides XRD. Furthermore, Vickers microhardness test and tensile test were conducted. The introduced reinforcement particles were found dispersed evenly throughout the surface by increasing the passes up to eight times. Among these reinforcements, Al 8011 – B4C composite has provided better strength than other composites due to following reasons: (i) high bonding of the interface between the sheets (ii) interlocking of B4C particles within the matrix (iii) higher hardness and strength. Hence, B4C reinforced Al composite claims greater significance for being recommended as an effective alternative for the aluminum material in load carrying applications.     

高能球磨工艺对B4C/Al复合粉体结构演变及分布均匀性的影响

制备B4C增强Al基复合材料存在的难点主要是B4C颗粒在Al基体中的均匀分布及界面结合。本研究采用卧式搅拌高能球磨法制备了B4C/Al复合粉体,研究了搅拌轴转速和球磨时间对B4C/Al复合粉体结构演变及分布均匀性的影响。结果表明,随搅拌轴转速的提高,复合粉体受磨球碰撞时所获能量增大,增强体颗粒瞬间被破碎同时使Al粉发生较大的塑性变形,随球磨时间的延长,破碎的B4C颗粒逐渐在Al基体中分散均匀并与基体焊合,利于粉体实现均匀分布和良好的界面结合。球磨过程中B4C沿颗粒棱边脆性断裂,在Al粉的冷焊变形过程中被嵌入,形成一种片状化的Al粉基体包裹B4C增强相的复合粉体。在搅拌轴转速为600/800r/min(交变转速,交变频率为1min),球磨时间为2h时,B4C/Al复合粉体的粒度得到细化,B4C颗粒在Al基体中分布均匀、界面结合紧密。     

多道次搅拌摩擦加工对SiCP/2A14铝合金复合材料显微组织和力学性能的影响

采用搅拌摩擦加工(FSP)技术对SiC颗粒增强2A14铝合金(SiC_P/2A14)复合材料进行处理,通过金相表征、电子背散射衍射(EBSD)、SEM、硬度测试及力学拉伸实验等分析了多道次搅拌摩擦加工对SiC_P/2A14复合材料微观组织、力学性能及超塑性变形行为的影响。研究表明:经搅拌摩擦加工后,SiC_P/2A14复合材料搅拌区内SiC颗粒分布明显均匀,晶粒细化,其中2道次搅拌摩擦加工的SiC_P/2A14复合材料的晶粒尺寸最小,为3.14 μm。随着搅拌加工道次的增加,SiC_P/2A14复合材料的硬度降低,室温抗拉强度和高温延伸率均先提高后降低,其中2道次搅拌摩擦加工的SiC_P/2A14复合材料的室温抗拉强度为319 MPa,相较于未经FSP处理的SiC_P/2A14复合材料提高了41%,在500℃、应变速率为1.0×10?3 s?1条件下高温延伸率为609%,相较于未经FSP处理的SiC_P/2A14复合材料提高了133%。      

A novel in-situ polymer derived nano ceramic MMC by friction stir processing

Friction stir processing (FSP) is a solid state technique used for material processing. Tool wear and the agglomeration of ceramic particles have been serious issues in FSP of metal matrix composites. In the present study, FSP has been employed to disperse the nanoscale particles of a polymer-derived silicon carbonitride (SiCN) ceramic phase into copper by an in-situ process. SiCN cross linked polymer particles were incorporated using multi-pass FSP into pure copper to form bulk particulate metal matrix composites. The polymer was then converted into ceramic through an in-situ pyrolysis process and dispersed by FSP. Multi-pass processing was carried out to remove porosity from the samples and also for the uniform dispersion of polymer derived ceramic particles. Microstructural observations were carried out using Field Emission Scanning Electron Microscopy (FE-SEM) and Transmission Electron Microscopy (TEM) of the composite. The results indicate a uniform distribution of ~ 100 nm size particles of the ceramic phase in the copper matrix after FSP. The nanocomposite exhibits a five fold increase in microhardness (260HV₁₀₀) which is attributed to the nano scale dispersion of ceramic particles. A mechanism has been proposed for the fracturing of PDC particles during multi-pass FSP.     

Formation mechanism of in situ Al3Ti in Al matrix during hot pressing and subsequent friction stir processing

In situ Al₃Ti/Al composites were fabricated by a combination of vacuum hot pressing (VHP) and friction stir processing (FSP). The formation mechanism of the Al₃Ti and the effect of VHP and FSP parameters on the resultant microstructure and mechanical properties were investigated. The Al₃Ti formed due to the reactive diffusion between Al and Ti during VHP, and the number of Al₃Ti particles increased with increasing the temperature and holding time of the VHP. FSP not only induced the Al–Ti reaction, but also resulted in significant refining of the Al₃Ti, thereby creating a homogeneous distribution of Al₃Ti particles in the Al matrix. These microstructural changes led to significant improvement in the tensile properties of the in situ Al₃Ti/Al composite. However, the change trends of the tensile properties of the FSP samples were dependent on the extent of the Al–Ti reaction during VHP.     

Producing of Al–WC surface composite by additive friction stir processing

In this research, additive friction stir processing (AFSP) was successfully employed to prepare the aluminum–tungsten carbide (Al–WC) surface composite upon 5083Al substrate. The resulting microstructures were detailedly characterized by X-ray diffraction, optical microscopy (OM), scanning electron microscopy, energy dispersive spectroscopy and electron backscattered diffraction. Microhardness tests and wear tests were used to evaluate the surface properties of the AFSP surface composite. Results showed that the prepared Al–WC surface composite by AFSP had a combination of homogeneous distribution of WC particles, excellent WC/Al interfacial integrity and remarkably refined grains. The continuous dynamic recrystallization (DRX) mechanism was mainly responsible for the grain refining of 5083Al during FSP. Adding WC particles into FSP Al not only boosted the DRX kinetics but also retarded the growth of resultant grains, thereby reducing grain size. The AFSP surface composite exhibited significantly improved hardness and wear resistance compared with the as-received Al.     

Evolution of reinforcement distribution in Al–B4C composites during accumulative roll bonding

The distribution of reinforcement particles in the matrix of a composite is one of the most important microstructural features affecting properties. In this study, nanostructured Al–B₄C composite sheets were processed by accumulative roll bonding (ARB), and the effect of the number of ARB cycles on the distribution of the B₄C particles in the Al matrix was evaluated. From optical microscopic studies accompanied by the radial distribution function analysis, it was realized that the microstructure uniformity is improved by increasing the number of ARB cycles. It was in good agreement with bulk hardness measurements in which the standard deviation of the hardness values was decreased by progression of the ARB process. In addition, the X-ray diffraction peak profile analysis revealed that the area weighted mean crystallite size of the Al matrix decreases to the nanometric scale (114 nm) after seven ARB cycles.     

In situ Al3Ti and Al2O3 nanoparticles reinforced Al composites produced by friction stir processing in an Al-TiO2 system

Al and TiO₂ powders were selected to fabricate in situ Al composites via multiple pass friction stir processing (FSP) based on the thermodynamic analysis. The microstructural investigations indicated FSP would induce reaction between Al and TiO₂. Al₃Ti and Al₂O₃ particles were formed after 4 pass FSP with 100% overlapping. The in situ particles were about 80 nm in size at various FSP conditions, and ultrafine matrix grains 602 nm in size were obtained when water cooling was applied during FSP. Tensile tests indicated that the in situ nanocomposites exhibited pronounced work hardening behavior and a good combination of strength and ductility.     

Reactive friction stir processing of AA 5052–TiO2 nanocomposite: process–microstructure–mechanical characteristics

Friction stir processing (FSP) is a solid state route with a capacity of preparing fine grained nanocomposites from metal sheets. In this work, we employed this process to finely distribute TiO₂ nanoparticles throughout an Al–Mg alloy, aiming to enhance mechanical properties. Titanium dioxide particles (30 nm) were preplaced into grooves machined in the middle of the aluminium alloy sheet and multipass FSP was afforded. This process refined the grain structure of the aluminium alloy, distributed the hard nanoparticles in the matrix and promoted solid state chemical reactions at the interfaces of the metal/ceramic particles. Detailed optical and electron microscopic studies showed that the microstructural homogeneity was improved with repetition of FSP up to four passes. The average grain size of the nanocomposite was ～2 μm, while nanometric MgO and Al₃Ti particles were formed in situ and homogenously distributed in the metal matrix. Mechanical characterisations showed that the yield strength and elongation were increased from 93±5 MPa and 13·8% to 117±3 MPa and 25·3% after employing four-pass FSP. Fractographic studies also revealed that agglomerated TiO₂ particles could operate as sites of crack initiation and propagation, which led to brittle fracture. By increasing the number of FSP passes, the agglomerates were disappeared and the ductility was enhanced remarkably.     

Fabrication and wear characterization of an A413/Ni surface metal matrix composite fabricated via friction stir processing

In the present study, friction stir processing (FSP) was used for the incorporation of Ni particles into the surface of an A413 alloy to fabricate a surface composite. FSP parameters were the rotation speed of 2000 rpm, the traverse speed of 8 mm/min and the tilt angle of 2°. Single pass and three-pass FSP were conducted on the samples. For the evaluation of microstructures, optical microscopy and scanning electron microscope were utilized. Also, for the investigation of intermetallic formation, energy dispersive spectroscopy was used. The wear resistance of different composites was investigated at ambient and elevated temperatures. Microstructural observations revealed that the FSP led to significant breakup of acicular Si particles, elimination of α­Al dendrites and heal the casting porosity. It was found that the hardness and wear behavior of A413 cast alloy were strongly influenced by applying FSP. Also, the in situ formation of Al₃Ni particles during FSP was a critical factor controlling the wear mechanism. Sliding wear tests revealed that the increase in the number of passes created a homogeneous distribution of Al₃Ni intermetallic particles and thereby resulting in a significant improvement in wear resistance at both room and high temperatures.     

双屏蔽(B4C-W)/6061Al层状复合板设计与性能

基于B₄C和W良好的屏蔽中子和γ射线性能,采用6061铝合金作为基体,设计了一种新型双屏蔽(B₄C-W)/6061Al层状复合材料,通过放电等离子烧结后加热轧制成板材,对制备的复合材料微观组织和力学性能进行了研究。结果表明,屏蔽组元B₄C和W颗粒均匀地分布在6061Al基体中,层界面、B₄C/Al、W/Al异质界面之间结合良好,无空隙和裂纹。在颗粒与基体界面处形成扩散层,扩散层的厚度约为6 μm (W/Al)和4 μm (W/Al)。轧制态的(B₄C-W)/6061Al层状复合板的屈服强度(109 MPa)和极限抗拉强度(245 MPa)明显优于烧结态的复合材料,但断裂韧性降低。强度提高的原因主要是轧制后颗粒的二次分布、均匀性及界面结合强度提高,基体合金的晶粒尺寸减小,位错密度增加。层状复合板的断裂方式为基体合金的韧性断裂和颗粒的脆性断裂。      

铝镁异种金属复合挤压成形及界面微观组织

基于Deform 2D有限元模拟优化挤压工艺参数,在挤压速率2mm/s,挤压温度470℃下对铝镁双金属进行复合挤压实验,并采用扫描电镜(SEM)、显微硬度测试以及电子背散射衍射(EBSD)对复合挤压件界面结合层进行微观组织观察与分析。结果表明:在铝镁合金接触区反应生成了界面层,层内新的物相为靠近AZ31镁基体一侧的Al_(12)Mg_(17)以及靠近铝基体一侧的Al_3Mg_2。Al_3Mg_2相显微硬度值最高,平均值约为210HV,Al_(12)Mg_(17)相平均硬度约为170HV,因而界面区硬度高于两侧基体母材,形成典型的脆硬结合层,电子背散射衍射(EBSD)结果显示,Al_(12)Mg_(17)相的平均晶粒尺寸为30μm,Al_3Mg_2相的平均晶粒尺寸约为20μm,复合界面结合层区域晶粒取向各异,晶粒尺寸大小也不均匀,而复合外层纯铝基体取向区域均匀,新生成相在晶界上有部分再结晶发生。     

高分散多壁碳纳米管增强铝基复合材料的制备(英文)

采用机械合金化技术制备高分散多壁碳纳米管(MWCNTs)-铝(Al)复合材料。将纯度99%的铝粉和质量分数2%的MWCNTs经超声和水平球磨处理使Al颗粒与MWCNTs间产生机械键合力。场发射SEM观察表明,MWCNTs分散在Al薄片的表面,随球磨时间的不同,颗粒大小和形貌各异。采用加压烧结手段将混合粉末加工成块体材料,其微观硬度测试表明,加入MWCNTs后Al基体的机械性能得到提高。     

Accumulative press bonding; a novel manufacturing process of nanostructured metal matrix composites

A new manufacturing process for metal matrix composites has been invented, namely accumulative press bonding (APB). The APB process provided an effective method to produce bulk Al/10 vol.% WC_p composite using tungsten carbide (WC) powder and AA1050 aluminum sheets as the raw materials. The microstructural evolutions and mechanical properties of the monolithic aluminum and Al/WC_p composite during various APB cycles were examined by scanning electron microscopy, X-ray diffractometry, X’pert HighScore software, and tensile test equipment. The results revealed that by increasing the number of APB cycles (a) the uniformity of WC particles in aluminum matrix improved, (b) the porosity of the composite eliminated, (c) the particle free zones decreased and (d) the cluster characteristics improved. Hence, the final Al/WC_p composite processed by 14 APB cycles showed a uniform distribution of WC_p throughout the aluminum matrix, strong bonding between particles and matrix, and a microstructure without any porosity and undesirable phases. The X-ray diffraction results also showed that nanostructured Al/WC_p composite with the average crystallite size of 58.4 nm was successfully achieved by employing 14 cycles of APB technique. The tensile strength of the composites enhanced by increasing the number of APB cycles, and reached to a maximum value of 216 MPa at the end of 14th cycle, which is 2.45 and 1.2 times higher than obtained values for annealed (raw material, 88 MPa) and 14 cycles APBed monolithic aluminum (180 MPa), respectively. Though the elongation of Al/WC_p composite lessened during the initial cycles of APB process, it increased at the final cycles of the mentioned process by 78%. Role of WC particles, uniformity of reinforcement, porosity, bonding quality of the reinforcement and matrix, grain refinement, and strain hardening were considered as the strengthening mechanisms in the manufactured composites.     

Investigations on the effect of friction stir processing on Cu-BN surface composites

The main aim of this investigation focuses on fabrication of copper surface composites through friction stir processing (FSP) reinforced with boron nitride (BN) particles of varying volume fractions (5%, 10%, and 15%). Surface composites developed through single pass FSP were characterized for its microstructural, mechanical and tribological properties. Microstructural characterization indicated that developed surface composites were of good quality with reduced grain size and the SEM characterization confirmed good bonding between copper matrix and BN with uniform dispersion. Micro hardness survey of the developed surface composites showcased minimal deviation in the stir zone with increased trend in respect to the volume fraction of BN. The ultimate tensile strength, yield strength and percent elongation of FSPed composites was found to have reduced when compared with that of pure copper. BN dispersion in surface composite was effective in reducing the ductility and so maximum volume percent (15%) of BN dispersed composite prompt to have higher strength. The wear rate and friction coefficient of the developed surface composite was found decreasing with respect to increase in the dispersion of BN. Amongst the FSPed copper surface composite, specimen with 15?vol% of BN has shown the least wear rate with low coefficient of friction.     

Achieving strength-ductility synergy in cold spray additively manufactured Al/B4C composites through a hybrid post-deposition treatment

Cold spray additive manufacturing (CSAM) provides a potential solid state manufacturing route to fabricate variety of aluminum matrix composites (AMCs) with reduced possibility of undesired chemical reactions and residual thermal stresses. This study presents a hybrid (i.e. hot compression + hot rolling) post-deposition treatment to reinvigorate the mechanical properties of cold spray additively manufactured Al/B₄C composites. The as-deposited samples were initially subjected to 30% thickness reduction via hot compression treatment at ∼500 °C followed by a hot rolling treatment with 40% thickness reduction in 2 passes. Electron backscatter diffraction (EBSD) and high resolution transmission electron microscopy (HRTEM) results revealed that after hybrid post-deposition treatment (involving 70% accumulative thickness reduction), the aluminum grains in the matrix were extensively refined due to simultaneous operation of continuous dynamic recrystallization (CDRX) and geometric dynamic recrystallization (GDRX). Furthermore, interfacial defects were remarkably reduced while the nature of Al/Al and Al/B₄C interfacial bonding was changed from sheer mechanical interlocking to metallurgical bonding which facilitated efficient transference of applied load to uniformly dispersed bimodal B₄C particles. As a result, ultimate tensile strength (UTS) and elongation (EL) of the as-deposited sample were simultaneously improved from ∼37 to 185 MPa and ∼0.3% to 6.2%, respectively.