Dispersion and Damage of Carbon Nanotubes in Carbon Nanotube/7055Al Composites During High-Energy Ball Milling Process

High-energy ball milling(HEBM) combined with powder metallurgy route was used to fabricate carbon nanotube(CNT) reinforced 7055 Al composites. Two powder morphology evolution processes(HEBM-1 and HEBM-2) were designed to investigate the dispersion and damage of CNTs during HEBM process. HEBM-1 evolution process involved powder fl attening, cold-welding and fracture, while HEBM-2 evolution process consisted of powder fl attening and fracture. For HEBM-1, the repetitive fracture and cold-welding process was effective for dispersing CNTs. However, the powder fl attening process in HEBM-2 was unsuccessful in dispersing CNTs due to two reasons:(1) the thickness of fl aky Al powders exceeded the critical value, and(2) the clustered CNTs embedded in fl aky Al powders could not be unravelled. Because of the broadening of D band and the appearance of a new defect-related D' band, product of I D/I G and full width half maximum of D band, rather than I D/I G, was used to evaluate the actual damage of CNTs. It indicates that the damage of CNTs was severe in powder fl attening and fracture stages, while the damage of CNTs was small in powder cold-welding stage.     

高能球磨结合粉末冶金法制备碳纳米管增强7055Al复合材料的微观组织和力学性能

采用高能球磨结合粉末冶金工艺制备了碳纳米管(CNT)含量(体积分数)分别为0、1%和3%的CNT/7055Al复合材料。采用OM、SEM、TEM以及拉伸实验等方法研究了CNT/7055Al复合材料的CNT分布、晶粒结构、近界面结构及力学性能,分析了复合材料的强化机制和各向异性。结果表明,CNT/7055Al复合材料为无CNT的粗晶区与富集CNT的超细晶区组成的双模态晶粒结构;CNT在Al基体的超细晶区中分散良好,CNT-Al界面干净清洁,界面反应产物少;3%CNT/7055Al复合材料沿挤压方向的抗拉强度达到816 MPa,但延伸率仅为0.5%。细晶强化和Orowan强化是CNT/7055Al复合材料主要的强化机制。由于CNT沿不同方向的增强效率不同以及粗晶条带组织的存在,复合材料表现出比基体合金更强烈的各向异性,在垂直挤压方向的拉伸性能要弱于沿挤压方向的拉伸性能。     

纳米碳管增强镁基材料的复合工艺及性能研究

采用正交试验方法研究了碳纳米管加入量、复合温度、搅拌时间等工艺参数对用铸造方法制备纳米碳管增强镁基复合材料过程的影响,并探讨了这些工艺参数对复合材料力学性能和显微组织的作用.试验结果表明:碳纳米管(CNTs)能明显细化复合材料的晶粒组织,提高复合材料的抗拉强度、伸长率.在3个工艺参数中,CNTs对材料的力学性能影响最大,其含量约为1%时对力学性能最为有利;其次是加热温度,温度取低值(680 ℃)较好;搅拌时间在3 min时,其综合性能较好.影响材料拉伸强度的3个因素最优组合为A 2B 1C 3,影响伸长率的3个因素的最优组合为A 2B 1C 3.     

Wear Behavior of the Uniformly Dispersed Carbon Nanotube Reinforced 6061Al Composite Fabricated by Milling Combined with Powder Metallurgy

The uniformly dispersed carbon nanotubes(CNTs) reinforced 6061Al composites(CNT/6061Al) with diff erent CNT concentrations were fabricated by powder metallurgy technology. It was found that the friction coe ffi cient as well as wear rate decreased fi rst and then increased as the CNT concentration increasing under 15 N as well as 30 N, and the minimum wear rate was achieved at the CNT concentration of 2 wt%. Adhesive wear and abrasive wear were the dominated wear mechanisms for the 1–2 wt% CNT/6...     

纳米碳管增强铝基复合材料的工艺及性能研究

采用正交试验方法研究了碳纳米管加入量、加入碳纳米管时的温度、凝固速度、浇注温度等工艺参数,对用半固态复合铸造法制备纳米碳管增强铝基复合材料过程的影响,并探讨了这些工艺参数对复合材料力学性能的作用。结果表明:碳纳米管(CNTs)能细化复合材料的晶粒组织,明显提高复合材料的抗拉强度、硬度。得出实验的最佳工艺参数为:碳纳米管的加入量为2%,加入碳纳米管时的温度为600℃,采用金属型铸造,浇注温度为680℃时,其综合性能最好;在4个工艺参数中,CNTs的加入量对材料的力学性能影响最大。     

Effect of Carbon Nanotube Orientation on Mechanical Properties and Thermal Expansion Coefficient of Carbon Nanotube-Reinforced Aluminum Matrix Composites

Carbon nanotube-reinforced 2009Al （CNT/2009Al） composites with randomly oriented CNTs and aligned CNTs were fabricated by friction stir processing （FSP） and FSP-rolling, respectively. The CNT/2009A1 composites with aligned CNTs showed much better tensile properties at room temperature and elevated temperature compared with those with the randomly oriented CNTs, which is mainly attributed to larger equivalent aspect ratio of the CNTs and avoidance of preferential fracture problems. However, much finer grain size was not beneficial to obtaining high strength above 473 K. The aligned CNTs resulted in tensile anisotropy, with the best tensile properties being achieved along the direction of CNT aligning. As the off-axis angle increased, the tensile properties were reduced due to the weakening of the load transfer ability. Furthermore, aligned CNTs resulted in much lower coefficient of thermal expansion compared with randomly oriented CNTs.     

Origin of Insignificant Strengthening Effect of CNTs in T6-Treated CNT/6061Al Composites

Carbon nanotube(CNT)-reinforced 6061 Al(CNT/6061 Al) composites were fabricated via powder metallurgy combined with friction stir processing(FSP). CNTs were dispersed after FSP and accelerated the precipitation process of the CNT/6061 Al composites. However, the strengthening effect of CNTs on the T6-treated materials was insignificant,while the composites under the FSP and solution treatment conditions exhibited increased strength compared to the matrix.Precipitate-free zones(PFZs) were detected around CNTs in the T6-treated CNT/6061 Al composites, and a model was proposed to describe the effect of PFZs on strength. The calculations indicated that the strength of PFZs was similar to that of the T6-treated 6061 Al. As a result, the strengthening effect of CNTs on the T6-treated CNT/6061 Al composites was insignificant.     

Fabrication and mechanical properties of in situ TiC/Ti metal matrix composites

In situ TiC particle reinforced titanium matrix composites (TMCs) were successfully fabricated by reactive sintering of Ti + Mo₂C and Ti + VC compacts. The results of the tensile tests at ambient and elevated temperatures show that the strength of the composites increases with increasing additive content (Mo₂C and VC), and decreases with increasing temperatures. Comparing the two types of TMCs, the Ti + VC composites have a lower strength than the Ti + Mo₂C composites, but can more effectively retain the strength to elevated temperatures. Microstructural analyses show that the main strengthening mechanisms of the TMCs are solid solution, grain refinement and particulate strengthening. Different dominant strengthening mechanisms in different composites are responsible for the variations of the mechanical properties. At elevated temperatures, the volume fraction of TiC particles is the main factor for increasing the strength.     

Microstructural Characteristics and Mechanical Behavior of Spark Plasma-Sintered Cu–Cr–rGO Copper Matrix Composites

Copper matrix composites were prepared through spark plasma sintering(SPS) process, mixing fixed amount of reduced graphene oxide(rGO) with the different amounts of Cr. In the sintered bulk composites, the layered rGO network and uniform Cr particles distributed in the Cu matrix. Both of mechanical blending and freeze-drying stages of the wet-mixing process obtained the Cu/Cr/rGO mixture powders, and then SPS solid-phase sintering realized the faster densification of these mixture powders. The hardness and compressive yield strength of the Cu–Cr–rGO composites depicted the higher values than those of pure Cu and single rGO-added composite, and they were gradually increased with increasing Cr. The rGO/Cr hybrid second-phases are believed to be beneficial to strengthening Cu matrix. The relevant formation and strengthening mechanisms involved in Cu–Cr–rGO composites were discussed.     

碳纳米管/ZM5镁合金复合材料的制备与力学性能研究

采用搅拌铸造法制备了碳纳米管/ZM5镁合金复合材料,研究了搅拌法加入碳纳米管的工艺特点,测试了复合材料的力学性能,并利用扫描电子显微镜和能谱分析对复合材料断口形貌进行了观察和分析.研究结果表明：当搅拌温度接近于ZM5镁合金液相线温度时,碳纳米管能较好的加入到镁合金熔体中.与基体合金相比,复合材料的抗拉强度、弹性模量、显微硬度显著增加,伸长率最大可提高110%,但是碳纳米管加入量过多会导致偏聚,使力学性能下降.碳纳米管能细化复合材料的晶粒组织,并且起搭接晶粒和承载变形抗力的作用.     

碳纤维增强热塑性复合材料螺旋铣磨制孔损伤研究

目的 研究碳纤维增强热塑性复合材料(CFRTP)螺旋铣磨制孔的切削温度和切削力的变化趋势,以及典型制孔损伤的特点,并分析切削温度的下降对制孔损伤的影响。方法 采用螺旋铣磨的方法开展CFRTP的制孔试验研究,通过改变工艺参数研究切削温度、切削力的变化趋势,分析各类典型制孔损伤的特点、形成原因及随工艺参数的变化情况,并研究添加冷却辅助降低切削温度对抑制制孔损伤的效果。结果 随着刀具自转转速、公转转速和螺距的升高,切削温度分别升高了约46.43%、12.06%和95.97%;切削力随着自转转速的升高而降低,随着公转转速和螺距的升高而增大。当螺距达到0.45mm时,轴向力会有所下降。入口损伤和出口损伤主要以毛刺为主,损伤会随着各工艺参数的升高而加剧,孔壁损伤主要表现为涂覆、变形、裂纹等3种形式。添加冷却辅助后,制孔质量得到显著提高,高温下的刀具涂覆问题基本解决。结论 切削温度是影响CFRTP制孔质量的主要因素,切削温度的升高导致树脂基体软化,使得切屑形貌从粉末状转变为连续薄片状,进而对切削力产生影响,树脂软化对制孔损伤有着明显的影响。冷却辅助能够明显地降低切削温度,从而起到抑制损伤的作用。     

碳纳米管预制块铸造法制备CNTs/AZ91复合材料研究

在氢气保护下,采用碳纳米管预制块铸造法制备了碳纳米管/AZ9I镁基复合材料.观察和分析了复合材料的微观组织,测试了其室温力学性能,并利用扫描电子显微镜(SEM)和能谱分析(SED)对复合材料拉伸断口形貌进行了观察和分析.研究结果表明:该方法能有效地将碳纳米管添加到镁合金熔体中并且均匀分散;随着碳纳米管的加入,复合材料的晶粒组织得到不断的细化,综合力学性能得到明显提高.     

粉末冶金法制备镁基复合材料的力学性能和增强机理研究

为了探讨MWNTs对镁基复合材料力学性能的影响和增强机理,采用粉末冶金的方法制备了多壁碳纳米管增强镁基复合材料,对其力学性能进行了测试,并对显微组织进行了观察和分析.结果表明:碳纳米管在基体中呈束状分布,没有出现团聚现象;MWNTs与镁基之间并没有反应发生,碳纤维与镁基体并未在界面处形成碳镁化合物;它们之间是无任何化学作用的机械结合;复合材料的硬度随着MWNTs含量的增加而增加,强度也相应提高;镁基复合材料的强化主要来自增强体的强化作用、细晶强化和析出强化.     

弹簧钢60Si2Mn疲劳试验断裂分析

对60Si2Mn弹簧钢进行了疲劳寿命试验。试验结果表明，疲劳寿命较低，未达到标准要求(不低于20万次)。采用化学成分检测、断口扫描观察、能谱分析和金相检验等方法，对疲劳试验中断裂弹簧进行了分析、检测。分析结果表明，钢丝表面微裂纹是导致弹簧疲劳断裂的直接原因，该裂纹是由于母材表面存在轧制缺陷，经过拉拔表面产生硬化组织，由于塑性不足，产生微裂纹；钢丝近表面存在超尺寸夹杂物，该夹杂物属于连铸过程中典型的外来宏观夹杂物，间接加速了弹簧疲劳断裂。     

Microstructure and mechanical properties of SiC-nanowire-augmented tungsten composites

The effect of an addition of SiC nanowire on the microstructure and mechanical properties of tungsten-based composites is investigated in this study. SiC-nanowire-augmented tungsten composites were prepared by a spray-drying process and an in situ spark plasma sintering process. Three distinctive reaction phases, tungsten, tungsten carbide (W₂C) and rod-type tungsten silicide (W₅Si₃) were formed during the sintering process. The flexural strength was significantly increased from 706 MPa to 924 MPa in tungsten composites augmented with SiC nanowires, as was the formation of W₂C and W₅Si₃ phases. The rod-type W₅Si₃ bears significant stress by both sharing a portion of the load and providing a bridging mechanism. Furthermore, a high ablation resistance at an elevated temperature was observed for tungsten composites augmented with SiC nanowires.     

Fatigue Behavior and Damage Evolution of SiC Fiberreinforced Ti-6Al-4V Alloy Matrix Composites

研究SiC纤维增强钛基复合材料(SiCf/Ti-6Al-4V)室温疲劳行为和损伤演化机制。疲劳试验条件:载荷控制、应力比0.1和加载频率10 Hz。采用疲劳断裂试验建立最大加载应力为600~1200 MPa内SiCf/Ti-6Al-4V的S-N曲线。采用疲劳中止试验以及SEM显微分析研究应力水平对SiCf/Ti-6Al-4V疲劳损伤演化的影响。结果表明,SiCf/Ti-6Al-4V疲劳损伤萌生模式与演化过程与应力水平密切相关。在高应力水平(Smax=1000 MPa),纤维开裂是主要损伤萌生模式。一旦2或3根纤维断裂后,纤维裂纹和基体裂纹开始联接并形成宏观扩展裂纹。在中等应力水平(Smax=800 MPa),基体裂纹萌生与扩展是主要损伤模式。多条基体裂纹萌生于试样外表面棱边和离外表面附近试样内部开裂的纤维基体界面处。基体裂纹均沿垂直于加载方向扩展,且大部分纤维未断裂并纤维桥接基体裂纹。在低应力水平(Smax=600 MPa),仅在C涂层和界面反应层之间和C涂层内部观察到局部界面脱粘现象。     

碳纳米管改性MoSi2复合材料的研制及结构性能研究

采用热压烧结技术制备了碳纳米管（CNTs）改性MoSi2复合材料，在制备过程中发现采用十二烷磺酸基钠（C12H25SO3Na）作为分散剂可以有效地解决碳纳米管的分散问题。利用XRD研究了复合材料的相组成与结构，结果显示加入碳纳米管并没有使材料的物相发生明显改变，其主要物相为四方结构的MoSi2，还有少量的Mo5Si3。利用SEM观察了复合材料的显微组织，研究发现碳纳米管的加入能降低材料的晶粒尺寸，使内部孔隙减小，孔径变小，从而促进了烧结坯块的致密化。     

Development of Flake Powder Metallurgy in Fabricating Metal Matrix Composites:A Review

Powder metallurgy(PM) is one of the most applied processes in the fabrication of metal matrix composites(MMCs). Recently, a novel PM strategy called flake PM was developed to fabricate MMCs with nano-laminated or hierarchical architectures. The name ‘‘flake PM' was derived from the use of flake metal powders, which could benefit the uniform dispersion of reinforcements in the metal matrices and thus result in balanced strength and ductility. Flake PM has been proved to be successful in the dispersion of nano aluminum oxides, carbon nanotubes, graphene nano-sheets, and microsized B4 C particles in aluminum or copper matrix. This paper reviews the technique and mechanism developments of flake PM in previous studies, and foresees the future develop of this new fabricating method.     

Microstructures of in-situ TiB2/7055Al Composites by the Ultrasonic and Magnetic Coupled Field

在声磁耦合场下,采用熔体直接反应法制备了纳米TiB2/7055复合材料,并对比无外场、单一磁场和单一超声场原位制备复合材料的微观形貌进行研究。结果表明:声磁耦合场下所制得的TiB2颗粒细小,尺寸为80～100 nm,圆球状,分布均匀,TiB2反应收得率高。当超声功率为0.8 kW,磁场频率5 Hz,励磁电流200 A时,约82.4%的TiB2增强颗粒处于0.2～0.5μm之间,处于0.8～1.2μm之间的颗粒减少至约1.6%,相比单一超声场0.8 kW下能达到近2倍的细化效果     

石墨烯增强钛基复合材料制备工艺与性能研究

以多层石墨烯为增强体,通过熔炼锻造(MF)和粉末冶金(PM) 2种工艺分别制备出规格为Φ10 mm的石墨烯增强钛基复合材料棒材。石墨烯在凝固过程中以TiC枝晶形态析出,变形后呈细小颗粒,其中Ti和C原子比约为2∶1。石墨烯和球形钛粉经过机械合金化和变形加工,在基体中反应形成薄片层。MF工艺对应的棒材拉伸强度可达476 MPa,延伸率保持在28%; PM工艺对应的棒材拉伸强度可达487 MPa,延伸率保持在30%。PM工艺可形成尺寸较小的薄片状石墨烯增强体,强化作用提升,同时塑性没有显著下降。