Effect of Spark-Plasma-Sintering Conditions on Tensile Properties of Aluminum Matrix Composites Reinforced with Multiwalled Carbon Nanotubes (MWCNTs)

In this study, aluminum (Al) matrix composites containing 2 wt.% multiwalled carbon nanotubes (CNTs) were fabricated by powder metallurgy using high-energy ball milling (HEBM), spark plasma sintering (SPS), and subsequent hot extrusion. The effect of SPS conditions on the tensile properties of CNT/Al composites was investigated. The results showed that composites with well-dispersed CNTs and nearly full-density CNT/Al can be obtained. During HEBM, CNTs were shortened, inserted into welded Al powder particles, bonded to Al, and still stable without CNT-Al reaction. After consolidation, Al₄C₃ phases formed in composites under different sintering conditions. With the increase of sintering temperature and holding time, the strength decreased. Conversely, the ductility and toughness noticeably increased. As a result, a good balance between strength (367 MPa in ultimate tensile strength) and ductility (13% in elongation) was achieved in the as-extruded CNT/Al composite sintered at 630°C with a holding time of 300 min.     

Effect of processing parameters on the microstructure and thermal conductivity of diamond/Ag composites fabricated by spark plasma sintering

Diamond/metal composites with 50 vol.% diamond have been produced by spark plasma sintering (SPS) using pure Ag as a matrix and diamond particles as reinforcement. Three kinds of powder mixing processes were used to prepare the mixture of diamond/Ag powders: dry mixing without milling medium, wet mixing and magnetic blending. Subsequently, they were all consolidated by SPS at various processing parameters to produce bulk diamond/Ag composites. Then samples were heat treated in order to obtain a higher thermal conductivity. The effect of processing parameters on the morphologies of the mixed powders, the microstructure and the thermal conductivity of the composites were investigated by comparing the experimental data. It reveals that particles were easy to agglomerate and the distribution of mixed powders was inhomogeneous by dry mixing method, and wet mixing method is too complex. The most favorable mixing process is magnetic blending by which the powders can be homogenously mixed and the composites prepared by optimized SPS processing parameters can obtain the highest relative density and the best thermal conductivity among the composites prepared by different processes. The magnetic blending diamond/Ag composites even have a 23% increase in thermal conductivity compared with pure silver sintered by SPS.     

放电等离子烧结温度对超细晶W-40Cu复合材料的影响

采用高能球磨法制备了W-40Cu超细晶复合粉体,继而进行了放电等离子烧结(SPS),获得了致密的超细晶W-40Cu块体复合材料,着重研究了烧结温度对复合材料组织和性能的影响.结果表明,随着烧结温度升高,材料的致密度、硬度和电导率也随之升高;在950℃烧结5 min的W-40Cu复合材料,W颗粒尺寸约300～500 nm,相对致密度达98％,显微硬度HV为287,电导率为17.9 MS/m.     

Process optimization,microstructures and mechanical/thermal properties of Cu/Invar bi-metal matrix composites fabricated by spark plasma sintering

An orthogonal experiment scheme was designed to investigate the effects of the Cu content, compaction pressure, and sintering temperature on the microstructures and mechanical and thermal properties of (30–50)wt.%Cu/ Invar bi-metal matrix composites fabricated via spark plasma sintering (SPS). The results indicated that as the Cu content increased from 30 to 50 wt.%, a continuous Cu network gradually appeared, and the density, thermal conductivity (TC) and coefficient of thermal expansion of the composites noticeably increased, but the tensile strength decreased. The increase in the sintering temperature promoted the Cu/Invar interface diffusion, leading to a reduction in the TC but an enhancement in the tensile strength of the composites. The compaction pressure comprehensively affected the thermal properties of the composites. The 50wt.%Cu/Invar composite sintered at 700 °C and 60 MPa had the highest TC (90.7 W/(m·K)), which was significantly higher than the TCs obtained for most of the previously reported Cu/Invar composites.     

WC_p/2024Al复合材料热学性能研究

利用粉末冶金法制备了WC颗粒体积分数分别为8%、11.8%、16.7%的WCp/2024Al复合材料,采用扫描电子显微镜、热膨胀分析仪、热导率测试仪等多种手段研究不同WC体积分数、挤压比和热处理对复合材料热膨胀系数（CTE）、热导率和微观结构的影响。结果表明：复合材料的热膨胀系数随WC体积分数的增大而明显降低,随挤压比的增大而提高,经过T4态热处理后,复合材料内应力的降低和第三相的析出导致其热膨胀系数降低,热膨胀系数的实测值与kermer模型的计算值相近。复合材料的热导率随WC体积分数的增大而降低。     

Microstructure and Physical Properties of Tb<Subscript>2</Subscript>TiO<Subscript>5</Subscript> Neutron Absorber Synthesized by Ball Milling and Sintering

Tb₂TiO₅ neutron absorber was synthesized by ball milling and sintering. Microstructure character of ball-milled Tb₄O₇-17.605%TiO₂ (mass fraction, %) powders and sintered bulks was analyzed using XRD, SEM and TEM. The microhardness, coefficient of thermal expansion and thermal conductivity of sintered bulks were measured. The experiment results showed that the nanocrystalline solid solution was obtained during ball milling. After 96 h of ball milling, TiO₂ was completely solved in Tb₄O₇ and the crystal size of Tb₄O₇ was up to 37 nm. The bulk materials prepared by cold isostatic pressing were sintered at 1300 °C. Tb₂TiO₅ bulks with an orthorhombic structure were obtained. The microhardness of sintered bulks, as well as the thermal conductivity, increased firstly with increasing ball milling time and then decreased. The coefficient of thermal expansion decreased initially and then increased with increasing ball milling time. For the sintered bulk with powder milled for 48 h, the highest values of both microhardness and thermal conductivity were observed, whereas the lowest coefficient of thermal expansion was exhibited. In addition, with increasing testing temperature, the thermal conductivity of sintered bulks initially fell and then rebounded while an opposite trend was found in the coefficient of thermal expansion.     

石墨烯纳米片增强铝基复合材料的制备与性能

采用高能球磨、放电等离子烧结以及热挤压工艺制备含量为5.0%(体积分数)的石墨烯增强铝基复合材料。分别采用X射线光电子能谱、透射电镜及拉伸试验研究挤压态复合材料的显微组织与力学性能,发现5.0%(体积分数)的石墨烯分散在铝晶界上,并且未与铝基体发生界面反应。最终,挤压态复合材料的屈服强度和抗拉强度高达462 MPa和479 MPa,分别比挤压态铝基体提高62%和60%。断口分析表明,在断裂过程中复合材料中分散的石墨烯起到明显的载荷传递的作用。上述结果表明,采用高能球磨、放电等离子烧结以及热挤压制备工艺可将高含量石墨烯分散于铝合金中,且能控制石墨烯和铝基体之间的界面反应。     

放电等离子烧结Ti-43Al-9V合金显微组织和力学性能(英文)

采用机械合金化和放电等离子烧结工艺制备细晶Ti-43Al-9V合金,研究不同烧结温度与显微组织和力学性能之间的关系。结果表明:机械球磨后粉末形状规则,尺寸在5～30μm之间,烧结所得块体材料主要由γ-TiAl、α2-Ti3Al和少量B2相组成。烧结温度为1150°C时,获得的等轴晶粒尺寸为300nm～1μm。烧结温度升高到1250°C时,等轴晶粒的尺寸明显增大,显微硬度从HV592降低到HV535,抗弯强度从605降低到219MPa,压缩断裂强度从2601降低到1905MPa,压缩率从28.95%降低到12.09%。     

Al2O3/Cu复合材料的导热性能研究

利用高能球磨及粉末冶金法制备了Al2O3/Cu复合材料,采用双试样叠加激光脉冲法测试室温条件下的导热性能.研究发现,随着Al2O3体积分数的增加,热导率逐渐下降,特别是当Al2O3体积分数大于10％以后热导率急剧下降,这说明热导率受Al2O3含量影响很大.要获得良好导热性能的Al2O3/Cu复合材料,应该严格控制Al2O3颗粒的体积分数不高于10％,尽量提高致密度,减少烧结体内的位错、空隙等缺陷.     

Governing the Inclination Angle of Graphite Flakes in the Graphite Flake/Al Composites by Controlling the Al Particle Size via Flake Powder Metallurgy

The inclination angle of the flake particle has a significant impact on the in-plane thermal conductivity of composites.The graphite flake/Al composites(50 vol%) with different inclination angles were fabricated via flake powder metallurgy,and the results show that with increasing the size of Al particle from 25.6 to 50.7 μm,the inclination angle of graphite flake decreases from 7.3° to 4.4°,while the in-plane thermal conductivity of composites increases from 473 to 555 Wm~(-1) K~(-1).Based on the rules of mixture,an effective model was established to qualify and quantify the relation between the inclination angle and the in-plane thermal conductivity of the corresponding composites.This model can also be applied to other flake particle-reinforced composites.     

Influence of Mixing Technique on the Mechanical Properties and Structural Evolution of Al-NiAl Composites

Fabrication and processing of 99.7% purity aluminum powder reinforced with 0, 5, 10% volume fractions NiAl intermetallic metal matrix composites were conducted. The mechanically alloyed nanostructured NiAl was mixed by both regular and high energy ball milling techniques. Powders of NiAl employed for reinforcement were milled for 18 and 31 h, and therefore denoted as NiAl18 and NiAl31, respectively. The mixed powders were consolidated via a combination of cold pressing followed by hot extrusion at 480 °C for 1 h at a reduction ratio 4:1. Hardness, tensile properties, and fracture behavior of the extruded composite powders were evaluated. Structural evolution of the milled composite powders was investigated before and after extrusion using optical microscopy, field emission scanning, and transmission electron microscopy. In addition, particle type identification was carried out via energy dispersive x-ray analysis. Introducing NiAl31 (0.8 µm) enhanced the mechanical properties of the composites compared to NiAl18 (1.0 µm). Moreover, powders milling enhanced the tensile properties post hot extrusion compared to the mixed conditions due to the enhanced reinforcement distribution and bonding with the Al matrices. Hot extruded milled composite powders of Al reinforced with 10% NiAl31 produced nanostructured high-angle grain boundary structure <200 nm.     

多壁碳纳米管增强银基复合材料的组织与性能

采用化学镀方法将银沉积在碳纳米管上,获得体积分数为8%的多壁碳纳米管/银(CNTs/Ag)复合粉末,通过高能球磨、压制烧结、热挤压粉末冶金手段制备了CNTs/Ag复合材料,并研究了复合材料的微观组织、导电率、抗拉强度及硬度。结果表明,化学沉积工艺能够显著改善CNTs和Ag之间的界面结合,进而提高CNTs/Ag复合材料的加工性能。与纯银比较,CNTs/Ag复合材料的抗拉强度增加了65%,硬度增加了近2倍,表明CNTs对银具有较好的强化作用。     

Study of characteristics and properties of spark plasma sintered WC with the use of alternative Fe-Ni-Nb binder as Co replacement

Most of all WC-based cemented carbides use cobalt as binder due to the excellent strength and ductility that this combination provides. Motivators to find alternative binders have been related to factors such as the shortage and price oscillations of the cobalt and toxicity of the WC-Co system. In this work, Fe-Ni-Nb was used as alternative binder for WC sintered via spark plasma sintering (SPS) technique. The composites were sintered at different sintering temperatures (1100 °C, 1200 °C and 1300 °C). In addition, WC-Co was sintered at 1200 °C via SPS for comparison purposes. X-ray diffraction and Scanning electron microscopy (SEM) were employed as characterization methods to investigate the crystalline phase's formation, sintering effectiveness, porosity and phase distribution. Mechanical properties such as Vickers hardness, fracture toughness, nanohardness, elastic modulus and thermal properties (thermal expansion coefficient) were evaluated. The results demonstrate Fe-Ni-Nb as a viable alternative binder to cobalt in hardmetal applications.     

超细WC-Co硬质合金的制备与性能研究

利用高能球磨法制备纳米级WC-Co混合粉末,采用脉冲电流烧结技术进行烧结。用能谱分析仪(EDX)对球磨后的粉末进行成分分析,用X射线衍射(XRD)对比分析球磨前后WC-Co混合粉末的衍射峰变化,用透射电子显微镜(TEM)和扫描电子显微镜(SEM)对所制备的粉末及烧结材料进行了组织形貌观察,并测定了烧结试样的硬度。结果表明:随着球磨时间的延长,WC-Co纳米粉末的粒度逐渐变小,当球磨时间超过30h后获得了粒度为100nm以下的WC-Co纳米粉末。脉冲电流烧结后获得超细WC-Co硬质合金,与传统的WC-Co硬质合金相比,超细WC-Co硬质合金具有更高的硬度(HRA92.5～94)和耐磨性。另外通过实验获得了最佳的烧结工艺参数。     

球磨时间和转速对CNTs／Al-2024复合粉末变化的影响

通过机械球磨和热挤出的方法制备碳纳米管（CNTs）增强铝基复合材料。在2024铝合金中加入1％CNTs,并在不同条件下进行球磨。通过X射线衍射仪（XRD）、场发射扫描电镜（FESEM）以及力学性能测试等方法对球磨过的粉末和块体材料的显微组织的变化和力学性能进行测试。研究碳纳米管浓度和球磨时间对CNTs／Al-2024复合材料显微组织的影响。通过对显微组织的观察,讨论粉末在球磨过程中的变形行为。结果表明：在CNTs含帚相同的条件下,粉末颗粒尺寸随着球磨时间和转速的增加而减小,当球磨时间达到15h,粉末颗粒尺寸最小。由于CNTs的加入,铝合金复合材料的拉伸性能有所提高。     

机械合金化对W-20Cu复合材料的显微组织与性能的影响

采用机械合金化结合粉末冶金技术制备W-20Cu（vo1％）复合材料。利用扫描电镜和金相显微镜对不同球磨时间的W-20Cu复合材料显微组织进行表征，并对材料的各项物理性能进行测试。结果表明，随着球磨时间的延长，W-20Cu烧结体的组织越来越均匀，Cu相分布也越来越均匀。W-20Cu烧结体密度、收缩率、硬度、抗弯强度随球磨时间的延长而增大；球磨20h的W-20Cu复合粉烧结体热导率达到峰值（130．61Wm^-1K^-1），继续球磨，热导率减小。综合考虑所有研究结果，通过机械合金化所制备的W-Cu复合粉体可以获得具有优异综合物理性能的W-20Cu复合材料。     

活化烧结制备W-Cu复合材料及其性能

研究添加元素Ni对W-Cu复合材料组织和性能的影响.利用预混粉、机械球磨和活化液相烧结法制备不同Ni含量W-Cu复合材料,采用电子扫描显微镜、X射线衍射仪、激光导热仪等对复合材料的显微组织、物相、热导率、热膨胀系数和硬度进行检测与分析.结果表明:当W-Cu复合材料中不添加Ni元素时,W颗粒团聚形成闭合孔隙,液相Cu无法...     

Microstructure and properties of copper composite containing in situ NbC reinforcement: Effects of milling speed

This paper presents a study on the effects of milling speed on the properties of in situ copper-based composite produced by mechanical alloying followed by cold pressing and sintering. A powdered mixture of copper, niobium and graphite with the composition of Cu–30%NbC was milled at various speeds (100, 200, 300 and 400 rpm). The NbC phase started to precipitate in the as-milled powder after 30 h milling at 400 rpm and the formation was completed after sintering at 950 °C. Enhancements of NbC phase formation with a reduction in Cu crystallite size were observed with the increase of milling speed. Density, hardness and electrical conductivity of the sintered composite were evaluated. An increase in milling speed resulted in an increase in sintered density and hardness but a reduction of electrical conductivity. The changes in the properties were correlated to the formation of NbC phase and refinement of copper and niobium carbide crystallite size since higher milling speed is associated with higher kinetic energy per hit.     

Consolidation of AA 7075-2 wt% ZrO_2 Composite Powders by Severe Plastic Deformation via ECAP

The powders of the AA 7075-ZrO_2 were mixed by mechanical milling, but it was found that the system presents a few disadvantages when processed by conventional sintering and hot extrusion, since intermetallic phases between ZrO_2 particles and alloying elements were formed. Equal channel angular pressing(ECAP) processing was proposed as an alternative method to consolidate the composite where there is no intermetallic formation. The analysis of the ECAP process showed that the intermediate temperature(220 ℃) produced a higher consolidation level than conventional sintering and hot extrusion(400 and 500 ℃, respectively). This fact was supported by relative density analysis. In the case of the sintered and hot-extruded sample, the relative density exhibited a value of 0.95, while ECAP sample showed a value of 0.98. Hardness values show that microstructural refinement obtained during mechanical milling was preserved during ECAP processing even when it was carried out at 220 ℃.     

不同SPS烧结温度Ti-45Al-5.5(Cr,Nb,B,Ta)合金的显微组织及力学性能(英文)

采用高能球磨和放电等离子烧结(SPS)技术,制备成分为Ti-45Al-5.5(Cr,Nb,B,Ta)的TiAl合金块体,随后对TiAl合金进行热处理。研究在不同SPS烧结温度下制备的TiAl合金经过热处理后的显微组织和力学性能。结果表明:高能球磨后的合金粉末形状不规则,粉末颗粒尺寸大约为几十微米。XRD分析表明,机械球磨后的粉末由TiAl和Ti3Al两相组成;烧结后的Ti-45Al-5.5(Cr,Nb,B,Ta)合金块体主要是TiAl相,以及少量的Ti3Al和TiB2相。当烧结温度为900°C和1000°C时,合金的显微组织为双相结构,并伴随有一些细小的等轴γ晶粒和细小的针状TiB2相。当烧结温度从900°C上升到1000°C时,Ti-45Al-5.5(Cr,Nb,B,Ta)合金的显微硬度变化不大,抗压强度从1812MPa提高到2275MPa,压缩率从22.66%增加到25.59%,合金的断裂方式为穿晶断裂。