Mechanical alloying and sintering of nanostructured tungsten carbide-reinforced copper composite and its characterization

Elemental powders of copper (Cu), tungsten (W) and graphite (C) were mechanically alloyed in a planetary ball mill with different milling durations (0–60 h), compacted and sintered in order to precipitate hard tungsten carbide particles into a copper matrix. Both powder and sintered composite were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM) and assessed for hardness and electrical conductivity to investigate the effects of milling time on formation of nanostructured Cu–WC composite and its properties. No carbide peak was detected in the powder mixtures after milling. Carbide WC and W₂C phases were precipitated only in the sintered composite. The formation of WC began with longer milling times, after W₂C formation. Prolonged milling time decreased the crystallite size as well as the internal strain of Cu. Hardness of the composite was enhanced but electrical conductivity reduced with increasing milling time.     

Mechanical alloying process and mechanical properties of Cu–SiCp composite

Abstract

A composite of copper powder and SiC particle reinforcement was prepared by mechanical ball milling and subsequent sintering. Proper choice of processing parameters ensured a homogenous distribution of SiC particles in the copper matrix. Microstructure, powder morphology and mechanical properties of the composite were investigated as a function of milling time. With increasing milling time, the dentritic copper powder became flattened, which subsequently became spherical shaped. Mechanical properties of the composites change with the distribution of SiC.     

原位生成Al2O3/Cu复合材料的新工艺

采用一种新型工艺制备了Al₂O₃/Cu复合材料。高能球磨制备亚稳态的Cu-0.8 wt% Al合金粉,再将Cu₂O粉与其一起进行高能球磨,然后将复合粉末压坯在真空炉中同时进行氧化和烧结。该工艺省略了还原剩余Cu₂O的环节,氧化和烧结时间仅为1 h。生成的Al₂O₃的粒径约250nm,颗粒间距约500 nm,均匀弥散分布;该材料冷加工后性能接近SCM制品性能。该配比的Al₂O₃/Cu复合材料的热稳定性良好,在800℃下循环冷淬20次无裂纹;软化温度为700℃。     

Pulvermetallurgische Erzeugung von SiC‐ und Al2O3‐verstärkten Al‐Cu‐Legierungen

Powder metallurgical fabrication of SiC and Al₂O₃ reinforced Al‐Cu alloys Based on metallographic studies the states of composite powder formation during high‐energy ball milling will be discussed. Spherical powder of aluminium alloy AA2017 was used as feedstock material for the matrix. SiC and Al₂O₃ powders of submicron and micron grain size (<2 μm) were chosen as reinforcement particles with contents of 5 and 15 vol.‐% respectively. The milling duration amounted to a maximum of 4 hours. The abrasion of the surface of the steel balls, the rotor and the vessel is indicated by the content of ferrous particles in the powder. High‐energy ball milling leads to satisfying particle dispersion for both types of reinforcement particles. Further improvements are intended. The microstructure of compact material obtained by hot isostatic pressing and extrusion was studied in detail by scanning and transmission electron microscopy. For both types of reinforcement the microstructure of composites is similar. The microporosity is low. The interface between reinforcement particles and matrix is free of brittle phases and microcracks. In the case of SiC reinforcement particles, a small interface interaction is detectable which implies a good embedding of reinforcement particles. High‐energy ball milling under air‐atmosphere leads to the formation of the spinel phase MgAl₂O₄ during the subsequent powder‐metallurgical processing. Because of the size, rate and dispersion of the spinel particles, an additional reinforcement effect is expected.     

FABRICATION AND CHARACTERIZATION OF Cu-SiCp COMPOSITES FOR ELECTRICAL DISCHARGE MACHINING APPLICATIONS

Cu-SiC_p composites made by the powder metallurgy method were investigated. To avoid the adverse effect of Cu-SiC_p reaction, sintering was controlled at a reaction temperature less than 1032 K. Electroless plating was employed to deposit a copper film on SiC_p powder before mixing with Cu powder in order to improve the bonding status between Cu and SiC particles during sintering. It was found that a continuous copper film could be deposited on SiC_p by electroless copper plating, and a uniform distribution of SiC_p in Cu matrix could be achieved after the sintering and extrusion process. The mechanical properties of Cu-SiC_p composites with SiC_p contents from 0.6 to 10 wt% were improved evidently, whereas electrical properties remained almost unchanged as compared with that of the pure copper counterpart. In the electrical discharge machining (EDM) test, the as-formed composite electrodes exhibited a character of lower electrode wear ratio, justifying its usage. The optimum conditions for EDM were Cu-2 wt% SiC_p composite electrode operating with a pulse time of 150 μsec.     

Fabrication of ultrafine W – Cu powders by mechanical alloying

Abstract

Ultrafine composite powders of W – 15 wt-%Cu, W – 25 wt-%Cu, and W – 35 wt-%Cu have been fabricated by mechanical alloying. The effects of type of mill, process control agent, temperature of milling, and ball/powder ratio on the final products have been evaluated. The results show that the planetary ball mill possesses a higher impact energy intensity than that of the vibratory ball mill. The optimum milling time is confirmed by the formation of a nanocrystalline microstructure in the planetary ball mill after optimisation of the milling parameters. A steady state between cold welding and fracture is attained with a milling time of up to 25 h in the planetary ball mill under optimised conditions. Crystallites with sizes of 7 – 8 nm for W – Cu composite powders have been obtained after 25 h of ball milling. The powders obtained after mechanical alloying have been characterised in terms of their size, shape, phase constitution, and microstructural features using X-ray diffraction and scanning electron microscopy.     

铜包裹碳化硅颗粒复合粉体的化学原位沉积制备与表征

以铜氨离子为铜源, 水合肼为还原剂, 在表面预氧化的SiC表面, 采用一步原位化学沉积法制备了均匀包裹Cu颗粒的SiC复合粉体. 采用扫描电子显微镜(SEM)、X射线衍射(XRD)、傅立叶红外光谱(FT-IR)、Zeta电位等测试表征手段研究了工艺条件对原位沉积反应的影响. 研究发现SiC表面预氧化形成的SiO2层能显著增强对铜氨离子吸附能力, 有助于原位还原生成单质Cu, 形成近乎连续包裹层. 控制反应体系中铜氨离子浓度和反应温度可以影响反应速率, 从而控制Cu颗粒的沉积速率和包裹效果. 对比研究表明, 在0.2 mol/L铜氨离子溶液中70℃反应, 在预氧化的SiC表面能够获得最佳包裹层.     

Synthesis of Bulk Nano-Al2O3 Dispersed Cu-Matrix Composite Using Ball Milled Precursor

Kinetics of solid-state reduction reaction during ball milling of CuO-Al and CuO-prealloyed Cu(Al) powder blends in dry and wet condition has been investigated by using X-ray diffraction (XRD), differential scanning calorimetry (DSC), and transmission electron microscopy (TEM) techniques. Direct reduction of CuO by Al has resulted into Al₂O₃ dispersed Cu-matrix composite through a self-propagating reaction only during milling in dry condition. However, indirect reduction of CuO by prealloyed Cu(Al) resulted into formation of nano-Al₂O₃ dispersed Cu-matrix composite either by continued ball milling in dry condition or by subsequent thermal treatment of wet milled powder precursor. The influence of milling conditions, that is, milling speed, and milling media, on the occurrence of reduction of CuO by elemental Al or Al in prealloyed Cu(Al) during ball milling have been explained by considering their effects on the rise of powder temperature due to collisions between balls and powder particles, and the rate of reduction of ignition temperature of the reaction due to microstructural refinement. TEM investigation has revealed that the size of Al₂O₃ particles in the composite power blend formed by the indirect reaction route (CuO-prealloyed Cu(Al)) is much finer than the same in case of direct reaction route (CuO-Al). It is suggested that the kinetics of the reduction reaction in the indirect reaction route is relatively sluggish in nature and amenable to processing of large amount of nano-Al₂O₃ dispersed Cu-matrix composite powder for industrial purpose.     

在酸性条件下采用高能球磨法制备 Cu2O纳米粉末

采用行星球磨机在pH=2的稀盐酸溶液中对Cu粉进行球磨，球磨机简体和磨球材质均为纯Cu，球料比为20：1，球磨机转速为300r／min，通过X射线衍射（XRD）、扫描电子显微镜（SEM）、透射电子显微镜（TEM）等对球磨产物进行了表征．XRD结果表明，球磨3h后，所加入的纯Cu粉末基本转化为Cu20粉末．球磨70h后得到纯的Cu20粉末，粉末粒度为50-100nm．并对Cu20纳米粉末的生成机制及球磨工艺参数对Cu20形成的影响进行了讨论．     

Effect of SiC Nanoparticles Content and Mg Addition on the Characteristics of Al/SiC Composite Powders Produced via In Situ Powder Metallurgy Method

In the present study, the effect of the nanosized SiC particles loading and Mg addition on the characteristics of Al/SiC composite powders produced via a relatively new method called “in situ powder metallurgy” (IPM) was investigated. Specified amounts of SiC particles (within a size range of 250 to 600 µm) together with SiC nanoparticles (average size of 60 nm) were preheated and added to aluminum melt. This mixture was stirred via an impeller at a certain temperature for a predetermined time. The liquid droplets created by this process were then subsequently cooled in air and screened through 250 µm sieve to separate micron-sized SiC particles from solidified aluminium powder particles containing nanosized SiC particles. Results of SEM and TEM studies together with microhardness measurements revealed that the commercially pure (CP) Al could not embed as-received SiC particles. However, the nanosized particles were distributed uniformly in the Al-1 wt% Mg powders. The process yield and microhardness of the Al-1Mg composite powders increased with increasing the contributed amount of nanosized SiC particles.     

Synthesis of Aluminium-Cementite Metal Matrix Composite by Mechanical Alloying

Cementite powder was prepared from elemental iron and graphite powder by mechanical alloying (MA) in a specially built dual-drive planetary mill. The phase evolution, particle-size distribution, and morphology of particles were studied during 40 hours grinding period. X-ray diffraction (XRD) shows formation of cementite and other iron carbides along with elemental iron after milling, whereas after annealing only cementite is present. Initially particle size increases with milling due to ductility of iron powder and then reduces with further milling.

Al-cementite composite was synthesized by mixing cementite with Al powders, and then by hot pressing or cold compaction and sintering. XRD analysis of Al-Fe₃C composite shows Fe₃C, FeAl, Al, and other iron carbides along with Al₄C₃ after sintering. Scanning electron microscope (SEM) micrograph of hot-pressed samples shows excellent compatibilility between Al matrix and cementite particles.     

高能球磨粉末冶金制备工艺对15%SiCp/2009Al复合材料性能的影响

采用高能球磨粉末冶金法制备了15%SiC_p/2009Al复合材料,研究了球磨转速、球磨时间、加热抽真空工艺、热压成型以及热挤压比对复合材料力学性能的影响。结果表明,球磨转速和时间、热压成型工艺是影响复合材料力学性能的重要因素。较长时间高转速球磨使SiC颗粒均匀分布,高温真空热压改善粉末之间的结合是获得高性能复合材料的关键。转速190 r/min、球磨6 h制备的复合粉末经高温真空热压、挤压后的复合材料SiC颗粒均匀分布,材料的抗拉强度高达650 MPa,延伸率大于5%。      

Impact of the SiC addition on the morphological,structural and mechanical properties of Cu-SiC composite powders prepared by high energy milling

The effect of the SiC content on the microstructural, mechanical, and magnetic properties of Cu(1 − x)SiC(x) composite powders (x = 0, 2, 10 and 15 wt%) prepared by high energy milling for 30 h was investigated. The results showed that Cu particles were severely deformed and formed plate like particles of different sizes, while SiC particles were fragmented and embedded in the Cu phase, thus, forming composite particles. As the SiC content increased, the average particle size decreased from 40.75 to 12.84 µm. Besides, XRD data showed a decrease in the crystallite sizes of the Cu phase (from 23.66 to 21.56 nm), accompanied by an increase in the lattice micro-strain (from 0.41 to 0.46%). Changes in the lattice parameters of the Cu phase were observed. The Vickers microhardness were measured in compacted powder samples and reached a maximum value of 135.22 HV for the sample with 15 wt% SiC. The samples showed hysteresis magnetic behavior at 300 K, and with a maximum saturation magnetization of 0.123 emu/g. The weak magnetic signal is mainly due to Co impurities present in the WC from the milling media.     

Processing of Cu-Fe and Cu-Fe-SiC nanocomposites by mechanical alloying

The Cu-Fe and Cu-Fe-SiC nanocomposite powders were synthesized by a two step mechanical alloying process. A supersaturated solid-solution of Cu-20 wt% Fe was prepared by ball milling of elemental powders up to 5 and 20 h and subsequently the SiC powder was added during additional 5 h milling. The dissolution of Fe into Cu matrix and the morphology of powder particles were analyzed by X-ray diffraction (XRD) and scanning electron microscopy (SEM), respectively. It was found that the iron peaks in the XRD patterns vanish at the early stages of mechanical alloying process but the dissolution of Fe needs more milling time. Moreover, the crystallite size of the matrix decreases with increasing milling time and the crystallite size reaches a plateau with continued milling. In this regard, the addition of SiC was found to be beneficial in postponing the saturation in crystallite size refinement. Moreover, the effect of SiC on the particle size was found to be significant only if it is added at the right time. It was also found that the silicon carbide and iron particles are present after consolidation and are on the order of nanometer sizes.     

Structural evolution in nano-crystalline Cu synthesized by high energy ball milling

Nano-crystalline copper with a mean crystallite size of 27 nm was synthesized through solid state reduction of Cu₂O by graphite using high energy planetary ball mill. The structural and morphological changes during mechanical milling were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The mean crystallite size and residual strain were determined by XRD peak broadening using the Williamson–Hall approximation. It was found that the reaction is completed in a manner like a nucleation and growth process. Although the crystallite size and internal strain changes in Cu₂O were regular during mechanical milling, there was an irregularity in both parameters in Cu particles. This irregularity was probably due to the progressive formation of copper during milling.     

非均相沉淀制备Cu包裹纳米SiC复合粉体颗粒

选用工业生产的立方相SiC纳米颗粒,尺寸约120nm,利用置换反应原理制得纳米Cu微晶。采用非均相沉淀方法将Cu包裹到纳米SiC颗粒表面,形成相分布均匀的复合颗粒,纳米Cu微晶吸附在SiC颗粒周围形成粗糙表面,复合粉体颗粒表面被一层连续、致密的Cu₂O层所包覆,Cu₂O的存在是纳米Cu微晶颗粒自发氧化的结果。     

Production and characterization of nanosized Cu/O/SiC composite particles in a thermal r.f. plasma reactor

An inductively coupled thermal plasma process was used to produce nanosized Cu/SiC composite particles. The powders were characterized by means of chemical analysis, energy dispersive X-ray spectroscopy (EDX), transmission electron microscopy (TEM), specific surface measurements (BET), X-ray powder diffractometry (XRD) and X-ray photoelectron spectroscopy (XPS). X-ray absorption fine structure analysis (EXAFS) was performed to determine the near range order structure of the nanosized particles.     

Structural studies on Ti–Cu alloy obtained by high-energy ball milling

ABSTRACT

Ti₅₀Cu₅₀ (at.-%) alloy has been produced from elemental Ti and Cu powders by high-energy ball milling in a planetary ball mill. Structural evolution of the alloy during milling and after subsequent heat treatment have been studied. It has been stated that high-energy ball milling of the investigated powder produces two nanocrystalline solid solutions: Cu(Ti) and Ti(Cu), both characterised by the fcc (Fm-3 m) structure. The transition of Ti structure from hcp (P63/mmc) to fcc (Fm-3 m) is observed during milling. Heat treatment of the milled powder leads to recrystallisation of Cu(Ti) and Ti(Cu) solid solutions.

This paper is part of a Thematic Issue on The Crystallographic Aspects of Metallic Alloys.     

Solid solubility extension of copper‐tin immiscible system during mechanical alloying

In this paper, copper‐5 wt.%‐tin (Cu‐5wt%Sn) powder mixture was mechanically alloyed in order to study the solid solubility extension during the alloying process. Nanocrystalline supersaturated solid solution has been prepared in this system by high energy ball milling. Based on the thermodynamic model, the Gibbs free energy change in this alloy system during the formation of solid solution is calculated to be positive, which means that there is no driving force to form solid solution in copper‐tin (Cu?Sn) immiscible system. It has been found that a large fraction of grain boundaries and a high density of dislocations play a significant role in the solid solubility extension of immiscible copper and tin.     

Synthesis of nanocrystalline SiC at ambient temperature through high energy reaction milling

This study investigated the in-situ synthesis of nanosized crystalline SiC powders at room temperature through high energy ball milling of elemental silicon and carbon mixtures. Milling conditions including the mill design, the milling speed, the milling time and the ball-to-powder weight ratio (i.e. the charge ratio) necessary for the in-situ synthesis were studied. It was found that uniform formation of nanosized crystalline SiC powders within the powder charge could be achieved with a correctly designed attritor and the contamination could be minimized with proper selections of milling conditions. The crystalline β-SiC powders synthesized were themselves in nanosize scale, quite different from many previous studies which have shown that it is the internal grain structure of milled powders that is the “nanocrystalline” component of the powders (typically 5–20 nm), while the powders are themselves typically 0.1 μm to > 1 μm in size. Furthermore, it was found that the product structures generated by high energy reaction milling depended strongly on the milling speed, the charge ratio and the milling time.