Particle fracture, retention, and fluid flow in metal matrix composite friction joints

Friction joining of metal matrix composite (MMC)/MMC and MMC/AISI 304 stainless steel base materials is examined using a combination of experimental testing and numerical modeling. In particular, the fracture of reinforcing particles during the friction-joining operation is investigated. The particle diameter and interparticle spacing decrease and the area fraction of particles markedly increases in material immediately adjacent to the bondline. Smaller particles are observed in frictionwelded joints produced using high friction pressures. The principal effect of the forging operation is in decreasing the interparticle spacing. There was excellent correspondence between predicted fluid flow in A1/A1 joints and experimental test results examining the transfer of Al₂O₃ particles during the alloy 6061/alloy 6061 friction-joining operation. It is suggested that small-diameter particles formed due to fracture early in the friction-joining operation are retained at the bondline of MMC/MMC joints as a direct consequence of the flow of plasticized material and reinforcing particles in the contact zone. A combination of numerical modeling of fluid flow and direct experimental testing have confirmed that Al₂O₃ particles transfer from the stationary to the rotating boundary in MMC/MMC friction joints. Also, limit cycles embedded within the flow favor the retention of smalldiameter fractured particles at the bondline of MMC/MMC joints. A quite different situation exists in dissimilar MMC/AISI 304 stainless steel joining. In dissimilar joints, a dynamically quiescent region is formed immediately adjacent to the stainless steel boundary. It is suggested that the absence of flow of plasticized material promotes retention of fractured alumina particles in dissimilar joints.     

精密微孔过滤机在超细粉末过滤与洗涤应用

简述了超细粉末在过滤、洗涤的特性,并介绍了高效精密微孔过滤机的原理及特点,通过超细碳酸钴粉末的生产实践证明:采用微孔过滤机进行洗涤过滤可大大提高物料的洗涤效率,减少洗水用量,提高金属回收率。并且采用机内顶洗涤,过滤与洗涤于一机内,不需将滤饼来回人工转移,使产品不受外界污染。确认完全适宜微米级与亚微米级的超细粉体生产中的过滤与洗涤工序。     

Degradation of rail-steel structure and properties of the surface layer

The change in the structure–phase states and defect substructure of the rail surface after prolonged operation (passed tonnage of 500 and 1000 million t) is studied by optical microscopy, by scanning and transmission electron diffraction microscopy, and by measurement of the microhardness and tribological characteristics. It is found that the wear rate increases by a factor of 3.0 and 3.4 after passed tonnage of 500 and 1000 million t, respectively, while the frictional coefficient is reduced by a factor of 1.4 and 1.1, respectively. After 500 million t, the cementite plates break down completely, and rounded cementite particles (10–50 nm) are formed. After 1000 million t, the initial stage of dynamic recrystallization is noted. Possible explanations of the observations are discussed. Two competing processes may occur in rail operation: (1) fragmentation of the cementite particles, with their subsequent entrainment in the ferrite grains or plates (in the pearlite structure); (2) fragmentation and subsequent solution of the cementite particles, with transfer of the carbon particles to dislocations (Cottrell atmospheres) and transportation of carbon atoms by dislocations within the ferrite grains (or plates), culminating in the formation of cementite nanoparticles.     

微米与亚微米级粘细微粒的精密过滤与滤饼洗涤

简述了微米与亚微米级粘细微粒在过滤、洗涤时的特性，并详细地介绍了高效精密微孔过滤机的特点及其用于微细颗粒物料过滤、洗涤的成功实例。     

高炉回旋区运动现象的数值模拟

风口回旋区是高炉内产生还原气体及热量的主要区域,颗粒相和气相在风口回旋区内的相互作用非常剧烈。回旋区的形状和大小决定了炉内煤气流的一次分布,是炉况顺行的基础。本文为了从颗粒尺度来描述回旋区内部气体和颗粒的运动行为,建立和发展了离散单元法和流体计算力学耦合模型。耦合模型考虑了多个相间力的作用(包括曳力、虚假质量力、升力和压力梯度力),得到了不同时刻风口前焦炭颗粒的分布图、体积分数云图、速度矢量图等。这些图表明在鼓风速度130 m/s时,风口前有颗粒被吹开,形成了明显的空腔,风口前及其附近区域的颗粒在做回旋运动,可以断定回旋区已经形成,且在6 s时风口回旋区达到稳定。     

Structural Features and Properties of Alloy 84% WC ― 16% Co,Obtained by Hot Pressing in the Solid and Liquid Phases. Part 1. Effect of the Temperature at which the Specimens are Prepared on Their Density and Structure

Studies are made of changes in the porosity and structure of a hard alloy obtained by hot pressing and sintering within a broad range of temperatures (950-1450°C). The effect of solid- and liquid-phase annealing on their porosity and structure is also examined. It is shown that the hot-pressed specimens are denser than the sintered specimens within the solid-phase region, other conditions being equal. Solid-phase annealing of hot-pressed and sintered specimens increases the density of both types of specimens, but the annealing operation is more effective in the former case. It is established that the open pore channels are 2-3 times smaller in the hot-pressed specimens than in the sintered specimens and are no larger than the average size of the tungsten carbide particles. Active growth of the carbide particles and redistribution of the ductile phase are observed even in the solid phase. The carbide particles grow considerably faster (by a factor of four) at sintering temperatures above 1200°C.     

多金属结核金属化还原多元合金磁性能

用自动矿物分析仪、金相显微镜和扫描电镜,从多元合金颗粒尺寸、锰含量、金相组织结构等进行研究,以饱和磁感应强度Ms和剩磁Mr来衡量合金磁性能变化规律,研究多金属结核金属化还原工艺中多元合金磁性能。结果表明,多金属结核金属化还原多元合金磁性能主要受合金颗粒尺寸和锰含量影响,多元合金晶粒尺寸越大,锰含量越低,合金颗粒磁性能越强。因此,工艺过程中应该尽可能增大多元合金晶粒尺寸,抑制锰的还原。     

Redistribution of Carbon Atoms in Differentially Quenched Rail on Prolonged Operation

The change in structure, phase composition, and defect substructure in the head of differentially quenched rail after the passage of gross traffic amounting to 691.8 million t is investigated over the central axis, at different distances from the top surface, by means of transmission electron microscopy. The results confirm that prolonged rail operation is accompanied by two simultaneous processes that modify the structure and phase composition of the plate-pearlite colonies: cutting of the cementite plates; and solution of the cementite plates. The first process involves cutting of the carbide particles and removal of their fragments, accompanied simply by change in their linear dimensions and morphology. The second process involves the extraction of carbon atoms from the crystal lattice of cementite by dislocations. That permits phase transformation of the metal in the rail, which is associated with marked relaxation of the mean binding energy of the carbon atoms at dislocations (0.6 eV) and at iron atoms in the cementite lattice (0.4 eV). The stages in the transformation of the cementite plates are as follows: the plates are wrapped in slipping dislocations, with subsequent splitting into slightly disoriented fragments; the slipping dislocations from the ferrite lattice penetrate into the cementite lattice; and the cementite dissolves with the formation of nanoparticles. The cementite nanoparticles are present in the ferrite matrix as a result of their transfer in the course of dislocational slip. On the basis of equations from materials physics and X-ray structural data, the content of carbon atoms at structural elements of the rail steel is assessed. It is found that prolonged rail operation is accompanied by significant redistribution of the carbon atoms in the surface layer. In the initial state, most of the carbon atoms are concentrated in cementite particles. After prolonged rail operation, the carbon atoms and cementite particles are located at defects in the steel’s crystalline structure (dislocations, grain and subgrain boundaries). In the surface layer of the steel, carbon atoms are also observed in the crystal lattice based on α iron.     

Substructure of the friction surface of copper and copper-graphite materials

Conclusions In friction at a sliding rate of 40 m/sec and a pressure of 0.1 MPa. a finely disperse mixture of particles of copper and its oxides forms on the surface of pure copper; these particles increase the strength of the surface layer of copper, reduce its wear, but do not prevent bonding processes from taking place.In friction of DGr-5 material at a sliding speed of 11 m/sec under a pressure of 0.1 MPa., surface films consisting of ultradisperse particles of copper and oxides form; the dimensions of the graphite particles are comparable with those of the initial particles. Since the graphite particles cannot extend completely along the prismatic planes to the friction surface and the amount of graphite is insufficient for ensuring the lubricating effect, DGr-5 material is not capable of efficient operation in these conditions.The surface films formed during friction on DGr-10 composite material are characterized by uniform distribution of the graphite particles and consist of ultradisperse copper and fineplate textured graphite with preferential orientation with the basal planes parallel to the friction surface; this results in higher values of the tribotechnical characteristics.Translated from Poroshkovaya Metallurgiya, No. 12(300), pp. 66–71, December, 1987.     

Flow Behavior in Z-Path Fluidized-Moving Bed with Inclined Perforated Plate

Ｔｈｅｓｔａｃｋｅｄ/ ｐａｃｋｅｄｂｅｄｉｓｇｅｎｅｒａｌｌｙｕｓｅｄｆｏｒｌａｒｇｅｐａｒｔｉｃｌｅｓ .Ｉｎｓｕｃｈａｂｅｄ ,ｇａｓ ｓｏｌｉｄｒｅａｃｔｉｏｎｉｓｒｅｌａｔｉｖｅｌｙｓｌｏｗ ,ａｎｄｐａｒｔｉｃｌｅｓｓｈｏｕｌｄｂｅｏｆｇｏｏｄｍｅ ｃｈａｎｉｃａｌｐｒｏｐｅｒｔｉｅｓ .Ｓｏ ,ｉｔｓａｐｐｌｉｃａｔｉｏｎｉｓｌｉｍｉｔｅｄ .Ｔｈｅｒａｉｎｉｎｇｂｅｄｉｓｏｐｅｒａｔｅｄｗｉｔｈｌｅｓｓｅｎｔｒａｉｎｍｅｎｔｏｆｐａｒｔｉｃｌｅｓ .Ｔｈｅｒｅａｒｅｆｅｗａｐｐｌｉｃａｔｉｏｎｓｉ…     

Structural Features and Properties of Alloy 84% WC ― 16% Co,Obtained by Hot Pressing in the Solid and Liquid Phases. Part 1. Effect of the Temperature at which the Specimens are Prepared on Their Density and Structure

Studies are made of changes in the porosity and structure of a hard alloy obtained by hot pressing and sintering within a broad range of temperatures (950-1450°C). The effect of solid- and liquid-phase annealing on their porosity and structure is also examined. It is shown that the hot-pressed specimens are denser than the sintered specimens within the solid-phase region, other conditions being equal. Solid-phase annealing of hot-pressed and sintered specimens increases the density of both types of specimens, but the annealing operation is more effective in the former case. It is established that the open pore channels are 2-3 times smaller in the hot-pressed specimens than in the sintered specimens and are no larger than the average size of the tungsten carbide particles. Active growth of the carbide particles and redistribution of the ductile phase are observed even in the solid phase. The carbide particles grow considerably faster (by a factor of four) at sintering temperatures above 1200°C.

     

Compositional Fragmentation Model for the Oxidation of Sulfide Particles in a Flash Reactor

A mathematical model to predict the size distribution and chemical composition of a cloud of sulfide particles during high-temperature oxidation in a flash reactor is presented. The model incorporates the expansion and further fragmentation of the reacting particles along their trajectories throughout the reaction chamber. A relevant feature of the present formulation is its flexibility to treat a variety of flash reacting systems, such as the flash smelting and flash converting processes. This is accomplished by computing the chemical composition of individual particles and the size distribution and overall composition of the particle cloud in separate modules, which are coupled through a database of particle properties previously stored on disk. The flash converting of solid copper mattes is considered as an example. The model predictions showed good agreement with the experimental data collected in a large laboratory reactor in terms of particle size distribution and sulfur remaining in the population of particles. The cumulative contribution and distribution coefficients are introduced to quantify the relationship between specific particle sizes in the feed and those in the reacted products upon oxidation, the latter of which has practical implications on the amount and chemical composition of dust particles produced during the industrial operation.     

闪速炼铜中烟尘的形成过程

从工业闪速炉及其排烟路径上的不同位置在线提取烟尘试样分析,研究了烟尘形貌、粒度等的变化及烟尘的形成条件,发现烟尘不是反应塔中没有反应的细颗粒精矿粒子,而是反应塔中未沉降到沉淀池的、过氧化的、粒度很小的熔融球形粒子;石英砂和吹炼渣粒子很难成为烟尘;反应塔高度对烟尘率有较大的影响,提高反应塔高度有利于降低烟尘发生率。提出了工业闪速熔炼生产中烟尘形成的过程机理。     

Liquid break-up in gas atomization of fine aluminum powders

Formation of powder particles has been studied in aconfined design atomizing nozzle. Liquid metal (AA 2014) is presented in the form of a thin film to the atomizing gas in this type of operation. Upon contacting, the film breaks up into large droplets of diameters up to 500 /im (primary break-up). These droplets undergo further disintegration in flight to produce the powder (secondary disintegration). Photographs taken using a high-speed flash indicate that this takes place by stripping. It is proposed that the fine range of the particles are the products of stripping break-up, while the coarse range are stable particles obtained when stripping stops and the remaining particle becomes too small to undergo further disintegration. Size distribution curves often contained two or more peaks providing support for different formation mechanisms for fine and coarse particles. All particles were dense and single droplets except for the very large ones (>55 μm)which had satellites of fine particles on the surface and showed porosity in some cases. Particles <30 μm in general were fully spherical, whereas larger ones also showed oblong features. No evidence was found for small particles agglomerating to produce large ones.     

莱钢SPHC钢铸坯中大颗粒非金属夹杂物的分析

利用大样电解法、LEO-1450型能谱分析仪和NEOPHOT-32型金相显微镜对SPHC钢铸坯中非金属夹杂物的种类、含量、来源、形状、尺寸进行分析研究。分析结果表明,铸坯中夹杂物主要为O-Ca-Si-Al-Na-S复合型。判断出转炉出钢下渣量大、浮渣卷入、耐火材料侵蚀、喂线工艺操作不当及钢液被空气二次氧化是钢中生成大颗粒夹杂物的主要原因。提出了减少钢中大颗粒非金属夹杂物数量,提高铸坯品质的相应工艺改进意见。     

Rational process of production of corrosion-resistant ferritic steel with nanocluster oxide hardening for atomic power engineering

The conditions of operation of metallic structural materials during intense neutron irradiation are considered, and the material that has the maximum radiation resistance is found to be a ferritic nickel-free fine-grained corrosion-resistant steel that has low carbon and nitrogen contents and is precipitation-hardened by oxide nanocluster particles. This steel can only be made using mechanical alloying (high-energy milling) in combination with granular metallurgy methods.     

Experimental investigation and three-dimensional computational fluid-dynamics modeling of the flash-converting furnace shaft: Part I. Experimental observation of copper converting reactions in terms of converting rate, converting quality, changes in particle size, morphology, and mineralogy

An experimental investigation was conducted to elucidate the main features of the processes taking place in the shaft of a continuous flash-converting furnace for solid copper mattes. The experiments were conducted in a large laboratory furnace. The test variables included the matte grade, oxygen content in the process gas, particle size of the feed material, and oxygen-to-matte ratio. The observed variables included the fractional completion of the oxidation reactions, fraction of sulfur remaining in the particles, copper-to-iron atomic ratio, particle-size distribution, morphology, and mineralogy of the reacted particles. The experiments showed substantial differences in the oxidation behavior of high-grade (72 pct Cu) and low-grade (58 pct Cu) matte particles. Low-grade matte particles reacted evenly throughout the furnace, increased in size, and experienced no substantial fragmentation during oxidation. High-grade matte particles tended to be oxidized unevenly and experienced severe fragmentation leading to generation of dust. The order of the effects of the test variables on the observed variables was found to be (1) the oxygen-to-matte ratio, (2) the particle size of the feed material, and (3) the oxygen content in the process gas. Microscopic examination revealed that the oxides of copper and iron were the main oxidation products, with little elemental copper present in the reacted particles. Potential implications of the experimental findings on the operation of an industrial flash-converting furnace are discussed.     

Development and Application of Magnetic Segregation Feeder in Sintering Machine

The size segregation of sintering materials in a chute flow is utilized to prepare well‐bedded feedstock for sintering quality improving, and magnets are installed below the chute to enhance size segregation. By the braking role of magnetic force, the particles of different sizes which poured down to sloping chute are separated:the coarse particles drop to the far‐side of the sloping chute and the fine particles drop near the sloping chute. As the sintering pallet is continuously moving, the coarse particles are distributed into the lower portions and the fine particles are aggregated on the top of the layer..By using the non‐contacting magnetic force,the technique of magnetic segregation feeding overcomes a series of defects such as adhering and wearing in the existing segregation feeding devices. and the device is characterized by simple structure, easy operation, no need of energy,and safety, etc. Discrete element method (DEM) simulations are carried out to explore the optimal arrangement of the magnets.The simulations show that proper magnetic field can significantly enhance the segregation,and the simulation results are in good agreement with the experiments and industrial systems designed with consultation to the results.Depend on those,the technique of magnetic segregation feeding have been developed and applied in the three sintering line of Baoshan Iron & Steel Co., Ltd..The results of industrial application show that the distributions of particles, carbon and FeO in sintering layer have been remarkably improved. In guaranteeing to the quality of sintering ore materials, the productivity of sintering strand raised 2.1% and the fuel ratio decreased 1.7%.     

溜槽截面形状及参数对高炉布料的影响

 高炉溜槽作为无钟炉顶装料设备的重要组成部分,其参数变化对布料操作有很大影响。比较常见的2种溜槽截面形状是半圆形溜槽和矩形溜槽。由于截面形状不同,颗粒在溜槽内的运动过程会发生变化。目前关于矩形溜槽布料过程的数学模型研究较少。通过分析颗粒在2种不同截面溜槽内的运动过程,研究截面形状变化对料流轨迹的影响,并将计算结果与模型试验测试结果进行对比。研究结果可为实际高炉溜槽截面形状的选择及不同溜槽布料操作提供理论指导。     

Microstructural features of friction welded MA 956 superalloy material

The microstructural features of MA 956 friction welds were examined using a combination of optical microscopy and transmission electron microscopy (TEM). The MA 956 base material contained a uniform distribution of small diameter (<20 nm) Y₂O₃ particles. Limited numbers of larger diameter (>100 nm), spherically shaped Al₂O₃, Ti(C,N), Y₂O₃-Al₂O₃, and Al-Ti-Y containing particles were also observed in the MA 956 base material. In the recrystallized region, the grain size was largest at the bondline and increased markedly in the radial direction of the welded joint. Increasing the forging pressure from 50 to 150 MPa during the friction welding operation markedly increased the strain rate and decreased the grain size at the joint centerline. The friction welding operation substantially altered the particle chemistry, dimensions, and shape in the joint region. The number of aluminum-rich or titanium-rich particles was substantially decreased and large irregularly shaped particles were formed.