References Wbw
1. R.M. German, Metallurgy of Iron and Steel, John Wiley amp Sons,1998 2. R. Heckel, Effects of Gas Composition on Gas-Solid Equilibrium During Sintering of Ferrous Powders, Prog. Powder Metall, Vol 35, 1979 3. T. Philips, Trouble-Shooting Guide for Sintering Furnace Atmospheres, Int. J. Powder Metall., Vol 26 No.3 , 1990, p 245-6250 4. H.S. Nayar, Status Report on Energy Consumption and Distribution in Powder Metal Industry, Prog. Powder Metall., Vol 34, 1978 5. Furnaces Atmospheres and Carbon...
Selected References Ubp
S. Abkowitz, Isostatic Pressing of Complex Shapes from Titanium and Titanium Alloys, Production to Near Net Shape Source Book, American Society for Metals, 1983 C.B. Boyer, J.H. Peterson, and F.D. Orcutt, Equipment for Hydrostatic Pressing of Metal Powders, Proc. National Conference on Fluid Power, Vol XXV, 27th Annual Meeting Chicago , Fluid Power Society and National Fluid Power Association, 19-21 Oct 1971 C.B. Boyer and J.C. Wahl, Equipment for Cold Isostatic Pressing, No. 74-PVP-21, Conf....
Acknowledgements
B. Lux and B. Zeiler would like to express their gratitude to Prof. W.D. Schubert of Vienna University of Technology for helpful and constructive discussions in preparing the section Production of Tungsten and Tungsten Carbide Powders. Dr. M. Spross, Managing Director of Wolfram Bergbau- und Huetten-GmbH Nfg KG, is gratefully acknowledged for his kind and benevolent support. Mr. C. Keller's help in preparing the figures is also appreciated. The section Other Refractory Metals was adapted from...
References Ffe
1. Standard Test Method for Density and Interconnected Porosity of Sintered Powder Metal Structural Parts and Oil-Impregnated Bearings, B 328, Annual Book of ASTM Standards, Vol 2.05, ASTM, 1998 2. Permeable Sintered Metal Materials, Determination of Density, Open Porosity and Oil Content, ISO 2738, International Organization for Standardization, American National Standards Institute 3. Standard Method of Sampling Finished Lots of Metal Powders, B 215, Annual Book of ASTM Standards, Vol 2.05,...
Water Atomization
In terms of tonnage, water atomization is now the preeminent mode of atomization for metal--especially ferrous metal-powders. The largest commercial application of water atomization is iron powder for press-and-sinter applications, and about 60 to 70 of the world's production of iron powder, which now totals some 600,000 to 700,000 metric tons year, is produced by water atomization. Water atomization is also used for the commercial production of copper, copper alloys, nickel, nickel alloys,...
Gas Atomization Cjl
A gas atomization process for titanium, designated TGA, was developed by Crucible Materials Corporation Ref 11, 12, 13 . The TGA process involves some unique characteristics such as Vacuum-induction skull melting a charge in a water-cooled copper crucible Tapping the furnace through the bottom into a nozzle Induction heating of the metal nozzle The resulting molten metal stream is atomized with inert gas. Starting stock for atomization can be virgin raw materials or prealloyed materials, such...
Thermal Spray Processes and Techniques
All thermal spray methods use chemical or electrical energy to heat feed materials injected into hot-gas jets to create a stream of molten droplets that are accelerated and directed toward the substrates being coated. Figure 3 shows how the various thermal spray processes can be broken down according to the energy source used combustion versus electrical , feed material form powdered or solid , and surrounding environment air, low pressure vacuum , inert gas, etc. . The thermal spray family of...
Sintering Variables
Several factors influence the sintering of tungsten and molybdenum, including time, temperature, particle size, atmosphere, purity of powders and compacts, compacted density, thermal gradients, heating rate, cooling rate, particle size distribution, compact weight, gravity, and friction, and additives such as dispersed oxides and sintering activators. These variables and their interrelationships are discussed in the following sections. Time and temperature are the fundamental determinants of...
Compacting Press Requirements
Although P M presses resemble stamping and forming presses, several significant differences exist. Press frames generally have straight sides. Gap-type or C frame presses are not suitable because the frame deflects in an arc under load, resulting in a slight out-of-alignment condition between the bed and side of the press. This arrangement produces a compacted part that is slightly out of parallel, top to bottom. Because P M tooling clearances are generally -'0.025 mm 25 mm 0.001 in. 1 in....
Particle Size
In practice, average particle size is controlled by the pressure of the water jets. Higher water pressure directly influences water velocity VW , as well as changing the particle size of the water droplets in the jet. These further control particle size, but in a complex and poorly understood way. The relation between dm and water pressure P is shown in Fig. 8 Ref 10 for various metal powders. Atomizing pressure, psi 0 15 30 75 150 300 750 1500 3000 0.5 1 2 5 10 20 50 100 200 500 Atomizing...
Sulfides
Sulfides are probably the most frequently used free-machining agents in both wrought and P M steels. Powder metallurgy offers more flexibility than wrought metallurgy. Sulfur can be prealloyed in the powder during the primary production process or admixed as sulfur or sulfides during the preparation of a press-ready powder premix. Premixing offers more flexibility in the composition and amount of sulfide formed in the final compact. Prealloy produces a somewhat finer dispersion of sulfides...
Particle Morphology
The morphology of atomized aluminum powders is influenced strongly by the amount of oxygen present in the gas phase during atomization. Particles atomized in an inert gas show spherical features, whereas air-atomized particles are of irregular shape also known as nodular powders . This effect of oxygen on morphology has been attributed to the pinning effect of the oxide nuclei that form on the droplets before they have solidified Ref 23 . Many such nuclei form rapidly on a droplet when there is...
Systems for Powder Classification
Classifiers may be divided into two categories counterflow equilibrium and crossflow separation. Counterflow can occur in either a gravitational or centrifugal field. The field force and the drag force act in opposite directions and particles leave the separation zone in one of two directions according to their size. At the cut size, particles are acted on by two equal and opposite forces hence, they stay in equilibrium in the separation zone. In gravitational systems these particles remain in...
techniques using a high volume fraction of Al2O3 5065 is made Metal Matrix
Characterization of Ceramic Matrix Composites Fabricated by Chemical Vapor Infiltration, D.P. Stinton, D.M. Hembree, Jr., K.L. More, and B.W. Sheldon, Chemical Vapor Deposition on Refractory Metals and Ceramics Symp., 29 Nov-1 Dec 1989 Boston, MA , T.M. Besmann and B.M. Gallois, Ed., Materials Research Society, 1990, p 273-280. A process for the preparation of fiber-reinforced SiC composites by chemical vapor deposition has been developed at Oak Ridge National Laboratory. Composites are...
References Jqy
1. P. Borchers and W. M ller, Proc. of the 5th Int. Tungsten Symp. Budapest , MPR Publishing Services Ltd., in cooperation with the International Tungsten Industry Association, 1990, p 40-55 2. S.W.H. Yih and C.T. Wang, Tungsten Sources, Metallurgy, Properties, and Applications, Plenum Press, 1979 3. H. Kolaska, Powder Metall. Int., Vol 24 No. 5 , 1992, p 311-314 4. J. Gurland and J.D. Knox, 3rd Int. Conf. on Tungsten and Refractory Materials, 1996, p 219-227 5. M. Maby, Met. Powder Rep., April...
Metal Carbonyls
Many metals form carbonyls in fact, all of the metals of the first, second, and third transition metal series have been converted into one or more types of carbonyls. Additionally, several of the lanthanides and actinides have formed carbonyls. Nickel forms a single carbonyl, Ni CO 4, in its zero valent form Nickel also forms a hydridocarbonyl, H2Ni2 CO 6, where nickel has an oxidation number of -1. The carbon monoxide ligands in nickel carbonyl can be replaced by other ligands such as...
References cited in this section Vhg
3. Materials Innovation New Powder Delivery System, Materials Innovation Inc., W. Lebanon, NH 4. Dorst America, Inc., Bethlehem PA 5. Adaptive Fill Control of a Compacting Press, Cincinnati, Inc., Cincinnati, OH 6. Compacting Press Automatic Fill Compensation System, Cincinnati, Inc., Cincinnati, OH 7. Tool Load Monitoring System for Multilevel Compacting Press, Cincinnati, Inc., Cincinnati, OH, see also Advances in Powder Metallurgy, Vol 2, 1993, p 11
Powder Shaping Technologies
General categories of powder shaping methods are as follows Ref 1 Binder-assisted extrusion long structures, small powders, constant cross section, relatively simple shapes Injection molding complex, small components, high-performance materials Slip casting very large structures, constant wall thickness, low precision Tape casting flat sheets, small powders, very simple shapes In general these methods employ binders that hold the particles together in the desired shape the particles are then...
Tap Density
Tap density is defined as the density of a powder when the volume receptacle is tapped or vibrated under specified conditions. Tapping or vibrating a loose powder induces movement and separation and lowers the friction between the powder particles. This short-term lowering in friction results in powder packing and in a higher calculated density of the powder mass. Tap density is always higher than the free-flow apparent density. Tap density is a function of particle shape, particle porosity,...
Gas Atomization
Gas atomization is the process where the liquid metal is disrupted by a high-velocity gas such as air, nitrogen, argon, or helium. Atomization occurs by kinetic energy transfer from the atomizing medium to the metal. Gas atomization differs from water atomization in many respects. Rather than being dominated by the pressure of the medium like water atomization, it is found that the gas-to-metal ratio is the dominant factor in controlling particle size, with median particle size being related...
Production Sintering Practices Sintering of Nickel and Nickel Alloys
Sintered nickel-base materials enjoy wide commercial usage due to their unique properties, such as corrosion resistance, wear resistance, mechanical strength at low and elevated temperatures, thermal expansion, electrical conductivity, and magnetic permeability. Commercial products represent a wide range of shapes, sizes, and microstructures. Sintered products with S 90 porosity are technologically as important as fully dense products. Sintering practices aimed at achieving such diverse...
Container Manufacture
Container Design. There are a number of methods used to make both simple and complex shapes by the HIP P M technology. The HIP component designer usually works with the end user to establish dimensional parameters that will meet the requirements of the application and still be compatible with the capability of the HIP process. The designer of the HIP container considers all the factors and then makes his decision on container type and material to give the best chance of successfully meeting the...
Sintering of Tungsten and Molybdenum
Tungsten and molybdenum sintering practices are similar consequently, they will be described together in this section. The achievement of high density is a primary goal when sintering tungsten and molybdenum, because high density is frequently required for performance. It is also required if metalworking operations are necessary, in which case at least 90 of theoretical density is essential. High-density values indicate that compact shrinkage has been significant, because pressed densities are...
The Domfer Process
The Domfer process of making iron and steel powder was developed in 1952 at Iberville, Quebec. It consists of water atomizing a high-carbon iron melt to a granular shot, which is then ball milled to powder size. The ground shot, which contains carbon, is mixed with ground mill scale iron oxide that contains oxygen. The carbon and oxygen are chemically combined in a belt furnace at sintering temperatures to form carbon monoxide gas, thus leaving a pure iron cake. The cake is disintegrated to...
Powder Manufacture
Chips produced by the multihead cutter are relatively coarse and must be ground or comminuted to fine particle sizes before consolidation into a homogeneous, fine-grained billet. Before discussing grinding and comminution, however, it is important to recognize the effects that the close-packed hexagonal structure and chemical reactivity have upon the powder-making processes and the physical and mechanical properties of the final product. During the late 1960s and early 1970s, mechanical...
Tungsten Metal Powder Production
Industrially relevant tungsten-bearing minerals are Wolframite Mn, Fe WO4 , Ferberite FeWO4 , Hubnerite MnWO4 and Scheelite CaWO4 . The tungsten concentration of workable ore starts at 0.1 to 0.3 wt WO3. Concentrations of more than 2 wt are rare. The average WO3 content is usually about 0.5 wt Ref 11, 12, 13 . Depending on the mineral type, different techniques are used to concentrate the ore up to typical WO3 contents about 60 to 70 , such as gravity methods and flotation. An important...
Powder Extrusion Practice
Extrusion of canned powder can be considered a special case of filled-billet extrusion. Filled billet refers to an extrusion billet or workpiece that contains more than a single material. For canned powder, there are at least two components, the powder and the can. More typical filled-billet workpieces, discussed below, may have two or more different materials arranged in a geometric array within a container. In the extrusion of a filled billet, it is important that the materials of the various...
References Gwt
1. R.L. Mond and A.E. Wallis, Researches on the Metallic Carbonyls, J. Chem. Soc., Vol 121, 1922, p 29-32 2. J.G. Stephenson, The Influence of Iron Ore Feed Characteristics on Direct Reduction, 16th Ann. Conf. Metall., CIM, 1977 3. J.K. Brimacoude and V. Venkateswaran, Literature Review of the Production and Use of Direct Reduced Iron, DRI--Technology and Economics of Production and Use, Iron and Steel Society of AIME, 1980, p 216 4. V. Bogdandy et al., Archiv Eisenh ttenwes., Vol 34, 1963, p...
Segregation Tendency
Providing a reliable, uniform mix or blend is critical in producing quality P M parts. This requires not only proper mixing methods, but also proper handling techniques through compaction to ensure a uniform delivery of the powder to the die. As such, much greater emphasis is now being placed on appropriate storing, feeding, and transporting of powders. The exact method of die fill depends on the specific compaction process being used e.g., hydraulic, mechanical, rotary, isostatic, etc. but...
Processing of High Performance Materials by Cold Sintering of Fine Elemental
Materials with fine microstructure can be produced by cold sintering of very fine elemental powders, followed by a homogenization treatment. The main advantage of this approach, compared to consolidation of prealloyed rapidly solidified or mechanically alloyed powders, is the higher compressibility of elemental powders. To utilize high compressibility, all the preconsolidation heat treatments removal of surface oxides, annealing, etc. should be performed at relatively low temperatures in order...
References cited in this section Jnv
5. E. Arzt, M.F. Ashby, and K.E. Easterling, Practical Applications of Hot Isostatic Pressing Diagrams Four Case Studies, Metall. Trans. A, Vol 13, Feb 1983, p 211-221 7. W.B. Eisen, Advances in Near Net Shape, High Performance Materials in Engine Technology, Vol 9, Advances in Science and Technology, Techna, 1995, p 485-496 8. S. Fallman, L.L. Jaktlund, R. Tegman, and T. Garvare, Numerical Modelling of Shrinkage during HIP, Proc. Int. Conf. Hot Isostatic Pressing, Centek Publishers, 1987, p...
Ni2 2NH3 H2 Ni
The presence of free ammonia is necessary to neutralize the hydrogen ions produced during reduction. At low pH and lower hydrogen potentials the reduction of the metal ions effectively ceases. During the reduction process, the slurry in the autoclave is agitated by impellers however, once reduction is complete the agitation is stopped and the nickel powder is allowed to settle. The spent solution or reduction end solution is then pumped out and the autoclave is filled with fresh nickel...
Electrodeposition
Electrodeposition of metals from aqueous solutions produces a variety of metal powders. This article discusses the methods used to produce powders electrolytically, and describes the types of metal powders made and their physical and chemical characteristics. Detailed information on the processing variables that permit close control of the chemical and physical properties of electrolytic powders can be found in the articles Production of Iron Powders, Production of Copper Powders, and...
Particle Shape Characterization
Brian H. Kaye, Department of Physics and Astronomy, Laurentian University Figure 10 shows a typical scanning electron micrograph of an array of iron particles for the type of powder grains encountered by the powder metallurgist in various areas of technology. Many of the techniques for characterizing the shape of powder grains make use of image analysis using pictures such as that shown in Fig. 10 a Ref 1 . When an array of fine particles to be characterized is inspected, the first thing to be...
The Pyron Process
Revised by Stephen Claeys, Pryon Inc. The Pyron process provides an alternative for the production of iron powders by the reduction of oxides. Instead of using ground iron ore as the raw material for reduced iron powders, the Pyron process uses mill scale taken from steel mills that produce plain carbon steel products, such as sheet, rod, wire,plate, and pipe. Mill scales containing alloying elements other than manganese are not used. A flowchart of the Pyron process is shown in Fig. 5. Fig. 5...
Electrostatic Atomization
ATOMIZATION is the dominant method for producing metal and prealloyed powders from aluminum, brass, iron, low-alloy steels, stainless steels, tool steels, superalloys, titanium alloys, and other alloys. Current atomization technology is the result of steady advances over the last 50 years since the first large-scale production of atomized iron powder during World War II. By the early 1980s atomized powders had accounted for more than 60 by weight of all metal powders produced in North America,...
References Yvf
1. M. Senna and H. Kuno, Polymorphic Transformation of PbO by Isothermal Wet Ball-Milling, J. Am. Ceram. Soc., Vol 54 No. 5 , May 1971 2. W.E. Kuhn and H. Lucky, Characterization of Ball-Milled Type 316-L Stainless Steel Powder, Fine Particles, W. Kuhn and J. Ehretsmann, Ed., The Electrochemical Society, Inc., 1974, p 95-121 3. A.A. Griffith, Trans. Roy. Soc. Lond, Vol A221, 1921, p 163 4. J.J. Gilvarry and B.M. Borgstrom, Fracture and Comminution of Brittle Solids, AIME Trans., Vol 220, 1961,...
Conclusions 1
Binder-assisted extrusion is a commercially used powder forming technique. In this technique, powders are mixed with a binder to produce a feedstock with rheological characteristics that facilitate extrusion. The process consists of four basic operations, each step is critical for producing a defect free product. The steps include 1 feedstock formulation and preparation, 2 extrusion for shaping, 3 binder removal, and 4 sintering. Feedstock preparation involves mixing the powders with the binder...
Introduction Oqg
BINDER-ASSISTED EXTRUSION is a plastic forming process in which a highly viscous feedstock, that is, a powder mixed with a binder and other rheology modifiers also termed the paste , is forced through a die to form a shaped product. The binder-assisted extrusion process is used commercially to produce ceramic parts, such as furnace tubes, bricks, insulators, pipes, tiles, tubular capacitors, catalyst supports, magnets, heat exchangers, wires, and springs Ref 1, 2, 3, 4, 5, 6, 7, 8 . However,...
Constitutive Behavior
Constitutive material models provide a mathematical description of the deformation response of the material to an applied stress. In their simplest form, constitutive material models can be reduced to the equations describing stress -strain behavior in elastic loading. In their more complex form, constitutive material models include the effects of strain strain hardening , strain rate, temperature, microstructure, anisotropy, and time creep or viscoelastic deformation on the stressstrain...
Compact Manufacture
Loading. Filling of powder into the hermetically sealed, preshaped metal container can be performed in air, under inert gas, or under vacuum conditions, with the latter to aid in the removal of adsorbed gases. In some cases, powder is still loaded in open air as it was 25 years ago however, most processing today is containerized to protect the product and prevent inhalation of the metal powder by operators Fig. 16 . Advanced filling systems have been developed to ensure clean, dry handling of...
Powder Metallurgy of Platinum
The metallurgy of platinum, as practiced in the 18th and 19th centuries in Europe, is considered to be one of the most important stages of development for modern powder metallurgy. For the first time, complete records were available that provided insight into the various methods of powder production and the processing of these powders into solid, useful implements. Between 1750 and 1825, considerable attention was given to the manufacture of platinum. In 1755, Lewis Ref 4 discovered that when a...
Transient LiquidPhase Sintering
Transient LPS is observed in mixed powder systems where the liquid phase has a high solubility in the base material. Some examples of transient LPS include the Cu-Sn, Cu-Al, Ni-Cu, Fe-Mo-C, Fe-P, and Fe-Ti alloys. Figure 15 gives two sample phase diagrams of systems that could be processed using a transient liquid from mixed A and B powders. When a liquid forms, it initially results in melt penetration and shrinkage due to rearrangement. Unlike classic LPS, which involves the presence of a...
Carbonyl Iron Powders
Revised by Sotiri Papoulias, International Specialty Products Very fine iron powders, like nickel powders, can be produced by carbonyl decomposition vapor metallurgy techniques. The first patents covering the carbonyl process were registered to Ludwig Mond in 1890. A brief review of early metal carbonyl research, with emphasis on his work, is presented in the article Production of Nickel-Base Powders in this Volume. In addition, some of the different types of metal carbonyls that can be formed...
Electrolytic Iron Powder
Revised by Prasan Samal, OMG Americas Iron powder made using electrolytic deposition has the highest level of purity among all types of commercially available iron powders. It possesses very irregular particle shape and consequently offers relatively large surface areas per unit mass typically 0.1 to 1.0 m2 g . As a result of its high purity and irregular particle shape, it exhibits excellent compressibility and green strength. Its high level of purity and large surface area also render it...
Wetting Powder Clumps into the Liquid
The primary consequence of inadequately wetting the clumps into the liquid is that air retained in the submerged clumps may remain in the system as small submerged bubbles whose sizes are included in and bias the reported PSD. A secondary consequence is that particles may remain attached to bubbles that rise to the top and thus be carried out of the analysis region, biasing the reported PSD. The wet-in process for a powder starts when a clump is dropped onto the liquid surface, continues as the...
Introduction Fsc
STEEL POWDERS can be classified into three general types Fig. 1 depending on the alloying process. The prealloyed powders are produced by melting and subsequent atomization, so that powder particles are of similar alloy composition. In contrast, admixed powders are alloyed during sintering, which requires sufficient diffusion and mass transport during the sintering process for homogenous alloying. The bonded or diffusion alloyed powders are the third type they are similar to admixed grades,...
Dry Mixing of Metal Powders
Dry mixing is the most common way to produce press-ready mixes. Metal powders and additives are charged into a blender, mixed until a homogeneous mixture is achieved, and discharged into containers. Adding elemental constituents to metal powders can affect the physical properties of the mix such as flow rate and apparent density. If the additives are very fine, they have a tendency to segregate and create dust during handling. It is a common practice in the P M industry to adjust the physical...
The QMP Iron Powder Process
In the Quebec Metal Powders QMP process, freshly refined high-purity iron passes through horizontal water jets, which produce granulated iron that is processed further by drying, grinding, decarburization, milling, and blending Fig. 11 . Because of the nature of the manufacturing process, the QMP iron powder grades ATOMET 25, 28, 29, and 30 are highly porous powders with high compressibility for low-and medium-density P M parts production. Fig. 11 Schematic flow diagram of the QMP iron powder...
Reduction of Copper Oxide
Reduction of particulate copper oxide is generally accomplished on a stainless steel belt in a continuous belt furnace. The depth of the oxide bed is approximately 25 mm 1 in. . The typical reduction temperature ranges from 425 to 650 C 800 to 1200 F . Reduction occurs gradually from top to bottom of the bed. The reducing atmosphere in the furnace generally flows countercurrent to the motion of the conveyor belt. Reducing atmospheres may include hydrogen, dissociated ammonia, water-reformed...