Extrusion

Extrusion is the pressing of the feedstock into and through a die of size and cross-sectional shape appropriate to that of the product. The specific steps (Ref 1) used in binder-assisted extrusion are (1) feedstock paste delivery into extruder, (2) consolidation and flow of feedstock paste through the barrel, (3) deformation and shaping of feedstock paste as it flows through the die, (4) flow of feedstock paste through the die land, and (5) part ejection. For the feedstock to flow through the...

Comparison of Mechanical and Hydraulic Presses

In terms of partmaking capability, no distinct advantage is gained by using either a mechanical press or a hydraulic press. Any part can be produced to the same quality on either type of machine. However, the following parameters influence press drive selection. Production Rate. A mechanical press produces parts at a rate one and one-half to five times that of a hydraulic press as a result of inherent design of the energy transfer systems and stroke length. Operating cost of a hydraulic press...

Part Classification

The Metal Powder Industries Federation has classified P M parts according to complexity. Class I parts are the least complex, and class IV parts are the most complex. To better understand the types of commercially available P M compacting presses, and their advantages and limitations, an understanding of P M part classification and tooling systems used to produce parts is necessary. Part thickness and number of distinct levels perpendicular to the direction of powder pressing determine...

Introduction

INJECTION MOLDING is widely recognized as a manufacturing approach that can form complicated shapes from plastics. Since the 1920s, there has been a progressive evolution of injection molding from strict use on plastics to use with metal and ceramic powders. This new technology, known as powder injection molding (PIM), combines the productivity of injection molding with the ability to fabricate metals and ceramics. Thus, complicated shapes emerge from materials capable of operating at high...

Inspection Considerations

Inspection techniques for finished parts should be based on concurrence between the customer and the supplier. There are many ways to gage most part print specifications, and the specific technique used can have a large effect on the results reported. A great many P M part attributes may be measured with the same techniques used in other industries. There are, however, significant exceptions as briefly described below. Hardness. In powder metallurgy there are generally two types of hardness...

Powder Characterization and Testing

Reliable techniques for powder characterization and testing are required to evaluate the chemical and physical properties of metal powders, both as individual particles and in bulk form. This is important to ensure adequate control of powder production processes and to ensure that the required properties for parts manufacturing are met. This Section also features a series of articles on characterization and testing of powders. The representativity of samples taken to test metal powders is key...

Production of Copper Powder by Hydrometallurgical Processing

Hydrometallurgical methods may be used to produce a number of metal powders, including copper, cobalt, and nickel. The basic processing steps consist of preparing pregnant liquor by leaching ore or another suitable raw material, followed by the precipitation of the metal from this solution. For copper, the most important precipitation methods are cementation, reduction with hydrogen or sulfur dioxide, and electrolysis. Use of several leach-precipitation steps or the inclusion of flotation,...

Fig 3 Feedstock pellets and worms for molding

Pelletized feedstock is injection molded into the desired shape by heating it in the molding machine and hot ramming it under pressure into the tool cavity. By virtue of the binder, the feedstock becomes low enough in viscosity that it can flow into the die cavity under pressure. Cooling channels in the die extract heat and solidify the polymer to preserve the molded shape. The shaping equipment is the same as that used for plastic injection molding. It consists of a die filled through a sprue,...

Materials Processed by PIF

A range of materials have been processed by PIF for a variety of applications. Early applications of the technique were for automotive applications for iron-base parts where high performance in either mechanical or magnetic properties was sought. Various aluminum applications for automotive use were also evaluated. In both applications, near-full density (98 or better) was achieved. Nickel and nickel aluminides have also been consolidated by PIF with good success (100 dense) by direct...

Process Variables

Conventional atomization pressures are typically in the range 0.5 to 4 MPa (70 to 600 psi), and gas velocities in the nozzles range from Mach 1 to 3. However, in free-fall atomizers, measured gas velocities in the impingement area normally have fallen to 50 to 150 m s (for air nitrogen). Typically, gas-atomized powder is spherical with a log normal size distribution. Mean particle size is usually in the range 10 to 300 m with a standard deviation of about 2. Oxygen content is about 100 ppm....

References cited in this section

Exner, Principles of Single Phase Sintering, Rev. Powder Metall. Phys. Ceram., Vol 1 (No. 1-4), 1979 2. H. Udin, A.J. Shaler, and J. Wulff, The Surface Tension of Solid Copper, Trans. AIME, Vol 185, 1949, p 186-190 3. R.M. German, Powder Metallurgy Science, 2nd ed., Metal Powder Industries Federation, 1994 4. G.C. Kuczynski, Self-Diffusion in Sintering of Metallic Particles, Trans. AIME, Vol 185, 1949, p 169-178 5. G.H. Gessinger, F.V. Lenel, and G.S. Ansell, Continuous Observation of the...

Monolithic Materials

Tungsten, molybdenum, rhenium, niobium, superalloys (nickel, iron, and cobalt base), zinc, aluminum, bronze, cast iron, mild and stainless steels, NiCr and NiCrAl alloys, cobalt-base Stellites, cobalt nickel-base Tribaloys, and NiCrBSi selffluxing Colmonoy have all been successfully thermal spray consolidated either as coatings or structural deposits. Recently Tribolite (FeCrNiBSi) and AmaCor (amorphous) alloys have also been developed for spraying and exhibit excellent wear and...

Mixtures and Segregation

Most P M powders are multicomponent systems and, therefore, are subject to segregation. Segregation is even possible in a one-component metal powder if, for instance, coarse and fine powder particles demix as a result of vibration. The opportunity for powder segregation exists in processes such as shipping and the filling of hoppers and compaction dies, where individual components exhibit different flow rates due to differences in particle size, shape, density, surface roughness, and other...

Specialty Applications

Roll compacting facilitates the production of small coils in which minor compositional changes can be made during blending. Because roll compacting produces materials with uniform and reliable properties, many specialty materials are produced by these methods (Ref 6). Specialty P M strip produced by roll compacting includes various compositions of nickel-iron strip produced for controlled expansion properties and special copper-nickel-tin alloys. The latter must meet stringent property...

Prealloyed Bronzes

Sintered bronze alloys are rather uncommon in powdered metal usage. This is primarily due to their relatively high cost compared to low-alloy steels. However, sintered bronze properties can be advantageous for non-magnetic applications that require very good corrosion resistance, good mechanical strength, and excellent ductility. Prealloyed 80Cu-9Sn-2Zn bronze powders with a select lubricant are intended for the fabrication of high-density P M structural components. Unlike many elemental...

Example 2 Machinability Evaluation Drilling of Sintered Steel

Blind hole drilling test was performed on a wide spectrum of P M qualities. Cylindrical blanks with a diameter of 80 mm and a height of 10 mm are used in the test. A survey test is performed in order to select the type of drill and cutting conditions. The main comparisons were made under dry condition using a HSS drill with a diameter of 4 mm and a point angle of 118 . Total breakdown of the drill is chosen as criterion, based on the fact that drilling is commonly used as a bulk removal...

Colloidal Stability

Because slip casting of metals is a wet process, some understanding of the interaction between the material and water must be established. Most materials when immersed in a polar solvent become charged. The different mechanisms by which the surface acquires such charge depend greatly on the type of material used. These mechanisms include ion dissolution and ion adsorption (Ref 4, 7). Ionic materials acquire their surface charge through preferential dissolution. A very well known example is Agl,...

References

Roitberg, On Cold Sintering of Metal Bonded Diamond Composites, Scripta Metall., Vol 13, 1979, p 11-15 2. E.Y. Gutmanas, Cold Sintering under Pressure Mechanisms and Application, Powder Metall. Int., Vol 15, 1983,p 129-132 3. E.Y. Gutmanas, Consolidation of Powders under High Pressure--Cold Sintering, New Materials by Mechanical Alloying Techniques, DGM Informationgesellschaft Verlag, Oberursel, 1989, p 129-142 4. E.Y. Gutmanas, Materials with Fine...

Elastoplastic Constitutive Behavior

The constitutive behavior is discussed within the framework of small deformation theory of plasticity, which allows the decomposition of the total strain into elastic and plastic components and development of relatively simple expressions for the constitutive response. In practice, large plastic straining of a body can occur during the compaction process. The general forms of expression are still applicable, provided appropriate measures of stress, strain, stress-rate, and deformation-rate for...

Pressure Assisted Reactive Sintering

Even though many of the examples discussed above can be reactively sintered to densities greater than 97 theoretical, this small amount of porosity can be detrimental to the mechanical properties--specifically tensile and fracture behavior--of these compounds. Commonly, a postreactive sintering routine, such as hot isostatic pressing (HIP), is used to fully densify these materials. Alternatively, the powders can be sintered under pressure by RHP or RHIP. Greater densities can be achieved in the...

Production of Copper Powder by Atomization

Water atomization of copper--that is, the disintegration of a molten stream of high-quality copper with high-pressure water jets--produces copper powders of compacting-grade quality. The resulting dried powder then may be subjected to an elevated-temperature treatment that further modifies its characteristics and engineering properties. Nearly spherical powders result from the atomization of liquid copper with inert gas or air. These powders are used in copper flake production and other...

Stainless Steel Powders

Water-Atomized Stainless Steel Powders. Early experiments concentrated on producing stainless steel powders from elemental components and from alloy powders by sensitization embrittlement and grinding of stainless steel sheet. Water atomization became the established process in the 1950s for producing stainless steel powders for conventional die compaction and sintering. Over the years, slight modifications to the existing wrought compositions led to improved compacting properties. Recently,...

Macroexamination

Macroexamination of sintered materials is not commonly practiced. In wrought or ingot-base materials, forging flow lines, oxide segregation, and stringers are studied extensively. These features are not usually found in P M materials, but there are certain other uses for macroexamination. In sectioning a heat treated P M steel, care must be taken not to overheat the specimen and temper or reharden it locally. The etching performed during grinding and polishing to help open the pores will...

Stainless Steel and High Alloy Powders

Samal, OMG AMERICAS Most stainless steel and other high-alloy powders are made by water atomization or by inert gas and centrifugal atomization. Information on these processes can be found in the article Atomization in this Volume. Water-atomized powders generally are of irregular particle shape and widely used for cold compaction and sintering. The densities of the resulting sintered parts are typically below about 95 of theoretical. It is for this reason that dynamic...

Bulk Deformation Processes

In powder forging, a preform shape is cold pressed to between 75 and 85 of full density, sintered, heated to a forging temperature, and then forged in trapped dies using one blow to produce a fully dense net or near-net shape. The sintering step is optional, but it is normally included as a particle surface cleaning step (deoxidation) and to improve the workability of the porous preform. Powder forging fundamentals and general applications are presented in the article Powder...

Activated Liquid Phase Sintering

Activated LPS can be used to improve the sintering behavior of systems with little or no solubility of the solid in the liquid. Densification is enhanced by the addition of elements that segregate to grain boundaries and lower the activation energy for solid-state diffusion. Such elements can be identified by phase diagram characteristics. Limited additive solubility in the liquid helps to ensure segregation to grain boundaries, while the formation of low-melting temperature intermetallic...

Normalized resolution

Fig. 19 Structural boundary fractal dimension (< 5S) relates to the gross morphology of the fine particle. Textural boundary fractal (< ST) relates to the smaller features of the profile. Fig. 20 Individual powder grain of Fig. 10(a) characterized by its fractal dimension and combined with size and chunkiness to form a single point in three-dimensional space. When a group of powder grains are treated in this way, they produce a cloud of points characteristic of the powder.

Applications

The physical and economic differences between the two types of powders result in clearly defined applications for each. Fine powders are used in both consolidated and unconsolidated forms. Markets include metal injection molding (MIM), electronic pastes and inks, thermal spray, additives, radar absorption coatings, and filtration. Metal Injection Molding. The growth forecasts for MIM encouraged development of fine powder production processes. The first MIM parts were made from available powders...

Sintering of Ferrous Materials

Pressed and sintered iron-base materials represent the largest segment of the P M parts industry. Ferrous P M parts are made from iron powders, alloy steel powders, or mixtures of (a) iron and graphite powders, (b) iron (or steel) and copper powders, or (c) iron, copper, and graphite powders (with or without powders of other metals). The overall sintering process consists of several stages and temperature regimes (Table 2). Excluding lubricant burnoff, the following reactions occur during...

Conventional Shape Factors

Particle shape is a fundamental characteristic of powder particles and thus influences the properties of particulate systems. Various shape terms have been proposed to quantitatively represent particle shape. Early systems tended to measure one specific feature of a particle. Table 3 (Ref 23, 24, 25, 26, 27, 28, 29, 30) lists some of the most frequently used shape terms. The applicability and or limitations of various shape factors, also referred to as shape parameters, are discussed in the...

Particle Shape Factors

The most common approach to describe and differentiate particle shapes has been the use of qualitative concepts. Two fundamental concepts have been used (a) the dimensionality of the particle and (b) the surface contour of the particle. By the use of these concepts, a model system of shape characterization is presented in Fig. 21. Photomicrographs of several types of loose powders described in the International Standards Organization standard ISO 3252 are shown in Fig. 22. Basic shapes are...

Other Infiltration Products

Influence of Liquid Metal Infiltration on the Superconducting Characteristics of Niobium Nitride, L.T. Summers, J.R. Miller, M.J. Strum, R.J. Weimer, and D.E. Kizer, Advances in Cryogenic Engineering, Plenum Press, Vol 34, 1988, p 835-842. A fully stabilized multifilamentary BN superconductor was prepared using a combination of physical vapor deposition of NbN on graphite followed by liquid metal infiltration using copper or aluminum. The resulting conductor assumed a finely divided...

Wet Bag Isostatic Pressing

In wet-bag pressing, the mold is filled, evacuated (if this step is used), and sealed outside the pressure vessel. Because these operations occur in a powder-handling area, contamination of external mold surfaces with metal powder can easily occur. Introduction of dirty molds into the vessel results in working fluid contamination with long-term effects similar to mold tearing and gross metal powder spillage. Thorough mold washing as an integral part of the process flow chart is necessary to...

Thermodynamic and Kinetic Factors

When a liquid forms during sintering, the microstructure consists of solid, liquid, and vapor phases. Successful LPS requires a reduction in surface energy as the liquid spreads across the surface of the solid particles. Thus, the solid-liquid surface energy must be less than the solid-vapor surface energy. In this case, the liquid wets the solid and provides a bonding force between the particles to aid densification. Wetting is aided by solubility of the solid in the liquid,...

Induction Hardening

Spur gears, bevel gears, splined hubs, and cams are ideal components to utilized P M production techniques. These parts usually require hard, wear-resistant surfaces in some areas, with retention of the ductility of the sintered matrix in the remainder of the part. Induction hardening is commonly specified for these applications. The process can be placed in an automated machining line to reduce handling and be a cost-effective hardening treatment when high volumes of parts are being produced....

Powder Fill

The important consideration in P M part production is the fill ratio required to produce parts to a density that is compatible with end use requirements. The fill ratios must remain constant for a given part to maintain dimensional reproducibility. Parts can be of single-level or multilevel design. Single-level parts, designated as class I by the Metal Powder Industries Federation (MPIF), present the least difficulty to the tool designer, regardless of the size or part configuration. The main...

Energy Relationship

When a metal is plastically deformed by cold working, most of the mechanical energy of the deformation process is converted into heat. However, a small amount (approximately 5 ) is stored in the metal, thereby raising its internal energy. The energy associated with permanent lattice strain or cold work is minimal for hard, brittle particles, but can be large for ductile materials. The energy expended to overcome the friction between particles is translated to heat and performs no useful work in...

Production of Tungsten and Tungsten Carbide Powders

Lux, Vienna University of Technology B. Zeiler, Wolfram Bergbau- und Huetten-GmbH Nfg KG Tungsten gained major industrial importance at the beginning of the 20th century due to its technical application as alloying element in high-speed steel and as filament wire in incandescent lamps (Ref 1, 2, 3). For both applications, pure tungsten was produced in powder form. From 1900 to 1912 only pure tungsten powders were used in high amounts for high-speed steels containing 16 to 24 tungsten (Ref...

Process Description

A flow diagram of the PIF process is shown in Fig. 1. Beginning on the left, P M materials are prepared in one of two forms a preform or a loose powder. A preform is consolidated to a near-net- or net-shape workpiece by one of several approaches, including conventional die pressing, cold isostatic pressing (CIP), or metal injection molding. The green pieces are often sintered before they are introduced to the PIF process. As a preform, the workpiece is prepared for PIF processing by a range of...

Binder Treatment of Metal Powder Mixes

This technique consists of binding the fine additives to the coarser ones by adding a small quantity of binding agent to the powder. This binder creates a thin film that covers the particles causing the fine additives to adhere to the base powder. Binders can be of two types liquid or solid (Ref 1). In the case of liquid binder (Fig. 5a), a dry mix is produced and the liquid binder is subsequently added to the mixture. Further homogenization is required to ensure that the liquid is evenly...

Die Compaction

The major difficulty with die compaction traces to die wall friction. This friction inhibits ejection and, more importantly, causes density gradients in the green compact. Punch motion against the powder is similar to plowing snow. Close to the punch, the packing is dense, but far removed from the punch, the powder is unaffected. This pressure decay with distance is because the powder spreads load to the die wall in the form of friction. Green density increases with compaction pressure....

Variables Affecting Green Strength

Many theories have been proposed to explain the precise mechanics of green strength. Because the strength of green compacts results mainly from mechanical interlocking of particle surface irregularities, particle shape is the most important factor contributing to green strength. Powders with irregularly shaped particles produce compacts of higher green strength than powders with spherical particle shape. Spherical particles provide the lowest degree of mechanical strength because of low initial...

Selecting a Dispersing Agent

The selection process suggested by Nelson (Ref 17) will soon be superseded by an ISO Standard 14887, Dispersing Procedures for Powders in Liquids, currently in preparation with the author as convenor of the working group. A brief summary of the considerations involved in finding an effective dispersing agent is given below for the major chemical categories of particles. Particles having a natural surface charge may be electrostatically stable to flocculation with no further treatment. If the...

Sampling Techniques

The most important step in any particle size analysis, but especially by microscopic techniques, is sampling from the bulk. Because an extremely small quantity of material is used to determine the particulate size, an accurate analysis cannot be obtained if the bulk material is not properly sampled. Particles tend to segregate according to size. If handling has caused vibration of the sample, coarse material tends to collect near the surface. When free-flowing material is poured into a pile,...

Sinter Hardening

Powder metallurgy alloys that can transform to the hard martensite phase upon cooling from the sinter temperature have been commercialized. This technique, termed sinter hardening, is rapidly gaining popularity in applications requiring high strength and hardness immediately after sintering. This manufacturing route has proven to be cost effective for a number of parts because it eliminates the need for a postsinter heat treatment. Prealloyed powders have been proven useful for this purpose....

Sintering

Most commercial sintering of stainless steel parts is completed in belt, pusher, walking beam, and vacuum furnaces. A wide range of processing parameters is common. Typical sintering atmospheres include hydrogen, dissociated ammonia, H2-N2 mixtures, and all of low dew point, as well as vacuum. Sintering temperatures range from 1120 to 1344 C (2050 to 2450 F), and sintering times range from 20 to 60 minutes. Insufficient sintering, either too short a time or at too low a temperature, will result...

Compressibility

In most cases, the bulk density of a material varies continuously as a function of the consolidating pressure acting on it. Therefore, it is not sufficient to describe a material simply in terms of its apparent density or tap density. Instead, this density-to-pressure relationship can be measured (Ref 7), and the results are often expressed as a straight line on a log-log plot (Fig. 18). In the bulk solids literature, this relationship is often called compressibility, although this term has...

Production of Silver Powders

Silver powders are used in a variety of electrical, electronic, and industrial applications. In powder metallurgy, silver powders are used in the manufacture of electrodes for primary batteries and storage cells, and as mixtures with other metals that are used in the preparation of electrical contacts and other P M parts containing silver. These mixtures include silver-tungsten, silver-iron, silver-tungsten carbide, silver-molybdenum, silver-cadmium oxide, silver-graphite, and silver nickel...

Secondary Operations

A variety of secondary manufacturing and finishing operations may be required to complete the part, to improve properties, or to calibrate dimensional tolerances. Because die-compacted parts have residual porosity that may affect the response to these secondary operations, several guidelines are provided in this section. Repressing. Die-compacted parts can be repressed in a second tool set in order to reduce the amount of porosity or reduce dimensional variation. By increasing the part density,...

Equipment for Blending and Premixing

Many different types of machines are available for blending and premixing solids. The high density, abrasive nature, frictional characteristics, and tendency to segregate of metal powders, however, reduce the suitability of some machines. A blender suitable for metal powders should Achieve a maximum blending in minimum time Have a gentle mixing action to avoid particle degradation Provide repeatability of blending Provide for complete batch discharge Provide accessibility for ease of cleaning...

Thermal Spray Processing Introduction

The term thermal spray describes the family of four or five processes that use the heat energy generated by chemical (combustion) or electrical (plasma or arc) methods to melt, or at least soften, and accelerate fine dispersions of droplets to velocities in the range 50 to > 1000 m s. The high particle temperatures and velocities achieved result in significant droplet deformation on impact at a surface, producing thin layers or lamellae, often called splats, which conform and adhere to the...

Production Methods

The production techniques used for fine (micron scale) powders generally fail in the submicron (nanometer) range. Methods like gas or water atomization have a lower particle size limit of to 5 'm. Milling is used for particle size reduction of very brittle materials like tungsten carbide or ceramics, but fail for ductile materials like precious metals. A variety of methods are available for the production of ultrafine powders with submicron particle size. Gas phase reactions, spray drying, or...

A typical HIP cycle for a coldloading coldwall autoclave is as follows

The powder-filled compacts are placed on fixturing designed to withstand the load weight and elevated temperature to which it will be subjected. This is usually done at a station that can also accommodate the furnace. To maximize efficiency, the load is built in a duplicate base heater while the vessel is actively running a cycle. 2. The furnace is placed over around the compacts and the base heater. The entire load is lifted and placed into the HIP vessel as a module. The base heater engages...

Solvent Based Binders for Room Temperature Extrusions

Solvent-based binder systems are used for room-temperature extrusion. Typically, a water soluble clay and or an organic polymer binder is dissolved in water (Ref 1, 3, 5, 17). The water uniformly disperses the binder throughout the powder and provides the rheological characteristics necessary for proper extrusion. The organic binder is used to increase the viscosity of the feedstock and to change the flow characteristics of the powder water feedstock from Newtonian to the desired pseudoplastic...

Milling Environment

Surface-active agents and lubricants generally are used to nullify the forces of welding (or autohesion) and thereby inhibit agglomeration. Surface-active agents adsorbed on a particle surface interfere with welding and lower the surface tension of solid material. Because the energy required for milling is equal to the product of new surface area generated times the surface tension, a reduction in surface tension results in the use of shorter milling times and or finer powders. Corrosion...

Types of Atmospheres

Conventional atmospheres used in sintering are endothermic gas, exothermic gas, dissociated ammonia, hydrogen, and vacuum. According to the Metal Powder Industries Federation, the most common atmosphere, endothermic gas, was used by - -83 of the industry in 1976 for sintering carbon steels (Ref 4). Endothermic gas is generated directly from partial combustion of natural gas. Exothermic gas, also a product of incomplete combustion of natural gas, was used by 5 of the industry for sintering...

Atomic Absorption Spectrometry

Atomic absorption spectrometry (AAS) is generally used for measuring relatively low concentrations of approximately 70 metallic or semimetallic elements in solution samples. The basic experimental equipment used is essentially the same as that of 30 years ago--enhanced by modern electronics, background-correction schemes, and alternate types of atomizers. The predominance of AAS in general-purpose trace-metal analysis has recently been somewhat eclipsed by modern atomic emission spectrochemical...

Mechanism of Milling Phenomenology

One type of milling mechanism consists of an initial microforging stage in which particles are deformed in the absence of agglomeration by welding and fracture. Eventually, particles become so severely deformed and embrittled by cold work that they enter a secondary stage, during which the particle fracture by a fatigue failure mechanism and or by the fragmentation of fragile flakes. Fragments generated by this mechanism may continue to reduce in size in the absence of strong agglomerating...

Container Fabrication

Tooling and Container Component Fabrication. Once the design has been established, the metal container is fabricated. This is not a trivial step because the container must be producible in an economical fashion or the finished part cannot be manufactured. The most economical and easily formed container material is low-carbon steel however, other materials (e.g., stainless steel, nickel alloys, titanium, etc.) can also be used. The process is constrained by existing metalforming techniques...

Fig 3 Scanning electron micrograph of the filamentarytype nickel powder produced by carbonyl decomposition 1000x

Extra fine nickel powders (e.g., Inco type 210) also have filamental morphology, but the filaments are finer and specific areas range from 1.5 to 6 m2 g depending on the grade. Semi smooth high-density nickel powders are available in fine and coarse sizes. The fine is 10 to 20 'm in diameter (Fig. 4) the coarse is -16+40 mesh. Powder apparent density ranges from 3.5 to 4.2 g cm3. Fig. 4 Scanning electron micrograph of high-density (fine) nickel powder produced by carbonyl decomposition. 1000x...

Palladium Powders

Palladium is used in the electrical and electronics industries in electrical contacts, multilayer ceramic capacitors, thick-film paste conductors, resistors, thermocouples, and heating pads. The corrosion resistance, high melting point, contact resistance, and reasonable electrical conductivity of palladium account for its use as an electrical contact material where long life and reliability are essential. Palladium can be preferred for low-current, long-life relays operating at low contact...

Sliding at Impact Points

Two key factors in chute design are the chute angle and the smoothness of the chute surface at the point of impact. Too shallow or too rough a surface in a chute impedes flow. The required minimum chute slope can be determined by placing a ring-type device containing a sample of the powder on a representative sample of the chute wall surface and applying a predetermined vertical load to simulate impact. Once the weight has been removed, the plate is raised to determine the angle at which the...

Process Control

A key aspect of process control philosophy is that shop floor operators be given as much ownership of their process as possible. Ideally, the operator gages the process, charts it, takes corrective action when it goes out of control, and makes the appropriate adjustments to the process when necessary. Certain process control procedures, however, cannot be practically conducted by the production operators. Some measurements cannot be accurately determined on the production floor. Examples...

Iron Copper and Iron Copper Graphite

The sintering of iron-copper mixtures involves (a) solid bonding of iron to iron, (b) solid bonding of copper to iron, (c) melting of copper, (d) solution and diffusion of copper in solid iron, and (e) solution and precipitation of iron in liquid copper. At typical sintering temperatures of 1095 to 1120 C (2000 to 2050 F), 7.5 to 9.0 Cu is soluble in iron. However, with this copper content and typical sintering conditions, some of the molten copper remains undissolved, or free, and can dissolve...

The Hoganas Process

The Hoganas process uses pure magnetite (Fe3O4) ore found in northern Sweden, which has an iron content of approximately 71.5 after beneficiation by grinding and magnetic separation. The impurities present in small amounts are not in solid solution in the oxide, but exist as discrete phases. The ore is of consistent quality and is available in sufficient quantities for continued usage. Coke breeze or another carbon source that provides the reducing agent is required to produce sponge iron...

Apparatus

Lea and Nurse (Ref 21) developed the apparatus shown in Fig. 4 to provide permeability measurements. The powder was compacted in the sample cell to a predetermined porosity. Air was permitted to flow through the bed, and the pressure drop (h1) was measured on the first manometer the air then passed through a capillary flowmeter, across which another pressure drop was measured as h2 on a second manometer. Fig. 4 Lea and Nurse permeability apparatus with manometer and flowmeter The capillary...

Cold Sintering of Metal Matrix Composites with Partial Surface Reduction of Ceramic Particles

Bonding integrity between a metal matrix and ceramic particles can be improved by partial (surface) reduction or metallization of the ceramic particles prior to consolidation of the composite to full density. Such an approach has been applied to the processing of iron-base matrix composites (cermets) reinforced with Cr2O3 and VC particles (Ref 31, 46). A schematic of the process is shown in Fig. 16. Metallization of ceramic particle surfaces result in an increased composite strength. The...

Properties and Applications

One of the most important properties of pure tungsten carbide is its high hardness (for properties, see Table 2), which is the basis for the application in hardmetals. Linear coefficient of thermal expansion (20-400 C), 10-6 K Hardmetals, also called cemented carbides, achieve an optimized balance between the high hardness of the tungsten carbide and the high toughness of a ductile binder metal, such as cobalt, nickel, or iron, whereby optimal interfacial bonding is achieved (Ref 56, 57). To...

Commercial Processes

Currently, Inco Ltd. produces high-purity nickel powders by the thermal decomposition of nickel tetracarbonyl. Gaseous nickel tetracarbonyl is formed by reacting carbon monoxide with nickel concentrates under controlled conditions subsequent thermal decomposition of the gas permits recovery of the nickel as a fine metallic powder and nickel pellets. The process, which affords a high degree of purity with respect to metallic elements other than nickel, produces nickel powders with extremely...

Nickel Base Alloys

Typical compositions of the commercially available mechanically alloyed nickel-base superalloys are presented in Table 2. The most significant advantage of oxide-dispersion strengthened superalloys is the increased stress rupture properties. Figure 10 compares the specific rupture strength (strength density) for a 1000 h life as a function of temperature for several nickel-base superalloys used for turbine blade applications. Mar-M200 is a nickel-base alloy containing by weight percent 9.0 Cr,...

Premix Diffusion Alloyed Bronzes

Premix or partially diffused bronzes are used extensively in the manufacture of porous, self-lubricating bushings and bearings and for more complex structures requiring superior bearing and mechanical strength. Self-lubricating bushings and bearings are produced at nominal densities (oil impregnated) of 5.8 to 7.2 g cm3, with oil contents ranging from 24 to 11 vol , respectively. Corresponding radial crush values (K strength constant) are approximately 69 MPa (10 ksi) of the lower density,...

Eq

This differential equation can be numerically integrated to obtain a distribution of densities at different applied temperature and pressure cycles. As can be seen from Eq 7, the rate of change in density strongly depends on the temperature and pressure. Other important characteristics of Eq 7 are a threshold value of temperature below which the dependency of density rate on the pressure is weak and a range of pressure magnitude below which the rate of change in the density weakly depends on...

Powders for Sprayed Composites

Discontinuously reinforced composites produced using thermal spray techniques use either composite powders or direct reactive synthesis approaches, as described below. Powders can be produced mechanically, chemically, thermomechanically, or by using high-temperature synthesis. Engineered powders defines powders in which different phases are incorporated to produce a microcomposition of the final desired structure. Typically these powders contain the desired sizes, size distributions, and...

Production of Copper Powder by Electrolysis

Production of electrolytic copper powder, as shown in Fig. 6, follows the same electrochemical principles that apply to the electrorefining of copper. The conditions of deposition, however, are changed to yield a powdery or spongy deposit, instead of the strongly adherent product desired in electrorefining. The formation of powdery deposits is favored by low copper ion concentration and high acid content in the electrolyte, as well as by high cathode current density. Fig. 6 Flowchart for...

Mercury Porosimetry

Giesche, School of Ceramic Engineering and Sciences, Alfred University Many commercially important processes involve the transport of fluids through porous media and the displacement of one fluid, already in the media, by another. The role played by pore structure is of fundamental importance in understanding of these processes. The quality of powder compacts is also affected by the void size distribution between the constituent particles. For these reasons, mercury porosimetry has long been...

The Mechanism of Cold Sintering

Plastic deformation of powder particles leading to intimate contact between oxide- and contamination-free surfaces results in the formation of chemical bonds and adhesion. This has been proved by transmission electron microscopy for pure aluminum powder (Ref 26). Broken oxide layers exist as islands at powder particle interfaces. Similar observations were made for cold sintered copper, nickel, iron, and stainless steel powders. In a consolidated material, the interface between powder particles...

Tool Materials

In the most common type of die construction, wear-resistant inserts or liners are held in place by clamping or shrink fitting. The amount of interference between the insert and the die case depends on the inside and outside diameter of each member and on the compacting pressure used. The powder can be considered a fluid in a closed container that transmits the compacting pressure in all directions therefore, the die must be designed as though it were a pressure vessel with internal...

Lot Traceability

The sophistication of a system for part traceability depends on customer requirements and the risk that the producer is willing to assume. Should a problem develop, discrete traceability to a specific production operation can help reduce the quantity that might be involved in a rejection or product recall. As a minimum, most P M suppliers maintain traceability to the material used. Each raw material (metal powder, lubricant, additive, etc.) is assigned a unique material lot number by its...

Microanalysis Methods

For many years, metallurgy has involved chemical analysis on a macroscopic scale with microscopic investigation of structure by means of metallography. Microanalysis is a method that combines structural (location specific) and compositional analysis in one operation. Microanalysis thus provides information concerning specimen composition on a microscopic scale hence, microanalytical processes relate to both chemical analysis and microscopy. Microanalysis typically involves the use of a scanning...

Mechanical Testing Tensile Testing

MPIF standard 10 describes specimens for tensile testing. Specimens include flat unmachined test bars or machined rounds. Unmachined flats are more prone to slippage of grips or breakage in the gauge region. For testing to be meaningful, it is important to verify that such bars are free of microlaminations (Ref 21), which requires careful metallographic evaluation. Highest quality bars are molded in well-bolstered die sets (890 kN, or 100 ton rating), with generous exit taper, high green...

Materials Processed by Powder Extrusion

The early development of powder extrusion processes concentrated on the search for materials with improved high-temperature performance and the development of methods for encapsulating and handling toxic materials. The use of an outer skin or container and a particulate workpiece also stimulated metalworkers to examine powder extrusion as a means for forming structural components from difficult-to-work material. These basic uses of powder extrusion still drive the industry. Examples are given...

Appendix Dispersion of Powders in Liquids

Nelson, Jr., DuPont Co., Wilmington, DE Preparation of a dispersion is not a trivial matter. Special equipment and chemicals have been developed to facilitate the three steps of preparing a stable dispersion Wetting powder clumps into the liquid Breaking up the wetted clumps Preventing flocculation of the dispersed particles The particle size distributions (PSDs) measured for successive dispersions made from aliquots of dry powder taken from a well-mixed powder sample will be...

Iron Base PM Materials

Pure iron or very-low-carbon steel is a common structural or bearing material. The microstructure is predominantly ferrite, with modest amounts of pearlite in proportion to the minor amounts of carbon in solution. Several kinds of iron powder are commonly used, including sponge, atomized, electrolytic, and carbonyl powders (Fig. 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52). They have widely differing properties because of differences in...

Hydride Dehydride Process

The hydride dehydride (HDH) process for making titanium powder is based on the reversible interaction of titanium and hydrogen. Titanium has a very high affinity for hydrogen and is easily hydrogenated by heating titanium in a hydrogen atmosphere. Hydrogenated titanium is very brittle and can be crushed to a fine powder. The hydrogen can then be simply removed by heating the powder in a dynamic vacuum. The minimum hydrogenation temperature for commercially pure titanium is about 400 C (750 F)...

General Theory

The general theory of light scattering was developed in the early 1900s (Ref 3) while practical application occurred somewhat later (Ref 4). The fundamental concept is the Mie theory (Ref 5), a complete equation that explains the scattering phenomenon. In the past this was difficult to use, and simplifying assumptions were made. The most common assumption is that the particles are opaque, circular obstructions in the beam of light (Ref 6). This allows the Mie equation to be simplified to...

Sieve Analysis

Standard sieves have been in industrial use for over a hundred years. Particle size distribution is controlled and certified by the powder producer and is frequently checked by the end user. Typically, a series of sieves is selected that spans the full range of particle sizes present in a powder. Sieves are stacked in order, with the largest mesh size at the top and a pan at the bottom (Fig. 1). An appropriate sample weight of metal powder is spread on the top sieve and covered. The stack of...

Stability of Sulfides

Neither sulfur nor sulfides are completely stable during sintering. Comparison of the sulfur content of the F-0008 premix ingredients to that of the sintered test pieces shows that the sulfur recovery was lower than anticipated (Table 10). Table 10 Sulfur recovery for sintered F-0008 sponge Table 10 Sulfur recovery for sintered F-0008 sponge The data show that manganese sulfide is stable under endothermic atmosphere sintering. The measured and predicted sulfur contents of the...

Ev

Given orientation to the plastic strain lJ. The surface for frictionless closed-die compaction, normalized by the hydrostatic stress, P, required to compact the material to the same density is shown in Fig. 9 for ' 0, where it is compared with the comparable surface for hydrostatic compaction. There are a number of important points to note The surface for closed-die compaction is extended in the direction of loading and contracted in the transverse direction compared to the surface for...

Plastic Binders for Hot Extrusion

Plastic binders, utilized for hot extrusion, are blends of organic and metall-organic polymers, with a small percent of modifying agents (Ref 7). Typically, the feedstock contains 65 vol powder, 35 vol binder, and has a viscosity between 200 and 500 Pa s, within the temperature range of 80 to 220 C, and at a shear rate of between 100 and 1000 s-1. Many of the exact binder feedstock formulations utilized for hot extrusion are proprietary. However, many binder feedstock combinations are based on...

Types of Presses

Anvil presses generally are limited to compaction of class I parts in a single direction. Anvil presses do not have an upper punch a moveable, solid, flat block seals the top of the die. Compacting is done by the lower punch, which, after the anvil is released and moved, moves farther to eject the compact from the die. Anvil presses are available with pressing capacities ranging from 6.7 to 310 kN (0.75 to 35 tons), with maximum depth of fill ranging from 1 to 75 mm (0.040 to 3 in.)....

Optical Sensing Zone

The light blockage principle (obscuration) was used by Carver in 1958 to develop a method for counting and sizing particulate contamination in hydraulic fluids (Ref 1, 2). To date, this principle has found application in other particle-fluid systems and has been used for the measurement of metal powder particles. In an apparatus using the light-obscuration principles, particles are suspended in a fluid with a refractive index that differs from the refractive index of the particles. The...

The Machining Process

The machining or metal cutting process is extremely complex. It has been widely studied for wrought (Ref 3, 4, 5) and P M steels (Ref 6, 7, 8, 9). The cutting process is generally illustrated by considering metal flow towards and over a simple cutting tool in an operation, such as turning or broaching (Fig. 1). During cutting, tool movement into the workpiece generates a complex stress field around the tool tip. These stresses initiate cracks in the workpiece ahead of the tool tip. The cracks...

Triaxial Tests

A brief description of the triaxial test and apparatus is presented in this section. For a more detailed treatment of the test, stemming from a soil mechanics perspective, see Ref 31. The triaxial test is important as it provides a convenient means of examining a variety of situations involving different ratios of the deviatoric and hydrostatic stress measures. A schematic of the triaxial test cell is shown in Fig. 12. The powder is placed in a container with a flexible wall, typically made of...

Oxide Dispersion Strengthened Alloys

Use of MA to synthesize metastable phases is a recent development. The major use of MA has been in the development of commercial ODS nickel-, iron-, and aluminum-base alloys. Mechanically alloyed materials are strong both at room and elevated temperatures (Table 1). The elevated temperature strength of these materials is derived from more than one mechanism. First, the uniform dispersion (with a spacing of -100 nm) of very fine (5 to 50 nm) oxide particles (commonly used are Y2O3 (yttria), ThO2...

Powder Production and Sintering

The design of a commercial reactor for large-scale production of materials is shown in Fig. 5. Typically it is a thick-walled stainless steel cylinder, with volume up to 30 L, that can be water cooled. The inner surface of the reactor is lined with an inert material to protect the vessel from extreme reaction temperatures. Graphite is generally used for lining during carbide, boride, or silicide synthesis, while boron nitride and silicon nitride provide protection during nitride synthesis. The...

Instrument Design

A typical laser light-scattering instrument consists of a light source, a particle-dispersion and delivery system, a detector to measure the scattering pattern, and a computer to control the system and determine the particle-size distribution. Older instruments were only capable of measuring the scattering pattern at low angles (< 20 ) and were limited to measuring particles > 1 'm. More modern instruments collect scattering information at more and larger angles. This can be accomplished by...

Supersolidus Liquid Phase Sintering

Supersolidus LPS involves heating a prealloyed powder between the solidus and liquidus temperatures to form a liquid phase (Ref 28, 29). The fundamental difference between classic LPS and SLPS lies in the sequence of events leading to densification. A schematic of the stages in SLPS is shown in Fig. 7. In the first stage, liquid forms as a prealloyed powder is heated above the solidus temperature. The commonly observed liquid formation sites are the grain boundaries within a particle, the...

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...

Inert Gas Condensation

Sketch Metal Inert Gas

The IGC method is performed by evaporating and condensing of the respective material in a vacuum cylinder filled with a low pressure of an inert gas (e.g., 10 mbar helium). Evaporation of the respective material can be completed by magnetron sputtering, electron beam, laser, or Joule heating of a crucible. The vapor nucleates homogeneously due to collisions with the cold inert gas atoms. The growth of particles within the convection gas flow occurs basically via coalescence. This type of growth...

Sintering Mechanisms

Important contributions to sintering arise from diffusion and viscous flow. Diffusion rates increase with increasing temperature because of the increased number of vacancies that promote diffusion of substantial alloying elements. Sintering temperature must be held very close to the solidus temperature to attain full density in a reasonable time. A sintering temperature 5.5 to 11 C (10 to 20 F) above the solidus reportedly forms a small amount of liquid, which allows high-diffusion rates for...