Showing papers in "Powder Metallurgy in 1990"

Effect of Carbon on Dimensional and Microstructural Characteristics of Fe–Cu Compacts During Sintering

Abstract: It used to be thought that addition of carbon to Fe–Cu compacts inhibited compact growth by reducing solubility of copper in iron, but this effect is in fact slight. The theory that formation of Fe–Cu–C ternary liquid phase promoted shrinkage by liquid phase sintering has also been discounted. It has more recently been shown that carbon additions reduce growth by preventing boundary penetration of iron by copper. The present study verifies the importance of the proportion of high and low dihedral angles which the copper phase forms with γ-iron: carbon inhibits compact growth by causing these angles to increase. PM/0516

Fatigue Design for Powder Metallurgy

Abstract: Powder metallurgy, among several competing mass production methods, plays an important role, not only as a means of saving material and energy, but also as a technique, delivering materials with good fatigue properties which are able to substitute for conventional materials. However, it is necessary to understand the interaction between strength behaviour and design determining factors such as service loading, component geometry, and manufacturing. After presenting definitions of fatigue strength, which is divided into the areas of low cycle (endurance limit N 2 × 106) fatigue under constant amplitude loading and the area of variable amplitude fatigue with 104

Production of Rapidly Solidified Aluminium Alloy Powders by Gas Atomisation and Their Applications

Abstract: Light engineering alloys based on aluminium have been the subject of a great deal of attention in the field of rapid solidification processing. As a parallel activity, considerable research effort ...

Expansion During Liquid Phase Sintering of Iron–Copper Compacts

Abstract: An attempt has been made to develop a quantitative approach to the swelling during isothermal liquid phase sintering of Fe–Cu compacts The time dependent expansion was followed during sintering at 1150°C by measuring anisotropic changes in dimensions using photography and micrometry Cylindrical compacts containing up to 20%Cu, pressed at 200, 250, and 300 MPa, were examined Differences were observed in the extent of swelling, sintering behaviour, and sintered structure between compacts containing ≤5%Cu and ≥10%Cu; these differences can be reasonably attributed to differences in the quantity of the fused melt The extent of swelling can be assessed satisfactorily on the basis of the bulk density of green compacts, which reflects both powder characteristics and compaction conditions Such an assessment enables quantitative comparison of results obtained under different sintering conditions PM/0501

Development and Applications of Soft Magnetic PM Materials

Abstract: A description of soft magnetic powder composites, such as sinters, dielectromagnetics, and magnetodielectrics, and the problems associated with their application as magnetic cores in electrical converters is presented. Typical magnetic properties and methods of processing are reviewed and criteria for choosing the type of composite for a particular magnetic core are discussed. Dielectromagnetics can be divided, both in terms of their present status and for future development, into conventional and special types. The problems associated with both these types are described. A brief review is given, based on the authors' experience with these problems, of the present status of and the prospects for soft magnetic powder composites. PM/0519

Mechanisms of Sintering in High Speed Steels with Phosphorus Alloying Additions

Abstract: Cu–P alloy powder additions to M3 class 2 high speed steels reduce the sintering temperature required to produce near full density by ∼100 K. Densification was found to occur in distinct stages, due to the successive formation of a series of liquid phases at various sintering temperatures. These phases, each of which gave rise to an identifiable change in densification rate, were identified as the ferrite-carbide-phosphide eutectic at ∼1050°C, melting of residual copper at 1090°C, and an austenite-carbide eutectic at 1150°C. An activated sintering model for densification by the formation of a phosphide rich grain boundary liquid was developed. This concluded that sintering occurs by rapid grain boundary migration due to solutionprecipitation across an unstable grain boundary liquid film. PM/0512

Modelling of Hipping Consolidation Applied to Ni3Al Powders

Abstract: Densification of Ni3Al powders has been simulated using a model that describes consolidation by the additive effects of plastic flow, power law creep, boundary diffusion, and Nabarro–Herring and Coble creep. The model has been used to develop maps that describe densification for any combination of time, temperature, and pressure. Using the best available material property data, and parameters from experiments, maps have been developed that describe hipping consolidation experiments with reasonable accuracy. Mechanical property characterisation has shown that although densification is possible through many combinations of consolidation parameters, the ductility is a sensitive function of the hipping temperature and pressure. Finite element models were developed as an extension of the hipping map approach to provide detailed simulations of particle deformation during densification. Preliminary results for both monosized and bimodal particle distributions indicate that this particle level approach is...

Effects of consolidation parameters on properties of sintered high speed steels

Abstract: A range of high speed steel powders were cold pressed and sintered under vacuum and gaseous atmospheres. The main objective was to evaluate the potential applications of these materials for wear resistant components. Dimensional stability, mechanical properties, and microstructural development as a result of varying experimental conditions were investigated. It was found that adequate dimensional stability could be achieved after sintering at temperatures up to 1200°C, and improvement in mechanical properties was obtained as the sintering temperature and sintering time were raised. However, above 1220°C the formation of excessive liquid phase led to the development of undesirable grain boundary carbide networks, resulting in a rapid drop in bend strengths. It was also observed that the mechanical properties of the porous compacts could be substantially improved by infiltration with copper. PM/0514

Infrared Thermal Imaging Measurement of Deposit Surface Temperatures During Spray Deposition

Abstract: An infrared thermal imaging camera has been used to measure surface temperatures of a 7075 aluminium alloy deposit during spray deposition The surface temperature rises rapidly, then remains approximately constant as a pseudosteady thermal state is established, and finally the deposit cools quickly when deposition is complete The temperature measurements are compared with a numerical model for one dimensional deposit heat flow PM/0517

Quantitative Assessment of Enhanced Sintering Concepts

Abstract: The theories of enhanced sintering identify three criteria for a sintering enhancer; high solubility of base material in the second phase, segregation of the additive at the interparticle boundaries, and easy diffusion of the base material through the segregated phase. Although these qualitative ideas are valuable in the selection of a sintering enhancer, a quantitative assessment would render them more meaningful. This study proposes a figure of merit relating to thermodynamic quantities, capable of identifying a sintering enhancer reliably. This figure of merit is defined as a weighted sum of solubility, segregation, and diffusion terms. It is a dimensionless quantity, and can easily be calculated from phase diagram features. The proposed figure of merit has been used successfully to identify effective sintering enhancers for iron, and the results have been compared with sintered density values obtained from a controlled experiment and from the literature. PM/0493

Laboratory Simulation of Commercial Brass Flake Manufacture

Abstract: The processes governing the conversion of ductile metal powders to flake have been identified through a study of the changes in particle morphology during laboratory scale milling of atomised brass powder. The study demonstrated that the laboratory milling procedures could be optimised to produce flake of commercial quality, offering opportunities for trial manufacture of new flake product ranges for a variety of industrial applications. PM/0537

Processing, Properties, and Applications of Rapidly Solidified Advanced Alloy Powders

Abstract: The major processes for the production of rapidly quenched particulate, and aspects related to their consolidation, are briefly reviewed and compared with respect to their efficacy in promoting microstructural and constitutional modifications for improved properties. The application of the technology is discussed for a range of selected materials, including aluminium, iron, nickel, and copper alloys and iron-rare earth magnetic alloys, and appropriate comparisons are drawn with spray formed and mechanically alloyed materials. PM/0538

Aspects of Powder Technology in Ancient and Medieval India

Abstract: The production, characterisation, and application of metal powder in ancient and medieval India have been investigated on the basis of literary evidence. It has been shown that metal powder was produced by a variety of methods, including mechanical comminution, amalgamation, atomisation, filing, and cementation. Aspects of powder characterisation are also described. Perhaps the first application of powders of metals such as gold, silver, copper, and tin was in coloured paints. An important application of very fine metal powders was in making bhasmas – compounds of the respective metals in powder form that are used medicinally. Evidence shows that metal in granular form was recognised as a means of enhancing the reaction rate in processes such as gold refining. An experimental study on the production of silver powder by an ancient Indian method based on mechanical communition of very thin silver leaves has been carried out, and it has been shown that fine, flake like powder is produced. The famous ...

Microstructure and Mechanical Properties of Osprey Processed Cu–15Ni–8Sn Alloy

Abstract: (1990). Microstructure and Mechanical Properties of Osprey Processed Cu–15Ni–8Sn Alloy. Powder Metallurgy: Vol. 33, No. 4, pp. 335-338.

Mechanical Properties of Sintered TiAl Prepared by Canning Hipping

Abstract: Centrifugally atomised powder and selfpropagating high temperature synthesis (SHS) alloy powder were canned and hipped. The compressive yield strength of the hipped atomised powder was ~390MN m−2 in the range of room temperature to 1073 K, and decreased above 1173 K. For both the atomised and SHS powders, the bending ductility was ~0·5% at room temperature in vacuum, and cleavage facets were observed on the fracture surfaces. Bending ductility increased with testing temperature up to 1073 K, and decreased above 1173 K. Ductility was much greater for the atomised than for the SHS powder. Grain boundary facets and prior powder boundary facets were observed at 973 and 1173K respectively, and bend strength and ductility were affected by an environment of air for both materials. Crack growth was detected in delayed fracture tests in air at room temperature for the specimens with a Vickers indentation, and grain boundary facets were observed on the delayed fracture surface. PM/0515

Surface Integrity Aspects of Machinability Testing of Fe—C—Cu Powder Metallurgy Components

Abstract: The surface condition produced by turning and boring secondary machining operations on Fe–C–Cu compacts has been examined by profilometric analysis. It was found that edge frittering, which may lead to component rejection, can be minimised by decreasing the feedrate or by changing tool nose radius or plan approach angle, as appropriate. Flank wear is the dominant tool wear mechanism and is promoted by the abrasive conditions existing when machining any PM component. The best results were obtained with low copper, low carbon additions, whereas increased flank wear and poor surface finish occur with high copper, high carbon compositions. Tool edge rounding produces surfaces characterised by high levels of plastic deformation and (in some cases) smearing of the surface, which should lead to compact rejection even though the metrological conditions are fulfilled. A new accelerated machinability test, a hybrid of the rapid facing and degraded tool tests, has been developed; the ISO P grades are found t...

Modelling of Metal Powder Production Using a Wax Atomiser

Abstract: The gas atomisation process for the production of fine metal powders was modelled using a laboratory atomiser in which wax was atomised under high air pressure. A ‘confined design’ atomising nozzle was used in a vertically upward direction. The wax particles obtained covered a wide range of sizes and showed good sphericity. Particle sizing using a Malvern laser particle sizer indicated that size distribution obeyed the Rosin- Rammler law, rather than the log-normal law applicable to metal powders. Theoretical considerations indicate that this is caused by the comparatively high viscosity, low surface tension, and low density of wax, and that the same liquid break· up mechanism is likely to be applicable to wax and liquid metals. Under a given set of gas flow conditions, the median diameter of the powder produced increased in proportion to the square root of the flowrate of wax supplied to the atomiser. Operation at higher wax temperatures led to refinement of particle size as a result of more fav...

Design of Sintered High Speed Steel Alloy Powders for Wear Applications

Abstract: High speed steel (HSS) powders of various compositions including some mixtures diluted with iron powder were compacted and sintered under a range of atmospheres. The aim was to assess the potential of the sintered materials for wear resistant components. The dependence of dimensional stability, mechanical properties, and microstructural development on processing parameters was investigated. It was found that adequate dimensional stability could be achieved after sintering at temperatures up to 1200°C. Above this temperature, dimensional instability occured due to the formation of a liquid phase. The mechanical properties of the compacts were improved by raising the sintering temperature and increasing sintering time. Above 1220°C, the presence of an excessive amount of liquid phase led to the development of grain boundary carbide networks in pure HSS samples and segregation of the carbide particles towards pore regions in diluted HSS compacts. In both cases this resulted in a sharp fall in bend strength. It was also observed that compositional homogenisation was slower than predicted in the HSSFe system. This phenomenon is explained in terms of the dissolution resistance of the carbide particles. PM/0531

Model for hot compaction of metal powders

Abstract: A mathematical model is proposed to describe the variation with time of pressure, relative density, and temperature for metal powders during hot compaction. The model includes instantaneous response, equilibrium response, and creep response and is based on a micromechanical (hollow sphere) analysis. However, the development is mostly empirical, based on experimental data from hot compaction of iron powder. The instantaneous and equilibrium responses are described by linear response laws, whereas time dependent densification is described by a power law creep response. The experimental data support these assumptions. Agreement between theoretical curves and experimental data is very good. PM/0500

Extrusion and Properties of 7075 Ingot and Particulate

Abstract: Hot extrusion has been carried out on 7075 alloy powder and cast ingot material canned in 6061 alloy to give identical surface and lubrication conditions. For mean extrusion temperatures around 400°C and extrusion ratios of 12: 1 to 26: 1, the mean flow stress of the degassed powder in the deformation zone is 87% of the value for the ingot material. The starting material and extrusion variables have little effect on the room temperature mechanical properties either in the as extruded or T6 conditions. Powder extrusion generally developed some porosity during heat treatment, indicating that the initial degassing treatment at 425°C had not been adequate when subsequent solution treatment was carried out at 465°C. PM/0485

Metallographic Changes During Sintering of Grade M High Speed Steels in Industrial Atmosphere and Vacuum

Abstract: The metallographic changes taking place in four M grade steels, M3/2, Px30 (a Powdrex SA water atomised powder equivalent to ASP 30), M2, and M42, during sintering at the optimum temperature and oversintering in vacuum and in a nitrogen based industrial atmosphere have been investigated using SEM and EDS techniques. M6C and MC primary carbides were observed after vacuum sintering and MX carbonitrides instead of MC carbides were found in the specimens sintered in the industrial atmosphere. Small amounts of a eutectic carbide rich in Cr and Fe were observed at the optimum sintering temperature. On oversintering in vacuum different types of eutectic carbides were observed MC, needle shape, and M6C but MC type eutectic carbides were not observed on oversintering the samples in the industrial atmosphere. PM/0535

Production of Superplastic Zn–Al Alloys from Rapidly Solidified Powder

Abstract: The feasibility of producing room temperature superplastic Zn–Al alloys by hot extrusion of gas atomised powders has been investigated. Commercially pure zinc, and Zn–8wt-%Al and Zn–28wt-%Al binary alloys were gas atomised; the resulting powders were cold compacted into cylindrical billets and extruded to form consolidated rod. Two extrusion temperatures (200 and 300°C) were used, chosen to lie on either side of the invariant (eutectoid) temperature of 275°C. It has long been established that in conventional cast alloys rapid quenching from above this temperature is required to produce a microstructure having superplastic properties. (It was anticipated that the 300°C extrusions would contain quantities of near equilibrium eutectoid and thus be unlikely to deform superplastically. The 200°C extrusions were expected to exhibit a non-equilibrium structure that might have potential in terms of superplastic deformation.) The microstructures of the extrudates were investigated by transmission electron ...

Microscale Homogenisation of Individual Components of Copper–Lead–Graphite System

Abstract: The effects of mixing parameters on the microstructural homogeneity of green and sintered compacts composed of 80 wt-%Cu, 12 wt-%Pb, and 8 wt-%C powders has been studied by quantitative metallographic analysis of the distribution of the three phases. Mixing for up to 1 h in a cycloidal (Turbula) mixer and for up to 8 h in an intermittent (Sigma) mixer was investigated. In all cases, homogeneity increased with increasing mixing time, eventually reaching a steady state value. Optimum mixing times were found to be 30–60 min and 4–8 h for the cycloidal and spiral techniques respectively, although the copper distribution reached an optimal value after only 10 min with the former. Use of irregular rather that spheroidal lead powder. gave greater homogenisation in the green compacts pressed from spiral mixed powder, but these differences largely disappeared after sintering, which was generally found to increase homogenisation, as measured by coefficient of variation, by ~20%. PM/0497

Progress in European Powder Metallurgy: Brief Survey of Current R&D with Emphasis on Industrial Applications

Abstract: Progress in European R&D on powders and PM processing techniques during recent years is briefly surveyed Mechanical properties and their relationship to structure are discussed and examples of new PM products and materials are presented Finally, some comments are given on European R&D as compared with that in the USA and Japan