Showing papers in "Powder Metallurgy in 1983"

Densification of powders by particle deformation

Abstract: Based on a previous experimental study of particle deformation during powder compaction, a model is developed for describing the densification behaviour of an irregular packing of spherical particles. Using the radial density function of a ‘random dense packing’, the increase in both the average size and the number of contact faces are calculated. A simple criterion for local yielding allows the compaction pressure to be determined for relative densities up to 90%. In the final stage of compaction, particle deformation, now constrained by neighbouring contacts, is modelled by extrusion into the remaining pore space. A compaction equation encompassing both stages is presented; its application to non-spherical powders elucidates the role of particle shape during powder densification. PM/0150

Nitrogen Ceramics: Liquid Phase Sintering

Abstract: The role of a minor silicate eutectic liquid phase as a transport medium in sintering hot–pressed silicon nitride (β Si3N4) ceramics was identified in the 1970s. A similar mechanism is applicable to hot–pressed Si–Al–O–N ceramic alloys which offer an advantage in control of the final liquid volume and hence in superior high temperature mechanical properties. By increasing the liquid volume it is possible to densify ceramic alloys without application of pressure at the sintering temperature and hence to fabricate components of complex shape. The Lucas Syalon ceramics typify the new range of pressureless–sintered ceramics based on the β Si3N4 structure. They are fabricated from the ultrafine compound powders α Si3N4, SiO2, Al2O3, Y2O3, and a polytypoid phase (a substitute for A1N). The ceramics consist of submicrometre solid solution crystals of general composition Si3−xAlxOxN4−x(x < 1) within a minor matrix phase which may be either a glassy Y–Si–Al oxynitride or be crystallized to form yttrogarnet...

Machinability of Sintered Steels

Abstract: Etude de l'usinabilite de l'alliage martensitique Distaloys A contenant Fe-Ni 1,8-Cu 1,5-Mo 0,5 fritte. Influence d'additions de soufre, de selenium, de tellure, de MnS, de MoS 2 , de graphite sur l'usinabilite et les caracteristiques mecaniques. Etude sur l'alliage Fe-P 0,45 avec additions de graphite et de MnS ou de Cu, ou de stearate de Zn. Le sulfure de manganese ameliore l'usinabilite sans modifier les caracteristiques du frittage

Internal or die wall lubrication for compaction of Al-powders?

Abstract: The influence of varying lubricant admixtures on the dimensional stability and on the green and sintered strength of Al–Cu compacts has been studied and compared to the properties of compacts made using only die wall lubrication, Admixed lubricant decreases the true green density and also the green strength of the compacts. The lubricant used here also contributes to the dimensional instability of the compacts through the volume effect of a solid state transformation of the wax, and through effects connected with the spreading of liquefied wax and the concomitant enclosure of gas in the compact during heating. Compacts containing lubricant are weakened during dewaxing whereas in lubricant free compacts the corresponding heat treatment produces a slight increase in strength. The sintered strength and the swelling-shrinking behaviour which is typical of the sintering of Al–Cu compacts is also influenced by the lubricant; the effects are compatible with the assumption that remnants of the wax impede...

Liquid Phase Sintering of Nickel Base Superalloys

Abstract: (1983). Liquid Phase Sintering of Nickel Base Superalloys. Powder Metallurgy: Vol. 26, No. 1, pp. 17-22.

Hot Isostatic Press Technology

Abstract: Hot isostatic pressing can be considered a rather new form of technology, even though it was first applied in the mid 1950S. During the past 10 years, however, a large increase in the number of applications has occurred. Equipment design has also evolved greatly. It can be said that hot isostatic pressing has become a generally accepted production technique and with the current state of the available equipment it offers a reliable and advantageous process for many applications. This paper examines some of the components of this process, the applications of which will surely increase as a result or constant developments in equipment design and extensive research in the PM field in general. PM/0229

Powder Metallurgy Techniques in Nuclear Technology

Abstract: (1983). Powder Metallurgy Techniques in Nuclear Technology. Powder Metallurgy: Vol. 26, No. 1, pp. 1-9.

Sintering of Porous Nickel

Abstract: Observations of sintering behaviour have been made during the preparation of nickel with densities below 70% porosity by loose sintering and compacting Inco carbonyl nickel powders. By following the strength development, porosity changes, surface structure modifications, and pore shape changes, it has been shown that densification does not occur until temperatures of about 600°C are used for sintering, although surface diffusion can result in some strength being developed. The major changes in strength and structure do not occur until a temperature of 950°C is reached. PM/0242

Energy Requirements of Structural Components: Powder Metallurgy v. Other Production Processes

Abstract: On the basis of increasing problems of energy availability and costs, the energy requirements for producing structural components by various possible production processes have been estimated. Also the energy requirements in raw material preparation (iron powders, cast iron, construction steels) have been taken into account. The production techniques considered are cold forming, hot forming (or closed die forging), and machining (turning, reaming, milling). For each kind of machining and for various materials the energy requirements corresponding to removal of unit weight or unit volume have been calculated. The comprehensive comparison between PM processes and other production processes has been made considering variable relative amounts of swarfs. The data show that the sintered components are generally less energy consuming than the equivalent ones produced by competitive production techniques. This favourable position of PM can be improved still more by increasing the efficiency of present sint...

Critical Review of Particle Size Analysis

Abstract: A considerable range of equipment exists for particle characterization. The author restricts his survey to recent developments in methods of particle size measurement in the areas of sieving, sedimentation equipment, centrifugal techniques, and light scattering and light attenuation methods. Further sources of information are suggested for aspects of the subject which, for reasons of time and space, could not be considered in the present paper. PM/0225

Raw Material and Energy Conservation in Production of Sintered PM Parts

Abstract: It can be regarded as proven that the PM production of structural parts for the processing industry is a forming method involving minimum utilization of energy and material. In the present paper, data on energy consumption are examined using industrial examples for the individual stages in the process. These stages are the production of the raw material, shaping, sintering, and secondary forming. On the subject of single and double sintering, two examples are given in each case of the economies attainable through the use of PM processes, and some ideas for further reductions in energy consumption are put forward. PM/0239

Effect of Heat Treatment on Structure and Mechanical Properties of Sintered Fe—Ni Alloys

Abstract: Des alliages frittes Fe-Ni ont ete recuits et testes en traction a temperature ambiante et temperature de l'azote liquide. L'effet de la temperature de recuit sur les proprietes de traction est explique par les changements de phase ferrite martensite austenite

Production of Components by Rotary Forging of Sintered Preforms

Abstract: Fabrication de bagues en fer pur et d'engrenages annulaires a dents en spirale en cuivre pur et en acier Mo0,3%. Etude de la densification des ebauches frittees

Short-time induction sintering of hardmetals

Abstract: Based on considerable technological development and comprehensive work in process engineering, a method has been developed for short-time induction sintering of hardmetals which combines increased production throughput with savings in treatment time and improvement of the final product. The process is applicable to conventional WC–Co and WC–TiC–Co hardmetals and can be readily transferred to other cemented carbide systems. PM/0217

Room Temperature Strength and Ductility of Rapidly Solidified White Cast Irons

Abstract: Caracteristiques mecaniques de 3 fontes obtenues par metallurgie des poudres (2.4%C, 3%C et 3%C+1.5%Cr)

Mechanical Properties and Cutting Performance of Sintered M2 High Speed Steel

Abstract: (1983) Mechanical Properties and Cutting Performance of Sintered M2 High Speed Steel Powder Metallurgy: Vol 26, No 3, pp 145-148

Microstructure and Properties of Extruded PM X7091 plate

Abstract: The microstructure and properties of an extruded X7091 plate made using the PM route have been characterized and compared with 7XXX ingot metallurgy alloys. Better combinations of tensile properties are obtained by the rapid solidification and PM consolidation methods. However, anticipated improvement in fatigue crack initiation resistance was not realized owing to the presence of oxides along grain boundaries. In order to obtain improved fatigue properties, processing procedures that dissociate the boundaries from the oxides should be utilized. PM/0275

Reappraisal of Results of Transverse Rupture Tests for Hardmetals

Abstract: (1) The current British Standardl for the determination of the transverse rupture strength for hardmetals recommends two testpieces, designated types A and B, with' the dimensions shown in Table 1. Both testpieces are loaded at midspan as shown in Fig. 1, with the centres I of the support cylinders arranged at 30 mm for type A and 14·5mm for type B. The British Standard reports that testpieces of type B result in strength values which are approximately 10% higher than those of type A. Although the value of the transverse rupture strength R is calculated from the simple bending theory, i.e.

Production of High Strength Aluminium Alloys by Extrusion of Atomized Powders

Abstract: The mechanism of powder consolidation in the extrusion chamber is analysed and it is shown that theoretically the specific pressures required to extrude initial powder compacts will be lower than an equivalent cast billet. The hot working range of metals is thus enlarged and inherently stiffer materials may be extruded. The extrusion of Al alloys from air atomized powders is described and the conditions required for meaningful increases in properties elaborated. The production of Al alloys reinforced by glass is also described and it is shown that although strength levels may be enhanced this type of reinforcement does not lead to a product having a combination of properties significantly more attractive than the cast and wrought product. Consideration is given to other forms of reinforcement. The extrusion of rapidly solidified AI10Mg powder shows that this non-heat treatable alloy has properties comparable with the strongest heat treatable Al alloy. PMj0257

Sintering Furnace — Which One?

Abstract: As the number of components manufactured by the PM route increases, encompassing more complex shapes and a wider range of materials, so the choice of plant available for sintering becomes more varied. The prime problem in sintering is the precise control of the time-temperatureatmosphere cycle. In commercial applications, the need for consistency combined with high production rates has resulted in a predominant use of the continuous furnace, although certain processes are better suited to a batch principle. The author reviews the range of equipment available from which the process engineer can make a decision as to what type of plant is best suited to his needs.

Strengths and Weaknesses of Modern PM Production Methods

Abstract: An attempt is made to explain the financial difficulties of the present day PM industry by a study of its ‘strengths and weaknesses’ which are decreasing or increasing these difficulties. Apart from the general business depression, attention is turned mainly to the lack of information about the mechanical properties of the products and the fact that prices are fixed by small firms, who are following the larger ones. These latter are forced to expand the market, and the cost of this expansion is not appreciated at its true worth. A few ideas are given to reduce costs in large firms. PM/0232