Showing papers in "Powder Metallurgy in 1993"
TL;DR: In this paper, the authors investigated the effect of hard ceramic particles (TiC or NbC) on the sintered high speed steel matrix and found that the steel matrix carbides were modified by a chemical reaction which occurred between the added ceramic particles and the high-speed steel matrix, the result of which was to give a substantial improvement in hardness.
Abstract: Efforts to improve the wear properties of sintered high speed steels have made use of the simultaneous addition of hard ceramic particles (TiC or NbC) alongside particles which might act as a solid lubricant (MnS or CaF 2 ). Preliminary investigations carried out to study interactions between such particles and a sintered high speed steel matrix indicated that the steel matrix carbides were modified by a chemical reaction which occurred between the added ceramic particles and the high speed steel matrix the result of which was to give a substantial improvement in hardness. The solid lubricant remained chemically unaltered by the sintering process, and tended to reduce hardness. Both types of particulate addition raised the sintering temperature needed to achieve full density due to their effect on solidus and liquidus temperatures
62 citations
TL;DR: In this paper, the finite element method is used for simulating the compaction process of powders and ceramics, and macroscopic constitutive laws are presented on the basis of an elastoplastic approach in which the elastic rebound effect after compaction can be taken into consideration.
Abstract: The finite element method is used for simulating the compaction process of powders. Attention is focused on both the metal powders and ceramics on which experiments have been conducted and test data made available for comparison purposes. The implementation of advanced finite element techniques such as adaptive remeshing and frictional interface elements are briefly discussed. Macroscopic constitutive laws are presented on the basis of an elastoplastic approach in which the elastic rebound, or springback, effect after compaction can be taken into consideration. Two case studies are presented to demonstrate the validation of the method
51 citations
TL;DR: In this paper, the Supersolidus Sintering of high speed steels is described as a special case of Molybdenum-based alloys, and the authors present a detailed discussion.
Abstract: (1993). Supersolidus Sintering of High Speed Steels: Part 1: Sintering of Molybdenum Based Alloys. Powder Metallurgy: Vol. 36, No. 3, pp. 213-219.
38 citations
TL;DR: Sintered high speed steels (HSSs) are assuming an increasingly important role as wear resistant and cutting tool materials, areas in which they are in competition with cemented carbides as mentioned in this paper.
Abstract: Sintered high speed steels (HSSs) are assuming an increasingly important role as wear resistant and cutting tool materials, areas in which they are in competition with cemented carbides. Research o...
32 citations
TL;DR: The intermetallic Fe3Al has been produced by the heat treatment of mechanically alloyed iron and aluminium powders and X-ray diffraction analysis has revealed the presence of a mixture of the intermetall FeAl and elemental iron.
Abstract: The intermetallic Fe3Al has been produced by the heat treatment of mechanically alloyed iron and aluminium powders. X-ray diffraction analysis of the mechanically alloyed powder revealed the presence of a mixture of the intermetallic FeAl and elemental iron. Following subsequent heat treatment, only the B2 (FeAl) structure was detected. This is unusual since the actual chemical composition of the compound was that of Fe3Al (D03). Mechanical alloying is a technique which introduces a very large degree of structural damage and the high number of defects created are responsible for the production of the B2 structure in preference to the D03 structure. Comparison has been made with the same material produced by rapid solidification, since a similar disordering effect has been observed using this technique. Hardness testing of the heat treated material indicated that the intermetallic produced by mechanical alloying is ductile and this has been attributed to a very fine grain size and good homogeneity....
24 citations
TL;DR: In this article, the surface chemistry of nickel ultrafine powders (UFPs) was examined by temperature programmed desorption (TPDP) measurements by measuring their dimensional changes, specific surface areas, crystallite sizes, and structural changes.
Abstract: The surface chemistry of nickel ultrafine powders (UFPs) was examined by temperature programmed desorption (TPD) measurements. Nickel UFPs exposed to air contained NiO and Ni(OH) 2 . The oxide phase increased during heating in vacuum mainly due to the adsorbed gases and to the decomposition of the Ni(OH) 2 . Sintering characteristics of three types of nickel UFP in vacuum and a stream of hydrogen were examined by measuring their dimensional changes, specific surface areas, crystallite sizes, and structural changes. In the case of vacuum sintering of clean nickel UFPs, neck growth by surface diffusion occurs even at room temperature and densification by grain boundary and/or lattice diffusion starts below 400 K
20 citations
TL;DR: The fracture toughness of a sintered high speed steel which contained copper phosphorus to aid sintering and to which had been added either titanium carbide or vanadium carbide particles as a means of improving its wear resistance was measured.
Abstract: The fracture toughness was measured of a sintered high speed steel which contained copper phosphorus to aid sintering and to which had been added either titanium carbide or vanadium carbide particles as a means of improving its wear resistance. Relatively low fracture toughness values were obtained and these were attributed to embrittlement caused by the presence of phosphorus, but the fracture toughness was relatively independent of the presence of any porosity or carbide enrichment. Reductions in bend strength brought about by heat treatment and by the carbide enrichment process were explained by the effects that the carbide additives had on crack initiation and by the changes caused to the fracture toughness of the steel matrix. In spite of the reductions in strength which occurred as a result of introducing ceramic carbide particles into the steel matrix, useful and promising properties were still obtained. PM/0601
19 citations
TL;DR: In this paper, the advantages of sintering high speed tool steels in a N 2 -H 2 -CH 4 atmosphere relative to in a vacuum have been investigated, and it was shown that an increase in temperature above the optimum for sinterding (minimum temperature at which the theoretical density is reached) causes a significant increase in the grain size, due to the dissolution of carbides and the increased amount of liquid phase.
Abstract: The advantages of sintering high speed tool steels in a N 2 -H 2 -CH 4 atmosphere relative to in a vacuum have been investigated. An increase in temperature above the optimum for sintering (minimum temperature at which the theoretical density is reached) in a vacuum causes a significant increase in the grain size, due to the dissolution of carbides and the increased amount of liquid phase. In addition, this liquid phase transforms on cooling to produce undesirable microstructures containing continuous eutectic films. Conversely, oversintering in the N 2 -H 2 -CH 4 atmosphere results in only a small increase in the grain size and the absence of eutectic carbides
16 citations
TL;DR: In this article, the sintering behavior of grade M(P×30) water atomized high speed steel powders under vacuum and an N2-H2-CH2 atmosphere is analyzed.
Abstract: The sintering behaviours of grade M(P×30) (composition similar to ASP 30) water atomised high speed steel powders under vacuum and an N2–H2–CH2 atmosphere are analysed. Sintering under the gas mixture allows high densities (99–100% theoretical) to be obtained at temperatures 30–45 K lower than for vacuum sintering of the same steel. Chemical analysis of gas sintered specimens has shown that a large amount of nitrogen is absorbed during atmosphere sintering (0·45–0·75%). Although MC and M6C primary particles are observed during vacuum sintering, in gas sintering the MC carbides change to MX carbonitrides. These particles are very fine (1 μm) and very resistant to coarsening during oversintering. The presence of these carbonitrides restricts the grain growth at and above the optimum sintering temperature. Sintering in the gas atmosphere allows significant oversintering to be reached (40 K) without the formation of eutectic films or excessive grain growth. PM/0566
14 citations
TL;DR: The results of tensile tests showed that microstructure plays a major part in determining mechanical properties, and that ductility requires an optimal composite micro-structure as mentioned in this paper, which is discussed in relation to the deformation and fracture behaviour of the alloys, by means of an extensive fracto graphic analysis.
Abstract: Phosphorus alloyed sintered steels of chemical composition in the range 0·25–0·7 wt-%C and 0·45–0·8 wt-%P produce alloys with pore morphologies characterised by shape factors varying between 0·52 and 0·68 and microstructures characterised by different percentages of phases with high (pearlite and phosphorus rich ferrite) and low (low phosphorus ferrite) hardness. The results of tensile tests show that microstructure plays a major part in determining mechanical properties. In particular, while tensile strength is improved when high hardness constituents predominate, ductility requires an optimal composite microstructure. This is discussed in relation to the deformation and fracture behaviour of the alloys, by means of an extensive fracto graphic analysis. The results of fatigue testing show that the alloy Fe–0·7C–0·8P, characterised by a predominantly pearlitic microstructure, has a lower fatigue limit than the alloy Fe-0·25C–0·6P which is predominantly ferritic, although the former has a higher te...
14 citations
TL;DR: In this paper, a study of the processing of steel of the same composition by an alternative PM route, using water atomised powder, die compacted and vacuum sintered, in order to obtain near net shapes.
Abstract: ASP60 high speed steel is produced from gas atomised powder, subsequently encapsulated and hot isostatically pressed below the solidus temperature, the billets being further rolled as bars or rods. The microstructures of this material show a very fine carbide distribution which results in high values of fracture strength and wear resistance. This paper presents results of a study of the processing of steel of the same composition by an alternative PM route, using water atomised powder, die compacted and vacuum sintered, in order to obtain near net shapes. The density achieved by supersolidus liquid phase sintering at ∼ 1240° C was ∼ 99.9 % of the theoretical, but the carbides were coarser, ∼ 20 μm, compared with < 4 μm for ASP60
TL;DR: In this paper, the effects of cold working and annealing at temperatures of up to 700° C on a series of binary tungsten-copper composites was studied.
Abstract: The effects of cold working and annealing at temperatures of up to 700° C on a series of binary tungsten- copper composites was studied. Strength was increased with increasing cold work and tungsten content. The increases in hardness of the composites, for deformations up to 25%, could be modelled by the assumption that deformation was substantially confined to the copper phase. Confirmation of this was provided by the lack of elongation of the tungsten particles after deformation and the hardness of the composites, annealed at 450° C, which showed that there was no increase in hardness attributable to cold working of the tungsten. This cold worked tungsten would not undergo recrystallisation at such low annealing temperatures
TL;DR: In this article, the ultrasonic gas atomisation of pure aluminium and aluminium alloy Al5Mn2.5Cr was applied to a room temperature to a humid atmosphere for 1 h, 1 day and 1 week.
Abstract: Rapidly solidified powders of pure aluminium and aluminium alloy Al5Mn2.5Cr were produced by the ultrasonic gas atomisation method. After exposure to a humid atmosphere the powders were analysed using ESCA and Auger spectroscopy. The powders were exposed at room temperature to a humid atmosphere for 1 h, 1 day and 1 week. The relative humidities (RH) were 60% and 80%. During exposure to conditions of 60% RH for 1 day or 80% RH for 1 h, a thin layer of hydroxide formed on the powder surfaces. Exposure for longer times causes formation on the surface of thicker Al(OH) 3 particles which were formed by hydration of the oxide and corrosion of the aluminium metal. The amount of Al(OH), formed increases with exposure time and relative humidity
TL;DR: In this article, microstructural analysis of quenched hot plane strain compression specimens has revealed key temperatures, strain levels, and strain rates in the development of the microstructure of compacted aluminium 2014 powder.
Abstract: Microstructural analysis of quenched hot plane strain compression specimens has revealed key temperatures, strain levels, and strain rates in the development of the microstructure of compacted aluminium 2014 powder. The removal of the rapidly quenched cast microstructure in the powder feedstock, the obliteration of prior powder particle boundaries, the onset of both partial and complete recrystallisation, and the beginning of hot shortness have been categorised in terms of critical temperatures, strains, and strain rates. It has been shown that restoration processes can produce non;uniform microstructures unless certain strain rates are achieved
TL;DR: In this paper, the search for a suitable degassing temperature for two high temperature Al-Fe-Ce alloys consolidated by hot extrusion is described, and the results show that the successful distribution depends on the efficient removal of water from the hydrated oxide.
Abstract: The use of powder metallurgy in the aluminium industry offers many advantages, e.g., improved homogeneity, refined microstructures, novel alloy compositions, etc. However the presence of an 'aluminium oxide surface layer on the powder particles is the cause of some concern. This aluminium oxide is prone to hydration. The mechanical properties of powder metallurgical aluminium alloys can be improved by uniformly distributing the aluminium oxide throughout the matrix. This successful distribution depends on the efficient removal of water from the hydrated oxide. Vacuum degassing has been used to achieve this objective. The present paper reports on the search for a suitable degassing temperature for two high temperature Al-Fe-Ce alloys consolidated by hot extrusion
TL;DR: In this paper, it is shown that the genesis of metal powder in ancient India is related to the discovery of naturally occurring gold powder in the form of alluvial placer deposits commonly found in river beds.
Abstract: New literary and documentary evidence on powder technology in ancient and medieval India is presented and discussed. It is shown that the genesis of metal powder in ancient India is related to the discovery of naturally occurring gold powder in the form of alluvial placer deposits commonly found in river beds. Philological explanation of some ancient Sanskrit words used for denoting gold confirms the antiquity of alluvial placer gold powder. The ‘Pipīlaka’ (ant) gold powder of the ‘Mahābhārata’, a typical placer gold powder obtained by washing auriferous sands dug and collected by ants in ancient India, is discussed. This was of great interest in ancient India because of its relatively high purity. It is shown that the ant gold powder reported by Herodotus and others has a different source from the Pipīlaka gold powder of the Mahābhārata: it was obtained by washing auriferous sands dug and collected by some animals, probably marmots, in the desert part of Ladakh in north western India. Literary e...
TL;DR: In this article, the thermoviscoplastic response and the densification behavior of porous alloy steel preforms under hot and upsetting conditions are investigated at various temperatures and strain rates.
Abstract: The thermoviscoplastic response and the densification behaviour of porous alloy steel preforms under hot upsetting conditions are investigated at various temperatures and strain rates. A higher den...
TL;DR: In this article, the authors demonstrate that the addition of nickel can inhibit the swelling of sintered iron and aluminium powder compacts and promote densification of the samples, and that where pores exist, they are formed in the intermetallic Fe 3 Al compound phase.
Abstract: Reactive sintering of rolled compacts consisting of elemental iron and aluminium powders has been studied. The results demonstrate that the addition of nickel can inhibit the swelling of sintered iron and aluminium powder compacts and promote densification of the sintered samples. Reactive sintering of rolled compacts of the powder mixture is an efficient method of obtaining high final densities (> 99% theoretical). Reactive sintering produces a two phase structure. It was found that where pores exist, they are formed in the intermetallic Fe 3 Al compound phase and that these pores largely disappear when nickel is added
TL;DR: In this article, the surface characteristics and the reflective properties of flake metal products depend critically on the shape of the powders before milling, and the importance of controlling flake morphology and reflective properties is demonstrated by the outstanding quality of the fingerprints which could be revealed on light or dark backgrounds of various textures using the pure iron and stainless steel flake products.
Abstract: Laboratory scale atomization/milling trials have established that the surface characteristics and the reflective properties of flake metal products depend critically on the shape of the powders before milling. For both pure iron and austenitic stainless steel flake particles, superior reflective properties were recorded for flake with smooth surfaces and rounded outlines produced by milling spherical powders, compared with flake having rough surfaces and jagged outlines obtained by milling irregularly shaped atomised powders. The importance of controlling flake morphology and reflective properties is demonstrated by the outstanding quality of the fingerprints which could be revealed on light or dark backgrounds of various textures using the pure iron and stainless steel flake products. PM/0598
TL;DR: In this paper, a computer program has been written to produce simulated images of powder size distributions using a fast, transputer based image processing system, which can be displayed in monochrome for comparison with scanning electron micrographs or in size coded colour to illustrate the distribution width.
Abstract: A computer program has been written to produce simulated images of powder size distributions using a fast, transputer based image processing system. The images can be displayed in monochrome for comparison with scanning electron micrographs or in size coded colour to illustrate the distribution width. The technique has been used to generate images from number or mass distributions obtained from a variety of instrumental and microscopical powder sizing methods, in order to clarify the advantages and disadvantages of the various methods. For example, serious problems have been identified with the data obtained from a laser diffraction method for powder sizing in class sizes below about 0·5 μm. PM/0605
TL;DR: In this article, commercial purity aluminium containing up to 8 wt-% mica have been prepared by a PM route, and three sets of identical green compacts were sintered at 883 K for 1 h under pure nitrogen and hydrogen atmospheres and in vacuo (10 mPa).
Abstract: Composites of commercial purity aluminium containing up to 8 wt-% mica have been prepared by a PM route. Aluminium and mica powders were mechanically mixed and compacted at a pressure of 472 MPa. Three sets of identical green compacts were sintered at 883 K for 1 h under pure nitrogen and hydrogen atmospheres and in vacuo (10 mPa). Sintered density, densification parameter, hardness, compressive strength, and wear of the sintered composites have been examined. The 4 wt-% composite sintered in nitrogen possessed the optimum properties and showed substantially better wear resistance than has previously been reported for similar composites prepared by a liquid metallurgy route. PM/0562
TL;DR: In this paper, the sintering behavior of a group of copper spheres in a three-dimensional close packed compact arrangement was investigated in order to examine the Sintering mechanisms previously proposed on the basis of a two-particle model and to identify a possible relation-ship between sinterability and packing geometry of sintered particles.
Abstract: The sintering behaviour of a group of copper spheres in a three-dimensional close packed compact arrangement was investigated in order to examine the sintering mechanisms previously proposed on the basis of a two particle model and to identify a possible relation-ship between sinterability and packing geometry of sintered particles. Spherical copper powders with particle sizes of 0.83, 0.76, and 0.65 mm were close packed in an alumina mould of tetrahedral shape and sintered at 900, 950, and 1000°C in hydrogen for a maximum of 20 h. Volume diffusion seems to be the dominant mechanism for material transport in the present sintering system. This result was also supported by the measured value of activation energy for the sintering process, 200 kJ mol −1