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Showing papers in "Powder Metallurgy in 2010"


Journal ArticleDOI
TL;DR: In this article, the cold compaction and vacuum sintering behavior of a Ti powder and a Ti hydride powder were compared, and the authors developed a master sinting curve model for both powders.
Abstract: The cold compaction and vacuum sintering behaviour of a Ti powder and a Ti hydride powder were compared. Master sintering curve models were developed for both powders. Die ejection force, green str...

83 citations


Journal ArticleDOI
TL;DR: In this article, a review of the low-cost press and sinter methods of powder metallurgy, consisting of cold pressing of mixed elemental powders followed by sintering without the application of external pressure, is presented.
Abstract: The development of novel extractive metallurgy techniques for titanium offers the prospect of lower cost Ti powder and therefore wider application of Ti. This review is largely confined to coverage of the low cost press and sinter methods of powder metallurgy, consisting of cold pressing of mixed elemental powders followed by sintering without the application of external pressure. Cold die compaction, sintering behaviour and densification are reviewed in detail. Some information on powders and cold isostatic pressing is included. Microstructure, mechanical properties and applications are considered in less detail. The review deals mostly with the sintering of alloys, but there is some reference to synthesis of intermetallic compounds, such as the shape memory alloy NiTi and titanium aluminides for high temperature applications. Densification is discussed in terms of the four fundamental processing variables: compaction pressure, particle size, sintering temperature and sintering time. Other factors such as alloy composition, the form of alloying addition, type and impurity content of powders and heating rate are also considered. © 2010 Institute of Materials, Minerals and Mining.

80 citations


Journal ArticleDOI
TL;DR: In this paper, the authors investigated the influence of the particle characteristics of powder to the mixing stage of the powder injection molding process to identify the best procedure with which to evaluate the optimal solids loading for feedstock fabrication.
Abstract: The aim of this work is to investigate the influence of the particle characteristics of powder to the mixing stage of the powder injection moulding process to identify the best procedure with which to evaluate the optimal solids loading for feedstock fabrication. To perform the present study, powder blends that are made from three bronze and four Inconel 718 powders, with different particle size distributions and morphologies, are mixed with a binder system that is based on polyethylene and wax. Powder–binder blends are prepared by varying the powder content to study how the powder characteristics affect the optimal solids loading. In addition, a new method is presented for determining the optimal solids loading in powder injection moulding feedstocks through the activation energy calculation of powder–binder blends that are prepared with different powder contents. This novel method is compared with the optimal loading values that have been determined by other ways as torque rheometry, determinati...

33 citations


Journal ArticleDOI
TL;DR: A critical review of the current state of the art of welding powder metallurgy components is presented in this article, where the intention is to identify preferred joining processes and identify technology gaps in joining of powder metal injection molded (MIM) parts, in terms of initial processing and technology gaps.
Abstract: Powder metallurgy (PM) processes have high productivity and are ideal for making near net-shape parts of complex geometries from a range of materials, which maximises material utilisation, and minimises or eliminates secondary operations such as machining. The secondary operations that are common for components made via liquid metal processing may result in additional manufacturing steps with substantial cost and waste implications. Despite this obvious advantage of PM components, including powder metal injection moulded (MIM) parts, the joining of sintered powder materials has been associated with difficulties related to their inherent characteristics, such as porosity, contamination and inclusions, at levels which tend to influence the properties of a welded joint. A critical review of the current state of the art of welding PM components is presented. The intention is to identify preferred joining processes and identify technology gaps in joining of PM parts, in terms of initial processing and...

30 citations


Journal ArticleDOI
R. D. Li, J. H. Liu, Y. S. Shi, Lin Zhang, M. Z. Du 
TL;DR: In this paper, the influence of processing parameters on the densification and microstructure of alloys were investigated through diffraction, energy dispersive X-ray spectroscopy and SEM respectively.
Abstract: 90W–7Ni–3Fe parts were fabricated via selective laser melting. The influences of processing parameters on the densification and microstructure were highlighted in this work. The compositions and microstructures of as produced alloys were investigated through X-ray diffraction, energy dispersive X-ray spectroscopy and SEM respectively. It is found that the phase structures are not evidently influenced by processing parameters. The density, surface characteristic and microstructure of final parts are dependent on processing parameters. Decreasing the scan speed is able to eliminate balling effect, diminish surface roughness, induce more melted W particles and yield better densification. Narrowing the scan interval is capable of creating a better bonding condition between scan tracks, obtaining a lower surface roughness and improved density. Decreasing the powder layer thickness is favourable for the layers bonding, leading to a higher densification.

19 citations


Journal ArticleDOI
TL;DR: In this article, the sintering behavior of injection moulded components in 316L stainless steel powder is investigated by means of the bending and dilatometric tests in the furnace.
Abstract: The sintering behaviours of injection moulded components in 316L stainless steel powder are investigated by means of the bending and dilatometric tests in the furnace. Various thermal cycles are realised for different tests. The experimental results are used to determine the parameters of uniaxial viscosity and sintering stress in the viscoplastic constitutive law, which is important for description of the sintering behaviours. The sintering models are implemented into the finite element solver, incorporated with the identified parameters, to simulate the size change and shape distortion of powder injection moulded components during the sintering process. The sintering simulation takes into account the green inhomogeneity caused by powder binder segregation in the previous injection process. The simulation results for the sintering process of a three-dimensional wheel component are compared with the experimental ones. It proved validity of the sintering model and the approaches for parameter deter...

18 citations


Journal ArticleDOI
TL;DR: In this article, the densification behavior of a boron doped 316L stainless steel during supersolidus liquid phase sintering (SLPS) is treated using a master sinterding curve (MSC) concept based on the integral time-temperature work of sinterings.
Abstract: Supersolidus liquid phase sintering (SLPS) is an important liquid phase sintering variant that is used to densify prealloyed powders. The densification behaviour of a boron doped 316L stainless steel during SLPS is treated using a master sintering curve (MSC) concept based on the integral time–temperature work of sintering. With this approach, the MSC analysis is able to identify a fundamental change in the densification rate that is indicative of a mechanistic shift during SLPS.

18 citations


Journal ArticleDOI
TL;DR: In this article, the authors reported that the onset of severe swelling during heating was associated with the formation of liquid phase as the solidus was crossed and that the mechanism of swelling is high gas pressure within closed pores.
Abstract: Compacts were prepared by pressing titanium and titanium hydride powders mixed with nickel powder and sintering under vacuum. Severe swelling was observed only for compacts based on TiH2 powder. Pressure changes in the vacuum furnace, dilatometry results and mass loss data all indicate that dehydrogenation of TiH2 powder compacts occurs at lower temperature than any significant sintering. Swelling appears to have been caused by a contaminant in the TiH2 powder rather than hydrogen. The onset of severe swelling during heating was associated with the formation of liquid phase as the solidus was crossed. However, some swelling appears to take place under solid state sintering conditions. Various results indicate that the mechanism of swelling is high gas pressure within closed pores. Large pores appear to form by breakage of ligaments between small pores followed by opening of the pore. It appears that the use of (uncontaminated) TiH2 powder in place of Ti powder would allow the benefit of lower gree...

18 citations


Journal ArticleDOI
Y. Xiong, M. Kim1, O. Seo1, Julie M. Schoenung, S. Kang1 
TL;DR: In this article, the effect of the laser engineered net shaping (LENS) process on the microstructure and mechanical properties of (Ti,W)C-Ni solid solution cermets was investigated.
Abstract: The effect of the laser engineered net shaping (LENS) process on the microstructure and mechanical properties of (Ti,W)C–Ni solid solution cermets was investigated. Nano-(Ti,W)C–Ni powder was synthesised, spray dried and densified by two different processes: sintering and LENS. Furthermore, all results were compared with conventional micrometre sized TiC–WC–Ni cermets. Solid solution (Ti,W)C–Ni cermets made by sintering resulted in a coreless and ultra fine microstructure, while the LENS processed specimens revealed inhomogeneous microstructure and particle coarsening. The hardness values of the LENS processed specimens range from 15 to 20 GPa, which is higher than for the ultra fine and conventional sintered composites (∼12 GPa). The measured toughness values show greater variability.

17 citations


Journal ArticleDOI
TL;DR: In this article, a mixture of 85W −15Cu (wt-%) powders with a composition of W and 15Cu were prepared by mixing, milling and mechanical alloying of W powders and electroless Cu coating onto W powder.
Abstract: Powders with a composition of 85W–15Cu (wt-%) were prepared by mixing, milling and mechanical alloying of W and Cu powders and electroless Cu coating onto W powder. Sinterability was improved by mechanical alloying and coating. The improvement due to mechanical alloying comes from a reduced particle size, assisted by activated sintering from transition element contamination in milling. Coating improved the copper dispersion, packing densities and led to a microstructure having reduced number of W–W particle contacts after compaction. Accordingly, rearrangement on liquid formation resulted in improved densification. Since copper wetting on tungsten is sensitive to oxygen contamination, coated powders ensure liquid copper dispersion throughout the compact without concern over wetting and liquid flow during liquid phase sintering.

13 citations


Journal ArticleDOI
TL;DR: In this paper, a fine tungsten powder with an average size of 8 μm was coated by electroless nickel plating with hydrazine and sodium hypophosphite reducing agents to obtain Ni and Ni-P coatings.
Abstract: Fine tungsten powder with an average size of 8 μm was coated by electroless nickel plating with hydrazine and sodium hypophosphite reducing agents to obtain Ni and Ni–P coatings, respectively. The influence of process parameters such as temperature, pH and time of electroless plating was investigated. As coated composite powders were characterised by energy dispersive spectrometer analysis and scanning electron microscopy. It was found that, high homogeneity Ni/Ni–P coatings are deposited around the tungsten particles. Also it was shown that deposited mass on the powders increases as the temperature and pH of bath increase, but with different deposition rates depending on coating type. Furthermore, other results indicate that at higher pH values, the P content in the Ni–P coating decreases, leading less impurity in the final composite powders.

Journal ArticleDOI
TL;DR: In this article, the effects of various sintering parameters (temperature, time and nitrogen pressure) on the density, nitrogen content and the mechanical properties of high nitrogen nickel free austenitic stainless steel (0Cr−17Mn−11Mo−3N) prepared by powder injection molding were investigated, and the influence of solution annealing on the microstructure and mechanical properties was also discussed.
Abstract: The effects of various sintering parameters (temperature, time and nitrogen pressure) on the density, nitrogen content and the mechanical properties of high nitrogen nickel free austenitic stainless steel (0Cr–17Mn–11Mo–3N) prepared by powder injection moulding were investigated, and the influence of solution annealing on the microstructure and mechanical properties was also discussed. The results show that the optimal sintering conditions are as follows: sintering temperature 1300°C, sintering time 2 h and nitrogen pressure 0·1 MPa, under which a favourable combination of the relative density of 99·1% and the nitrogen content of 0·78 wt-% can be obtained. After solution annealing at 1150°C for 90 min, the yield strength and ultimate tensile strength can reach 580 and 885 MPa respectively, which are about 2·9 and 1·7 times greater than those of 316L Metal Injection Molding (MIM) stainless steel. Before solution annealing, the sintered specimens mainly consist of γ-austenite, α-ferrite and network ...

Journal ArticleDOI
TL;DR: In this article, gas and water atomised 316L stainless steel powders with similar powder morphology and particle size were injection molded and sintered, and microstructural analysis revealed that SiO2 particles dispersed as a second phase in the compacts prepared from the atomised powder, which accounts for the property behaviour.
Abstract: Gas and water atomised 316L stainless steel powders with similar powder morphology and particle size were injection moulded and sintered. The results show that compacts prepared from the gas atomised powder exhibit higher density and tensile strength, whereas those prepared from the water atomised powder exhibit higher elongation, finer grain size and superior corrosion resistance. Chemical analysis shows that the water atomised powder has a higher Si and O content, and microstructural analysis of the sintered compacts reveals that SiO2 particles disperse as a second phase in the compacts prepared from the atomised powder, which accounts for the property behaviour. Due to the presence of SiO2, the porosity increases, whereas the pore coarsening and grain growth are inhibited. Besides, SiO2 particles can also improve the passivation effect of stainless steel, and hence increase the corrosion resistance.

Journal ArticleDOI
TL;DR: In this paper, the effect of melt chemical composition (silicon content) on the size characteristics and morphology of the resultant powder particles was investigated and it was concluded that the minimum average size in the powder particle size is achieved for Al-6Si alloy attributable to its relatively low fluidity.
Abstract: Powder particles of a commercially pure aluminium as well as some Al–Si alloys containing different amounts (6, 12 and 20 wt‐%) of Si were produced via a relatively new process termed solid assisted melt disintegration (SAMD) method. In this process, melt disintegration is achieved by introducing a solid media (i.e. NaCl) into the molten metal and stirring the slurry to produce droplets which form the powder particles after solidification. The effect of melt chemical composition (silicon content) on the size characteristics and morphology of the resultant powder particles was investigated. It was concluded that the minimum average size in the powder particle size is achieved for Al–6Si alloy attributable to its relatively low fluidity. However, SEM studies revealed that the silicon content did not have any considerable effect on the morphology of the SAMD produced powders. The powders of diameter above 38 μm were mostly spherical while powders less than 38 μm were agglomerated and showed irregular...

Journal ArticleDOI
TL;DR: In this paper, the advantages and disadvantages of warm powder warm die processing and die heating only have been discussed with practical part production with mechanical properties achievable via high density processing, with the main asset of the powder metallurgy route is its ability to produce structural components that meet functional requirements in a cost efficient manner.
Abstract: The main asset of the powder metallurgy route is its ability to produce structural components that meet functional requirements in a cost efficient manner. Many PM parts are produced at densities lower than 7·1 g cm−3 because achieving higher densities often requires additional processing steps, which result in increased part cost. Although warm powder warm die processing is not new, new methods that employ die heating only have been introduced that enable high green density via single press/single sinter. This simplified processing will potentially lead to greater market acceptance of high density PM parts. However, drawbacks of die heat only are part size restrictions and higher compaction loads. Both processes are useful in the production of high density PM components. This paper will detail the advantages and disadvantages of both processes. Practical part production will be discussed with mechanical properties achievable via high density processing.

Journal ArticleDOI
TL;DR: In this paper, a detailed transmission electron microscopy study of the structure of aluminium nitride formed during sintering of powder injection molded aluminium is presented, where a polycrystalline layer formed on Al particle surfaces exposed to a nitrogen atmosphere.
Abstract: A detailed transmission electron microscopy study of the structure of aluminium nitride formed during sintering of powder injection moulded aluminium is presented. A polycrystalline layer formed on Al particle surfaces exposed to a nitrogen atmosphere. This layer consisted of fine, rod-like crystallites of hexagonal AlN typically aligned normal to the Al surface. A double layer of AlN separated by a thin layer of Al was observed at the interfaces between Al grains. In this report, the structure of the nitride is characterised and its influence on sintering is discussed.

Journal ArticleDOI
TL;DR: In this article, microstructural analyses were performed by scanning electron microscopy (SEM) coupled with energy dispersive X-ray spectroscopy (EDS), Xray diffraction (XRD), and simultaneous thermal analysis (STA) in order to determine the temperature and chemical composition of the phases formed during sintering.
Abstract: Al–5·6Zn, Al–5·6Zn–2·5Mg and Al–5·6Zn–2·5Mg–1·6Cu (wt-%) powder blends were compacted at 350 MPa and sintered in nitrogen at different temperatures to study microstructural evolution during sintering. Densification, dimensional changes and mechanical properties of the Al alloys were investigated. Microstructural analyses were performed by scanning electron microscopy (SEM) coupled with energy dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), and simultaneous thermal analysis (STA) in order to determine the temperature and chemical composition of the phases formed during sintering. It was shown that various liquids and intermetallic phases including Al0·71Zn0·29 at 438°C, Al0·58Mg0·42 and Al32(Mg,Zn)49 at 450°C, Al3Mg3Zn3 at 500°C, and most probably η and S phases at 600°C were formed during the heating cycle. Magnesium was found to be the most effective alloying element on the densification and microstructural development during sintering, and eventually on the mechanical properties of...

Journal ArticleDOI
TL;DR: In this paper, the authors investigated the microstructure and microcomposition of fine ferromanganese particles in dry 25%H2 + 75%N2 for 3 min at 770, 1040, 1080, 1170 and 1220°C.
Abstract: Mn was introduced, with graphite, as fine ferromanganese particles to form compacts of Fe–3%Mn–0·5%C. Each was sintered in dry 25%H2 + 75%N2 for 3 min at 770, 1040, 1080, 1170 and 1220°C respectively, held for 3 min and quenched. The surface of a successively heated specimen was similarly examined. Specimens were sectioned and, especially the reacting ferromanganese particles and adjoining regions, investigated using light and scanning electron microscopy and EDX. Development of microstructure and microcompositions during sintering was related, from 740°C, to diffusion and condensation of Mn vapour on iron particle surfaces and subsequent chemical reactions. Above 1080°C microstructures included features resulting from a transient liquid phase, in accord with a ∼45 wt%Mn ternary eutectic calculated by ThermoCalc. The thicknesses of the highly Mn enriched regions were substantially higher than those resulting from bulk Mn diffusion in the Fe lattice; our interpretation invokes predominant operation...

Journal ArticleDOI
TL;DR: In this article, the effects of stearic acid (SA) as the process control agent on powder characteristics were investigated using X-ray diffractometer, laser particle size analysis and scanning electron microscopy.
Abstract: The Fe–48 at.-%Al powder used for powder injection moulding (PIM) was prepared by mechanical alloying in a high energy planetary ball mill and subsequent vacuum annealing. The effects of stearic acid (SA) as the process control agent on powder characteristics were investigated using X-ray diffractometer, laser particle size analysis and scanning electron microscopy. The dependence of solvent debinding efficiency of PIM feedstock on the powder characteristics was also studied. The results indicate that a low SA content for ball milling helps to prepare near spherical, coarse powder particles that exhibit good solvent debinding efficiency. On the contrary, a high SA content leads to thin layered, small particles with poor PIM solvent debinding efficiency. An intermediate SA content such as 1 wt-% makes the ball milled powder combine the advantageous characteristics for PIM process.

Journal ArticleDOI
TL;DR: In this article, the factors that contribute to the structure and mechanical properties of sintered Mn steels are summarised, and the PM industry follows also possibilities in order to develop Ni free, Ni-free, and diffusion alloyed Ni-containing sinterred steels which render as high mechanical properties as diffusion alloying Ni containing sintered steels and further fulfil the requirements of health protection.
Abstract: Ni, Cu and in some cases Mo are the alloying elements which have traditionally been used in sintered steels. High performance of powder metallurgy (PM) structural parts from Fe powders is reached mainly by alloying of Ni. The use of Mn in Fe base PM structural parts has been avoided because of its high affinity to oxygen. It is difficult to sinter Mn steel, without oxidation, in industrial atmospheres. However, the PM industry follows also possibilities in order to develop Ni free sintered steels which render as high mechanical properties as diffusion alloyed Ni containing sintered steels and further fulfil the requirements of health protection. In recent years Mn have been introduced as alloying element in Fe based structural parts, on laboratory scale and also for pilot scale production. In this paper the factors that contribute to the structure and mechanical properties of sintered Mn steels are summarised.

Journal ArticleDOI
TL;DR: In this article, an attempt has been made to synthesis Mo-Si-B nanocomposite alloys using a combination of mechanical alloying (MA) and heat treatment in various primary elemental compositions.
Abstract: In this study, an attempt has been made to synthesis Mo–Si–B nanocomposite alloys using a combination of mechanical alloying (MA) and heat treatment in various primary elemental compositions. For this purpose, Mo–14Si–10B, Mo–57Si–10B and Mo–47Si–23B (at.‐%) elemental powders were separately milled using an attritor mill. Mechanically alloyed (MAed) powders were annealed in an atmosphere controlled furnace under constant temperature for 10 h. Metallurgical characteristics of MAed and/or annealed powders were evaluated by atomic absorption spectrometry, SEM, TEM and X‐ray diffraction. The results did not show any formation of related intermetallics after MA. However, MoSi2, Mo5Si3, Mo5SiB2, MoB and Mo were successfully formed, when the MAed Mo–57Si–10B powders were subjected to annealing at a high temperature.

Journal ArticleDOI
TL;DR: In this paper, a new three-parameter Weibull analysis is presented, in which it is taken to be the fracture strength minus six standard deviations, in case of powder metallurgy manganese steels are under commercial consideration and this approach is applied to 12 variants of such laboratory processed specimens.
Abstract: Powder metallurgy (PM) parts acceptance is determined by compositional and processing parameters and their controls. Statistical procedures are used for assessment; normal distribution and 'six sigma' appear to predominate. For fatigue of metallic materials and strengths of ceramics, fibres and composites, however, Weibull probability of survival analyses are widely used. The original analysis considers a threshold stress at which the probability of failure is zero. This stress is frequently taken to be zero, simplifying the analysis to two parameters. The yield stress has been suggested for the threshold stress, probably not sufficiently conservative for less ductile PM materials. A new three-parameter Weibull analysis, in which it is taken to be the fracture strength minus six standard deviations, is presented. Powder metallurgy manganese steels are under commercial consideration and this approach is applied to 12 variants of such laboratory processed specimens. It is compared with the two-param...

Journal ArticleDOI
TL;DR: In this paper, the influence of macro-and micropores on carbon diffusion depth in the process of vacuum carburising of iron compacts with density within 5·6 to 6·4 g cm-3.
Abstract: The research work was aimed at determining the influence of macro- and micropores on carbon diffusion depth in the process of vacuum carburising of iron compacts with density within 5·6 to 6·4 g cm–3. Vacuum carburising of the compacts made of iron powder ASC100·29 was performed at 1050°C in a laboratory vacuum furnace. The carburising effects were compared and evaluated in terms of thickness, structure and surface carbon content of the case. Simplified carbon concentration gradients in the carburised layers were determined for the examined densities. Empirical relationships were formulated for carbon content in the case at a fixed distance from the surface as a function of the compact density for the accepted process parameters. It was found that interconnected macropores are decisive for the carburising depth.

Journal ArticleDOI
TL;DR: In this article, finite element method and X-ray diffraction measurement were used to determine the thermal stress distribution of functionally graded WC-Co composites and the calculated results showed that high stress concentration occurs in the cobalt gradient zone, tensile stress pile-up occurs in cobalt rich zone and compressive stress pile up occurs in surface zone.
Abstract: In this study, finite element method and X-ray diffraction measurement were used to determine the thermal stress distribution of functionally graded WC–Co composites. The calculated results show that high stress concentration occurs in the cobalt gradient zone, tensile stress pile-up occurs in the cobalt rich zone and compressive stress pile-up occurs in the surface zone. As the sintering time is increased, compressive residual stress in the surface zone has a tendency of decreasing. The maximum value of compressive stress in the surface zone is 250 MPa. The results are in good agreement with X-ray diffraction measurement results. For the purpose of this work, the material design method is achieved by changing the calculated parameters.

Journal ArticleDOI
TL;DR: In this article, the graphite powder was replaced by the nanoscale carbon black powder, which provided more uniform distribution, higher apparent density, and faster flow rate for the Fe-0·8%C powder mixture.
Abstract: Graphite powder is the most widely used source of carbon in making powder metallurgy components. In this study, the graphite powder was replaced by the nanoscale carbon black powder. Compared to graphite powder, the carbon black powder provides more uniform distribution, higher apparent density, and faster flow rate for the Fe–0·8%C powder mixture. After sintering, the homogenisation of carbon, microstructure, and hardness are all similar between the two carbon powders. But a higher amount of spring back during ejection and thus lower green density was attained by using carbon black powders. Nonetheless, the compacts using carbon black powder had higher amounts of shrinkage, which compensated for the spring back effect during sintering, thus giving the same density as the graphite powder.

Journal ArticleDOI
TL;DR: In this article, thin and thick walled tubes made of 430L stainless steel for porous metal supported solid oxide fuel cells (SOFCs) were prepared by powder extrusion molding (PEM).
Abstract: Thin and thick walled tubes made of 430L stainless steel for porous metal supported solid oxide fuel cells (SOFCs) were prepared by powder extrusion moulding (PEM). A gas atomised metal powder and a binder composed by 50 vol.‐% high density polyethylene and 50 vol.‐% paraffin wax were chosen. The most suitable powder loading for feedstock (68 vol.‐%) was determined by means of torque experiments and rheological measurements. Mixing temperature was selected taking into account the results from differential scanning calorimetry. The extrusion of tubes was carried out in a single screw extruder and two kinds of tubes with two different wall thicknesses were obtained. In order to investigate the homogeneity of feedstock, microstructure of green tubes was evaluated by SEM. Thermal debinding was performed on the basis of thermogravimetric analysis results. After sintering, tubes with good dimensional stability and without defects were obtained. Different wall thicknesses extruded were 150 and 500 μm.

Journal ArticleDOI
TL;DR: In this paper, the influence of the microstructure on the wear behavior of some hardened sintered steels produced with diffusion bonded powders and subjected to through hardening, carburising and sinterhardening was investigated.
Abstract: The influence of the microstructure on the wear behaviour of some hardened sintered steels produced with diffusion bonded powders and subjected to through hardening, carburising and sinterhardening was investigated In dry sliding, wear was oxidative in nature and the localised surface deformation caused delamination, which further reduce the wear resistance In these conditions, the harder the microstructure, the better the resistance to plastic strain In lubricated rolling–sliding, wear occurs by rolling contact fatigue Cracks nucleation was caused by the stress localisation at the pores edges In this case, a brittle virgin martensite has a negative effect Tempering reduces martensite brittleness, and makes its resistance to nucleation and propagation of the rolling contact fatigue comparable to that of Fe–Ni austenite

Journal ArticleDOI
TL;DR: In this article, the authors used backscatter diffraction to map the microhardness of powder metallurgy steels with a lateral resolution of as little as 5 μm and with up to 104 indents.
Abstract: New methods of characterising multiple phase powder metallurgy steels have been investigated. Mapping of microhardness with a lateral resolution of as little as 5 μm and with up to 104 indents can produce distributions of mechanical properties which are characteristic of different steel grades. Maps of these properties can be correlated with the different phases observed in etched microstructures, and quantification of size and interconnectivity of the regions with, for example, different hardness or stiffness is then possible. Electron backscatter diffraction can also produce simultaneously highly detailed maps of the different phases in a powder metallurgy steel with chemical composition information. Percentages of the different phases present can be determined from the crystallography and morphology of the grains observed, but the technique is limited by the speed with which maps can be acquired.

Journal ArticleDOI
TL;DR: In this paper, the preparation of 25 wt-%Si3N4 nanocomposite powders via high energy ball milling (HEBM) was reported, and the phases and morphologies of as-milled powders with various milling times were investigated using X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscope (TEM).
Abstract: The present work reported the preparation of Cu–25 wt-%Si3N4 nanocomposite powders via high energy ball milling (HEBM). The phases and morphologies of as-milled powders with various milling times were investigated using X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The experimental results showed that with increasing the milling time, the irregularly shaped Cu powder became flattened, and, subsequently, refined and near spherical. After 12 h milling, the particle size of Cu–Si3N4 composite powders was in the range of 200–300 nm, while the grain size of Si3N4 particulates, 10–25 nm, was well within a nanometre scale. A uniform distribution of the nanosized Si3N4 reinforcing phase throughout the Cu matrix was successfully obtained. A reasonable mechanism for the formation of Cu–Si3N4 nanocomposite powders during HEBM was also proposed.

Journal ArticleDOI
TL;DR: In this article, the use of microwave assisted plasma sintering (MaPS) technology has been evaluated for processing nickel-diamond composites, and the results showed that it produced similar or superior mechanical properties to traditional furnace sinterings, but with a cycle time reduced by up to 95%.
Abstract: There is considerable interest in processing technologies which can lead to more energy efficient sintering of metal powders. Microwave sintering has been shown to reduce energy usage as volumetric heating is more efficient than resistance heating. Plasma sintering meanwhile delivers heat via uniform excitation of the processing gas. The use of a rapid, novel microwave-assisted plasma sintering (MaPS) technology has been evaluated for processing nickel-diamond composites. Discs fired in a low pressure microwave plasma under a hydrogen atmosphere were compared with discs sintered in a conventional tube furnace. MaPS is very rapid, with full disc strength being achieved within 10 min, compared with 8 h for furnace treatment. MaPS produced similar or superior mechanical properties to furnace sintering but with sintering cycle time reduced by up to 95%.