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  • 1.
    Akhtar, Farid
    Institute of Powder Metallurgy, University of Science & Technology, Beijing.
    A new method to process high strength TiCN stainless steel matrix composites2007Inngår i: Powder Metallurgy, ISSN 0032-5899, E-ISSN 1743-2901, Vol. 50, nr 3, s. 250-254Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Layered composites of Ti(C, N) reinforcements and stainless steel have been prepared successfully by powder technology. The layer composite consisted of two layers. The upper layer consisted of TiCN reinforcements and stainless steel as binder material. The lower layer was entirely of binder material (stainless steel). The micro structural study revealed that the upper layer (TiCN/465 stainless steel) showed core–rim microstructure of conventional cermets and the lower layer showed the structure of sintered steel. An intermediate layer was formed due to diffusion reaction of upper and lower layers. This intermediate layer showed a gradient microstructure. The bending strength of the layered material measured was remarkably higher. Ninety per cent increase in the bending strength in the case of 50 wt-% reinforcement in the upper layer was found. The fracture morphologies of upper, lower and intermediate layers are also reported

  • 2.
    Akhtar, Farid
    et al.
    Institute of Powder Metallurgy, Materials Science Department, University of Science and Technology Beijing.
    Guo, SJ
    Institute of Powder Metallurgy, Materials Science Department, University of Science and Technology Beijing.
    Shah, KA
    Institute of Powder Metallurgy, Materials Science Department, University of Science and Technology Beijing.
    Effect of Cu3P addition on sintering behaviour of elemental powders in the composition of 465 stainless steel2006Inngår i: Powder Metallurgy, ISSN 0032-5899, E-ISSN 1743-2901, Vol. 49, nr 1, s. 28-33Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The addition of Cu3P for developing the high strength 465 maraging stainless steel from elemental powders was studied. The sintering parameters investigated were sintering temperature, sintering time and wt-%Cu3P. In vacuum sintering, effective sintering took place between 1300 and 1350°C. The maximum sintered density of 7·44 g cm−3 was achieved at 1350°C for 60 min with 4–6 wt-%Cu3P. More than 6 wt-%Cu3P content and temperature >1350°C caused slumping of the specimens. The sintered specimens were heat treated and a maximum ultimate tensile strength (UTS) of 767 MPa was achieved with 4 wt-%Cu3P content. The maximum hardness of 45·5 HRC was achieved in heat treated condition with 4 wt-%Cu3P content. Above 4 wt-%Cu3P content increase in density was observed whereas the response to heat treatment decreased. Fracture morphologies of the sintered specimens were also reported. A comparison of sintering behaviour and mechanical properties of elemental powders with prealloyed powders was also given in the present study

  • 3.
    Arén, Björn
    et al.
    Luleå tekniska universitet.
    Navara, Eric
    Luleå tekniska universitet.
    Modelling shape change of parts produced by hot isostatic pressing1988Inngår i: Powder Metallurgy, ISSN 0032-5899, E-ISSN 1743-2901, Vol. 31, nr 2, s. 101-105Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Models for analysing shape changes during the hipping of powder compacts enclosed in preshaped containers are presented. Two limiting mechanisms are considered: homogeneous densification and the motion of a sharply defined densification front through the compact as hipping proceeds. The shape changes and shrinkages occurring in a number of simple one, two, and three dimensional shapes are analysed and illustrated. Although some of the assumptions implicit in the model are at variance with the conditions found in practice, it is concluded that useful insights are provided into the shape changes occurring during hipping

  • 4.
    Arén, Björn
    et al.
    Luleå tekniska universitet.
    Navara, Eric
    Luleå tekniska universitet.
    Modelling shape change of parts produced by hot isostatic pressing of powders1988Inngår i: Powder Metallurgy, ISSN 0032-5899, E-ISSN 1743-2901, Vol. 31, nr 2, s. 101-105Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Models for analysing shape changes during the HIPping of powder compacts enclosed in preshaped containers are presented. Two limiting mechanisms are considered: homogeneous densification and the motion of a sharply defined densification front through the compact as HIPping proceeds. The shape changes and shrinkages occurring in a number of simple one, two, and three dimensional shapes are analysed and illustrated. Although some of the assumptions implicit in the model are at variance with the conditions found in practice, it is concluded that useful insights are provided into the shape changes occurring during HIPping

  • 5.
    Arén, Björn
    et al.
    Luleå tekniska universitet.
    Nilsson, Annika
    Luleå tekniska universitet.
    Die tool dimensioning by finite element method1987Inngår i: Powder Metallurgy, ISSN 0032-5899, E-ISSN 1743-2901, Vol. 30, nr 2, s. 87-96Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Stress and strain are studied using the finite element method in the dimensioning of prestrained die tools for powder compaction. The die geometry has been varied and the die has also been subjected to different types of load. The study shows that the mean pressure transverse to the pressing direction is a dimensioning factor, but that the distribution itself is not very important. For a linear pressure distribution, the stress and strain within the die will differ little from results produced under the assumption of an exponential pressure distribution. Attention is also paid to the possibilities of treating the three-dimensional situation in a real die by different methods of two-dimensional FEM analysis

  • 6.
    Bergquist, Bjarne
    Luleå tekniska universitet, Institutionen för ekonomi, teknik och samhälle, Industriell Ekonomi.
    Factor analysis of iron-phosphorus PM steel2000Inngår i: Powder Metallurgy, ISSN 0032-5899, E-ISSN 1743-2901, Vol. 43, nr 2, s. 143-148Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Alloy design and choice of process parameters are often tasks where different investigations lead in different directions and the process of selecting the best parameter settings is difficult. Multivariate statistics are capable of bringing order in such situations, and here data from four different invesigations on the Fe-P-C system are collected and evaluated. Effects of chemical composition, comapction pressure, sintering time, and sintering temperature on properties including density, tensile strength, impact energy, proof stress, and elongation are studied. The investigation is based on principal factor analysis. Dimensional reduction is presented and discussed. The study compares the different investigations and the results for the Fe-P-C system show how different properties interact.

  • 7.
    Bergquist, Bjarne
    Luleå tekniska universitet, Institutionen för ekonomi, teknik och samhälle, Industriell Ekonomi.
    New insights into influencing variables of water atomization of iron1999Inngår i: Powder Metallurgy, ISSN 0032-5899, E-ISSN 1743-2901, Vol. 42, nr 4, s. 331-343Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Trace amounts of surfactants have an acute influence on measured surface tension of melts and may influence viscosity. A water atomisation experiment was performed to investigate if variations of these elements could affect quality. Effects of water pressure, melt superheat, and sulphur content, iron scrap oxygen content, and aluminium content were studied. Responses studied were particle size distribution, apparent density, flow, powder chemistry, morphology, green density, and dimensional change. A large sulphur addition reduced the particle size, as a result of a reduction of surface tension, but the largest effect came from changing water pressure. Higher water pressures also resulted in powders with lower apparent density, lower flowrate, and reduced swelling during sintering. An empirical water atomisation model is proposed. Aluminium additions reduced the powder size standard deviation and increased the carbon content of the powder. A reduced powder size standard deviation was seen also for melts with raised superheating.

  • 8.
    Bergquist, Bjarne
    et al.
    Luleå tekniska universitet, Institutionen för ekonomi, teknik och samhälle, Industriell Ekonomi.
    Ericsson, T.
    Division of Engineering Materials, Department Mechanical Engineering, Linköpings universitet.
    Robustness simulation of water atomisation2000Inngår i: Powder Metallurgy, ISSN 0032-5899, E-ISSN 1743-2901, Vol. 43, nr 1, s. 37-42Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    One of the main purposes of water atomisation is to keep the powder size distribution within a close range. The process is difficult to monitor and thus the state of today's process control is poor. To investigate this process, both a laboratory scale and an industrial scale atomisation facility were modelled where melt flow and thermal flow were investigated. The results showed that metal temperature is important if stable particle sizes are to be obtained from batch to batch.

  • 9.
    Bergquist, Bjarne
    et al.
    Luleå tekniska universitet, Institutionen för ekonomi, teknik och samhälle, Industriell Ekonomi.
    Hjortsberg, E.
    Chalmers University of Technology.
    Filling induced density variations in metal powder2002Inngår i: Powder Metallurgy, ISSN 0032-5899, E-ISSN 1743-2901, Vol. 45, nr 2, s. 146-153Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Filling induced density variations is a problem that has long been overlooked by powder metallurgy scientists. In this paper,densityvariations are addressed, both why they occur and what problems they may cause. A test method, including a test rig, is presented that is able to link several different factors to resulting powder densities. The relations are analysed and several density affecting mechanisms are suggested. These mechanisms could be used either to minimise density differences within parts or to control density by directing powder to critical areas.

  • 10. Eriksson, Magnus
    et al.
    Häggblad, Hans-åke
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Berggren, C.
    Nobel Biocare AB.
    Andersson, M.
    Nobel Biocare AB.
    Holmersson, R.
    Nobel Biocare AB.
    Carlström, E.
    Swedish Ceramic Institute, PO Box 5403, SE-402 29 Göteborg.
    New semi-isostatic high velocity compaction method to prepare titanium dental copings2004Inngår i: Powder Metallurgy, ISSN 0032-5899, E-ISSN 1743-2901, Vol. 47, nr 4, s. 335-342Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A new method to prepare titanium dental copings from titanium powder was tested, involving high velocity compaction and various elastic forms, which were used to achieve a semi-isostatic effect during the impact. The tooth preparation die (mandrel) and the powder were placed inside an elastic form. The impact struck the elastic form, and the powder was compacted against the tooth preparation die. Several different elastomers were tested to find the best one. Cross-sections of the powder bodies were studied for density variations. The soft, flexible elastomer worked best to compact the powder. The highest densification could be focused closest to the mandrel where the coping should be milled out. The density in the highest density areas could locally reach 98-99%. If the method with elastic forms could be optimised to give as high a density as without elastic forms, a lower shrinkage and possible deformation of the copings could be reached.

  • 11. Federzoni, L.
    et al.
    Riedel, H.
    Coube, O.
    Oldenburg, Mats
    Häggblad, Hans-åke
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Gethin, D.
    State of the art review - Comparison of computer models representing powder compaction process.1999Inngår i: Powder Metallurgy, ISSN 0032-5899, E-ISSN 1743-2901, Vol. 42, nr 4, s. 301-311Artikkel i tidsskrift (Fagfellevurdert)
  • 12.
    Geassy, Abdel Hady El
    et al.
    Central Metallurgical Research and Development Institute (CMRDI), Helwan, Cairo.
    Nassir, Nassir
    Royal Institute of Technology, Stockholm.
    Ahmed, Hesham
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Industriell miljö- och processteknik.
    Seetharaman, Sishadri
    Royal Institute of Technology, Stockholm.
    Simultaneous reduction nitridation for the synthesis of tungsten nitrides from Ni–W–O precursors2013Inngår i: Powder Metallurgy, ISSN 0032-5899, E-ISSN 1743-2901, Vol. 56, nr 5, s. 411-419Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Tungsten nitrides were synthesised from NiO–WO3 and NiWO4 precursors at 973–1273 K in a flow of H2–N2 gas mixture. The reduction–nitridation reactions were carried out isothermally in fluidised bed reactor, and the off-gas from the reactions was continuously analysed by gas chromatography. The effect of reaction temperature and precursor composition on the rate of formation of Ni–W nitrides was studied. The different phases developed during the reduction– nitridation reactions were identified by X-ray diffraction analysis technique. The morphology and the grain structure of the precursors were examined by SEM, and the elemental composition in the structure was analysed by electron dispersive spectrometry. The results showed that the reduction of Ni–W–O precursors proceeded in a stepwise manner (NiWO4RNi–WO3RNi– WO2RNi–W). Tungsten nitrides (WN and WN2) were formed from the reaction of the freshly reduced W metal with N2 gas and WN was the predominant phase detected at higher temperatures. The reaction mechanisms were elucidated from the apparent activation energy values and the application of different formulations derived from the gas–solid reaction model at early and later stages of reactions. It was concluded that the interfacial chemical reaction is the rate determining step at initial stages, while a combined effect of gaseous diffusion and interfacial chemical reaction controlled the reaction at later stages. At final stages, the nitridation reactions contributed to the reaction mechanism leading to produce tungsten nitrides.

  • 13.
    Gedda, Hans
    et al.
    Luleå tekniska universitet.
    Kaplan, Alexander
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Powell, John
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik.
    Rüstig, Katja
    Material Science and Materials Technology, Technische Universitat Bergakademie, Freiberg.
    Laser wire casting2003Inngår i: Powder Metallurgy, ISSN 0032-5899, E-ISSN 1743-2901, Vol. 46, nr 3, s. 199-201Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A new technique has been developed for the production of solid wire or rods from powder by laser melting. Three techniques have been developed to ensure that the molten powder solidifies as a rod or wire rather than a series of droplets. The straight rods or wires produced in this way have near-circular cross-section, are several millimetres in diameter and can be pore free. The techniques can be used to produce welding rods, tensile test samples and other solid pieces from a wide range of powder mixes. The rapid thermal cycle involved means that it is now possible to produce hitherto difficult mixtures and alloys in the solid form in seconds.

  • 14.
    Häggblad, Hans-åke
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Oldenburg, Mats
    Numerical simulation of powder compaction for two multilevel ferrous parts, including powder characterisation and experimental validation2002Inngår i: Powder Metallurgy, ISSN 0032-5899, E-ISSN 1743-2901, Vol. 45, nr 4, s. 335-344Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The paper presents a summary of two case studies that were carried out by the scientific team in the Thematic Network PM Modnet. During the life of this project, the compaction of complex multilevel ferrous components was investigated. These formed a vehicle to explore methods to characterise the yield and friction properties of the powder, perform simulation of the compression stage of the forming process, complete experimental trials, and compare experimental and simulated results. Density comparisons were made with results from Archimedes, quantitative metallography, and computerised tomography and force levels were compared with recordings from the pressing trials. The results highlight differences between equipment and experimental techniques used in characterising powders. They also show that hardness, metallographic analysis, and computerised tomography may be used to measure density variations throughout the compact. The prediction of density variation was reasonably consistent when using different simulations, whereas punch force prediction showed good consistency. It was found that predicted and measured density distributions agree within 0·05 to 0·5 g cm-3 and that punch force levels may be predicted within 10 to 30%. The study effectively establishes a benchmark with which to compare and improve future simulations.

  • 15. Li, W.B.
    et al.
    Häggblad, Hans-åke
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Constitutive laws for hot isostatic pressing of powder compact1997Inngår i: Powder Metallurgy, ISSN 0032-5899, E-ISSN 1743-2901, Vol. 40, nr 4, s. 279-281Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The present state of hipping modelling is briefly reviewed using the principles of densification theory and plastic deformation theory for porous materials on the basis of a macro- and microscopic approach. The features of these two approaches are discussed. The constitutive equation for a porous compact relating the strains and stresses (macroscopic approach) is modified by incorporating the rate equations for densification mechanisms (microscopic approach). A new modified constitutive equation is then derived which combines the advantages of both approaches. Based on this equation, the hipping process can be simulated. The density and shape change of a porous compact during densification or deformation processes under conditions of either isostatic or nonisostatic pressure can be predicted

  • 16.
    Li, Wei-Bin
    et al.
    Luleå tekniska universitet.
    Easterling, Kenneth E.
    Luleå tekniska universitet.
    Cause and effect of non-uniform densification during hot isostatic pressing1992Inngår i: Powder Metallurgy, ISSN 0032-5899, E-ISSN 1743-2901, Vol. 35, nr 1, s. 47-52Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Hot isostatic pressing (hipping) is an extremely efficient way of densifying ceramic and high alloy metallic powders, or for healing porosity in castings. However, depending on the parameters of pressure, temperature, rate of heating, and sample size, hipping can result in a non-uniform mode of densification. This mainly occurs when a rapidly heated sample, or a sample of large dimensions, densifies quickly at the surface to produce, if effect, a fully dense, hard shell. It is shown that there can be a number of negative factors resulting from this, including reduced rates of densification, sample sample shape change, non-uniform shrinkage, and the development of residual stresses in the sample. Criteria for predicting whether or not non-uniform densification will occur are presented and evaluated. Steel and Cu are discussed.

  • 17.
    Solimanjad, Naghi
    Luleå tekniska universitet.
    New method for measuring and characterisation of friction coefficient at wide range of densities in metal powder compaction2003Inngår i: Powder Metallurgy, ISSN 0032-5899, E-ISSN 1743-2901, Vol. 46, nr 1, s. 49-54Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In order to investigate the friction behavior of powder during compaction, a new method has been developed. Compaction is a complicated process and direct and continuous measurement of the coefficient of friction is not easy, because the coefficient of friction varies due to changes in such process parameters as pressure distributions, powder surface deformation etc. In this paper, a new device for measuring the coefficient of friction between metal powder particles in contact with the die wall during compaction is presented. Using the conventional methods for direct measurement of the radial pressure during compaction is very difficult. The new device offers the possibility of investigating the normal pressure on the powder particles directly and continuously by keeping the green density constant. The measurements are performed using strain gauges mounted on the upper punch. The upper punch surface in the new device corresponds to the die wall in a conventional press. The sliding velocity, compaction velocity, normal load and temperature can be monitored and controlled. Measurement of the coefficient of friction at low densities is one of the advantages and possible applications of this apparatus. The investigation shows that the powder compaction is controlled by a combination of powder rearrangement and elastic and plastic deformation of particles. At densities below 4 g cm-3 the dominant process is particle rearrangement. No plastic deformation occurs at such low values of density. At densities above 4.5 g cm-3 the plastic deformation of the powder surface in contact with the die wall seems to be completed and the coefficient of friction is more or less constant

  • 18. Wikman, Bengt
    et al.
    Solimannezhad, N.
    Larsson, Roland
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    Oldenburg, Mats
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Häggblad, Hans-åke
    Wall friction coefficient estimation through modelling of powder die pressing experiment2000Inngår i: Powder Metallurgy, ISSN 0032-5899, E-ISSN 1743-2901, Vol. 43, nr 2, s. 132-138Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Forming of PM components through powder pressing is a process, which is influenced by the friction between the powder and the tool walls. For good performance of the pressing process it is of great interest to understand and estimate the effects of powder-wall friction. However, quantification of the friction coefficient between the powder and the tool is a delicate task. Local contact conditions, such as contact stress, must be measured or otherwise estimated in order to evaluate the coefficient of friction. Here, the friction coefficient is estimated by combining an experiment with modelling of the experiment. Two methods for assessment of friction are presented, an optimization approach using finite element analyses and an analytical approach. Experimental data are taken from the single action cold pressing of a cylinder shaped component.

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