Showing papers in "Powder Metallurgy in 2013"
TL;DR: In this article, a brief overview of laser metal deposition from a PM perspective is presented, with an emphasis on underlying mechanisms and attendant metallurgical issues, and potential applications combining PM and LMD are identified.
Abstract: By combining laser and powder processing, laser metal deposition (LMD) enables the manufacture of high precision near-net shape components from powders, so enhancing materials utilisation. Rapid prototyping, in situ repair and surfacing are among the capabilities of LMD; applications cover the medical, defence and aerospace sectors, with potential applications in oil and gas and other sectors. To take full advantage of the rapid fabrication of complex geometries and automated repair offered by LMD, there is a need to develop understanding of the process–microstructure–property relationships, particularly the effect of powder characteristics on process variables and on the metallurgy and resulting mechanical properties. A brief overview of LMD from a PM perspective is presented, with an emphasis on underlying mechanisms and attendant metallurgical issues. Recent developments in the state-of-the-art are discussed and potential applications combining PM and LMD are identified.
102 citations
TL;DR: The science of sintering started to emerge in the 1940s and matured in the middle 1980s as discussed by the authors, and many important products and concepts, ranging from porcelain dinnerware to automotive structural components, and included platinum crucibles, tungsten lamp filaments, cemented carbide drawing dies, bronze bearings and bonded abrasives.
Abstract: Sintering is well established as a component fabrication approach. It has been applied to ceramics for 26 000 years. Metallic sintering is more recent, and cemented carbides are a relatively modern application. The science of sintering started to emerge in the 1940s and matured in the middle 1980s. Previously, empirical approaches developed many important products and concepts, ranging from porcelain dinnerware to automotive structural components, and included platinum crucibles, tungsten lamp filaments, cemented carbide drawing dies, bronze bearings and bonded abrasives. This article outlines how these products arose in an empirical trial and error approach before conceptualisations of sintering theory.
37 citations
TL;DR: In this paper, the authors reviewed the recent trends in the technology, production and applications of diamond tooling, focusing on diamond wires for the cutting of granite and other rock and providing another focus for materials and technology advances.
Abstract: Recent trends in the technology, production and applications of diamond tooling are reviewed. The continuing fall in the price of synthetic diamond as production volumes increase provides a strong incentive for tooling companies to reduce the cost of matrix materials and of their manufacturing processes, with an accompanying need for research in these areas. Diamond wires for the cutting of granite and other rock continues to grow in application and provides another focus for materials and technology advances.
36 citations
TL;DR: In this paper, the speciation of surface oxide phases on fine inert gas atomised (GA, <45 and <4 μm) and water atomised powders was investigated using X-ray photoelectron and Auger electron spectroscopy.
Abstract: New insights are presented on the speciation of surface oxide phases on fine inert gas atomised (GA, <45 and <4 μm) and water atomised (WA, <45 μm) stainless steel AISI 316L powders. X-ray photoelectron and Auger electron spectroscopy, scanning electron microscopy, Raman spectroscopy, and cyclic voltammetry were applied for the characterisation. Oxidised manganese was strongly enriched in the outermost surface oxide of the GA powders (13 and 47 wt-%), an effect increasing with reduced particle size. Manganese and sulphur were enriched in oxide nanoparticles on the surface. Oxidised silicon (59 wt-%) was enriched on the WA powder surface. Tri- or tetravalent manganese oxides were observed on the GA particles in addition to α-Fe2O3, and Cr2O3. The oxide of the WA powder revealed in addition the likely presence of a silicate rich phase, mainly consisting of tetravalent Si, di- and/or trivalent Fe, and hexavalent Cr, which was confirmed not present as chromate.
28 citations
TL;DR: In this paper, the distribution of the reinforcement phase in the composite was evaluated as a function of the milling time and the amount of SiC. The processed materials were characterized by scanning electron microscopy and energy dispersive spectroscopy for the morphology and composition and X-ray diffraction.
Abstract: Al based alloys reinforced with different amounts (5, 12 and 20 wt-%) of nanosized SiC particulates were synthesised by mechanical alloying and consolidated by the spark plasma sintering (SPS) technique. The distribution of the reinforcement phase in the composite was evaluated as a function of the milling time and the amount of SiC. The processed materials were characterised by scanning electron microscopy and energy dispersive spectroscopy for the morphology and composition and X-ray diffraction. Continuous reduction in crystallite size was observed as milling progressed and after milling for 20 h the resulting powders reached a grain size of <100 nm. These Al–SiC composites were successfully consolidated by the SPS method at different sintering temperatures of 400, 450 and 500°C. It is suggested that a higher hardness can be achieved even at 20 wt-%SiC when a higher sintering temperature, for example, above 500°C, is used.
28 citations
TL;DR: In this paper, a concise but thorough compilation of melt disintegration phenomenology is provided, with emphasis on high pressure gas atomisation, inclusive of notation on mean particle diameters, the role of viscosity, density and other dimensionless ratios that enter as variables in highpressure gas atomization and spray forming, as well as break up of a liquid column and theories of drop disintegration in flight.
Abstract: Gas atomisation phenomenology of liquid metals and alloys is both intriguing and instructive. Predating atomistic studies of melt disintegration by almost three decades, it provides a functional means of correlation between drop sizes and processing parameters, as is the case in liquid metal spray forming. In this article a concise but thorough compilation of melt disintegration phenomenology is provided, with emphasis on high pressure gas atomisation, inclusive of notation on mean particle diameters, the role of viscosity, density and other dimensionless ratios that enter as variables in high pressure gas atomization and spray forming, as well as break up of a liquid column and theories of drop disintegration in flight. The article concludes by introducing the very efficient Surface Wave Formation principle which facilitates the treatment of complex atomisation geometries and turbulent regimes.
27 citations
TL;DR: In this paper, the fracture surface of silicon carbide reinforced copper matrix composites containing 50-80 vol.-%SiCp were fabricated by hot pressing copper-coated SiCp powder, and the results showed that the densification, thermal expansion coefficients, flexural strength, and thermal conductivity of the composites reinforced by electroless copper plating and their corrosion resistance in 5% NaCl solution are better than those without electroless plating.
Abstract: Silicon carbide reinforced copper matrix composites containing 50–80 vol.-%SiCp were fabricated by hot pressing copper coated SiCp powder. The results show that the densification, thermal expansion coefficients, flexural strength, and thermal conductivity of Cu/SiCp composites reinforced by electroless copper plating and their corrosion resistance in 5%NaCl solution are better than those without electroless plating. Physical properties and flexural strength of the composites decrease with an increase in SiCp content, whereas the corrosion resistance increases with an increase in SiCp volume fraction. By observing the fracture surface after a flexural test, it can be seen there are two types of fracture model: the cracking of Cu/SiCp interface and the pulling out of SiCp particles. The experiment also proved that the bonding strength of the Cu/SiCp interface and the pressure of the hot pressing operation are the two main factors which influence the fracture of these composites.
22 citations
TL;DR: In this paper, an optimised description of this Co-free system, using phase analysis following long term vacuum heat treatment in a laboratory furnace, with the aim of identifying potentially brittle phases is presented.
Abstract: Previous studies have demonstrated that it is possible to compensate for the absence of Co in a W–Ni–Fe liquid sintered composite alloy under industrial conditions by appropriate control of the process parameters, to achieve mechanical properties close to those of Co containing alloys. The present investigation offers an optimised description of this Co-free system, using phase analysis following long term vacuum heat treatment in a laboratory furnace, with the aim of identifying potentially brittle phases. This optimised system has been evaluated in tests with a small industrial kinetic penetrator (APFSDST CT40) against a semi-infinite target and inclined armour plate. Results show no degradation of the ballistic performance relative to conventional Co containing alloys.
21 citations
TL;DR: In this article, the effect of alloying and sintering temperature on the mode of particle rearrangement, and consequently on graded densification, by microstructural and fractographic analysis was examined.
Abstract: It would be useful to be able to produce brass and bronze components made from prealloyed powders by supersolidus liquid phase sintering. The microstructures obtained in such alloys are sensitive to constituent alloying elements and small change in sintering temperature. Although the formation of liquid during sintering is potentially attractive for densification, the effects of gravity on the liquid phase can result in graded densification. Evaporation of alloying elements and their solubility in the base metal also affect the extent to which heterogeneous cross-sections are obtained. The aim of the present study was to examine the effect of alloying and sintering temperature on the mode of particle rearrangement, and consequently on graded densification, by microstructural and fractographic analysis. Comparing the fracture morphology from top to bottom of the fracture surface is also helpful in developing a model to describe the phenomena during sintering of similar alloys.
19 citations
TL;DR: The low-alloy steel powder Distaloy as mentioned in this paper, which is widely used in applications demanding high strength and wear resistance, was designed half a century ago in the USA, and it was a partial prealloy, i.e. the alloying elements were bonded in particulate form to the basic iron particles.
Abstract: The low alloy steel powder Distaloy, is today widely used in applications demanding high strength and wear resistance. Its basic properties and composition were designed half a century ago in the USA. The advantage lay in the fact that it was a partial prealloy, i.e. the alloying elements – copper, nickel and molybdenum – were bonded in particulate form to the basic iron particles, thus avoiding impairment of the compressibility. By balancing the contents of nickel and copper it was possible to minimize dimensional change on sintering. Bonding the alloy particles to the iron particles minimised segregation and also contributed to dimensional stability. Carbon was added conventionally as fine graphite. However, the new powder, marketed as Ancoloy, did not take off in North America, due to the lack of suitable applications, the cost of the alloying elements and – above all – the poor compressibility and high oxygen content of the iron powder then available. The high, variable oxygen content made it ...
19 citations
TL;DR: In this article, the microstructure sensitive multistage fatigue model captured the fatigue life of a powder metal FC-0205 steel alloy, and the uniaxial strain controlled fatigue data and micro-structure information from sets of high and low porosity specimens calibrated the model.
Abstract: The microstructure sensitive multistage fatigue model captured the fatigue life of a powder metal FC-0205 steel alloy. Uniaxial strain controlled fatigue data and microstructure information from sets of high and low porosity specimens calibrated the model. Strain–life behaviour depicted that above the plastic strain limit of 0·002 mm mm−1 in the low cycle fatigue regime, where ubiquitous plasticity occurred, the different porosity levels gave distinct, visibly different results. However, specimens tested below the plastic limit in the high cycle fatigue regime, where failure was dominated by local cyclic microplasticity, showed unclear fatigue lives at different porosity levels. Fractography using scanning electron microscopy showed no clear presence of striations; however, asserted striations in powder metal specimens were similar to geometrical features observed on fracture surfaces of monotonically loaded specimens. The experimental and microstructure data calibrated a fatigue model that allowe...
TL;DR: In this paper, the authors proposed a hypothesis for the interpretation of shrinkage anisotropy during sintering of an Fe-Cu-C alloy based on the effect of the structural modifications of the powder, due to the prior compaction, on the mass transport phenomena.
Abstract: This work proposes a hypothesis for the interpretation of shrinkage anisotropy during sintering of an Fe–Cu–C alloy based on the effect of the structural modifications of the powder, due to the prior compaction, on the mass transport phenomena Dislocations are introduced by cold compaction in the contact regions between particles, with different densities along the compaction direction and the transversal one Therefore, the mass transport by volume diffusion is strongly activated in both directions, and a prevailing effect in the compaction direction is shown The volume diffusion coefficients derived from the kinetic model correspond to the dislocation pipe diffusion mechanism
TL;DR: In this paper, a case study is given of an existing furnace installation using Sinterflex technology which allows continuous monitoring and/or control of the furnace atmosphere, the reduction of oxides and carbon potentials to optimise the production parameters is described.
Abstract: The challenges in controlling carbon potential during sintering of steel powder have been discussed in many experimental and theoretical studies. The main issues lie within the complex thermodynamics and kinetics of processing atmosphere chemistry in continuous sintering furnaces. Although many models have been proposed to address the problem, these have rarely come to reality and entered industry practice. The purpose of this article is to summarise these discussions and investigate the interaction of the atmosphere constituents with the sintered compact within a sintering furnace. An important aim is to provide the PM industry with a fresh understanding of furnace operations and to provide recommendations to improve the control of furnace conditions. A case study is given of an existing furnace installation using Sinterflex technology which allows continuous monitoring and/or control of the furnace atmosphere. The reduction of oxides and carbon potentials to optimise the production parameters is described.
TL;DR: Porous pure titanium coatings, obtained by a PM processing route based on the electrophoretic deposition of TiH2 followed by thermal treatment in vacuum, significantly reduced bacterial colonisation of the surface compared with a state-of-the-art vacuum plasma sprayed coating.
Abstract: Bone ingrowth into and through porous coatings on orthopaedic implants can substantially improve fixation. However, the introduction of pores increases surface roughness and also the risk of bacterial adherence, which can lead to infection (in extreme cases, to death) and complicate implant surgery due to the high risk of revision being required. Improving osseointegration without increasing infection risk is therefore a major challenge in implantology. Staphylococcal adhesion and biofilm formation on Ti surfaces of varying roughness and porosity have been investigated in vitro. Porous pure titanium coatings, obtained by a PM processing route based on the electrophoretic deposition of TiH2 followed by thermal treatment in vacuum, significantly reduced bacterial colonisation of the surface compared with a state-of-the-art vacuum plasma sprayed coating. Further reduction of biofilm formation could be obtained by additional surface modification.
TL;DR: In this paper, the crystallite size and internal strain of the Co2FeAl Heusler alloy were calculated using the Williamson-Hall equation. But the internal strain has increased with the increase in milling time.
Abstract: Mechanical alloying (MA) has been used to fabricate the Co2FeAl Heusler alloy with a nanocrystalline structure. The formation mechanism of the alloy has been investigated. Rietveld analysis showed that all the samples that were milled for >15 h had an L21 structure with a space group of Fm3m. The crystallite size and internal strain of the samples were calculated using the Williamson–Hall equation. The crystallite size of Co2FeAl increased to ∼22 nm by increasing the MA time from 15 to 20 h, and after 20 h of MA, the crystallite size decreased. In contrast, the internal strain has increased with the increase in milling time. The powder obtained after 20 h of MA was split into three parts and separately annealed at 300, 500 and 700°C for 5 h. A considerable increase was observed in the hardness value of powder particles with the increase in annealing temperature up to 500°C. However, the hardness value of the sample annealed at 700°C decreased. It seems that this feature is related to parameters su...
TL;DR: In this paper, the authors showed that the mode of pore distribution in the matrix makes a greater contribution compared to the pore size towards controlling the end properties of the samples.
Abstract: Ti foam has been synthesised by powder metallurgy route using acicular and fine urea particles as space holder. Pore morphology and distribution and compressive behaviour of samples have been studied for different urea particle morphologies and volume fractions. Acicular urea particles generated islands of acicular porous regions with a large number of micropores. Fine pores with improved homogeneity were obtained using finer urea particles. The plateau regions in the case of using acicular particles were much distinct and obtained at a lower level of porosity compared to those incorporated with fine urea particles. Acicular urea particles became more effective towards attaining higher ductility and plateau area, the latter suggesting superior energy absorption (damping) capacity of the processed (foam) samples. The study also demonstrates that the mode of pore distribution in the matrix makes a greater contribution compared to the pore size towards controlling the end properties of the samples.
TL;DR: In this paper, a constitutive model for the densification of metal powder during hot isostatic pressing is proposed, which considers an inelastic deformation resulting from time dependent (viscoplastic) and time independent (plastic) mechanisms during loading.
Abstract: A constitutive model is proposed for the densification of metal powder during hot isostatic pressing. The model considers an inelastic deformation resulting from time dependent (viscoplastic) and time independent (plastic) mechanisms during loading. With employing the Abouaf’s formalism for viscoplastic part, the paper is focused mainly on the plasticity contribution including the hardening effects of both relative density and the equivalent plastic strain. The proposed plastic–viscoplastic model is summarised to an equation expressing the densification rate under hydrostatic loading. The gas atomised 316LN stainless steel powder was used in this study. Model parameters necessary for simulation of HIP process during a given pressure ramp at constant temperature are identified using previously published data. The identified model is then verified using experimental data obtained from HIP trials performed at another fixed temperature but with varied pressure ramp rates. A good agreement was found between th...
TL;DR: In this article, Porous PM Fe-Cr oxide dispersion strengthened alloys for use as MSC supports have been developed, which provide mechanical and chemical long term stability in typical SOFC atmospheres at operation temperatures up to 850°C.
Abstract: In the past few decades, stationary solid oxide fuel cell (SOFC) systems have been developed that can generate electricity and heat from the energy stored in hydrogen or hydrocarbons with total efficiencies up to 95%. While the mechanical cell support of stationary systems is commonly supplied by thick ceramic cell components (i.e. anode and electrolyte supported concepts), mobile systems demand a more robust design. This is ensured by a strong yet porous metallic substrate which serves as the mechanical backbone of thin film membrane electrode assemblies [metal supported cell (MSC) concept]. Porous PM Fe–Cr oxide dispersion strengthened alloys for use as MSC supports have recently been developed. These materials provide mechanical and chemical long term stability in typical SOFC atmospheres at operation temperatures up to 850°C. The substrates support a multilayer anode–electrolyte–cathode thin film assembly, constituting a high performance MSC repeat unit. These units are the building blocks for...
TL;DR: In this paper, a typical α−β Widmanstatten microstructure with a precipitated α phase layer along the grain boundaries was found in a metal injection molding (MIM) application.
Abstract: Titanium alloys containing β stabilising elements such as Nb, Zr and Ta are particularly promising as implant materials because of their excellent combination of low modulus, high strength, corrosion resistance and biocompatibility A low elastic modulus is important for implants to avoid stress shielding and associated bone resorption The difficulty of producing complex shapes of these alloys by conventional methods makes metal injection moulding (MIM) attractive Ti–17Nb alloy parts with densities 94% of theoretical have been produced by MIM of a feedstock based on blended elemental powders Scanning electron microscopy reveals a typical α−β Widmanstatten microstructure with a precipitated α phase layer along the grain boundaries The parts exhibit an ultimate tensile strength of 768 MPa and a plastic elongation of over 5% The modulus of elasticity, about 84 GPa, is more than 20% lower than that of cp Ti and Ti–6Al–4V
TL;DR: In this paper, two Ti-6Al-4V powder preforms were sintered through spark plasma sintering (SPS) and then hot compressed in a horizontal dilatometer.
Abstract: Powder preform forging is a technology that comprises the preparation of near net shape preforms through powder metallurgy and a subsequent hot forging in order to obtain the desired final shape. In this work, two Ti–6Al–4V powder preforms were sintered through spark plasma sintering (SPS) and then hot compressed in a horizontal dilatometer. Varying the temperature of the process, two full density preforms having different microstructures were produced: sintering at 950°C, a plate-like α was obtained, whereas sintering at 1050°C, an acicular α was obtained. The behaviour of the preforms under hot forging has been studied through hot compression tests carried out in a quenching and deformation dilatometer in a range of temperature and strain rates typically used in hot forging this alloy (850–1050°C, 0·01–1 s−1). Hot workability has been evaluated by measuring the stresses required for deformation and by analysing both the stress–strain curves recorded during testing and the microstructures after d...
TL;DR: In this article, the authors investigated the porosity defects in sintered Cr60Cu40 alloy targets produced via vacuum sintering followed by hipping and showed that hipping treatment can effectively eliminate internal pores and improve their electrical properties.
Abstract: Owing to ingredient segregation, non-uniform microstructure and porosity defects in Cr–Cu alloys are frequently produced by melting process. Even subsequent heat treatment and hot working would not be able to completely resolve the problem. Therefore, this study investigated Cr60Cu40 alloy targets produced via vacuum sintering followed by hipping. Experimental results showed that the relative density of the sintered Cr60Cu40 alloy targets reached 99·69%, the apparent porosity decreased to 0·31% and transverse rupture strength increased to 553 MPa after hipping treatment at 1050°C at 175 MPa for 4 h. In addition, the closed pores were almost completely eliminated after the hipping treatment. The resistivity decreased to 643×10−8 Ω cm, and the International Annealed Copper Standard value was enhanced to 26·81% after optimal hipping treatment. This study shows that hipping treatment can effectively eliminate internal pores of sintered Cr60Cu40 alloy targets and also improve their electrical properties.
TL;DR: In this paper, an improved process for sintering Fe 3Cr 0·5Mo 0·6C steel in nitrogen, in a box, additionally containing sources of manganese vapour (ferromanganese lumps) and nascent carbon (naphthalene).
Abstract: An improved process is proposed for sintering of Fe–3Cr–0·5Mo–0·6C steel in nitrogen, in a box, additionally containing sources of manganese vapour (ferromanganese lumps) and nascent carbon (naphthalene). The use of a semiclosed container with a labyrinth seal minimises compact interaction with the flowing furnace atmosphere and thus ensures that a dry local ‘microclimate’ exists within and around the sintered specimens. Nascent carbon, from ∼1000°C, is significantly chemically more active than graphite (previously used) and the microclimate thus included, from ∼700°C, manganese vapour. The latter additive ensures that manganese is oxidised in preference to chromium, whereby oxygen uptake to the compact is inhibited and reduction rather than oxidation of chromium occurs. A favourable comparison is made of resultant mechanical properties for the same material sintered also in hydrogen, with published properties of similar Cr–Mo–C steels and with MPIF standard for Cu and/or Ni containing steels.
TL;DR: In this paper, a round robin assessment of methods for measuring friction for die compaction of powders has been undertaken as part of the European PM Modnet programme, and the potential accuracy of friction measurement required as input to models of the compaction process has been assessed using results from modelling sensitivity studies where friction was varied, together with specifications from industry of the accuracy of model output required.
Abstract: A ‘round robin’ assessment of methods for measuring friction for die compaction of powders has been undertaken as part of the European PM Modnet programme. Measurements have been made on a Distaloy AE with 0·5% graphite and 1·0% wax using five different shear based techniques and six techniques using instrumented dies. The potential accuracy of friction measurement required as input to models of the compaction process has been assessed using results from modelling sensitivity studies where friction was varied, together with specifications from industry of the accuracy of model output required. These studies suggest that an accuracy of measurement of friction coefficient of ±0·01 is preferred, but that an accuracy of ±0·02 will still give predictions of acceptable levels of accuracy. Friction data have been compared by separating the measurements into three regimes, respectively relevant to: • surfaces perpendicular to punch movement during compaction (Type 1), • surfaces parallel to punch movement...
TL;DR: In this article, phase evolution, thermal stability and interfacial structure of the oxides were characterised, and the formation mechanism of the complex oxides was clarified, where the oxide particle size was controlled by the relative amount of Y−Al-O and Y−Hf-O oxides.
Abstract: Co based oxide dispersion strengthening (ODS) alloys strengthened by oxide nanoparticles and γ′ precipitates are promising high temperature structural materials. Phase evolution, thermal stability and interfacial structure of the oxides were characterised, and the formation mechanism of the complex oxides was clarified. Co based ODS alloys exhibit inhomogeneous dispersion of the oxides due to the presence of relatively large Y–Al–O and fine Y–Hf–O complex oxides. Oxide particle size was controlled by the relative amount of Y–Al–O and Y–Hf–O oxides. The addition of Hf inhibits the formation of Y–Al–O oxides, resulting in the refinement of the oxides. The coherency of the matrix/oxide interface is size dependent. Large Y–Al–O complex oxides are incoherent with the matrix, while small Y–Hf–O nanoparticles tend to be partially coherent with the matrix. The extremely fine Y2Hf2O7 complex oxides demonstrate excellent thermal stability during heat treatment. Based on the observations of partially crystal...
TL;DR: In this article, the processing of three types of soft magnetic materials such as Fe 6·5Si, Fe 9·5 Si and Fe 50Ni compacts through the MIM techniques using different types of powders.
Abstract: Powder metallurgy is an effective way to produce the complex shaped soft magnetic materials, and also to decrease the eddy current loss in high frequency by subdividing the eddy current area due to the small grains. Especially, metal injection moulding (MIM) process allows nearly full dense and net shaping of a variety of engineering materials. The application of MIM process to hard and brittle materials such as ferromagnetic materials demonstrates the potential of this novel process. This study considers the processing of three types of soft magnetic materials such as Fe–6·5Si, Fe–9·5Si–5·5Al and Fe–50Ni alloy compacts through the MIM techniques using different types of powders to obtain high performance of soft magnetic properties.
TL;DR: In this paper, an investigation to identify the chlorides in hydrogenated-dehydrogenated Kroll processed titanium powder was carried out, where Jigsaw-like agglomerates containing submicroscopic particles were observed on titanium particles.
Abstract: An investigation to identify the chlorides in hydrogenated–dehydrogenated Kroll processed titanium powder was carried out in this study. Jigsaw-like agglomerates containing submicroscopic particles were observed on titanium particles, and the microcompositional analysis suggests the presence of magnesium and chlorine. Further detailed surface chemical analysis carried out by X-ray photoelectron spectroscopy and corresponding curve fitting work revealed that the magnesium and chlorine mainly exist as Mg(OH)Cl and titanium chloride respectively. A mechanism is provided to explain the presence of these chlorides in the Ti powder. The chlorides are considered to arise from the decomposition of hydrated magnesium chloride during the hydrogenation–dehydrogenation process and are supported by thermal analysis of a pure hydrated magnesium chloride. This analysis suggests that the Mg(OH)Cl can further decompose into hydrogen chloride gas and magnesium oxide at high temperature. The implications of the formation of...
TL;DR: In this article, the interface of bimetallic CoCrMo/cp2-Ti discs produced by either co-spark plasma sintering (SPS) or SPS bonding at a nominal temperature of 1273 K is made of a bonding layer and a diffusion layer.
Abstract: The interface of bimetallic CoCrMo/cp2-Ti discs produced by either co-spark plasma sintering (SPS) or SPS bonding at a nominal temperature of 1273 K is made of a bonding layer and a diffusion layer. The bonding layer is made of three sublayers with different Co, Cr, Mo and Ti contents. The diffusion layer is made of two layers with different microstructure: beta titanium close to interface and lamellar alpha–beta over the whole diffusion distance of Co, Cr and Mo. The measured diffusion profiles correspond to a slightly higher (40 K) temperature than the measured one into the die wall during sintering. Some residual porosity is observed in the cobalt alloy due to the effect of titanium, which sinters at a lower temperature, reducing the efficiency of the particular heating mechanism of SPS.
TL;DR: In this paper, the locally endurable stress amplitude for different loading modes and mean stresses is derived for a diffusion alloyed 4%Ni sintered steel (Distaloy AE) via the highly stressed volume approach.
Abstract: The increasing implementation of sintered steel parts for highly loaded engine and gear box applications is accompanied by the need for reliable fatigue design, especially in the pre-development phase. In most cases necessary characteristic values for the fatigue design of PM components, especially for sharply notched areas, are not available. In the present study, the locally endurable stress amplitude for different loading modes and mean stresses is derived for a diffusion alloyed 4%Ni sintered steel (Distaloy AE) via the highly stressed volume approach. The correlation of the locally endurable stress amplitude with the highly stressed volume, defined as Vx, is estimated for x = 80% and 90%, to evaluate both approaches with regard to PM steels. The applicability of assessing local cyclic behaviour by the highly stressed volume approach is demonstrated for a typical design detail of a highly loaded PM part. Characteristic values for the fatigue design of PM components are recommended.
TL;DR: In this paper, the densification and sintering behavior of a cryomilled copper powder (grain size of 17±2 nm and dislocation density of 6·26±0·04×1016 m−2) were investigated and compared to those of an atomised copper powder with the same mean particle size.
Abstract: The densification and sintering behaviour of a cryomilled copper powder (grain size of 17±2 nm and dislocation density of 6·26±0·04×1016 m−2) were investigated and compared to those of an atomised copper powder with the same mean particle size in order to highlight the effect of the nanostructure on spark plasma sintering (SPS). Oxygen and nitrogen contamination of the cryomilled powder gives rise to extensive degassing during SPS up to 400°C. The cryomilled powder is more resistant to plastic deformation than the atomised one, but the huge density of dislocations and grain boundary activates sintering at low temperature. Densification is therefore promoted by deformation in the atomised powder and by sintering shrinkage in the cryomilled one. As a consequence, in the SPS conditions investigated, the atomised specimen is densified but not sintered, while the cryomilled one is effectively sintered and consequently densified.
TL;DR: In this paper, an alternative description of wick debinding in the 2D compact-wick material combination is developed by numerical simulation, and the predictions of debinding time versus compact thickness squared and the debinding rate agree well with those issued by German and Vetter et al.
Abstract: Thermal debinding in metal powder injection moulding (MIM) is an intricate phenomenon. An alternative description of wick debinding in the 2D compact–wick material combination is developed here by numerical simulation. To simplify the problem and to qualitatively investigate the wick debinding process, the assumptions of a single component binder and fully saturated compact with molten binder are adopted. As the flow of molten binder is a moving boundary phenomenon, which is similar to a fluid flowing through porous media, a new numerical technique, body fitted FEM, is used to generate grids inside the physical domain and to calculate the distributions of pressure and other relative properties. Results show that the predictions of debinding time versus compact thickness squared and the debinding rate agree well with those issued by German and Vetter et al., respectively; this identifies the reliability and accuracy of the present numerical analysis. Low Reynolds number Re and low capillary number ...