Showing papers in "Powder Metallurgy in 2014"
TL;DR: In this article, the dependency of room temperature tensile ductility on oxygen was investigated for α-Ti, (α+β)-Ti and β-Ti alloys fabricated via traditional ingot metallurgy (IM), powder metallurgical (PM) and additive manufacturing (AM) or three-dimensional printing methods.
Abstract: Room temperature tensile ductility is an important property of titanium (Ti) and titanium alloys for structural applications This article reviews the dependency of tensile ductility on oxygen for α-Ti, (α+β)-Ti and β-Ti alloys fabricated via traditional ingot metallurgy (IM), powder metallurgy (PM) and additive manufacturing (AM) or three-dimensional printing methods and recent advances in understanding the effect of oxygen on ductility Seven mechanisms have been discussed based on case studies of individual titanium materials reported in literature The dependency of ductility on oxygen is determined by both the composition and microstructure of the titanium alloy For Ti–6Al–4V (wt-%), as sintered Ti–6Al–4V shows a critical oxygen level of about 0·33 wt-% while additively manufactured Ti–6Al–4V exhibits different critical levels ranging from about 0·22% to well above 0·4% depending on microstructure Rare earth (RE) elements are effective scavengers of oxygen in titanium materials even just wi
190 citations
TL;DR: In this article, the microstructural and mechanical properties of Ti-6Al-4V and stainless steel 316L have been compared under similar conditions, and their microstructures and mechanical behaviours have been analyzed in details.
Abstract: Ti–6Al–4V and stainless steel 316L have been processed by selective laser melting under similar conditions, and their microstructures and mechanical behaviours have been compared in details. Under the investigated conditions, Ti–6Al–4V exhibits a more complex behaviour than stainless steel 316L with respect to the occurrence of microstructural and mechanical anisotropy. Moreover, Ti–6Al–4V appears more sensitive to the build-up of internal stresses when compared with stainless steel 316L, whereas stainless steel 316L appears more prone to the formation of ‘lack of melting’ defects. This correlates nicely with the difference in thermal conductivity between the two materials. Thermal conductivity was shown to increase strongly with increasing temperature and the thermophysical properties appeared to be influenced by variations in the initial metallurgical state.
127 citations
TL;DR: In this paper, a criterion of "mechanically efficient volume" is defined for stiffness prediction from 3D X-ray microtomography images, and a variation of this criterion with process parameters, strut size and orientation has been studied.
Abstract: Additive manufacturing is a novel way of processing metallic cellular structures from a powder bed. However, differences in geometry have been observed between the CAD and the produced structures. Struts geometry has been analysed using X-ray microtomography. From the 3D images, a criterion of ‘mechanically efficient volume’ is defined for stiffness prediction. The variation of this criterion with process parameters, strut size and orientation has been studied. The effective stiffness of struts is computed by finite element analysis on the images obtained by X-ray tomography. Comparison between the predicted stiffness and the effective one tends to show that the efficient volume ratio leads to a slight underestimation of the stiffness. Finally, the effective stiffness is used at the scale of a unit cell. This can help define the build orientation and loading direction that lead to the highest stiffness.
53 citations
TL;DR: In this paper, the sliding wear behavior of nickel alloy powders was investigated after sintering, and the results revealed that the density of the material increased with raising the sinting temperature and holding time.
Abstract: In this study, nickel alloy powders were consolidated by spark plasma sintering. Experiments were performed between 700 and 750°C temperature range under 50 MPa pressure with holding times from 5 to 10 min. In addition to these main spark plasma sintering parameters three different heating rates ranging from 100 to 235°C min−1 and two different particle size ranges (75–106 μm narrow size distribution and −45 μm wide size distribution) were used for the experiments. After sintering, the sliding wear behaviour of the samples was investigated. The results revealed that the density of the material increased with raising the sintering temperature and holding time. However, heating rate and particle size also played an important role in the densification and these parameters were investigated in detail.
30 citations
TL;DR: In this article, the production of biomedical and biodegradable Mg alloy parts and implants by powder metallurgy and metal injection molding (MIM) respectively offers the opportunity for economic manufacturing of parts with mechanical properties matching those of cortical bone tissue, as well as the provision of porous surface structures beneficial for cell ingrowth and vascularisation.
Abstract: Currently, commercial biodegradable implants are mainly made from degradable polymers, such as polyglycolic acid or polylactide acid (PLA). These polymer implants, produced by injection moulding technique, suffer from long degradation times between 18 and 36 months, poor mechanical properties and acidic degradation behaviour. On the other hand, magnesium alloys are drawing increasing interest as biodegradable medical implant material for orthopaedic applications in bone tissue; thus, a replacement of polymers by Mg would be attractive. The production of biomedical and biodegradable Mg alloy parts and implants by powder metallurgy and metal injection moulding (MIM) respectively offers the opportunity for economic manufacturing of parts with mechanical properties matching those of cortical bone tissue, as well as the provision of porous surface structures beneficial for cell ingrowth and vascularisation. Furthermore, the technique guarantees a homogenous microstructure being crucial for a predictabl...
27 citations
TL;DR: In this article, metal injection molding was applied to fabricate Ti-22Nb alloy as a low modulus material for biomedical applications, and the nature of the titanium carbide precipitates in the as-sintered Ti-2C alloy was investigated.
Abstract: Metal injection moulding was applied to fabricate Ti–22Nb alloy as a low modulus material for biomedical applications. Tensile test specimens were injection moulded, followed by debinding and sintering. Sintering was at 1500°C for 4 h under vacuum (10–3 Pa). Selected as-sintered Ti–22Nb samples were hot isostatically pressed at 915°C/100 MPa for 2 h. The nature of the titanium carbide precipitates in the as-sintered Ti–22Nb alloy was investigated. Selected area electron diffraction patterns revealed that the carbides are Ti2C with a fcc structure. The calculation of the phase diagram showed a significant decrease of carbon solubility in Ti–22Nb compared with that in Ti from 500 to 1500 °C, contributing to the carbide precipitation in Ti–22Nb. Due to the carbide precipitation, the as-hipped Ti–22Nb alloy exhibited higher tensile strength but lower elongation than conventionally processed Ti–22Nb.
26 citations
TL;DR: In this paper, the authors used a confined electrolyte jet (Jet-ECM) to shape a hard metal, WC6Co, with Co as a binder to obtain the final shape.
Abstract: Electrochemical machining (ECM) is a complex technology used to shape conductive materials, for example hard metals. The workpiece material is removed by anodic dissolution in aqueous electrolytes at extremely large current densities. Hard metals are non-homogeneous and consist of hard particles, e.g. carbides, embedded in a softer matrix formed by metals such as cobalt, nickel, iron or alloys. The final shape is determined by a custom made tool, the cathode, or by a new technique with a confined electrolyte jet (Jet-ECM). An optimisation of this process intents to ascertain detailed information about the influence of current and potential distribution, composition of electrolyte, electrolyte flow geometry, electrochemical behaviour and dissolution mechanism of the components and structure of the interface material/electrolyte. Experiments on WC6Co, a common hard metal consisting of WC particles with Co as a binder, are presented as an example.
24 citations
TL;DR: In this paper, the effect of corrosion damage on cemented carbides was investigated, including residual strength assessment and detailed fractographic inspection of corroded specimens as well as detailed 3D FIB-FESEM tomography characterisation.
Abstract: The effect of corrosion damage on cemented carbides was investigated. The study included residual strength assessment and detailed fractographic inspection of corroded specimens as well as detailed 3D FIB-FESEM tomography characterisation. Experimental results point out a strong strength decrease associated with localised corrosion damage, i.e. corrosion pits acting as stress raisers, concentrated in the binder phase. These pits exhibit a variable and partial interconnectivity, as a function of depth from the surface, and are the result of heterogeneous dissolution of the metallic phase, specifically at the corrosion front. However, as corrosion advances the ratio between pit depth and thickness of damaged layer decreases. Thus, stress concentration effect ascribed to corrosion pits gets geometrically lessened, damage becomes effectively homogenised and relatively changes in residual strength as exposure time gets longer are found to be less pronounced.
23 citations
TL;DR: In this paper, high energy ball milling is used to reduce the diffusion distance for densification and introduce an additional densification mechanism allowing mass transport from the interior of the particle to the neck zone.
Abstract: Studies are performed to enhance low temperature sintering of Ti–6Al–4V High energy ball milling is found to be effective in lowering the sintering temperature through the mechanisms of particle size reduction and nanograin formation The former reduces the diffusion distance for densification, whereas the latter introduces an additional densification mechanism allowing mass transport from the interior of the particle to the neck zone Together, these two effects can reduce the onset temperature for densification by about 300uC Spark plasma sintering can further improve low temperature sintering when compared with radiant heat sintering and microwave sintering The enhanced densification is discussed on the basis of the applied pressure (50 MPa) and the intrinsic joule effect that leads to increase in the local temperature at the contact point between particles
21 citations
TL;DR: In this article, the effect of composition and milling time on mechanical properties and wear resistance of the composites were studied and wear tests were carried out using a block-on-ring tribometer at a load of 30 N with varying sliding speed.
Abstract: Copper–graphite (Cu–Gr) composites with 0, 5, 10 and 15 vol.-% graphite were processed via powder metallurgy route. The effect of composition and milling time on mechanical properties and wear resistance were studied. With increase in vol.-% of graphite, there was decrease in hardness of the composites. However, increasing milling time showed significant increase in hardness of the composites. Compressive strength of the composites containing 5 and 10 vol.-% of graphite was found to be 515 and 393 MPa respectively. The wear tests were carried out using a block-on-ring tribometer at a load of 30 N with varying sliding speed. The wear performance of the composites was found to be better with increase in milling time. The worn surfaces were analysed using FESEM. With increase in graphite content from 5 to 15 vol.-%, the coefficient of thermal expansion of the Cu–Gr composites decreased from 14·1 to 12·2×10−6/°C.
19 citations
TL;DR: In this article, porous parts are processed from titanium hydride based feedstocks containing space holders, and two formulations have been developed: a feedstock with a polyethyleneglycol based binder and NaCl space holder, and a feed stock with a paraffin based Binder and PMMA space holders.
Abstract: Biocompatibility, bone-like mechanical properties, and good bone-to-implant anchorage are current requirements for permanent implants. Porous titanium can satisfy these requirements provided that sufficient porosity, large enough pores and interconnections allowing bone ingrowth can reliably be obtained with controlled processes. In the present work, porous parts are processed from titanium hydride based feedstocks containing space holders. Two formulations have been developed: a feedstock with a polyethyleneglycol based binder and NaCl space holders, and a feedstock with a paraffin based binder and PMMA space holders. Depending on the sintering conditions, porosity levels between 30 and 60% and open porosity between 10 and 40% are obtained, with pore sizes in the range 50–500 μm. The microstructure, porosity and mechanical properties of porous titanium sintered at various temperatures have been characterised by scanning electron microscopy and compression tests.
TL;DR: The feasibility of using this route to process fit for purpose, complex parts is assessed in this article, where powder injection molding of titanium from metal hydride powders and binders composed of polyethylene, paraffin wax and stearic acid is presented.
Abstract: Recent developments are presented on powder injection moulding of titanium from metal hydride powders and binders composed of polyethylene, paraffin wax and stearic acid. The feasibility of using this route to process fit for purpose, complex parts is assessed. Titanium hydride offers a low cost solution compared with pure titanium powders. Feedstocks for powder injection moulding were prepared in a sigma mixer. Tensile test specimens and demonstration parts were injection moulded. Solvent debinding in heptane was followed by thermal debinding and dehydrogenation under argon. Titanium parts were sintered at 1200°C under argon. Sintered parts exhibit a linear shrinkage of about 20%, good shape preservation and reproducibility. The yield strength (519 MPa), ultimate tensile strength (666 MPa), elongation to fracture (15%) and interstitial content measured by quantitative analysis meet the requirements for titanium grade 4.
TL;DR: In this article, a combination of limited grain growth and minimised porosity was achieved on semi-industrial compact steels using spark plasma sintering (SPS) and the homogeneity of SPSed materials was characterized by electron microprobe and microhardness.
Abstract: Oxide dispersion strengthened steels are new generation alloys that are usually processed by hot isostatic pressing (HIP). In this study, spark plasma sintering (SPS) was studied as an alternative consolidation technique. The influence of the processing parameters on the microstructure was quantified. The homogeneity of the SPSed materials was characterised by electron microprobe and microhardness. A combination of limited grain growth and minimised porosity can be achieved on semi-industrial compact. Excellent tensile properties were obtained compared to the literature.
TL;DR: In this paper, Scanning electron microscopy image analysis, along with coarsening model, was used to predict eutectic and primary phase undercooling of particles.
Abstract: Impulse atomisation in helium and nitrogen and water atomisation have been utilised to produce powders of D2 tool steel. It was determined that higher cooling rates result in a lower percentage of eutectic. Scanning electron microscopy image analysis, along with coarsening model, was used to predict eutectic and primary phase undercooling of particles. Small particles exhibited a higher amount of undercooling. The particles exposed to a He atmosphere during atomisation had a larger amount of eutectic undercooling. The fraction of primary phase that solidified during the recalescence was then calculated based on the amount of primary phase undercooling under adiabatic conditions. In smaller particles, there was a larger amount of primary phase solidified during recalescence due to a higher amount of primary undercooling. Based on primary phase undercooling values, critical nuclei radius of austenite and assuming homogenous nucleation, the number of austenite unit cells in the stable nucleus was calculated.
TL;DR: In this article, the shrinkage kinetics on cold isostatic pressed iron specimens in the 550-730°C temperature range were investigated, showing that dimensional contraction is much higher than that predictable on the basis of shrinkage models, which neglect the effect of the prior cold compaction.
Abstract: Dilatometry experiments have been carried out to investigate the shrinkage kinetics on cold isostatic pressed iron specimens in the 550–730°C temperature range, showing that dimensional contraction is much higher than that predictable on the basis of the shrinkage kinetics models, which neglect the effect of the prior cold compaction. The greater shrinkage is due to an enhanced diffusivity which may be attributed to the large density of structural defects accumulated in the powder particles during compaction (structural activity). A time depending effective lattice diffusion coefficient was determined, with an Arrhenius type dependence on temperature.
TL;DR: In this article, the authors investigated the relationship between local mechanical behavior and strain distributions at the micro-scale in relation to the local microstructure of powder metallurgy (PM) steels.
Abstract: Microstructural features of sintered steels, which comprise both phases and porosity, strongly condition the mechanical behaviour of the material under service conditions. Many research activities have dealt with this relationship since better understanding of the microstructure–property correlation is the key of improvement of current powder metallurgy (PM) steels. Up to now, fractographic investigation after testing has been successfully applied for this purpose and, more recently, the in situ analysis of crack evolution through the microstructure as well as some advanced computer assisted tools. However, there is still a lack of information about local mechanical behaviour and strain distributions at the microscale in relation to the local microstructure of these steels, i.e. which phases in heterogeneous PM microstructures contribute to localisation of plastic deformation or which phases can impede crack propagation during loading. In the present work, these questions are addressed through the...
TL;DR: In this article, the effect of using combinations of debinding and sintering atmospheres in the micropowder injection molding of Invar 36 feedstocks based on cellulose acetate butyrate binders was studied.
Abstract: Micrometal injection moulding (μ-MIM) is a promising alternative for fabricating micro parts. Low coefficient of thermal expansion Fex–Ni1−x alloys are suitable to meet high dimensional stability with temperature keeping acceptable mechanical properties. However, these alloys are sensible of elements contamination during the debinding and sintering stages, and their dimensional stability and mechanical properties could be affected. The present work studies the effect of using combinations of debinding and sintering atmospheres in the micropowder injection moulding of Invar 36 feedstocks based on cellulose acetate butyrate binders. Microtensile specimens were successfully injected. Densification and microstructure at different conditions were linked with mechanical and physical properties of the parts. The processing conditions, and thus, the residual C, O and especially H influence severely these properties.
TL;DR: In this paper, the effect of post-sintering quenching treatment on the microstructure and mechanical properties of powder injection molded Ti-17Nb has been investigated.
Abstract: Ti–Nb alloys are attractive as biomaterials because of their excellent combination of low elastic modulus, high strength, corrosion resistance and enhanced biocompatibility. The effect of a post-sintering quenching treatment on the microstructure and mechanical properties of powder injection moulded Ti–17Nb has been investigated. Tensile test specimens were produced using a feedstock based on blended elemental powders, some of which were solution-treated in the β phase field and water quenched. Both as-sintered and quenched alloys had densities 95·5% of theoretical. The as-sintered material showed an α−β structure, whereas after quenching a fully martensitic α″ structure was obtained. The modulus of elasticity of the water-quenched alloy (∼45 GPa) was about 40% lower than that of the as-sintered alloy (∼76 GPa).
TL;DR: In this article, the authors developed a methodology to quantitatively determine the initial powder density distribution inside hot isostatic pressing (HIP) capsules, which were precompacted by different techniques.
Abstract: The final shape of powder metallurgy hot isostatic pressing (HIP) components is determined by many factors, including the shape and size of the capsule, the initial density distribution of the powder before HIP, and HIP process parameters. Current HIP simulation, which usually assumes that the powder inside the capsule is homogeneous, cannot predict non-uniform shrinkage. Therefore, the purpose of this work is to develop a methodology to quantitatively determine the initial powder density distribution inside HIP capsules, which were precompacted by different techniques. The relative density distribution obtained from experimental work is used as the initial condition for numerical simulations. The final shapes of the capsules produced by HIP are compared to simulation results. The paper shows the sensitivity of the final shape on the initial powder density distribution and illustrates the need to implement the initial powder distribution into the finite element model to improve the quality of the ...
TL;DR: In this paper, the structural evolution of Cu-12 wt ·%Ge (∼Cu-11 at·%Ge) alloy processed by means of mechanical alloying (MA) with subsequent heat treatment was studied using X-ray diffraction profiles, scanning electron microscopy, TEM and high resolution TEM observations as well as differential thermal analysis.
Abstract: The structural evolution of Cu–12 wt·%Ge (∼Cu–11 at·%Ge) alloy processed by means of mechanical alloying (MA) with subsequent heat treatment was studied using X-ray diffraction profiles, scanning electron microscopy, transmission electron microscopy (TEM) and high resolution TEM observations as well as differential thermal analysis(DTA). The fcc Cu(Ge) solid solution (α) was produced at early stages of MA and amorphised upon further milling. This was followed by the formation of ζ−Cu5Ge intermetallic nanocrystals after 40 h of milling. The subsequent annealing process led to the nanocrystallisation of the amorphous powder. The X-ray crystallite size data showed the exceptional thermal stability of the alloy prepared. The mechanism of the stability was also investigated. In addition, a thermodynamic analysis based on Miedema’s semiempirical model was carried out for the evaluation of the experimental results and a good agreement was found between them.
TL;DR: In this paper, Selective laser melting (SLM) offers a way to integrate the entire RFID tag in a metallic instrument while keeping the original shape, allowing small wall thicknesses and a reduced temperature impact on the RFID.
Abstract: Radio frequency identification (RFID) applications are becoming more and more important in logistics, especially for the purpose of tracking and managing items. Real time tracking of medical instruments during a surgical operation belongs to the state-of-the-art applications of this technology. The metallic environment in the operating room represents a big challenge, hampering the readability of the RFID tag. Currently, transponders are joined to metal instruments by bonding or clamping them inside a polymer shell, containing as little metal as possible. Assembling the tags is a time consuming process, which changes the usual shape of the instrument. It also represents a point of failure because of the possibility of losing the tag during the instrument’s life cycle. Selective laser melting (SLM) offers a way to integrate the entire RFID tag in a metallic instrument while keeping the original shape. Instrument manufacturing by SLM allows small wall thicknesses and a reduced temperature impact on the RFID...
TL;DR: The precipitation mechanism of small hafnium carbides in the sintered and thermo-mechanically processed molybdenum based alloy MHC (Mo −0·65Hf − 0·65C (at.-%)) is reported in this article.
Abstract: The precipitation mechanism of small hafnium carbides in the sintered and thermo-mechanically processed molybdenum based alloy MHC (Mo–0·65Hf– 0·65C (at.-%)) is reported. Light and scanning electron microscopy revealed hafnium oxides, large hafnium carbides and molybdenum carbide layers at the grain boundaries in the as-sintered material. Additionally, atom probe tomography showed a residual dissolved content of 0·12 at.-%Hf, but no carbon in solid solution. After thermo-mechanical processing of the as-sintered material in a deformation dilatometer, transmission electron microscopy revealed small hafnium carbides with diameters of 10–100 nm. These carbides were preferentially located at dislocations and dislocation networks. Without deformation prior to aging, no formation of small hafnium carbides was observed. X-ray diffraction confirmed that decomposition of molybdenum carbides had occurred, which delivered the carbon for the formation of strain induced precipitates.
TL;DR: In this paper, a modified preparation method of combining planetary and vibratory ball milling was proposed to prepare Mg-based hydrogen storage alloy powders, and the comparison of micromorphology and hydrogen storage behavior between Mg2Ni prepared using the modified and conventional preparation methods were investigated experimentally.
Abstract: In this study, the modified preparation method of combining planetary and vibratory ball milling was proposed to prepare Mg based hydrogen storage alloy powders. The comparison of micromorphology and hydrogen storage behaviour between Mg2Ni prepared using the modified and conventional preparation methods were investigated experimentally. The comparison results showed that the combination of first planetary and then vibratory ball milling has more favourable effect on improving both the kinetics and the thermodynamics of ball milled Mg2Ni alloys. The sample synthesised by first planetary milling for 40 h and then vibratory milling for 30 h has faster hydrogen absorption kinetics and lower dehydriding onset temperature than those prepared by the single method of planetary or vibratory milling and hydriding combustion synthesis owing to its popcorn-like microstructure. Moreover, this kind of modified method reduces the reaction enthalpy and activation energy by up to ∼18 and 22% respectively.
TL;DR: In this paper, the influence of the process parameters on various powder quality features has been investigated, using copper-tin alloys as feedstock material, including particle size distribution, appearance of satellite particles, particle circularity and the flowability.
Abstract: As part of a project to develop a small batch metal atomisation system, based on free fall atomisation and close-coupled atomisation, the influence of the process parameters on various powder quality features has been investigated, using copper–tin alloys as feedstock material. Particle size distribution, appearance of satellite particles, particle circularity and the flowability were recorded as criteria of particle quality. From the data obtained in these experiments, the effects of the main process parameters (atomisation pressure, mass melt flow, and height of the spray chamber as well as the atomiser system) have been evaluated with respect to powder quality features. The atomisation system was optimised to produce high quality powder with narrow particle distributions (d84·3/d50·3 = 1·6 for free fall) and high circularity with mass melt flows in the range of 100 kg h−1 using melt volume between 100 and 1000 mL.
TL;DR: In this paper, the authors proposed defect detection and classification capability for automatic analysis of digital radiographic images from powder metallurgy (PM) parts potentially allows integration into multiple-view inspection systems, which should enhance quality control in the PM manufacturing and production environment.
Abstract: Digital radiography is a promising non-destructive testing tool for powder metallurgy (PM) parts, in which transmitted X-rays are recorded to generate data for an advanced defect detection system. An important part of this system is the data processing platform for pattern recognition in X-ray images. Combinations of advanced techniques for noise reduction, contrast enhancement and image segmentation are employed. Algorithms of registration for images in regions of interest are discussed, e.g. the scale invariant feature transform (SIFT). Modern pattern recognition methodologies such as smoothing, moment representation, image alignment and optical flow towards feature classification are evaluated. The proposed defect detection and classification capability for automatic analysis of digital radiographic images from PM parts potentially allows integration into multiple-view inspection systems, which should enhance quality control in the PM manufacturing and production environment. Defect detection s...
TL;DR: In this paper, the tensile and high cycle fatigue properties of powder injection molding (PIM) samples were examined at room temperature and elevated temperatures, and the inferior properties of the MIM material were caused by considerable remaining porosity, enlarged grain size and increased interstitial content.
Abstract: Tensile and high cycle fatigue properties of Ti–6Al–4V samples fabricated by powder injection moulding (PIM) are examined at room temperature and elevated temperatures. Standard wrought Ti–6Al–4V material is used for comparison. The tensile and the fatigue strength of samples fabricated by powder injection moulding are found to be significantly lower than conventional wrought material. On the other hand, strength and ductility of metal injection moulded (MIM) samples are high enough to be of large practical interest, in particular if the low processing costs for intricate shapes are taken into account. The inferior properties of the MIM material are caused by considerable remaining porosity, enlarged grain size and increased interstitial content. Prolonged sintering times lead to improved density and strength. At the same time, the room temperature ductility is observed to drop to very low levels, presumably because of additional grain growth.
TL;DR: In this article, a thermal analysis of the reducing power of various sintering atmospheres (active gas content ≤ 10 vol.-%) and their combined effect with graphite has been investigated.
Abstract: Development of strong inter-particle necks requires successful removal of surface oxides, present on the powder particles, during the initial stages of sintering. In the case of water-atomised powder prealloyed with chromium, the surface oxide consists mainly of an iron oxide layer with some more stable fine particulate oxides. The formation of sufficiently strong inter-particle necks requires as a minimum full removal of the iron surface oxide layer. This can be achieved by gaseous reducing agents (e.g. H2, CO or a mixture of both) or by carbon, typically admixed in the form of graphite. The reducing power of various sintering atmospheres (active gas content ≤10 vol.-%) and their combined effect with graphite has been investigated by a thermal analysis technique. Results indicate that a combination of a dry hydrogen-containing atmosphere and fine graphite allows successful sintering of chromium alloyed PM steels.
TL;DR: In this paper, the Ni plated Ti powder was characterised by scanning electron microscopy, energy dispersive spectrometer analysis and X-ray fluorescence, and it was found that a pure/uniform Ni layer may be deposited on the Ti powder particles.
Abstract: In this study, Ti powder (average size: 45 μm) was plated/coated by electroless Ni with hydrazine hydrate as reductant. The Ni plating was carried out at 85°C and pH 9–10. The influence of process parameters such as plating period as well as reductant concentration was investigated. The Ni plated Ti powder was characterised by scanning electron microscopy, energy dispersive spectrometer analysis and X-ray fluorescence. It is found that a pure/uniform Ni layer may be deposited on the Ti powder particles. The deposited mass increases as plating period/reductant concentration increases.
TL;DR: Powder metallurgical (PM) steels with elemental Ni additions exhibit non-homogenous microstructures with soft Ni rich areas, lean in C, after conventional sintering.
Abstract: Powder metallurgical (PM) steels with elemental Ni additions exhibit non-homogenous microstructures with soft Ni rich areas, lean in C, after conventional sintering. Though, the exact correlation b ...
TL;DR: In this article, the authors investigated the magnetic properties of soft magnetic composites with different particle sizes under a cryogenic condition and confirmed the influence of temperature on magnetic parameters, showing that total power loss density has increased with decreasing temperature.
Abstract: Magnetic properties of Fe based composite materials with different particle sizes under a cryogenic condition have been investigated. Realisation of this venture has been carried out at the liquid nitrogen temperature. Results of energy loss density were obtained from measurements of the static (dc) hysteresis cycles ranging from 0·1 to 1·0 T. In turn, results of power loss density were obtained from measurements of the dynamic (ac) hysteresis cycles ranging from 50 to 1000 Hz and at the maximum flux density of 0·5, 0·8 and 1·0 T. The study confirmed the influence of temperature on magnetic parameters. It has been shown that total power loss density has increased with decreasing temperature. We report changes in a nature of energy loss after immersing specimens made of soft magnetic composites in liquid nitrogen. Measurements of the maximum relative permeability were also conducted.