Additive manufacturing of metal components is commonly performed by laser or electron beam melting for direct consolidation of powders, but there are also other techniques available, e.g. the ink-jet on powder bed used by Digital Metal®. Höganäs Digital Metal has been involved in additive manufacturing since 2010, with a technology that utilizes separate forming and consolidation processes. Precision inkjet on powder bed is used for production of green components, and these components are then sintered to obtain final density and strength. The technique is successfully used to produce components in 316L stainless steel, but basically all types of metals or alloys, available as powders with suitable morphology and particle size can be used to print components. The following sintering process then can be optimized for each individual alloy, making processing of a wide selection of alloys possible. In this study, possibilities and challenges with different alloys are discussed.
As Ni-based superalloy has poor workability, direct laser forming (DLF) would be a powerful tool for fabricating the complex shaped Ni-based superalloy parts. We focused on the microstructure of the parts produced by DLF, the crystal grains of which grow along the building direction. This anisotropic microstructure is one of the major features of the parts produced by DLF, and which may cause anisotropic mechanical properties.In this work, the optimum laser-forming conditions such as laser power, laser scan speed, and powder feeding rate were determined by evaluating the density of the produced parts. Three types of tensile test pieces and two types of fatigue test pieces were fabricated in different building direction. They had higher ultimate tensile strength than that of JIS standards in wrought materials. However, their elongation was lower than that of JIS standards, and also the dispersion of elongation was large. On the other hand, fatigue limit was a little lower than the standard value. It was confirmed that the mechanical properties of Ni-based superalloy parts produced by DLF were different by a difference in building direction.
This paper reports on the effect of sintering temperature on the density, hardness and strength of Co30Cr6Mo fabricated by Metal Injection Molding (MIM). Palm stearin and polyethylene have been used as the binder system. The feedstock was injected by injection molding machine to produced micro dumbbell shape part. The specimens were solvent debound in n-hepthane for 15 minutes and thermally debound in argon atmosphere for an hour. The sintering was carried out in vacuum furnace at temperature 1250 °C, 1300 °C and 1350 °C for an hour. The density, hardness and tensile strength were then measured. The specimens that have been sintered at 1350 °C showed highest density and tensile strength compared with samples sintered at 1250 °C and 1300 °C. The samples which has been sintered at 1350 °C has highest relative density (93 %), compared with the same sample sintered at 1250 °C (87 %) and 1300 °C (76 %). As the temperature increased, the tensile strength increased gradually 400 MPa to 700 MPa and the micro hardness also increased from 200 Hv to 540 Hv. The morphology of sintered specimen showed that the morphological bonding between powder particles becomes denser at highest sintering temperature of 1350 °C.
Ti and its alloys show the excellent characteristics such as low density, high strength, high corrosion resistance and high biocompatibility. Therefore, they have been widely used for various industrial and medical applications. However, they have poor workability, it is difficult to produce the complicate shaped and precise parts. Therefore, the metal injection molding (MIM) is hoped to be a suitable technique for fabricating the complex shaped Ti or its alloy parts with low cost.In our previous studies, it was found that the strengthening of sintered Ti-6Al-4V alloy compacts were available by addition of Fe or Cr powders because of their solution strengthening of beta phase.In this study, the metal injection molding process has been applied to fabricate high strength Ti alloy compacts using mixed elemental powders. The alloy composition was replaced V with Fe, Cr or Mo in Ti-6Al-4V alloy. Eventually, more than 1100 MPa of strength and 8 % of elongation were achieved in Ti-6Al-12.5Mo alloy compact by MIM process.
Titanium alloys show not only the excellent mechanical properties but also good biocompatibility. However, they show normally poor machinability, which become the disadvantage of high processing cost. Metal injection molding (MIM) process is one of the techniques to improve that drawback. Because MIM process can produce the three dimensional complex shaped parts at low cost. Ti-6Al-4V is a typical titanium alloy and the MIM compacts show high static strength as same as wrought materials. However, their fatigue strength is a little low level as compared to wrought materials. To improve the mechanical properties of Ti-6Al-4V alloy compacts, it is important to refine the grain size and increase the relative density. In this study, the effects of the particle size of the powders on the mechanical properties were investigated. The use of a fine powder improved the mechanical properties because of their high density. Moreover, the crystal grain growth was restrained as compared to the case of the same relative density using larger powder.
Ti-6Al-4V alloy has attracted a lot of attention from the automotive and aerospace industries because of their outstanding specific strength and corrosion resistance. On the other hand, Ti-6Al-4V alloy has normally poor workability because of the low thermal conductivity and the low elastic modulus. Metal injection molding (MIM) process is expected to manufacture a complex part with near net shape and reduce the manufacturing cost. However, Ti-6Al-4V alloy compacts by MIM process had a problem of low fatigue strength compared to wrought material.In this study, we tried to add a minor amount of boron using TiB2 powder for improving the fatigue strength. Addition of boron resulted refinement of the grain size of lamellar structure, which lead to increase the high cycle fatigue strength and fatigue limit. In addition, tensile properties at high temperature was investigated.
It is not easy to fabricate the complicate shaped titanium aluminide (Ti-Al) components by conventional methods such as machining or forging, and casting leads to inhomogeneous microstructures. Metal injection molding (MIM) has the potential to be a cost-efficient process and near net shape technique, especially for the complex shaped mass-produced components. In this study, Ti-Al intermetallic alloy compacts were fabricated through MIM technique. Sound compacts with over 95 % of relative density and without any warpage or defects were obtained thorough MIM process. Different microstructures of duplex, near lamellar, and full lamellar were obtained by changing the sintering temperature. Their tensile strength at room and high temperature is 85 to 90 % of that of wrought material. Tensile strength of MIM compact would be expected the same level with cast materials by optimization of sintering conditions, densification by HIP treatment and so on.
Superalloy has been used for aerospace application because of their excellent attributes of high strength and corrosion resistance at high temperature. Inconel 718 is one of the representative Ni-based superalloy. Generally, superalloy has poor workability, especially high tool wear by machining, so that it is not easy to produce the components of complex shaped parts at low cost. To overcome such as the problem, metal injection molding (MIM) process would be a useful technique which offers net shape production, high design flexibility, and high cost efficiency for mass production. In this study, gas-atomized fine alloy powder of Inconel 718 was prepared for MIM process, and the mechanical properties of injection molded compacts were investigated. The relative density over 99.7 %, which is much higher than density of usual MIM compacts, was obtained by supersolidious liquid-phase sintering. Furthermore, injection molded Inconel 718 showed high fatigue strength comparable to the wrought materials, because the pore size of the MIM compacts was smaller than the inclusion size of wrought materials. And it was found that the grain size was more dominant than pore size against the fatigue failure of MIM Inconel 718 with near full density.
Metal injection molding (MIM) was applied to Al powders. Sintered Al compacts were prepared by MIM in this study. At first, sintered pure-Al compacts were prepared under various process conditions. The relative densities of the compacts debound in Ar gas and sintered at 650 °C for 2 hr in vacuum of 10−3 Pa order were 86 %, 90 % and 96 % when the average particle size were 20 μm, 10 μm and 3 μm, respectively. The 3 μm powder compact had the excellent tensile strength of 120 MPa and elongation at fracture of 19 % at room temperature. Next, the addition of Si powder to Al powder was examined to improve sinterability of Al powder. Regardless of Al powder size, the addition of Si powder widely enhanced densification of sintered Al compacts. Using Al powder of 35 μm, the relative density of the sintered pure-Al compact was only 66 %, while that of the sintered Al-1 mass%Si compacts went up to 89 %. When Al powder of 11 μm was used, the sintered Al-1Si compacts had the relative density of 97 % and the tensile properties close to annealed wrought pure-Al.
Metal Injection Molding (MIM) is an effective way to manufacture small components with low cost and high precision. However, in the case of large components, it becomes difficult to control the distortion and cracking because of the big shrinkage during debinding and sintering process. Therefore it is important to optimize the condition of each process to reduce the distortion of MIM compacts. Moreover, powder size is also one of the most important parameters. The small particle powder shows high shrinkage and high density as compared to large particle powder during sintering process. In this study, blending of both powders was conducted and the influence of powder size distribution on the distortion of complex shaped parts was evaluated. A coordinate measuring machine, which is a 3D device for measuring the physical geometrical characteristics of an object, was used to measure the distortion. Finally, through controlling the distribution of particle size, distortion of the comparatively large and complex shaped MIM compacts was successfully restrained.
The interfaces between diamond and metal (Al or Ag) in the diamond/50 vol%Al and diamond/50 vol%Ag composites were characterized by Raman scattering spectroscopy. In the diamond/50 vol%Al composite, graphitization of diamond has been partly detected in the diamond region close to the interface between diamond and Al. On the other hand, a fairly thick graphitized layer of about 8 μm has been formed in the diamond/50 vol%Ag composite. It is concluded that the thick graphitized layer is attributed to the higher sintering temperature in the diamond/50 vol%Ag composite.
FeB-Ni hard materials were consolidated by both electroless plating and spark sintering processes for the development of ubiquitous hard materials. Uniform nickel layers were formed quantitatively on as-received FeB powder surfaces. The amorphous Ni layers transformed to poly-crystalline during spark sintering. Sintering curves of FeB-Ni compacts showed the similar behaviors regardless of Ni contents, although their apparent relative densities were increased with the increment of Ni contents. Moreover, the sintering mechanism of FeB-Ni and pure Ni compacts consisting of both the plastic deformation and power law creep deformation occurred during spark sintering. Their maximum points of Ḋ were shown in the D of approximately 0.78. The plastic and power law creep deformation were predominantly consolidation mechanisms before and after maximum Ḋ, respectively. Values in HRA of FeB-Ni compacts were decreased with increment of the Ni contents. The compressive stress of FeB-Ni compacts was decreased with the increment of the Ni contents in contrast to the compressive strain.
Higher manganese silicide (HMS) is promising as one of eco-friendly p-type thermoelectric materials which are useful to power generation system using the waste heat with medium temperature from 600 to 900 K. We investigated about the doping effect of cobalt and iron on thermoelectric properties of the HMS compounds in this study. A combined process of vibration ball milling (VBM) and pulse discharge sintering (PDS) is used for fabricating the HMS compounds. Mn and Si powders milled individually using VBM were mixed with Co or Fe fine powders in argon atmosphere. The powder mixtures were sintered and simultaneously the HMS compounds were synthesized using the PDS process. Syntheses of Co-doped and Fe-doped HMS compounds were confirmed. The lattice parameters of a-axis in (Mn1−xCox)15Si26 compound decreased with Co content (x ≤ 0.01) and held constant within the range of x = 0.01~0.1, and that in (Mn1−yFey)15Si26 compound decreased linearly with Fe content (y ≤ 0.1). The doping limit of Co in HMS existed around x = 0.01. The thermoelectric performance ZT was decreased with Co content. On the other hand, the maximum ZT of 0.55 was achieved at 773 K by doping Fe with y = 0.005.
A pre-alloyed powder metallurgy method has been investigated in order to produce high-strength titanium alloy at a lower cost than by currently executed blended elemental powder method. Ti-6Al-4V alloy bars containing 3.5 %Fe and 4 %Cu of ϕ 22 mm were produced using Ti-6Al-4V alloy powder as a starting material by hot isostatistic pressing (HIP) followed by forging and hot-rolling. The material densified to almost 100 % density through HIP process. Microstructure after hot rolling at the temperature of (α + β) region showed fine equi-axial grains. Tensile characteristics of Fe and Cu containing alloys were strongly influenced by heat treatment condition. Just after hot rolling or heat treatment, especially air-cooling, the addition of Fe and Cu resulted in high strength but poor elongation. Water-cooled material showed enough elongation but a little bit poorer strength. These tensile characteristics seem to be explained by the β phase ratio in the alloy. This result shows that tensile properties of Ti-6Al-4V alloys containing Fe and Cu can be controlled by heat treatment condition, and possess high potential in the application for airplane and automobile.
In cold spray deposition, powder particles accelerated to several hundred meters a second impact the substrate and deform into splats that are stacked up to form dense coatings on the substrate. These deposited splats, however, are usually not fully bonded to each other, making deposited materials less ductile than wrought materials. An ultrasonic washing test, applied to Cu coatings sprayed on Al substrates, revealed poor splat bonding along spray boundaries and spray layer boundaries. Thickness measurements of coatings deposited with a single linear spray traverse yielded profiles that are approximately Gaussian curves but with reduced edges. We attribute the reduced edges of the thickness profiles to lower particle impact velocities and temperatures in the outer regions of the spray cone. A simulation model was developed that can predict locations of poor-bonded regions in coatings produced by multi-traverse cold-spray deposition from experimentally determined thickness profiles of single-traverse coatings.
Micro channels made of polymers are commonly used for MEMS and μTAS (micro-total analysis system) devices. In this research, we developed a process for fabricating a ceramic sheet with micro channels. The developed process is based on powder metallurgy process. A compound material, a mixture of ceramic powder and polymer, was prepared as sheet material. We employed laser machining to machine the sacrificial layer to form micro channels inside the sheet. We also employed imprinting, which is a process of pressing with a mould while heating, to form a structure with surface patterns and micro channels curving along with it. After the imprinted sheet was debound and sintered by heating, a ceramic sheet with micro-surface patterns and micro channels was obtained. As ceramics have high heat durability and low chemical reactivity, ceramic micro channels can be used for flow sensors or chemical reaction testers operated in harsh environments, such as high temperature or mechanical parts operated with reactive chemicals. In addition, by imprinting wavy patterns, the surface area can be increased. Therefore high efficiency heat exchangers can be built. Moreover, this method can be applied on SOFCs (solid oxide fuel cell) by fabricating YSZ (yttria stabilized zirconia) micro channels.
Yttria-stabilized zirconia (YSZ) has been used for an electrolyte of solid oxide fuel cells (SOFC). To enhance the efficiency of SOFC, we developed a corrugated, or wavy-shaped, YSZ sheet for the electrolyte. As the corrugated sheet has larger surface area than a flat-type sheet, higher energy density can be obtained. We have proposed micro powder imprint (μPI) with multi-layer imprint process to fabricate micro scale pattern on the both surfaces of a thin YSZ sheet. The μPI is a combined process of nano imprint lithography and powder metallurgy; the resolution is high, and the process is mass-productive. In this work, we selected a compound material containing YSZ powder and a binder consisting of thermoplastic resin as a starting material. The compound sheet was prepared by tape casting from slurry and was imprinted by a fine-patterned mold with stacked on a silicone rubber sheet. The silicone rubber was so flexible that micro patterns on the both sides of the compound sheet was obtained after imprint. In the present work, the process condition of μPI and the heat program of debinding and sintering were also considered. As a result, a wave-type sintered YSZ sheet without significant defects was successfully obtained.
All-ceramic artificial teeth were produced using a high-speed centrifugal compaction process (HCP) combined with a resin shell-mold made by a 3D printer. Slurries of alumina or zirconia fine powders filled the inside and outside of the mold and then rotated at between 7,000 and 11,500 rpm in a centrifuge (HCP buried compaction method). Using this method, crack-free green compacts were produced. The shell-molds were not deformed or broken because the inner and outer pressures generated during the HCP were quasi-balanced. Two methods for mold-releasing, thermal decomposition and mechanical de-molding by hand, were investigated. Thermal decomposition introduced the critical problem of sintering inhibition. To obtain the final products, the compacts were air sintered after being released from the molds. For alumina, green compacts of high packing density (63 %) were sintered homogenously without considerable deformation. For zirconia, the packing density reached approximately 55 % with a density gradient. The zirconia compacts were sintered inhomogeneously, which resulted in a density gradient and deformation. The density gradient and shape deformation of the sintered compacts are discussed.
This work explored porous metal impregnation via a high temperature centrifugation process. Impregnation was accomplished by combining a low Tm (411 K) Sn-Bi alloy and P/M-processed stainless steel or alumina matrices (normally exhibiting poor wettability by the alloy) in a capsule, followed by heating to 673 K. This capsule was subsequently set in a heat-insulating vessel and rotated in a centrifuge up to 10,000 rpm. By this process, the molten alloy was forcibly impregnated into the pores of the matrices. The minimum pore size at which the alloy penetrated the matrix was found to increase as the centrifugal force was increased. At the maximum centrifugal force, the alloy could be impregnated into pores only several microns in size. The impetus for impregnation was found to be the pressure applied to the molten alloy by the centrifugal force. The pore size that could be impregnated at a given centrifugal force (which correlated with the pressure generated) could be readily predicted using the Washburn equation.
Diesel nozzle tips with tapered spray holes (inwardly larger) were produced using newly developed powder metallurgy (P/M) processing. Spray holes were formed by resin cores made by a three-dimensional printer. A 2.6 μm steel powder (SCM415) was prepared as a slurry, and was compacted using a high-speed centrifugal compaction process into the resin mold with the core. The mold, core, and binder in the green compacts were eliminated by thermal decomposition, and the compacts were sintered by successive heating. Nozzle tips with three tapered holes were made in the sintered products without cracking or breakage. Although some problems exist in the remaining pores, large outlet holes (about 200 μm) and a carbon residue, the holes can be used for spray examination.
We aimed to develop a new powder metallurgy process to produce next generation common rail diesel nozzles with tiny and complexly shaped holes. High-speed centrifugal compaction and powder metallurgy were used. Three nozzle samples with holes of straight and tapered (8°, 16°, enlarged inwardly) were made. Three samples without external and inner defects were examined by spray test, which was performed with an ambient pressure of 1 and 4 MPa, an injection pressure of 150 MPa, and was studied by filming using a high-speed camera at 8000 fps. The measuring parameters were the penetration, spray angle, and spray cone angle from the spray aperture. As the taper angle increased, the penetration and spray cone angle increased.
Carbon is a key element for powder metallurgy. For example, carbon is the basic alloying element in PM sintered steel, and carbon powders are used as a carbon source for the production of hard metals. However, there are only a few studies about the mechanisms of carbon dissolution and reactivity in dependence on the carbon sources with solid metals/oxides.
This work presents the effect of the carbon source (different graphite and carbon black types) on the reactivity and efficiency of oxides reduction during the sintering of PM steels and on the synthesis of nanocrystalline WC powders.
This experimental work sets the basis for optimizing the production of PM steel parts and nano-WC powders based on raw material selection and process conditions.
Magnesium based composite containing 10 vol% Al2O3 particle was produced by a mechanical milling (MM) and spark plasma sintering (SPS) process and the nanoparticle formation by Mg/Al2O3 interfacial reaction was investigated in detail. The microstructural observation of the MM powder and SPS compact was carried out by scanning electron microscopy (SEM), X-ray diffraction (XRD), and transmission electron microscopy (TEM). TEM / EDS analysis and XRD result reveal that the nano Mg17Al12 and MgO phases are formed by Mg/Al2O3 interfacial reaction. The solute oxygen by Mg/Al2O3 interfacial reaction and magnesium of the matrix may immediately produce MgO, because magnesium barely dissolves oxygen. Therefore, many MgO particles are formed at the Mg/Al2O3 interface. On the other hand, magnesium can dissolve aluminum to some extent and the aluminum over the solubility limit may bond to magnesium, resulting in the formation of Mg17Al12.
SrTiO3 is attracting much attention as a photocatalytic material for water splitting. SrTiO3 powders have been conventionally prepared by a solid-state reaction at around 1000 ºC. Our group has taken an alternative approach by developing a novel method for preparing perovskite oxide powders at low temperature (< 50 ºC) without the use of solvents such as water or organic solvent. We found that a highly crystallized SrTiO3 fine powder could be obtained at room temperature simply by letting a powder mixture of Sr(OH)2·8H2O and TiO2·nH2O gel stand for a number of days. In this study we investigated how the water included in the TiO2·nH2O gel affected the crystallinity and particle properties of the SrTiO3. The photocatalytic activity of the material was also investigated.
A TG-DTA analysis was performed to determine the n values of various kinds of TiO2·nH2O gels prepared by changing the duration of drying at 100 ºC. The crystallinity of fine particles evaluated from the integral width of the XRD pattern improved as the n value increased.
By virtue of their small particle size, SrTiO3 fine particles decomposed methylene blue via UV irradiation more effectively than a powder prepared by solid-state synthesis.
Friction powder sintering (FPS) is a recently-developed technique to produce particulate metal matrix composites (PMMCs). In FPS, powders including metallic and ceramic particles are compacted by the pressure and frictional heat induced by a rotating tool. We have applied FPS to obtain Al-50 vol.% SiC PMMCs and evaluated the thermal conductivity of the composites. FPS has been performed under the tool rotating rate of 1500 rpm and tool pressure of 31 MPa. By extending the sintering time from 1 minute to 2 minute, the relative packing density has increased from 81 % to 91 %, and the thermal conductivity has been enhanced from 66 W/mK to 110 W/mK. It has been noted that the further densification of the composites is necessary to draw the potential thermal conductivity.
Bending durability tests were carried out using P/M spur gears made from 1.5Cr-0.2Mo pre-alloy sintered steel powder (FL520X) with a density of 7.40 Mg/m3 (GH1) and 7.55 Mg/m3 (GH2). The P/M gear specimens were machined from the sintered packs made by the single-press single-sinter route, and some were surface-rolled using a CNC form-rolling machine of two roller-dies type. All of the test gears were case-carburized. The bending durability was investigated by single tooth bending fatigue tests using a pulsator. A two-dimensional finite element simulation model were constructed and examined the effects of the void distributions and the surface densification depths on the bending stress distributions at the critical section on the root fillet of gear tooth flank. Both the experimental and the analytical results show that the bending durability and the stress level of surface-rolled GH1 completely matches that of GH2, whose bending fatigue strength is higher than the target level of 1 GPa.
A newly developed Ni-free pre-alloyed steel powder, Fe-0.5 %Cr-0.2 %Mn-0.2 %Mo (JIP® 5CRA) shows a rotating bending fatigue limit of 510 MPa after compacting, sintering and case-hardening process. This is approximately 40 % higher than that of a case-hardened sintered steel based on a conventional diffusion bonded steel powder, Fe-4 %Ni-1.5 %Cu-0.5 %Mo (4Ni). This is attributed to the higher compressive residual stress of the 5CRA based material. In spite of the higher fatigue limit, its tensile strength is lower than that of the 4Ni based material. The difference in the microstructural transformation behavior is a possible cause of this reverse phenomenon.
Effects of graphite additive contents and processing parameters on the mechanical properties of sintered and case-hardened compacts made of molybdenum hybrid-alloyed steel powder have been investigated. High tensile strength and impact value were obtained in the conditions of the medium internal carbon content, higher sintering temperature, lower carbon potential or shorter carburizing time. The mechanical properties are deteriorated due to increasing hard martensite phases with high carbon content. It is believed that the reduction of these mechanical properties are mainly caused by increasing of brittle fracture by an internal notch effect of the pores, because the hard martensite phase have a high notch sensitivity.
Diffusion bonded alloy powders such as Fe-4 %Ni-0.5 %Mo-1.5 %Cu (AE) and Fe-1.75 %Ni-0.5 %Mo-1.5 %Cu (AB) are widely used for many PM components due to their high mechanical strength. This is primarily an effect of the unique heterogeneous microstructure with martensitic structure around pores that is created already after ordinary sintering, i.e. not sinter hardening. Consequently, these materials achieve much higher strength than the traditional Fe-Cu-C alloying system. These alloying systems also achieve higher densities in comparison to pre-alloyed powder due to their higher compressibility. On the other hand to increase the competitiveness of PM a leaner diffusion bonded alloy powder Fe-0.5 %Ni-0.5 %Mo (AQ) and some lean pre-alloyed powders have been developed. The as-sintered mechanical properties of them are not adequate in comparison with AE or AB. However, if the heat-treated properties of them are comparable to AE or AB, those leaner alloys would introduce as a more cost effective alternative. First, in order to clarify what the advantage or the disadvantage of AE, AB and AQ is, static and dynamic mechanical properties of them were compared in this study. Second, the mechanical properties of AQ were compared with properties obtained with the lean pre-alloyed materials Fe-0.85 %Mo (85Mo) and Fe-0.45 %Mo (45Mo) at different heat treatment conditions.
Numerous automotive and non-automotive components are currently manufactured by powder metallurgy (PM) using stainless steel powders. Compared to ferrous PM powders, stainless steel powders have higher flow rates, lower apparent densities and lower green strength. These differences in powder properties can make the manufacture of PM stainless steel components more challenging compared to ferrous PM mixes. A new lubricant system has been developed taking into account the unique morphology and particle size distribution of stainless steel powders. The new lubricant system was evaluated against currently industry standard lubricants for powder properties, mechanical performance and corrosion resistance. The new lubricant system was observed to have superior performance over the standard lubricants.
Machining of sintered steel parts is sometimes necessary in order to produce complicated geometries like undercut which are hard to realize by uniaxial pressing and to meet customer requirements of higher dimensional accuracy. Although cutting costs account for a high percentage of the total manufacturing cost of sintered steel parts, and improvement of the machinability of sintered steel is desired. In this paper, performance characteristics of newly developed additive to improve the machinability of sintered steel were investigated on several conditions. The amounts of tool wear were significantly different according to the tool materials and cooling condition of cutting. However, in comparison with sintered steels without an additive and with the manganese sulfide, the machinability of sintered steel with new additive was improved simultaneously in drilling and turning for remarkable effects under various conditions.
The advent of direct injection turbocharged engines has increased the need for higher performance connecting rods, able to withstand higher compressive loads in operation. In this respect, the compressive yield strength of the materials used to manufacture connecting rods is of paramount significance as it becomes the most important design factor. Connecting rods are currently designed using mechanical properties obtained at room temperature; however, the operating environment in an engine can have negative effects on their performance, as the strength of most materials declines at higher temperatures. Nevertheless, tests conducted at engine operating temperatures have shown an improvement in mechanical properties of the materials used to manufacture powder-forged connecting rods as a result of copper precipitation strengthening. Scanning and transmission electron microscopy were employed to investigate nano precipitates of copper in the specimens tested at higher temperatures as well as in connecting rods that have been running in engines for appreciable amounts of time. In light of these results, there is an opportunity to reduce the cross section in the I-beam of powder-forged connecting rods by using in design the higher compressive yield strength values obtained at engine operating temperatures, thus resulting in mass savings.
A new double perovskite Ca2FeMnO6 with a layered arrangement of Mn4+ and the unusually high valence Fe4+ was obtained by oxidizing the brownmillerite Ca2FeMnO5 with ozone at 200 °C. The low-temperature topotactic reaction kept the layered cation arrangement of the brownmillerite but oxidized Mn3+ to Mn4+ and Fe3+ to Fe4+. The crystal structure with a P21/c space group was analyzed with the synchrotron X-ray diffraction data. The changes in the valence states of Fe and Mn were confirmed by bond valence sum calculations, X-ray absorption spectroscopy, and Mössbauer spectra measurements.
The cubic perovskite structure was stabilized in solid solution of SrFeO3 and SrNiO3. The compounds were obtained by high pressure synthesis and contained high valence state of Fe4+ and Ni4+ ions in the corner-sharing oxygen octahedra. SrFe1−xNixO3 with x = 0.4 and 0.5 showed ferromagnetic-like behaviors at room temperature, in contrast to the end member perovskite SrFeO3 (x = 0) with helical antiferromagnetism (TN = 134 K). Ni substituton for Fe in the cubic antiferromagnetic SrFeO3 induced the ferromagnetism.
Dense n-type Bi2Te2.85Se0.15 bulk thermoelectric materials with Cu doping were fabricated by mechanical alloying (MA) and spark plasma sintering (SPS) technique. The effect of Cu doping on microstructure and thermoelectric properties of CuxBi2Te2.85Se0.15 has been investigated. At a sintering temperature of 300 °C, the effect of Cu doping on thermoelectric properties was not significant. At 400 °C, however, the carrier concentration decreased significantly with increasing Cu content, and thus causing a significant increase in the Seebeck coefficient. A largest dimensionless figure of merit value of 0.58 was achieved at room temperature for Cu0.03Bi2Te2.85Se0.15 sample sintered at 400°C.
Recently, soft magnetic metal powders are widely used for electric components such as inductors. These are required further improvement of magnetic properties. Fe-Ni soft magnetic alloys are called “Permalloy” and are known as high magnetic permeability alloys. In particular, “Permalloy B (JIS)”, Fe-45~50Ni, is expected for application of inductors because of high saturation magnetic flux density. We researched the effect of Si addition into “Permalloy B” on the magnetic properties in high frequency range. Powders were prepared by gas atomization process and mixed with resin and lubricant, and then compacted into toroidal shape cores. These cores were heat-treated for hardening resin and release of internal stress by compaction. Effective permeability was measured by LCR meter up to 100 MHz and core loss was measured by B-H analyzer up to 5 MHz. As a result, permeability was slightly decreased but core loss was reduced by Si addition. Core loss was also reduced by using finer powders (mean particle diameters are less than 10 μm). Moreover, the permeability increased by the heat treatment of core after compaction. We found the availability of soft magnetic metal powders in high frequency over 3 MHz for using inductors.
Fe-Si-Al of soft magnetic materials are known as high permeability alloys, and these are used as dust cores. In general, Fe-Si-Al powders, what is called “Sendust”, have poor compressibility because of their hardness, therefore it is difficult to increase the packing fraction of their core. We researched the effect of packing fraction on magnetic properties in order to mix the powders which have different mean particle size. In case of mixing the coarse powders and fine powders, it is assumed that fine particles penetrate into the opening gaps which are located in close packing of coarse particles. They are called 6-, 4- and 3-configuration. The sizes of opening gap in close packing are 0.414, 0.225 and 0.154 of coarse particle size, respectively. Fe-9.5Si-5.5Al alloy powders were prepared by gas atomization process. Mean particle size of coarse powders are fixed about 40 μm and fine powders are prepared the size by classifier. Coarse powders and fine powders were mixed to the optional ratio. Relative permeability and core loss up to 1 MHz were measured. Packing fraction of core was improved more than 80 % by optimization of the mixing ratio of fine powders. As a result, relative permeability was increased with the packing fraction.
Substitution of Dy for Nd is a widely used method to improve the thermal stability of sintered NdFeB magnets. However, there are serious concerns over the stable supply of Dy due to its looming shortage and rising prices. Therefore, it is essential to develop (Nd,Dy)FeB magnets with reduced Dy content. In this study, we investigated the influence of casting conditions of Nd10.85Dy3.21Fe80.12B5.82 alloys prepared by mold casting and strip casting on the constituent phases and elemental distribution to improve the magnet coercivity. Microstructural observations revealed the formation of primary crystals (α-Fe) at all selected positions in the mold cast samples. In contrast, no primary crystals were found in the strip cast samples. To obtain sintered (Nd,Dy)FeB magnets with high coercivity, the optimum thickness of the starting alloy was found to be 0.3 mm. The melting behavior was studied in a temperature range from 773 K to 1173 K and the melting temperature increased after pre-heating at 973 K and 1073 K for the strip cast samples. These results indicate that cooling below 900 K during strip casting influenced the melting behavior of the alloy. Furthermore, it could affect the densification during sintering of the magnets.
The influence of specific surface area (SSA) of Fe2O3 was investigated while evaluating the raw material of Sr ferrite preparation. For hard ferrite magnet, SSA of Fe2O3 was found markedly affects the grain growth and the magnetic properties. Increasing of SSA of Fe2O3 resulted in the increase of remanence (BR) and (BH)max, but also causes a decline in intrinsic coercive force (iHC). The SSA of Fe2O3 is most important factor in determining the reactivity of the ferrite specimens during calcinations and sintering processes. A larger SSA promotes reactivity, which results in larger grain size of either calcined or sintered powder, consequently larger BR and smaller iHC were achieved, whereas, the opposite trend was observed for small SSA of Fe2O3. Results are also confirmed that, when less impurity in Fe2O3, the microstructure and magnetic properties of Sr-ferrite have smaller sensitivity to the SSA of Fe2O3. As found in this study, well control of raw material Fe2O3 is shown to be very critical in tailoring suitable BR and iHC for customized Sr-ferrite manufacturing process.
Recently, there’s been a growing trend toward a low carbon society from rise on the interest of the environment. In the automotive industry, environmentally-friendly vehicles, like hybrid electric vehicles and plug-in hybrid electric vehicles, are replacing petrol vehicles. Due to this trend, the demand of power supply devices, such as converters, increase more and more. And there devices are required good conversion efficiency and downsizing. Therefore, these devices require the soft magnetic materials which have excellent alternative current (AC) magnetic property.The authors have developed the soft magnetic powder cores which are made by compacting soft magnetic powder coated with the insulation film and then heat-treating to remove the compacting strain. The cores have high performance of AC magnetic property, low iron loss and high flux density. In this study, the effect of particle size distribution on the permeability at a high magnetic field and iron loss of FeSiAl alloy soft magnetic powder core was reported from the view point of demagnetizing coefficient.
Nd-Fe-B hot-deformed magnets were produced by the spark plasma sintering (SPS) method from bulk materials prepared by the SPS method. The bulk materials, prepared by the SPS method from commercially available Nd-Fe-B melt-spun ribbon (MQ powder), consisted of the Nd2Fe14B phase and were magnetically isotropic. The subsequent hot deformation induced magnetic anisotropy in the Nd-Fe-B magnets. The optimally hot-deformed magnet showed a high remanence of 1.39 T with a maximum energy product of 240 kJm−3.
We synthesized polycrystalline samples of ternary compounds Ln2Co12P7 (Ln = Y, Pr, Nd, Sm, Gd and Dy) with the Curie temperature being about 150 K and measured magnetization to clarify magnetism of Co sublattice and also to clarify behavior of magnetic moments of Ln3+ in ferromagnetic phase. As a result, magnetism of Y2Co12P7 was found to be a possible weakly itinerant electronic ferromagnetism and found to be similar to that of Lu2Co12P7, indicating that magnetism of Co sublattice does not change with Ln. From results for Ln2Co12P7, we found that spin components of magnetic moments of Ln3+ ferromagnetically couple with exchange field of ferromagnetic moments of Co sublattice. This result means that behavior of magnetic moments of Ln3+ can be described as the single ion model applied to the permanent magnets (LnCo5, Ln2Fe14B etc.) though the sign of coupling constant is opposite of the cases of permanent magnets. This is because magnetic moments of Co and Ln couple through P, not a direct coupling in cases of permanent magnets.
Magnesium is promising as a light weight material because its density is lower than that of aluminum. In order to enhance this advantage, various alloying elements have been studied. However, embrittlement caused by the simple addition of alloying elements is problematic. In this study, an atomized powder obtained by adding an element to improve the properties of the magnesium was prepared, then sintered by pulse current pressure. The strength property of magnesium sintered compacts was assessed by a transverse rupture test. Based on the results of the transverse rupture test and microstructure observations, the effect of the mean size of the intermetallic compounds on the strength and ductility was discussed.
Sm-doped CeO2 ceramics were prepared by conventional solid state method. The electrical conductivity of the samples was measured under conventional heating and 24 GHz millimeter-wave (MMW) heating, and the results were compared. During MMW heating, 5 mol% Sm-doped CeO2 pellets with different thickness were used as susceptors, meanwhile Al2O3 fiber board was used as thermal insulator and its design varies by the number of open channels. The aforementioned susceptors and thermal insulators dependency of conductivity values during MMW heating were studied. Conductivity of samples under MMW heating was found to be higher than under conventional heating. Results showed that the different susceptor thickness and thermal insulator design could result in different conductivity values. These results were attributed to the phenomenon of heat dissipation from surface and the amount of direct radiation reached the sample. Specific susceptor thickness and specific insulator design which leads to highest conductivity were identified. By combining these two effects, the largest enhancement of conductivity of ceria based ceramics was obtained.
Calcium oxide and small amount of alumina powders were mechanically milled in a planetary ball milling system using ZrO2 pot and balls, in order to refine the sizes of the powders and promote the reactions between the raw powders. The obtained powders were subjected to an accelerated degradation test in CO2/H2O atmosphere, and the antiviral activity was evaluated by using an avian influenza virus strain (H5N3). The mechanically milled powders revealed a significant improvement in durability of antiviral activity after the powders were hydrated. One of the reasons seems to be associated with the solid solution of Al2O3 into calcium oxide and agglomeration of the powders during the mechanical milling. Moreover, it was found that ZrO2 has an effect similar to Al2O3. The incorporation of ZrO2 in CaO by either addition of ZrO2 powder or contamination from milling media can also improve the durability of antiviral activity of CaO.
Harmonic-structured Al-Cu alloys were produced via mechanical milling followed by spark plasma sintering, and their microstructure and mechanical properties were investigated in detail. The microstructure of the mechanically milled powders and spark plasma sintered compacts was characterized using scanning electron microscopy (SEM)/energy dispersive X-ray spectroscopy (EDS) and X-ray diffraction (XRD). The mechanical properties of the spark plasma sintered compacts were evaluated on the basis of the tensile tests and Vickers hardness tests. SEM/EDS micrographs and XRD profiles indicated that the harmonic-structured Al-Cu alloy compact has a network region composed of Al-Cu alloy with Al2Cu precipitates and a dispersed region composed of pure Al. The harmonic-structured Al-Cu alloy compacts exhibit the superior hardness. Harmonic-structured control is effective for improving of the mechanical properties of the precipitation-hardened materials.
Spinel-type LiNi0.5Mn1.5−xTixO4 powder library was prepared using the electrostatic spray deposition (ESD) method. Deposited powder was heat-treated at 700 °C for 3 hours in air. Phase identification of the X-ray diffraction patterns of the LiNi0.5Mn1.5−xTixO4 (0 ≤ x ≤ 0.5) prepared showed multi-phases of spinel, a slight amount of rock-salt-type LiyNi1−yO. In first charge-discharge capacities of LiNi0.5Mn1.5−xTixO4 (0 ≤ x ≤ 0.5) at current rates of 0.1 C and 1 C, LiNi0.5Mn1.5O4 (x = 0) and LiNi0.5Mn1.4Ti0.1O4 (x = 0.1) each showed a discharge capacity of about 100 mAh/g. LiNi0.5Mn1.4Ti0.1O4 was also found to retain its discharge capacity at a higher rate than LiNi0.5Mn1.5O4. The charge-discharge capacities were lower than those observed in the previous report, however, because the powders obtained included LiyNi1−yO type oxides as a second phase. Also, it was found that the decrease of rock-salt phase (LiyNi1−yO) was able to control by changing the atmospheric and powder shape-forming conditions.
We have investigated the orientation relationship between TiB2 particles and Ni binder phase in TiB2-15 vol.%Ni cermet. About 25 % TiB2 particles showed the six types of orientation relationships with Ni. These TiB2/Ni interfaces were delimited by prismatic or basal plane of TiB2, and the most frequently observed relationship was (0 0 0 1)TiB2 // (1 1 1)Ni, [1 1 −2 0]TiB2 // [−1 1 0]Ni. This orientation relationship comprised about 50 % of the observed orientation relationships.
In the present work, three experimental WC-17 Co plasma sprayed coatings were developed from submicrostructured, conventional and bimodal (composing of 30 wt.% submicrostuctured and 70 wt.% conventional WC grain) agglomerated powder. The effect of carbide size distribution on the microstructure, phase structure and properties such as microhardness, fracture toughness and sliding wear performance of three coatings were measured. The experimental results indicated that bimodal coating had little porosity of microstructure with lower degree of decarburization of the WC phase to W2C and Co6W6C phases, consequently, showed both high microhardness and fracture toughness, e.g. the microhardness is similar to that of the submicrostuctured one and the fracture toughness is comparable to that of the conventional one. The coefficient of friction for the coatings decreased slightly with increasing test load, and that friction coefficient of bimodal coating was lower than the other ones. The wear loss of both submicrostuctured and conventional coatings were higher than the bimodal coating and increased with increasing test load. The microscopic analyses of the wear surface showed the cobalt extrusion followed by carbide fracture, or pulled out were the predominant failure mechanism. Besides that, fatigue cracking of the submicrostuctured coating at a high test load played an importance on the wear mechanism.
The main objectives of the paper are numeric calculations of retention of diamond particle in metallic-diamond segments of circular saws. The segments are produced by means of the technology of powder metallurgy. The analysis has been preformed for cobalt, cobalt-iron and cobalt-tungsten sinters. The effective use of diamond impregnated tools is strongly depended on the retentive properties of the metal matrix, which must hold diamond grits firmly. Due to mismatch between thermal expansion coefficients of the matrix and diamond, the mechanical fields are generated in the matrix at diamond surroundings. The fields play a major role for retentive properties of matrix. It has been postulated that the potential retentive capability of a matrix can be associated with the amount of elastic and plastic deformation energy which occurs in the matrix around diamond particles.