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 H_RA 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.

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.

Dense n-type Bi₂Te_2.85Se_0.15 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 Cu_xBi₂Te_2.85Se_0.15 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 Cu_0.03Bi₂Te_2.85Se_0.15 sample sintered at 400°C.

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 Nd_10.85Dy_3.21Fe_80.12B_5.82 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 (B_R) and (BH)_max, but also causes a decline in intrinsic coercive force (_iH_C). 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 B_R and smaller _iH_C 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 B_R and _iH_C for customized Sr-ferrite manufacturing process.

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 LiNi_0.5Mn_1.5−xTi_xO₄ 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 LiNi_0.5Mn_1.5−xTi_xO₄ (0 ≤ x ≤ 0.5) prepared showed multi-phases of spinel, a slight amount of rock-salt-type Li_yNi_1−yO. In first charge-discharge capacities of LiNi_0.5Mn_1.5−xTi_xO₄ (0 ≤ x ≤ 0.5) at current rates of 0.1 C and 1 C, LiNi_0.5Mn_1.5O₄ (x = 0) and LiNi_0.5Mn_1.4Ti_0.1O₄ (x = 0.1) each showed a discharge capacity of about 100 mAh/g. LiNi_0.5Mn_1.4Ti_0.1O₄ was also found to retain its discharge capacity at a higher rate than LiNi_0.5Mn_1.5O₄. The charge-discharge capacities were lower than those observed in the previous report, however, because the powders obtained included Li_yNi_1−yO type oxides as a second phase. Also, it was found that the decrease of rock-salt phase (Li_yNi_1−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.