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Injection molded Ti-6Al-4V compacts have normally a coarse lamellar microstructure, because it is sintered above the β transus temperature and it is cooled slowly in furnace. However, static mechanical properties such as tensile strength and ductility are equivalent to those of wrought materials, but they have the disadvantage that the fatigue strength is significantly lower than wrought materials. Therefore, improvement of fatigue strength is needed for injection molded Ti alloy compacts. In this study, injection molded Ti-6Al-4V compacts having equiaxed microstructure were prepared by sintering at α + β region temperature which is very lower than normal sintering temperature. When sintering is carried out in α + β region, sinterability is remarkably poor. Therefore, long-time sintering is required. Since the grain growth of the prior β grains was suppressed by the pinning effect of α grains and pores, it was possible to obtain the significantly fine grains as compared with the β region sintered compacts. The α + β region sintered compacts showed high strength, high elongation and also high fatigue strength. Furthermore, by applying HIP treatment, the mechanical properties were improved to satisfy the standard value of wrought Ti-6Al-4V material.

We have synthesized n- and p-type clathrates Ba8−dAuxSi46−x−y with various Au contents (4.6 < x < 6.0) by arc-melting, annealing at 1173 K, and spark plasma sintering at 1073 K. The Au compositions found by wavelength-dispersive x-ray spectrometry for the synthesized samples were slightly lower than the nominal compositions. Ba7.8Au4.6Si41.4 and Ba7.7Au4.9Si41.1 samples showed n- and p-type conduction, respectively. According to the electron count (Ba2+)8Au(3−)5.33Si40.67, the clathrate composition with x = 5.33 is expected to be an intrinsic semiconductor. Our experimental results show that increase of the Au composition causes a transition from n-type to p-type conduction between x = 4.6 and 4.9. We have also calculated the band structures of the Ba8AuxSi46−x clathrate including a vacancy by ab initio calculation based on density functional theory with structure optimization. It was found that the vacancy behaves like an electron acceptor and the numbers of vacancies at 24k sites for the synthesized Ba8AuxSi46−x−y clathrates can be estimated as ∼0.4 in a unit cell.

Single-crystalline Ba8Al x Ga y Si46−x−y clathrates were synthesized by the arc melting method and Czochralski method without subsequent treatment, and their thermoelectric properties were compared with those of Ba8Al x Ga y Si46−x−y and Ba8Al x Si46−x clathrates with almost the same carrier concentration as estimated from the similar Seebeck coefficient and the Zintl concept. The resistivity of Ba7.8Al5.3Ga7.4Si33.3 was lower than that of Ba7.9Al12.6Si33.4. The specific electrical resistance of Ba7.9Al12.6Si33.4 and Ba7.8Al5.3Ga7.4Si33.3 was 0.573 mΩ cm and 0.282 mΩ cm at 750 K, respectively. The band structure of Ba8Al8Ga8Si30 and Ba8Al16Si30 was estimated by first-principle calculations using density functional theory with the local density approximation. Based on these calculations, it was found that the shape of the bottom of the conduction band for Ba8Al x Si46−x clathrate changed slightly on Ga doping and the radius of curvature of the bottom of the conduction band for Ba8Al8Ga8Si30 clathrate was lower than that for Ba8Al16Si30 clathrate. These results indicate that the mobility was enhanced by Ga doping of Ba8Al x Si46−x clathrate. We also synthesized single-crystalline Ga-doped Ba8Al x Si46−x clathrate. The electrical resistivity decreased dramatically due to the single-crystallization because of reduced electron scattering on grain boundaries. These results suggest that Ga doping and single-crystallization are effective for improvement of the thermoelectric properties of Ba8Al x Si46−x clathrate.

A micro patterning process for thin ceramic sheets is proposed and developed in this paper. Thin sheets with a micro pattern have been expected to improve performance of solid oxide fuel cell. The authors focused on imprinting and powder metallurgy processes, and have developed the combined process, which has been named micro powder imprinting process. In this process, ceramic powder and polymer binder materials are mixed with pure water by milling machine. After drying out the water from the slurry, a thin compound sheet was obtained. Subsequently, the sheet was pressed using a fine patterned mold with heating to transcribe a micro pattern on the sheet. Finally, the imprinted sheet was heated for removing the polymer binder and for sintering. As further improvement of the process, a compound sheet was stacked on a pure polymer sheet during the imprint process to transcribe a micro pattern on the both sides of the sintered sample. The technique is useful for improved solid oxide fuel cell.

In this paper, two kinds of advanced powder processing techniques Metal Injection Molding (MIM) and Direct Laser Forming (DLF) are introduced to fabricate complex shaped Ti alloy parts which are widely used for medical and aerospace applications. The MIM process is used to strengthen Ti-6Al-4V alloy compacts by addition of fine Mo, Fe or Cr powders. Enhanced tensile strength of 1030 MPa with 15.1% elongation was obtained by an addition of 4 mass%Cr because of the microstructural modification and also the solution strengthening in beta phase. However, their fatigue strength was lower compared to wrought materials, but was improved by HIP. Subsequently, the effect of feeding layer height (FLH) on the characteristics of the DLF compacts was investigated. In the case of 100 FLH, surface roughness was improved and nearly full density (99.8%) was obtained. Also, tensile strength of 1080 MPa was obtained, which is higher than the ASTM value.

A study is presented of an improved interfacial structure between the electrode and electrolyte of a solid oxide fuel cell. An imprint process, which is considered as a powerful tool to transcribe nano to micropatterns on materials, was employed to imprint fine patterns onto a ceramic sheet of electrolyte. In the presented work, a sheet of ceramic compound material was prepared, and micropatterns were imprinted on its surface. After debinding and sintering, a dense ceramic sheet with fine micropatterns was obtained. To investigate the effect of micropatterns on the overall performance of a fuel cell, three kinds of electrolyte sheets with different surface patterns were employed for this technique. After applying anode and cathode layers, the three fuel cell samples were assembled to test the cell performance. The result was that the finer pattern caused better performance in the three samples by exhibiting the highest overall voltage and power density, and the effective factors of patterns on ion conductivity were discussed as well. Based on the investigation, some further improved three-dimensional microstructures were proposed and fabricated by the method of micro powder imprinting (μPI).

Superalloys have been used especially for aerospace and atomic energy applications because of their excellent attributes of high corrosion and oxidation resistance, and high temperature strength. A Inconel 718 is one of representative Ni-base superalloys. However, it is not easy to produce the complicate shaped parts with low cost due to their poor workability. In this study, Metal Injection Molding (MIM) process, one of near net-shape powder forming, has been applied to fabricate the Inconel 718 alloy compacts using two type of powders; gas and water atomized powders. By optimizing the MIM process, their obtained relative density was near full density (98∼99 %). However, the fatigue strength of heat treated sintered Inconel 718 compacts showed 65 % of heat treated wrought materials due to the remained pores. The effect of remained pores on fatigue strength was discussed by the prediction equation of endurance limit considering the inclusion.

Surface rolling were carried out using P/M spur gears of 0.6Mo-0.2C partially alloyed sintered steel with the density of 7.18 g/cm3. A CNC form rolling machine of axis intersection type was employed, and an unmodified screw-shaped rolling tool was prepared. Then, porosity distributions in the surface layer of rolled gear teeth root were measured and the effects of the surface rolling on the selective surface densification behaviors were evaluated. Moreover, to obtain higher fatigue strength, reverse rolling was introduced to standard gears. As a result, the porosities in the tooth root were sufficiently reduced at 700 μm feed in rolling process. Furthermore, a profile shifted gear was prepared to increase the effect of surface rolling. After case hardening, the single tooth bending fatigue durability reached to about 83 % of the case hardened wrought steel gears of SCM415.

This study aims at reducing costs of high load gear manufacturing, and substituting P/M gears for conventional wrought steel gears. In order to improve the fatigue strength of P/M gears, we focused on the rolling and the high performance sintered and heat treated 4600 series alloy steels with mezzo-heterogeneous microstructure which were made from the mixed elemental powders. The fatigue strength was determined by single tooth root bending fatigue test machine, and the effect of mezzo-heterogeneous microstructure and rolling on the fatigue strength was mainly investigated. The endurance limit at N=3.0×106 of the 500 μm rolled 6 % Ni alloy steel gear compact showed 950 MPa which value is about 2/3 of the case hardened wrought steel (SCM415) gears. However, the endurance limit of rolled and heat treated gear compact showed lower value (630 MPa) as compared to as-rolled gear compact. This seems to be due to the decreasing the compressive residual stress by heat treatment and unfavorable mezzo-heterogeneous microstructures.

Superalloys have been used especially for aerospace and atomic energy applications because of their excellent attributes of high corrosion and oxidation resistance, and high temperature strength. A Inconel 718 is one of representative Ni-base superalloys. However, it is not easy to produce the complicate shaped parts with low cost due to their poor workability. In this study, Metal Injection Molding (MIM) process, one of near net-shape forming of powders, has been applied to fabricate the Inconel 718 alloy compacts using different type of powders; gas and water atomized powders. By optimizing the MIM process, their obtained relative density was near full density (98∼99 %) and the tensile property of as-sintered compacts was the strength of 1000 MPa and the elongation of around 10 %, which are similar to those of wrought materials. The tensile properties were improved to the strength of 1250 MPa and the elongation of around 8 % by heat treatment.

This study aims cost reduction of high load gear manufacturing, and attempts to substitute P/M gears for conventional wrought steel gears. In order to improve the fatigue strength of the P/M gears, we focused attention on the high performance 4600 sintered alloy steels with heterogeneous microstructure which were made from the mixed elemental powder in comparison with homogeneous microstructure from the prealloyed powders. The fatigue strength was measured by a two cylinder type rolling contact fatigue testing machine, and the effect of the different microstructure on the fatigue strength was mainly investigated. As the result, the endurance limit at N=1.0×107 of the mixed elemental powder compacts showed 1.45 GPa, which was slightly higher than that of the prealloyed powder compacts (1.32 GPa). Also, their values are about 75 % of the endurance limit of wrought steels (SCM415 case-hardened).

Titanium and it's alloys have been widely used for aerospace applications because of their excellent attributes of light weight, high strength, heat resistance and corrosion resistance material. However, it is not easy to produce the complicate shaped parts due to the poor castability and machinability. Metal Injection Molding (MIM) technique is expected to be one of useful advanced powder processing route as complicated shape forming for titanium and it's alloy powders. The purpose of this study is to produce the large Ti alloy products by MIM process. MIM process condition is the most important to control the quality of final products. Five different disk specimens with difference sizes of diameter and thickness are prepared, and the effect of debinding and sintering conditions on the deformation of compacts are investigated. In this paper, the evaluation of the deformation was established by using a non-contact laser displacement measuring equipment.

Ferrous soft magnetic materials are required several efforts to realize high performance magnetic properties. In powder metallurgy processing, both high density and high purity are necessary to obtain the excellent soft magnetic properties. Metal injection molding (MIM) process is hoped to be an effective technique to produce the high density and more complex shaped parts from Fe-Si hard metal powders. In this study, Fe-6.5Si sintered compacts were produced by MIM process using elemental powders and their magnetic properties were investigated. The oxygen contents of sintered compacts were strongly influenced by the original powder, and the lower oxygen content powder showed high density and good soft magnetic properties.

The Ti-6Al-7Nb alloy has been developed for a more suitable biomaterial in place of the Ti-6Al-4V alloy, due to the toxicity of vanadium to the human body. However, the cost of the starting material powder for MIM Ti-6Al-7Nb alloy is understood to be expensive. This study investigates the feasibility of using commercially available powders…

Producing micro size parts by metal injection molding (μ-MIM) needs more sophisticated technique than conventional MIM. Especially, to fill the micro groove cavities which size are smaller than 10 μm with feedstock by μ-MIM technique, much smaller particle size of powders than that of conventional MIM are required. Also, various properties such as powder loading and viscosity of feedstock, debinding behavior of compacts, relative density and mechanical properties of sintered compacts would be changed by using fine powders. In this study, the effects of particle size of powders on the properties of stainless steel (SUS316L) compacts were investigated for μ-MIM processing. The sintered compacts using fine powder which mean particle size is 3 μm showed high density and tensile strength.

Due to the continual improvements of powder metallurgy techniques, it is possible for sintered materials to compete the wrought materials even in some of the most demanding applications. However, strength of sintered materials was inadequacy, because they have a lot of pores. This paper describes a study on the effect of rolling on the contact fatigue strength of sintered ferrous alloy compacts. The effects of rolling were evaluated by measuring the hardness and porosity distributions at the vicinity of the surfaces of rolled compacts. The effects of the amount of rolling on the contact fatigue strength, and the contact fatigue damage mechanisms were also investigated. Porosity at the vicinity of the surfaces of rolled compacts was decreased with increasing the amount of radial feed, from which the contact fatigue strength of rolled compacts was improved.

It has been found that the sintered MIM Ti-6Al-4V alloy compacts were strengthened by addition of fine Mo powder because of the microstructural modification. In this study, the metal injection molding process has been applied to strengthen Ti-6Al-4V compacts by addition of Fe or Cr powders, which are the same beta stabilizing elements as Mo and are more cost effective powders as compared to Mo powder. The effect of Fe or Cr contents and sintering conditions on the mechanical properties, oxygen content and microstructures of the sintered compacts were mainly investigated. The microstructures of sintered compacts were consisted of acicular alpha phase and intergranular beta phase, and the acicular alpha phase showed fine with increasing Cr content. The tensile strength of sintered compacts was increased with increasing Fe or Cr contents, and the effect of Fe addition for strengthening the sintered compacts was larger than Cr or Mo addition. Eventually, the tensile strength of sintered compacts added 2 mass% of Fe was improved to be 1010 MPa with 11.2 % of elongation, and the compacts added 4 mass% of Cr showed the excellent tensile strength of 1040 MPa with 16.1 % of elongation.

Ferrous soft magnetic materials are required several efforts to realize high performance. In powder metallurgy processing, both high density and high purity are necessary to obtain the excellent soft magnetic properties. Metal injection molding (MIM) process is an effective technique to produce the high density and more complex shaped parts from Fe-Si hard metal powders.In this study, MIM process using several types of Fe-6.5Si powders were performed, and their magnetic properties were investigated. Moreover, in order to improve the density and purity of injection molded compacts, the thermal debinding and sintering atmospheres were mainly investigated. The sintered compacts which have lower oxygen content showed high density and good soft magnetic properties.

Sintered ferrous alloy gears are used in wide engineering fields. However, it is difficult for them to be applied to the parts loading at high stress levels, because their strength is poorer than that of the wrought materials. In this study, sintered ferrous alloy gears were rolled and their tooth root bending fatigue strengths were investigated. The effect of rolling conditions on the porosity distribution and hardness at tooth root, and the tooth root bending fatigue strength were determined. As the amount of stock rolled was increased, the porosity of the vicinity of the surface was decreased and the hardness was increased, and also the tooth root bending fatigue strength was increased to certain level, and then the fatigue strength was decreased. This seemed to be due to the shaving when the gear was rolled.