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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).

Poly-crystalline Ba8Cu6Ag2Si38 clathrates were synthesized by the arc-melting method and a subsequent annealing treatment. The main phase of all the samples was type-I clathrate. However, there were some precipitates which rich in Cu, Ag or Si in the grain boundary of the as-synthesized sample and the precipitates gradually reduced with the increase of annealing time. The transition metal content in the clathrate increased with the annealing time because of the diffusion of the Cu and Ag atoms from precipitates phase into clathrates phase. The as-synthesized sample was n-type material. For the 576 hours annealed sample, the carrier type changed from n-type to p-type because of the increase of Cu and Ag content in the clathrate.

Titanium and its alloys have been widely used for medical and aerospace applications because of their excellent attributes of high specific strength, corrosion resistance, and biocompatibility. However, it is not easy to produce the complex shaped parts due to their poor castability and machinability. Metal injection molding (MIM) is one of suitable processing technique to produce the complex shaped parts in order to reduce the manufacturing cost. In this study, complex shaped Ti-6Al-4V compacts was prepared by MIM process for airplane application. The effects of high molecular binder content and different compact’s set-up during thermal debinding on the distortion of complex shaped compacts were measured and evaluated. The binder with 10 % APP (Atactic polypropylene) was found to have better shape retention for the parts. Furthermore the results indicate that high distortion occurs at early stage of thermal debinding process. The use of supports during thermal debinding can significantly reduce the distortion of the final parts.

In this paper, two kinds of advanced powder processing techniques such as Metal Injection Molding (MIM) and Direct Laser Forming (DLF) were introduced to fabricate complex shaped Ti alloy parts which have been widely used for various industrial and medical applications because of their excellent characteristics of low density, high corrosion resistance and high biocompatibility but need high processing cost because of poor workability. The MIM process has been tried to strengthen Ti-6Al-4V alloy compacts by addition of fine Mo, Fe and Cr powders, and enhanced tensile strength of 1030 MPa with 15.1 % elongation was obtained by an addition of 4 mass%Cr because of the microstructural modification but also the solution strengthening in beta phase. DLF process has been tried to improve the honeycomb porous structure from Ti-6Al-7Nb powder material, and the honeycomb structure with 300 m holes showed good mechanical compatibility and superb biocompatibility in osteoblasts culturing.

Ti-10V-2Fe-3Al is one of super elastic Ti alloys, which is the b type Ti alloy and shows the excellent properties such as high specific strength and corrosion resistance. By the combination of Cold working and heat treatment, high strength as same as the steels are obtained. Therefore, Ti-10V-2Fe-3Al is hoped to be a next generation’s spring material. In this study, Metal Injection Molding of super elastic Ti alloy materials are investigated by changing the process parameters such as powder type (mixed elemental or alloy), debinding and sintering conditions, and heat treatment conditions to obtain the excellent super elastic properties. Tensile strength of injection molded Ti-10V-2Fe-3Al compacts sintered at 1250 with mixed elemental powders showed approximately 85% of wrought materials. On the other hand, alloy powder compacts showed about 80% strength of wrought materials. Their super elastic behavior depended strongly on the heat treatment conditions.

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.

Titanium and its alloys have been widely used for medical and aerospace applications because of their excellent attributes of light metal, high strength, high corrosion resistance and high biocompatibility. Especially, Ti-6Al-7Nb alloy has been developed as a more suitable biomaterial to replace Ti-6Al-4V alloy, because vanadium is toxic element to the biological body. However, it is not easy to fabricate the complex shaped and precise parts by the conventional methods due to their poor castability and machinability. In this study, laser forming technique has been applied to solve the above problems. The precise structure was obtained by optimizing the laser forming parameters. Using this technique, a honeycomb structure was fabricated effective to grow the neighboring tissue and also encourage osseointegration. Finally, mouse osteoblasts were cultured on the formed structures, resulted in the effectiveness of the honeycomb structure for biocompatibility.

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.