HA (hydroxyapatite)/β-TCP (tricalcium phosphate) biomaterial (BCP; biphasic calcium phosphate) is widely used as bone cement or scaffolds material due to its superior biocompatibility. Furthermore, NH4HCO3 as a space holder (SH) has been used to evaluate feasibility assessment of porous structured BCP as bone scaffolds. In this study, using a spark plasma sintering (SPS) process at 393K and 1373K under 20MPa load, porous HA/β-TCP biomaterials were successfully fabricated using HA/β-TCP powders with 10~30 wt% SH, TiH2 as a foaming agent, and MgO powder as a binder. The effect of SH content on the pore size and distribution of the BCP biomaterial was observed by scanning electron microscopy (SEM) and a microfocus X-ray computer tomography system (SMX-225CT). The microstructure observations revealed that the volume fraction of the pores increased with increasing SH content and that rough pores were successfully fabricated by adding SH. Accordingly, the cell viabilities of BCP biomaterials were improved with increasing SH content. And, good biological properties were shown after assessment using Hanks balanced salt solution (HBSS).

An optimum route to synthesize Ti-Mo system powders is investigated by analyzing the effect of the heat treatment atmosphere on the formation of the reaction phase by dehydrogenation and hydrogen reduction of ball-milled TiH2-MoO3 powder mixtures. Homogeneous powder mixtures with refined particles are prepared by ball milling for 24 h. XRD analysis of the heat-treated powder in a hydrogen atmosphere shows TiH2 and MoO3 peaks in the initial powders as well as the peaks corresponding to the reaction phase species, such as TiH0.7, TiO, MoO2, Mo. In contrast, powder mixtures heated in an argon atmosphere are composed of Ti, TiO, Mo and MoO3 phases. The formation of reaction phases dependent on the atmosphere is explained by the partial pressure of H2 and the reaction temperature, based on thermodynamic considerations for the dehydrogenation reaction of TiH2 and the reduction behavior of MoO3.

A cold roll-bonding process was applied to fabricate an AA1050/AA6061/AA1050 laminate complex sheet. Two AA1050 and one AA6061 sheets of 2 mm thickness, 40 mm width and 300 mm length were stacked up after surface treatment that included degreasing and wire brushing; material was then reduced to a thickness of 3 mm by one-pass cold rolling. The laminate sheet bonded by the rolling was further reduced to 1.2 mm in thickness by conventional rolling. The rolling was performed at ambient temperature without lubricant using a 2-high mill with a roll diameter of 210 mm. The rolling speed was 5.0 m/sec. The AA1050/AA6061/AA1050 laminate complex sheet fabricated by roll bonding was then hardened by natural aging T4) and artificial aging (T6) treatments. The microstructures of the as-roll bonded and the age hardened Al complex sheets were revealed by optical microscope observation; the mechanical properties were investigated by tensile testing and hardness testing. The strength of the as-roll bonded complex sheet was found to increase by 2.9 times compared to that value of the starting material. In addition, the hardness of the complex sheets increased with cold rolling for AA1050 and age-hardening treatment for AA6061, respectively. After heat treatment, both AA1050 and AA6061 showed typical recrystallization structures in which the grains were equiaxed; however, the grain size was smaller in AA6061 than in AA1050.

Ni-C composite films were prepared by co-deposition using a combined technique of plasma CVD and ion beam sputtering deposition. Depending on the deposition conditions, Ni-C thin films manifested three kinds of microstructure: (1) nanocrystallites of non-equilibrium carbide of nickel, (2) amorphous Ni-C film, and (3) granular Ni-C film. The electrical resistivity was also found to vary from about 102 μΩcm for the carbide films to about 104 μΩcm for the amorphous Ni-C films. The Ni-C films deposited at ambient temperatures showed very low TCR values compared with that of metallic nickel film, and all the films showed ohmic characterization, even those in the amorphous state with very high resistivity. The TCR value decreased slightly with increasing of the flow rate of CH4. For the films deposited at 200 oC, TCR decreased with increasing CH4 flow rate; especially, it changed sign from positive to negative at a CH4 flow rate of 0.35 sccm. By increasing the CH4 flow rate, the amorphous component in the film increased; thus, the portion of Ni3C grains separated from each other became larger, and the contribution to electrical conductivity due to thermally activated tunneling became dominant. This also accounts for the sign change of TCR when the filme was deposited at higher flow rate of CH4. The microstructures of the Ni-C films deposited in these ways range from amorphous Ni-C alloy to granular structures with Ni3C nanocrystallites. These films are characterized by high resistivity and low TCR values; the electrical properties can be adjusted over a wide range by controlling the microstructures and compositions of the films.

The recent rise in applications of thermoelectric materials has attracted interest in studies toward the fabrication of thermoelectric materials using mass production techniques. In this study, we successfully fabricate n-type Bi2Te2.7Se0.3 material by a combination of mass production powder metallurgy techniques, gas atomization, and spark plasma sintering. In addition, to examine the effects of hydrogen reduction in the microstructure, the thermoelectric and mechanical properties are measured and analyzed. Here, almost 60% of the oxygen content of the powder are eliminated after hydrogen reduction for 4 h at 360°C. Micrographs of the powder show that the reduced powder had a comparatively clean surface and larger grain sizes than unreduced powder. The density of the consolidated bulk using as-atomized powder and reduced atomized powder exceeds 99%. The thermoelectric power factor of the sample prepared by reduction of powder is 20% better than that of the sample prepared using unreduced powder.

P-type ternary Bi0.5Sb1.5Te3 alloys are fabricated via mechanical alloying (MA) and spark plasma sintering (SPS). Different ball sizes are used in the MA process, and their effect on the microstructure; hardness, and thermoelectric properties of the p-type BiSbTe alloys are investigated. The phases of milled powders and bulks are identified using an X-ray diffraction technique. The morphology of milled powders and fracture surface of compacted samples are examined using scanning electron microscopy. The morphology, phase, and grain structures of the samples are not altered by the use of different ball sizes in the MA process. Measurements of the thermoelectric (TE) transport properties including the electrical conductivity, Seebeck coefficient, and power factor are measured at temperatures of 300- 400 K for samples treated by SPS. The TE properties do not depend on the ball size used in the MA process.

Egg SCP ( –47.2 ±1.0℃) of Red-spotted Apollo butterfly, Parnassius bremeri, was lower than larva(–35.0 ±0.9℃). The difference (12℃) between egg and larva was revealed by chorion through scanning electron microscope (COXEM EM-30, Korea). But considering of about 6 months’ pharate 1st instar in egg from June to November, function of egg seems not to be overwintering mechanism but rather estivation. In order to identify estivation function of chorion heat stress was carried out. Experiment was conducted on the 4 conditions such as high temperatures of 25, 35, 45 and 55 °C for 2 hour, then allowed them to recover at 25 °C for 1 hour. Total 65 samples 0f 31 eggs and 34 pharate 1st instar out of an egg were used and replicated 3 times. All pharate 1st instar in egg and pharate 1st instar out of egg survived at 25℃ and 35℃. In case of 45℃ survival rate of pharate 1st instar in an egg (91.6±3.5%) was significantly higher than those (37.8±9.4%) of pharate 1st instar out of an egg. All was dead at 55℃.

A roll-bonding process was applied to fabricate an AA1050/AZ91/AA1050 laminate complex sheet. Two AA1050 and one AZ91 magnesium sheets of 2 mm thickness, 30 mm width and 200 mm length were stacked up after surface treatment that included degreasing and wire brushing; material was then reduced to a thickness of 3 mm by one-pass cold rolling. The laminate sheet bonded by the rolling was further reduced to 2 mm in thickness by conventional rolling. The rolling was performed at 623K without lubricant using a 2-high mill with a roll diameter of 210 mm. The rolling speed was 15.9 m/min. The AA1050/AZ91/AA1050 laminate complex sheet fabricated by roll bonding was then annealed at 373~573K for 0.5h. The microstructure of the complex sheets was revealed by electron back scatter diffraction (EBSD) measurement; the mechanical properties were investigated by tensile testing and hardness testing. The strength of the complex sheet was found to increase by 11 % and the tensile elongation decreased by 7%, compared to those values of the starting material. In addition, the hardness of the AZ91 Mg region was slightly higher than those of the AA1050 regions. Both AA1050 and AZ91 showed a typical deformation structure in which the grains were elongated in the

Niobium is one of the most important and rarest metals, and is used in the electronic and energy industries. However, it’s extremely high melting point and oxygen affinity limits the manufacture of Nb coating materials. Here, a Nb coating material is manufactured using a kinetic spray process followed by hot isotactic pressing to improve its properties. OM (optical microscope), XRD (X-ray diffraction), SEM (scanning electron microscopy), and Vickers hardness and EPMA (electron probe micro analyzer) tests are employed to investigate the macroscopic properties of the manufactured Nb materials. The powder used to manufacture the material has angular-shaped particles with an average particle size of 23.8 μm. The porosity and hardness of the manufactured Nb material are 0.18% and 221 Hv, respectively. Additional HIP is applied to the manufactured Nb material for 4 h under an Ar atmosphere after which the porosity decreases to 0.08% and the hardness increases to 253 Hv. Phase analysis after the HIP shows the presence of only pure Nb. The study also discusses the possibility of using the manufactured Nb material as a sputtering target.

A bulk-type Ta material is fabricated using the kinetic spray process and its microstructure and physical properties are investigated. Ta powder with an angular size in the range 9-37 μm (purity 99.95%) is sprayed on a Cu plate to form a coating layer. As a result, ~7 mm-sized bulk-type high-density material capable of being used as a sputter material is fabricated. In order to assess the physical properties of the thick coating layer at different locations, the coating material is observed at three different locations (surface, center, and interface). Furthermore, a vacuum heat treatment is applied to the coating material to reduce the variation of physical properties at different locations of the coating material and improve the density. OM, Vickers hardness test, SEM, XRD, and EBSD are implemented for analyzing the microstructure and physical properties. The fabricated Ta coating material produces porosity of 0.11~0.12%, hardness of 311~327 Hv, and minor variations at different locations. In addition, a decrease in the porosity and hardness is observed at different locations upon heat treatment.

Effects of conventional rolling(CR) and differential speed rolling(DSR) on the microstructure and mechanical properties of Cu-Ni-Si alloy were investigated in detail. The copper alloy with thickness of 3 mm was rolled to 50 % reduction at ambient temperature without lubricant with a differential speed ratio of 2:1. The conventional rolling in which the rolling speed of upper and lower rolls is identical was performed under identical rolling conditions. The shear strain introduced by the CR showed positive values at positions of upper roll side and negative values at positions of lower roll side. However, it showed zero or positive values at all positions for the samples rolled by the DSR. The microstrucure and texture development of the as-rolled copper alloy did not show any significant difference between CR and DSR. The tensile strength of the DSR processed specimen was larger than that of the CR processed specimen. The effects of rolling methods on the microstructure and mechanical properties of the as-rolled copper alloy are discussed in terms of the shear strain.

Microstructural examination of the Nb-Si-B alloys at Nb-rich compositions is performed. The Nb-rich corner of the Nb-Si-B system is favorable in that the constituent phases are Nb (ductile and tough phase with high melting temperature) and T2 phase (very hard intermetallic compound with favorable oxidation resistance) which are good combination for high temperature structural materials. The samples containing compositions near Nb-rich corner of the Nb- Si-B ternary system are prepared by spark plasma sintering (SPS) process using T2 and Nb powders. T2 bulk phase is made in arc furnace by melting the Nb slug and the Si-B powder compact. The T2 bulk phase was subsequently ballmilled to powders. SPS is performed at 1300oC and 1400oC, depending on the composition, under 30 MPa for 600s, to produce disc-shaped specimen with 15 mm in diameter and 3 mm high. Hardness tests (Rockwell A-scale and micro Vickers) are carried out to estimate the mechanical property.

본 연구에서는 silicalite-1 제올라이트 분리막 합성 시에 종결정 코팅용액 pH 변화가 제올라이트 분리층 미세구조에 미치는 영항을 고찰하였다. 75 nm 크기로 합성된 종결정은 에탄올에 분산된 후 침지코팅법으로 지지체 표면에 코팅되었으며 분산용액의 pH는 2.2, 7.0, 9.3으로 조절되었다. pH가 7인 경우, 균일하고 두께가 3~4 μm인 silicalite-1 제올라이트 분리층이 형성되었고 분리층 결정입 크기는 100 nm로 미세하였다. 반면, pH가 2.2와 9.3인 경우, 분리층 두께가 얇고 불완전하였으며 분리층 결정입 크기도 약 1 μm로 조대하였다. pH 7에서 완전한 제올라이트 분리층이 형성된 것은 침지코팅 중에 지지체와 종 결정이 서로 다른 부호의 전하를 가져 정전기적 인력이 작용하여 균일하고 조밀하며 두껍고 다층의 종결정 코팅층이 형성되었 기 때문이었다. 반면에 pH가 2.2와 9.3인 경우, 침지코팅 중에 지지체와 종결정이 서로 같은 부호의 전하를 가져 정전기적 반 발력이 작용하기 때문에 불완전한 덮힘에 의하여 불완전한 분리층이 형성된다고 판단되었다. 결론적으로, 종결정 코팅용액의 pH가 silicalite-1 제올라이트 분리층의 두께, 결정립 크기 등 미세구조를 결정하는 중요한 인자임을 확인할 수 있었다.

Fe-base superalloy powders with Y2O3 dispersion were prepared by high energy ball milling, followed by sparkplasma sintering for consolidation. High-purity elemental powders with different Fe powder sizes of 24 and 50mm were usedfor the preparation of Fe-20Cr-4.5Al-0.5Ti-O.5Y2O3 powder mixtures (wt%). The milling process of the powders was carriedout in a horizontal rotary ball mill using a stainless steel vial and balls. The milling times of 1 to 5 h by constant operation(350 rpm, ball-to-powder ratio of 30:1 in weight) or cycle operation (1300 rpm for 4 min and 900 rpm for 1 min, 15:1) wereapplied. Microstructural observation revealed that the crystalline size of Fe decreased with an increase in milling time by cyclicoperation and was about 15nm after 3 h, forming a FeCr alloy phase. The cyclic operation had an advantage over constantmilling in that a smaller-agglomerated structure was obtained. The milled powders were sintered at 1100oC for 30 min invacuum. With an increase in milling time, the sintered specimen showed a more homogeneous microstructure. In addition, ahomogenous distribution of Y-compound particles in the grain boundary was confirmed by EDX analysis.

In this study, to confirm the effect of alloying elements on the phase transformation and conditions of the friction stir process, we processed two materials, SS400 and SM45C steels, by a friction stir process (FSP) under various conditions. We analyzed the mechanical properties and microstructure of the friction stir processed zone of SS400 and SM45C steels processed under 400RPM - 100mm/min conditions. We detected no macro (tunnel defect) or micro (void, micro crack) defects in the specimens. The grain refinement in the specimens occurred by dynamic recrystallization and stirring. The microstructure at the friction stir processed zone of the SS400 specimen consisted of an α-phase. On the other hand, the microstructure at the friction stir processed zone of the SM45 specimen consisted of an α-phase, Fe3C and martensite due to a high cooling rate and high carbon content. Furthermore, the hardness and impact absorption energy of the friction stir processed zone were higher than those of base metals. The hardness and impact absorption energy of FSPed SM45C were higher than that of FSPed SS400. Our results confirmed the effect of alloying elements on the phase transformation and mechanical properties of the friction stir processed zone.

The GaN-powder scrap generated in the manufacturing process of LED contains significant amounts of gallium. This waste can be an important resource for gallium through recycling of scraps. In the present study, the influence of annealing temperatures on the structural properties of GaN powder was investigated when the waste was recycled through the mechanochemical oxidation process. The annealing temperature varied from 200oC to 1100oC and the changes in crystal structure and microstructure were studied. The annealed powder was characterized using various analytical tools such as TGA, XRD, SEM, and XRF. The results indicate that GaN structure was fully changed to Ga2O3 structure when annealed above 900oC for 2 h. And, as the annealing temperature increased, crystallinity and particle size were enhanced. The increase in particle size of gallium oxide was possibly promoted by powder-sintering which merged particles to larger than 50 nm.

The effect of adding Ca on the microstructural and mechanical properties of as-cast Mg-11Li-3Zn-1Sn(wt%) alloys were investigated. Mg-11Li-3Zn-1Sn-0.4Mn with different Ca additions (0.4, 0.8, 1.2 wt%) were cast under an SF6 and Co2 atmosphere at 720 oC. The cast billets were homogenized at 400 oC for 12h and extruded at 200 oC. The microstructural and mechanical properties were analyzed by OM, XRD, SEM, and tensile tests. The addition of Ca to the Mg-11Li-3Zn-1Sn-0.4Mn alloy resulted in the formation of Ca2Mg6Zn3, MgSnCa intermetallic compound. By increasing Ca addition, the volume fraction and size of Ca2Mg6Zn3 with needle shape were increased. This Ca2Mg6Zn3 intermetallic compound was elongated to the extrusion direction and refined to fine particles due to severe deformation during hot extrusion. The elongation of the 0.8 wt% Ca containing alloy improved remarkably without reduction strength due to the formation of fine grain and Ca2Mg6Zn3 intermetallic compounds by Ca addition. It is probable that fine and homogeneous Ca2Mg6Zn3 intermetallic compounds played a significant role in the increase of mechanical properties.

This study investigated the microstructure and wear resistance property of HPHT (high pressure high temperature) sintered PDC (polycrystalline diamond compact) in accordance with initial molding pressure. After quantifying an identical amount of diamond powder, the powder was inserted in top of WC-Co sintered material, and molded under four different pressure conditions (50, 100, 150, 200 kgf/cm2). The obtained diamond compact underwent sintering in high pressure, high temperature conditions. In the case of the 50 kgf/cm2 initial molding pressure condition, cracks were formed on the surface of PDC. On the other hand, PDCs obtained from 100~200 kgf/cm2 initial molding pressure conditions showed a meticulous structure. As molding pressure increased, low Co composition within PDC was detected. A wear resistance test was performed on the PDC, and the 200 kgf/cm2 condition PDC showed the highest wear resistance property.

In this study, the effect of the friction stir welding (FSW) was compared with that of the gas tungsten arc welding (GTAW) on the microstructure and microhardness of Cu-Ni alloy weldment. The weldment of 10 mm thickness was fabricated by FSW and GTAW, respectively. Both weldments were compared with each other by optical microstructure, microhardness test and grain size measurement. Results of this study suggest that the microhardness decreased from the base metal (BM) to the heat affected zone (HAZ) and increased at fusion zone (FZ) of GTAW and stir zone (SZ) of FSW. the minimum Hv value of both weldment was obtained at HAZ, respectively, which represents the softening zone, whereas Hv value of FSW weldment was little higher than that of GTAW weldment. These phenomena can be explained by the grain size difference between HAZs of each weldment. Grain size was increased at the HAZ during FSW and GTAW. Because FSW is a solid-state joining process obtaining the lower heat-input generated by rotating shoulder than heat generated in the arc of GTAW.