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The beta gamma alloys of Ti - 43.8Al - 4Nb - 2Cr - 0.2B - 0.2C at % (9CN) were prepared using induction skull melted (ISM) cast ingots. In order to make a fine fully lamellar structure with some minor phases, two step cooling was performed using two furnaces after heat treatments in the α + β phase region. The heat-treatments produced an ~50 μm fully lamellar structure with α2 / γ + γ + B2 (HIP) → α + β (heating) → α / γ (FL) + γ + B2 → α2 / γ (FL) + γ + B2 phase change. For the two step heat treatment, the specimen was heat treated at 1340 ℃(or 1350 ℃) and transferred to another furnace, which was maintained at 950 ℃, in order to minimize any phase transformations between the temperatures. Fully lamellar specimens with some phases were compression-tested at RT, 700 ℃, 800 ℃, 900 ℃ and 1000 ℃, and showed excellent compressive strength at high temperature. The resultant material property determined via this cooling pr℃ess was superior to that of other materials such as Ni based superalloys or commercial TiAl alloys. The microstructures ass℃iated with the cooling effect were discussed in terms of materials properties and phase transformation.

keyword : TiAl, colony size, lameller structure, hall petch relation, two step cooling

This study investigated the microstructure and mechanical properties of 17-4PH precipitation hardened martensite stainless steel and Fe-Cr-B based alloy mixed material manufactured using powder injection molding. 17-4PH stainless steel powder was mixed with 5 wt%, 10 wt% and 20 wt% Fe-Cr-B based alloy (M alloy) powder to manufacture three different PIM mixed materials. Initial microstructural observations confirmed the δ-ferrite phase and martensite phase in the matrix region in all three PIM mixed materials, and (Cr, Fe)2B phase was found in the strengthening phase, boride region. Room temperature tensile tests determined the yield strengths of the 5 wt%, 10 wt% and 20 wt% M added mixed materials to be 568.2 MPa, 674.0 MPa and 697.7 MPa, and the ultimate tensile strengths to be 1141.5 MPa, 1161.0 MPa and 1164.6 MPa, respectively. Fracture surface observation confirmed ductile fracture in the ferrite phases, and brittle fracture in the martensite phase and (Cr, Fe)2B phase. Also, as the M powder fraction increased, the fracture mode of the (Cr, Fe)2B phase was confirmed to shift from intra-phase fracture to inter-phase fracture. Based on the above-mentioned findings, the deformation and fracture behavior of new mixed materials manufactured using powder injection molding was identified, and its application possibilities were also discussed.

keyword : 17-4PH, Fe-Cr-B, powder injection molding, mixed material, tensile property

When 2.25Cr-1Mo steel was hot-dip aluminized, a coating consisting of (Al-rich topcoat)/(Al13Fe4 layer)/(Al5Fe2 layer) formed. With increment of oxidation temperature, the transform of Al→Al₁₃Fe₄→Al₅Fe₂→AlFe→AlFe₃→α-Fe(Al)→α-Fe ℃curred through interdiffusion between the coating and the substrate as follows. The oxidation at 700 ℃ changed the coating to (α-Al2O3 scale)/(α-Al₂O₃, Al₁₃Fe₄, Al₅Fe₂)-mixed layer)/(Al₅Fe₂ layer)/(AlFe layer)/(AlFe₃ layer)/(α-Fe(Al) layer). The oxidation at 800 ℃ changed the coating to (α-Al2O3 scale)/((α-Al2O3, Al5Fe2)-mixed layer)/(Al5Fe2 layer)/(AlFe layer)/(AlFe₃ layer)/(α-Fe(Al) layer). The oxidation at 900 ℃ changed the coating to (α-Al₂O₃ scale)/((α-Al₂O₃, AlFe)-mixed layer)/(AlFe layer)/(AlFe₃ layer)/(α-Fe(Al) layer). The oxidation at 1000 ℃ changed the coating to ((α-Al₂O₃, Fe₂O₃)-mixed layer))/(AlFe₃ layer)/(α-Fe(Al) layer).

keyword : hot dipping, aluminizing, P22 steel, oxidation

This study attempted to utilizing the kinetic spray process to manufacture tantalum coating layer and investigated the effect of carrier gas on the microstructure and macroscopic properties of the coating layer. The initial powder feed stock was a massive powder with an average particle size of 24.35 μm and 99.99% purity. Tantalum coating layers were obtained utilizing kinetic spraying with two carrier gases, N2 and He. The manufactured tantalum coating layers featured dense structures without impurities at α-Ta phase regardless of the carrier gas used. The hardness and porosity of the layers were found to be 285 Hv and 0.04% at the He coating layer, and 270 Hv and 0.28% at the N2 coating layer. The measurement found that the coating layer produced with He gas had higher hardness and density than those of the coating layer produced with N2 gas. Through observation of the manufactured layer microstructure, the coating layer using He gas showed a particle laminating maneuver caused by larger plastic deformation. It is possible that, compared to the case of using N2 gas, higher particle speed can be applied when using He carrier gas to deposit tantalum powder. Based on observations above, this study also discussed possible methods to improve the physical properties of kinetic sprayed tantalum coating layer.

keyword : kinetic spraying, tantalum, carrier gas, nitrogen, helium, density, bond strength

This study examined the effects of the Sn content in a pure active metal filler Ag-Cu-Ti for the brazing of a Cu/ Al₂O₃ joint. The optimal content of Sn to effectively wet alumina was 5 wt%. The microstructure of the brazed joint showed the presence of an Ag-rich matrix and a Cu-rich phase, and Cu- Ti intermetallic compounds were observed along the bonded interface. The intermetallic compounds (IMCs) in the filler are found to increase when the Sn content in the alloy approaches to 10 wt%. These results suggest an extremely significant bonding strength of Cu/Al₂O₃ joint using the Ag-Cu-Ti+Sn filler. The shear strength of the brazed joint increased with Sn content up to 5 wt%, reaching a maximum at ?15 MPa. In addition, the strength decreased when the Sn content was higher than 5 wt%.

keyword : metal, active brazing, diffusion, intermetallic compounds, alumina

Microstructure evolution and the creep fracture characteristics of dissimilar welds between Ni-based superalloy Inconel 740H and High Cr ferritic steel Gr.92 were investigated. The dissimilar welds were fabricated by shielded metal arc (SMA) welding pr℃ess with Ni-based austenitic Inconel 182 superalloy. Postweld heat treatment at 760 ℃ for 4 hours was conducted to temper the fresh martensite formed in the heat-affected zone (HAZ) of Gr.92, and to form γ' strengthener in Inconel 740H. The weld interface between the Gr.92 and weld metal was characterized by a discrete line with minimal inter-diffusion, whilst the weld interface on the Inconel 740H side showed an unmixed zone having epitaxial columnar growth from the base metal. It was observed that the fresh untempered martensite formed at the Gr.92-sided coarse-grained HAZ next to the weld interface during PWHT. This may be due to higher Ni contents diffused from the Ni-based weld metal. A sharp increase in hardness was detected at the coarse-grained HAZ of Gr.92 while the hardness minimum ℃curred at the fine-grained and intercritical HAZ (FG/IC HAZ). Fracture after creep at 650 ℃/80 MPa and 700 ℃/35 MPa ℃curred at the FG/IC HAZ of Gr.92, commonly known as a type IV fracture. This may be attributed to the strain l℃alization at the FG/IC HAZ due to the smaller grain size as well as the lowest hardness. The elemental migration across the weld interface was not significant. It was also found that a needle-like Nb-rich δ-phase formed at the interdendritic region of the weld metal after creep at 700 ℃/35 MPa.

keyword : Ni-based superalloys, ferritic steels, welding, microstructure, creep, transmission electron microscopy, (TEM)

The methane reduction (MR) of SnO< SUB >2< /SUB > has been proposed as a highly efficient method for recovering Sn from SnO< SUB >2< /SUB > containing industrial wastes. The MR of SnO< SUB >2< /SUB > also produces a mixture of H2 and CO, which can be further utilized as a syngas for the production of various fuels through the Fisher-Tropsch process. To optimize the process parameters, we studied the effect of the amount of supplied CH4 (CH4/SnO< SUB >2< /SUB > molar ratios of 1, 3, or 5) on the recovery of Sn from SnO< SUB >2< /SUB > and the H2/CO ratio in the produced gas. Through a combination of thermodynamic simulation and experimental confirmation, we found that the recovery rate of Sn, and the molar ratio of H2/CO in the product gas, increased as a function of the supplied-CH₄/SnO< SUB >2< /SUB > ratio. We found that the recovery of Sn increased as a function of supplied-CH4 (95.5% at CH₄/SnO< SUB >2< /SUB >=5) however, the purity of Sn was consistent for all studied samples (~99.90%). Our results confirm that 3N quality highpurity Sn can be easily recovered from SnO< SUB >2< /SUB > containing industrial wastes by direct solid-gas reduction.

keyword : SnO₂, CH₄, reduction, syngas, thermodynamic simulation, recovery rate

The addition of CMC (Carboxymethylcellulose, Sodium Salt) may improve the hydriding and dehydriding properties of Mg since it has a relatively low melting point and the melting of CMC during transformation-involving milling may put the milled samples in good states to absorb and release hydrogen rapidly. Samples with compositions of 95 wt% Mg + 5 wt% CMC (named Mg-5CMC) and 90 wt% Mg + 10 wt% CMC (named Mg-10CMC) were made using transformation-involving milling. Mg-5CMC was activated in about 3 hydriding-dehydriding cycles. After activation, Mg-5CMC had a larger amount of hydrogen absorbed in 60 min, Ha (60 min), than Mg-10CMC and milled Mg. At the fourth cycle (CN=4), Mg-5CMC had a very high beginning hydriding rate (1.45 wt% H/min) and H_a (60 min) (7.38 wt% H), showing that the activated Mg-5CMC has an effective hydrogen-storage capacity of about 7.4 wt% at 593 K in hydrogen of 12 bar at CN=4. Mg-5CMC after transformation-involving milling contained Mg and very small amounts of β- MgH₂ and MgO, and Mg-5CMC dehydrogenated at 593 K in hydrogen of 1.0 bar at the 4^th cycle contained Mg and tiny amounts of β-MgH₂ and MgO, with no evidence of the phases related to CMC. The milling of Mg with CMC in hydrogen is believed to introduce defects and cracks and lessen the particle size. To the best of our knowledge, this study is the first in which a polymer CMC is added to Mg by transformation-involving milling to improve the hydriding and dehydriding properties of Mg.

keyword : hydrogen absorbing materials, mechanical milling scanning electron microscopy (SEM), X-ray diffraction, a polymer CMC (Carboxymethylcellulose, Sodium Salt) addition

Aluminum-induced crystallization(AIC) is one of the ways to improve characteristics of thin-film poly-crystalline (TFPC) silicon solar cell since it shows large grain size and good properties for TFPC silicon solar cell. In AIC process, aluminum is firstly deposited on foreign substrate. Then, silicon is deposited on aluminum. Annealing was done below the eutectic temperature of aluminum and silicon(577 oC). Afterward, amorphous silicon layer is crystallized by aluminum-inducing process. In this paper, we report amorphous silicon layer thickness effects to crystallized silicon and hillock characteristics since the amorphous silicon layer is important layer for AIC.Crystallized silicon properties were analyzed dependent upon silicon thickness (50 % - 200 % than aluminum layer thickness). In case of the thick amorphous silicon (above 300 nm), hillocks grew on the crystallized silicon layer, Even though silicon hillock showed high crystallinity as a result of Raman spectroscopy, it had not enough grain size (average 4 μm). Therefore, as results, samples which had 113 % - 120 % silicon and aluminum thickness ratio showed proper thickness to use as a seed layer.

keyword : crystallization, solar cells, silicon

Industrially meaningful hydrogen production process from mixture or syngas certainly must have a cooling process, which is typically pressure swing adsorption (PSA). However, the PSA process involves an exothermic reaction during adsorption. Recently, hydrogen separation research has been in progress in order to develop a cooling process to minimize or eliminate high temperature. Proton conducting ceramics with high proton conductivity, due to their many potential applications, are used in fuel cells and in the separation of hydrogen. Especially, the proton conducting ceramic Sr1.0Ce0.95Yb0.05O3-δ (SCYb) has a relatively large surface area and good chemical stability at high temperature. Therefore, SCYb composites with nanosize particles are expected to have a good influence on the Knudsen diffusion mechanism. In this work, in order to achieve effective hydrogen separation at high temperature, Ni-SCYb nano-composites were prepared by sol-gel process and ball-milling at low temperatures. Synthesized Ni-SCYb nano-composites were characterized by SEM(FE-SEM, JEOL- 7500F), XRD(Bruker D8 Focus) and BET(BEL SOROP-miniII). The hydrogen permeation properties of Ni-SCYb membrane were measured by Sievert’s type hydrogen permeation membrane equipment. Through BET analysis, Ni-SCYb composite powders were measured and specific surface area was found to be 0.5399 m2/g. Hydrogen permeability of Ni-SCYb was found to be 5.77 × 10-7 mol/ms Pa1/2 at 973 K under 0.3 MPa.

keyword : hydrogen permeation, proton conducting ceramics, Ni-Sr1.0Ce0.95Yb0.05O3-δ nano composites, sol-gel, process, cermet membrane