• Journal of Powder Materials
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• v.26 no.6
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• pp.471-476
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• 2019

Additively manufactured metallic components contain high surface roughness values, which lead to unsatisfactory high cycle fatigue resistance. In this study, high cycle fatigue properties of selective laser melted Ti-6Al-4V alloy are investigated and the effect of dry-electropolishing, which does not cause weight loss, on the fatigue resistance is also examined. To reduce the internal defect in the as-built Ti-6Al-4V, first, hot isostatic pressing (HIP) is conducted. Then, to improve the mechanical properties, solution treatment and aging are also implemented. Selective laser melting (SLM)-built Ti64 shows a primary α and secondary α+β lamellar structure. The sizes of secondary α and β are approximately 2 ㎛ and 100 nm, respectively. On the other hand, surface roughness Ra values of before and after dry-electropolishing are 6.21 ㎛ and 3.15 ㎛, respectively. This means that dry-electropolishing is effective in decreasing the surface roughness of selective laser melted Ti-6Al-4V alloy. The comparison of high cycle fatigue properties between before and after dry-electropolished samples shows that reduced surface roughness improves the fatigue limit from 150 MPa to 170 MPa. Correlations between surface roughness and high cycle fatigue properties are also discussed based on these findings.

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2018.06a
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• pp.25-25
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• 2018

Electron beam melting (EBM) is one of powder based additive manufacturing technology used to produce parts for high geometrical complexity and directly with three-dimensional computer aided design (CAD) model. It is kind of the most promising methods with additive manufacturing for a wide range of medical applications, such as orthopedic, dental implant, and etc. This research has been investigated the microstructure and mechanical properties of as fabricated and hot iso-static pressing (HIP) processed specimens, which are made by an Arcam A1 EBM system. The Ti-6Al-4V titanium alloy powder was used as a material for the 3 dimensional printing specimens. Mechanical properties were conducted with EBM manufacturing and computer numerical control (CNC) machining specimens, respectively. Surface morphological analysis was conducted by scanning electron microscopy (SEM) for their surface, dissected plan, and fractured surface after tensile test. The mechanical properties were included tensile stress-strain and nano-indentation test as a analysis level between nano and macro. As following highlighted results, the stress-strain curves on elastic region were almost similar between as fabricated and HIP processed while the ductile (plastic deformed region) properties were higher with HIP than that of as fabricated processed.

• Journal of Powder Materials
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• v.26 no.2
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• pp.138-145
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• 2019

In this study, Al-Si-Mg alloys are additively manufactured using a selective laser melting (SLM) process from AlSi10Mg powders prepared from a gas-atomization process. The processing parameters such as laser scan speed and laser power are investigated for 3D printing of Al-Si-Mg alloys. The laser scan speeds vary from 100 to 2000 mm/s at the laser power of 180 and 270 W, respectively, to achieve optimized densification of the Al-Si-Mg alloy. It is observed that the relative density of the Al-Si-Mg alloy reaches a peak value of 99% at 1600 mm/s for 180 W and at 2000 mm/s for 270W. The surface morphologies of the both Al-Si-Mg alloy samples at these conditions show significantly reduced porosities compared to those of other samples. The increase in hardness of as-built Al-Si-Mg alloy with increasing scan speed and laser power is analyzed due to high relative density. Furthermore, it was found that cooling conditions after the heat-treatment for homogenization results in the change of dispersion status of Si phases in the Al-Si matrix but also affects tensile behaviors of Al-Si-Mg alloys. These results indicate that combination between SLM processing parameters and post-heat treatment should be considered a key factor to achieve optimized Al-Si alloy performance.

• Journal of Powder Materials
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• v.28 no.2
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• pp.97-102
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• 2021

Powder quality, including high flowability and spherical shape, determines the properties of additively manufactured products. Therefore, the cheap production of high-quality powders is critical in additive manufacturing. Radio frequency plasma treatment is an effective method to fabricate spherical powders by melting the surface of irregularly shaped powders; in the present work, mechanically milled Zr powders are spheroidized by radio frequency plasma treatment and their properties are compared with those of commercial Zircaloy-2 alloy powder. Spherical Zr particles are successfully fabricated by plasma treatment, although their flowability and impurity contents are poorer than those of the commercial Zircaloy-2 alloy powder. This result shows that radio-frequency plasma treatment with mechanically milled powders requires further research and development for manufacturing low-cost powders for additive manufacturing.

• Journal of Powder Materials
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• v.11 no.5
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• pp.383-390
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• 2004

In order to investigate behavior of abnormal expansion of the iron-copper compacts, we compared the dilatometric curves of the compacts which mixed the copper powder to the iron powder with those of compacts which mixed the copper powder to the iron-copper alloy powder. The dilatometric curves were obtained below the sintering conditions, which heated up to 115$0^{\circ}C$ by a heating rate of 1$0^{\circ}C$/min, held for 60min at 115$0^{\circ}C$ and cooled down at a rate of 2$0^{\circ}C$/min to room temperature. The dilatometric curves of the compacts showed the different expansion behavior at temperatures above the copper melting point in spite of same chemical composition. All of the compacts of former case showed large expansion, but all of the compacts in latter case showed large contraction. The microstructures of sintered compacts also showed the different progress in alloying of the copper into the iron powder. Namely we could observe the segregation at alloy part of copper into iron powder in case of the sintered compacts, which mixed the copper powder to the iron powder, but could not observe the segregation in compacts which mixed the copper powder to the iron-copper alloy powder. But the penetration of liquid copper into the interstices between solid particles was occurred at both cases. Therefore, the showing of the different dimensional changes in the compacts in spite of same chemical composition is due to more the alloying of copper into iron powder than the penetration of liquid copper into the interstices between solid particles.

• Progress in Superconductivity
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• v.7 no.1
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• pp.97-101
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• 2005

Bi-22l2 tubes for fault current limiter (FCL) were fabricated by centrifugal melting process. $SrSO_4$ ($10\;wt.\;\%$) was added to Bi-2212 powder to lower the melting point of Bi-22l2 and to improve the mechanical properties. The BSCCO powder was completely melted at $1300\;^{\circ}C$ using the RF furnace and then poured into rotating steel mold. The steel mold, preheated at $450\;{\circ}C{\sim}550^{\circ}C$ for 2 hour was rotated at $1020{\sim}2520\;RPM$. The solidified BSCCO tube was cooled down to room temperature in the furnace for 48 hours and separated from the mold between Bi-2212 and the mold. $ZrO_2$ solution was used to separate it easily from the mold and Ag tape was attached in the mold inner wall of the mold to analysis electrical property. Bi-22l2 tube was often cracked when the cooling rate was high. BSCCO tubes with $70{\Phi}{\times}100\;mm,\;50{\Phi}{\times}100\;mm$ and $30{\Phi}{\times}150\;mm$ size were fabricated by centrifugal melting process. The $J_{c}s$ of tubes with $50{\Phi}{\times}100\;mm{\times}4.0\;t$ and $50{\Phi}{\times}100\;mm{\times}4.l\;t$ were 178 and $74.2\;A/cm^2$ at 77K, respectively. The processing condition for Bi-2212 tube fabrication was investigated using XRD and SEM analyses.

• Journal of Powder Materials
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• v.6 no.3
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• pp.224-230
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• 1999

Oxide powders of $Cr_2O_3 \;and\;Cr_2O_3+3{\%}TiO_2$ were prepared by spray drying, plasma densification and fused+crushed processes. The oxide coating layers were made by plasma spray and characterized by microstructure, hardness, adhesion strength and relative density. The optimum spray distance for the high quality coatings by spraying dried powders was found to be 9cm. A small amount addition of $TiO_2\;in\;Cr_2O_3$ powder significantly improved coating characteristics by lowering the melting point of powders. The hardness and relative density of coating layers of the plasma densified powders were comparable to fused and crushed powders, however, the adhesion strength was much higher in the former case.

• Journal of the Korean Ceramic Society
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• v.29 no.6
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• pp.451-458
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• 1992

Dense glass-ceramics for low firing temperature substrate were prepared by addition of CeO2 flux to the glass of MgO-Al2O3-SiO2 system. Glass powders were fabricated by melting at 150$0^{\circ}C$ and ball milling. Glass powder compacts were sintered at 800~100$0^{\circ}C$ for 3h. The crystallization and the shrinkage behaviors of glass powder compacts were analyzed by XRD, DTA and TMA. The shrinkage of glass powder compact increased with increasing the amount of CeO2. Because the softening temperature decreased and the crystallization temperature increased with increasing the amount of CeO2. Apparently, addition of CeO2 prevented formation of $\mu$-cordierite phase from the glass-ceramics and improved formation of $\alpha$-cordierite phase. Therefore crystallization properties were enhanced.

• 한국초전도학회:학술대회논문집
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• v.10
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• pp.211-215
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• 2000

Bi-2212 HTS tube was fabricated by CFP(Centrifugal Forming Process). Slury was prepared in the mixing ratio of 8:2 between powder and binder and ball-milled for 24 hrs. Slurry was initially charged into the rotating mold with 300${\sim}$450 rpm and heated at the temperature ranges of 840${\sim}$860$^{\circ}$C for partial melting to finally obtain a uniformly textured tube shape. It was observed the plate-like grains with more than 20 ${\mu}$m were well oriented along the rotating axis and the measured T$_c$ was around 67K. In this paper we will discuss and analyze the tube characteristics depending on many different processing parameters such as, powder composition, binder mixing ratio between powder and binder, motor speed, heating temperature and etc.

• Journal of Powder Materials
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• v.1 no.2
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• pp.190-197
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• 1994

The densification behavior during a sintering of M2 and T15 grade high speed steel powder compacts was reported. Sintered densities over 98% theoretical were achieved by a liquid phase sintering in vacuum for both grades. The optimum sintering temperature range where full densification could be achieved without excessive carbide coarsening and incipient melting was much narrower in M2 than in T15 grade. The sintering response was mainly affected by the type of carbides present. The primary carbides in M2 were identified as $M_6C$ type whereas those in T15 were MC type which provides wider sintering range. The addition of elemental carbon up to 0.3% lowered the optimum sintering temperature for both grades, but had little effect on expanding the sintering range and sintered structure.