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열간 등압 성형된 니켈기 초내열 합금 IN 713C 분말 소결체의 특성 평가
김영무,김은표,정성택,이성,노준웅,이성호,권영삼,Kim, Youngmoo,Kim, Eun-Pyo,Chunga, Seong-Taek,Lee, Seong,Noh, Joon-Woong,Lee, Sung Ho,Kwon, Young-Sam 한국분말야금학회 2013 한국분말재료학회지 (KPMI) Vol.20 No.4
Nickel-based superalloy IN 713C powders have been consolidated by hot isostatic pressing (HIPing). The microstructure and mechanical properties of the superalloys were investigated at the HIPing temperature ranging from $1030^{\circ}C$ to $1230^{\circ}C$. When the IN 713C powder was heated above ${\gamma}^{\prime}$ solvus temperature (about $1180^{\circ}C$), the microstructure was composed of the austenitic FCC matrix phase ${\gamma}$ plus a variety of secondary phases, such as ${\gamma}^{\prime}$ precipitates in ${\gamma}$ matrix and MC carbides at grain boundaries. The yield and tensile strengths of HIPed specimens at room temperature were decreased while the elongation and reduction of area were increased as the processing temperature increased. At $700^{\circ}C$, the strength was similar regardless of HIPing temperature; however, the ductility was drastically increased with increasing the temperature. It is considered that these properties compared to those of cast products are originated from the homogeneity of microstructure obtained from a PM process.
티타늄 합금 분말 소결체의 고온 변형 거동 및 미세조직 연구
김영무,송영범,이성호,권영삼,Kim, Youngmoo,Song, Young-Beom,Lee, Sung Ho,Kwon, Young-Sam 한국분말야금학회 2014 한국분말재료학회지 (KPMI) Vol.21 No.4
The effects of processing parameters on the flow behavior and microstructures were investigated in hot compression of powder metallurgy (P/M) Ti-6Al-4V alloy. The alloy was fabricated by a blended elemental (B/E) approach and it exhibited lamellar ${\alpha}+{\beta}$ microstructure. The hot compression tests were performed in the range of temperature $800-1000^{\circ}C$ with $50^{\circ}C$ intervals, strain rate $10^{-4}-10s^{-1}$, and strain up to 0.5. At $800-950^{\circ}C$, continuous flow softening after a peak stress was observed with strain rates lower than $0.1s^{-1}$. At strain rates higher than $1s^{-1}$, rapid drop in flow stress with strain hardening or broad oscillations was recorded. The processing map of P/M Ti-6Al-4V was designed based on the compression test and revealed the peak efficiency at $850^{\circ}C$ and $0.001s^{-1}$. As the processing temperature increased, the volume fraction of ${\beta}$ phase was increased. In addition, below $950^{\circ}C$, the globularization of phase at the slower strain rate and kinking microstructures were found. Based on these data, the preferred working condition of the alloy may be in the range of $850-950^{\circ}C$ and strain rate of $0.001-0.01s^{-1}$.
타이타늄 합금 분말 형상 및 치밀화 기구에 따른 미세조직 및 기계적 물성 영향 연구
김영무,권영삼,송영범,이성호,Kim, Youngmoo,Kwon, Young-Sam,Song, Young-Beom,Lee, Sung Ho 한국분말야금학회 2019 한국분말재료학회지 (KPMI) Vol.26 No.4
The objective of this study is to investigate the influence of powder shape and densification mechanism on the microstructure and mechanical properties of Ti-6Al-4V components. BE powders are uniaxially and isostatically pressed, and PA ones are injection molded because of their high strengths. The isostatically compacted samples exhibit a density of 80%, which is higher than those of other samples, because hydrostatic compression can lead to higher strain hardening. Owing to the higher green density, the density of BE-CS (97%) is found to be as high as that of other samples (BE-DS (95%) and P-S (94%)). Furthermore, we have found that BE powders can be consolidated by sintering densification and chemical homogenization, whereas PA ones can be consolidated only by simple densification. After sintering, BE-CS and P-S are hot isostatically pressed and BE-DS is hot forged to remove residual pores in the sintered samples. Apparent microstructural evolution is not observed in BE-CSH and P-SH. Moreover, BE-DSF exhibits significantly fine grains and high density of low-angle grain boundaries. Thus, these microstructures provide Ti-6Al-4V components with enhanced mechanical properties (tensile strength of 1179 MPa).
전기 도금 법으로 제조된 Cu 박막 구조물의 탄성계수와 미세조직과의 연관성 연구
김영무(Youngmoo Kim),한준희(Jun-Hee Hahn),이창승(Chang Seung Lee),박준협(Jun-Hyub Park),홍순형(Soon Hyung Hong) 대한기계학회 2003 대한기계학회 춘추학술대회 Vol.2003 No.8
This paper reports on the manufacturing, surface morphology and Young's modulus of Cu thin films used as MEMS (micro-electro-mechanical systems) devices. Nanoindentation test and microcantilever bending test were performed to evaluate the mechanical properties, especially Young's modulus of these thin films. Cu thin film specimens were produced by MEMS fabrication techniques such as sputtering, electrochemical deposition, lithography and silicon bulk micromachining. Surface morphologies of specimens were measured by atomic force microscopy (AFM). Young's moduli of Cu electrodeposited films were decreased with increasing the thickness of specimens. From these results, it was shown that Young's modulus of Cu thin films had anisotropy with crystal orientations. Elastic moduli were varied with the thickness of thin film due to the texture of Cu thin films. Young's modulus of Cu thin films can be predicted by using two methods. One is to use the elastic modulus of single crystal and the information of distribution of crystal orientation, Voigt model. The other is to calculate it from load-deflection curves computed with ABAQUS. The theoretical estimation of elastic modulus using texture analysis showed good agreement with the results of nanoindentation test. But in computational modeling, Young's moduli were different from the results of bending test with isotropic and anisotropic Cu beams having (001) texture.