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송건 ( Song Geon ),홍영환 ( Hong Yeong Hwan ) 한국열처리공학회 2003 熱處理工學會誌 Vol.16 No.4
N/A Honeycomb structure has been fabricated by brazing method using 0.1 wt%C and 1.0wt%C carbon steel core and STS304 stainless steel face sheet. Core shear strength ratio in W and L directions was 1:1.03 in 7 ㎜ cell size, whereas 1:1.45 in 4 ㎜ cell size. Flexural strength on face sheet was 166.4 MPa (0.1 wt%C, W direction), 171 .I MPa (0.1 wt%C, L direction), and 120.2 MPa (1.0 wt%C, W direction) in 7 ㎜ cell size. And in 4 ㎜ cell size specimen, it was 169.2 MPa (0.1 wt%C, W direction), 224.2 MPa (0.1 wt%C, L direction). This means that flexural strength of 0.1 wt%C core material was higher than that of 1.0 wt%C core material, which was contrary to expectation. SEM and EDS analysis represented that grain boundary diffusion had occurred in 0.1 wt%C core, but no grain boundary diffusion in 1.0 wt%C core. And corrugated surface of 0.1 wt%C core was flat, whereas that of 1.0 wt%C core was not flat. As a result, contact area between two 1.0 wt%C cores was much less than that of 0.1 wt% cores. It is thought to be main reason for lower flexural strength of 1.0 wt%C core.
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기계적 분쇄화 및 스파크 플라즈마 소결에 의한 TiAl 합금의 제조
김민수 ( Kim Min Su ),김준식 ( Kim Jun Sig ),황승준 ( Hwang Seung Jun ),홍영환 ( Hong Yeong Hwan ),오명훈 ( O Myeong Hun ) 한국열처리공학회 2004 熱處理工學會誌 Vol.17 No.1
N/A In the present study, newly developed spark plasma sintering(SPS) technique was introduced to refine the grain size of γ-based TiAl intermetallic compounds. Ti-46AI-1.5Mo and Ti-46AI-1.5Mo-0.2C(at%) prealloyed powders were produced by mechanical milling(MM) in high-energy attritor. The mechanically milled powders were characterized by XRD and SEM for the microstructural evolution as a function of milling time. And then, the MMed powders were sintered by both spark plasma sintering and hot pressing in vacuum (HP). After the sintering process, MM-SPSed specimens were heat-treated in a vacuum furnace (SPS-VHT) and in the SPS equipment(MM-SPS) for microstructural control. It was found from microstrutural observation that the microstructure consisting of equiaxed γ-TiAl with a few hundred nanometer in average size and α₂-Ti₃Al particles were formed after both sintering processes. It was also revealed from hardness test and three-point bending test that the effect of grain refinement on the hardness and bending strength is much higher than that of carbon addition. The fully lamellar microstructures, which is less than 80㎛ in average grain size was obtained by SPS-VHT process, and the fully lamellar microstructure which is less than 100um in average grain size was obtained by MM-SPS for a relatively shorter heat-treatment time.
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