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조남정,박익민 ( Nam Jung Cho,Ik Min Park ) 한국주조공학회 1986 한국주조공학회지 Vol.6 No.3
The effect of pulverizing methods on sintered strength of degraphitized gray cast iron swarf was investigated. The main results are as follows: 1) The compressive fracture strength level of sintered cast iron powder is in the order of cutter mill powder, mortar grinding powder and ball mill powder; This is considered to be due to the increase in surface roughness. The increase in surface roughness factor leads to the increase in green strength and sintered strength. 2) The compressive fracture strength of sintered products which were compacted at 12t/㎠ and sintered at 1150℃ for 90min in the vacuum atmosphere, is higher than that of parent gray cast iron by the factor 2.5. 3) The increase in sintered strength is due to the spheroidal graphite precipitation at the finely dispersed round pore.
용탕단조한 AC4A Al / Al2O3+SiCp 하이브리드 금속복합재료의 미세조직과 기계적 성질
김민수,조경목,박익민 ( Min Soo Kim,Kyung Mox Cho,Ik Min Park ) 한국주조공학회 1994 한국주조공학회지 Vol.14 No.3
N/A AC4A Al/Al₂O₃+SiC_P hybrid composites were fabricated by the squeeze infiltration technique. Effect of applied pressure, volume fraction of reinforcement(AL₂O₃and SiC) and SiC particle size(4.5㎛, 6.5㎛ and 9.3㎛) on the solidification microstructure of the hybrid composites were examined. Mechanical properties were estimated preliminarly by fractographic observation, hardness measurement and wear test. Results show that the microstructure of the hybrid composites were quite satisfactory, namely revealing relatively uniform distribution of reinforcements and refined matrix. Some aggregation of SiC particle caused by particle pushing was observed especially in the hybrid composites containg in fine particle(4.5㎛). Refined matrix was attributed to applied pressure and increased nucleation sites with addition of reinforcements. Fractured facet also revealed finer for the hybrid composites possibly due to refined matrix. Hardness and wear resistance increased with volume fraction of reinforcements. For hybrid composites with 9.3㎛ SiC, hardness was somewhat lower and wear resistance higher than other composites.
벌크형 비정질 Zr계 합금의 결정화 열처리에 따른 동적변형 거동
장재준,이병주,황진일,박익민,조경목,조영래,Chang J. J,Lee B. J,Hwang J. I,Park I. M,Cho K. M,Cho Y. R 한국재료학회 2004 한국재료학회지 Vol.14 No.3
The mechanical properties of a bulk amorphous alloy ($Zr_{41.2}$ $Ti_{13.8}$ /$Cu_{10}$ $Ni_{10}$ $Be_{22.5}$ /at.%) before and after an annealing treatment were investigated. For the bulk amorphous alloy, the compressive strength was about 2.0 GPa, irrespective of the strain rates in the range of $10^{-4}$ to $10^3$$ sec^{-1}$ . Fine-sized nanocrystalline particles (10~100 nm) were precipitated homogeneously in the bulk amorphous matrix after the annealing treatments. Compared to the bulk amorphous materials, these composite materials, composed of the nanocrystalline phases and a bulk amorphous matrix had much different mechanical properties. The strength and strain of coposite materials measured by a compressive test showed a peak-maximum values at 7 vol.% of the nanocrystalline phases. The values in higher volume fraction of the crystalline phases in the amorphous matrix were decreased, as measured by both quasi-static and high strain rate. The decrease in fracture strength is due to presence of the dispersed large-crystalline phases in the amorphous matrix.