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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.
용탕단조법으로 제조된 AZ91 Mg / Al Borate 휘스커 복합재료의 미세조직 및 기계적 특성
김광천,조영서,이성학,박익민 ( Kwang Chun Kim,Young Su Cho,Sung Hak Lee,Ik Min Park ) 한국주조공학회 1996 한국주조공학회지 Vol.16 No.6
N/A This study aims at investigating the correlation of microstructure and mechanical properties of the AZ91 Mg/Al borate whisker composites fabricated by squeeze casting technique with a variation of applied pressure. Microstructure observation and in-situ fracture tests were conducted on the composites to identify the microfracture process. Detailed microstructural analyses indicated that the grain refinement could be achieved with applied pressure and the little change in volume fraction on reinforcing whiskers could be carried out. It was also found clearly from in-situ observation of crack initiation and propagation that in the composite processed by the lower applied pressure, microcracks were initiated earily at whisker/matrix interfaces, thereby resulting in the drop in strength. In the composite processed by the higher applied pressure, on the other hand, planar slip lines were well developed in the matrix, and then propagated through whiskers without whisker/matrix decohesion. Thus, the effect of the applied pressure on microstructure and mechanical properties can be explained by grain refinement, increased amounts of reinforcements, and improvement of whisker/matrix interfacial strength as the applied pressure in increased.