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J 적분법을 이용한 Ni-Cr-Mo-V 강의 파괴인성 평가
주영한,한봉기 대한금속재료학회(대한금속학회) 1988 대한금속·재료학회지 Vol.26 No.9
Elastic-plastic fracture toughness(J_(IC)) of Ni-Cr-Mo-V steel with different yield strengths has been evaluated by two different testing methods (ASTM E8l3 JSME S001) and compared with K_(IC) and Charpy V-notch (CVN) impart value. At high yield strength levels, J_(IC) values measured by ASTM and JSME method are almost equal, however, at low yield strength levels, J_(IC) values by the ASTM method exceed those by the JSME method. This difference in J_(IC) values is due to variation in the method of considering crack extension on the specimen fracture surface. The comparison of K_(IC) with J_(IC) and CVN impact values shows that a very good correlation, exists between 93- 144 ㎏/㎟ yield strength levels. Therefore, it is possible to predict K_IC value with J_(IC) and CVN impact test.
김영환,배동수,주영한 대한금속재료학회(대한금속학회) 1997 대한금속·재료학회지 Vol.35 No.7
The anneal-induced enthalpy relaxation behavior was examined calorimetrically for the amorphous (Al_(1-x)Y_x)_(80)Ni_(20)(0.25≤X≤0.75) alloys with a ribbon shape. When the samples annealed at temperatures below T_g or T_x are heated, an excess endothermic reaction (enthalpy relaxation) occurred above the annealing temperature (T_a) followed by a broad exothermic reaction. The onset peak temperature (T_m) of the endothermic reaction increased in a continuous manner with the annealing time (t_a). The exothermic reaction is thought to be due to the annihilation of various kinds of frozen-in defects and the endothermic one to the development of topological and compositional short-range ordering among the constituent atoms. The enthalpy relaxation was easily occurred with Y content. The easiness of the structural relaxation with Y content can be well explained by the interaction between Al and Y atoms as predicted from the difference in the melting temperature of compounds corresponding their compositions in the equilibrium phase diagrams. A bulky amorphous alloy with a diameter of 2㎜ was obtained by water quenching for Al_(20)La_(50)Ni_(20) composition. The amorphous nature of bulky alloy had a relaxed structure more than that of a ribbon shape, while a n amorphous nature was nearly the same.
MA-Plasma 법에 의한 MoSi2 화합물 및 MoSi2/Nb 복합체의 조직과 성질
박용호,배차헌,정해용,이성열,주영한 대한금속재료학회(대한금속학회) 1997 대한금속·재료학회지 Vol.35 No.8
MoSi₂ is one of the most promising candiate for high-temperature structural materials because of its high melting point and excellent oxidation resistance. However, the low room temperature fracture toughness and ductillity, etc. of MoSi₂ still remains as major obstacles to potential high temperature structural applications. The fracture toughness of brittle matrix ran be improved by the incoporation of a ductile second phase such as metallic Nb. The purpose of this study is to improve the room temperature fracture toughness and ductillity of sintered MoSi₂ and MoSi₂/Nb composites respectively by densification, refining of microstructure and minimizing of interfacial reactions between matrix and Nb. These compound and composite are prepared by mechanical alloying(MA)-spark plasma sintering process(SPS). The microstructures and material properties of these sapmle were investigated by optical microscopy, SEM, XRD, EPMA, microhardness measurement and 4-point bending test. The Vickers hardness, bending strength and fracture toughness increased with the incorporation of metallic Nb.