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논문 : 기계적 성질 ; 용탕단조된 Mg-Al-Zn-Si합금의 미세조직 및 파괴거동
김재중 ( Jae Joong Kim ),추성훈 ( Seong Hun Choo ),김도향 ( Do Hyang Kim ),김락준 ( Nack J. Kim ) 대한금속재료학회 ( 구 대한금속학회 ) 1998 대한금속·재료학회지 Vol.36 No.6
Microstructure and fracture behavior of the squeeze cast Mg-Al-Zn-Si alloys (AZ91-Si, AZ51-Si, AZ51 Si-Ca) have been investigated in the present study. To clarify the fracture behavior, in-situ fracture test and fractographic observation were conducted. The higher Al content promoted formation of the polygonal type Mg2Si, but resulting in reduction of the ductility due to increase in amount of Mg17Al12 and to presence of coarse Mg2Si. The lower Al content favored formation of the chinese script type Mg2Si which promoted the brittle fracture along the Mg2Si/matrix interface. AZ51-Si alloy had a higher ductility than AZ91-Si, because a number of slip lines were developed inside grains and cracks were blunted by matrix. The addition of Ca eliminated the chinese script type Mg2Si. Instead, fine Mg2Si particles were present in a polygonal shape, resulting in improvement of mechanical properties.
고에너지 전자빔 투사방법으로 제조된 VC / 탄소강 표면합금화 재료의 템퍼링에 의한 경도향상
이성학(Sung Hak Lee),어광준(Kwang Jun Euh),김용찬(Yong Chan Kim),신기삼(Kee Sam Shin),김락준(Nack J. Kim) 대한금속재료학회 ( 구 대한금속학회 ) 2002 대한금속·재료학회지 Vol.40 No.9
This study aimed at improving hardness by tempering of VC/carbon steel surface-alloyed material fabricated by high-energy electron-beam irradiation. The mixture of VC powders and flux (50%MgO-50%CaO) was placed on a plain carbon steel substrate, and then electron beam was irradiated on this mixture using an electron beam accelerator. The surface-alloyed layer of 1.8 mm in thickness was homogeneously formed without defects. The microstructural analysis indicated that VC particles were coarsely formed along solidification cell boundaries, and the matrix inside cells was mostly composed of lath-type martensite and fine cuboidal VC particles. A large amount (10.1 vol.%) of these VC particles in the lath-type martensitic matrix improved hardness four times greater than that of the substrate. When the VC/steel surface alloyed material was tempered, a number of fine VC particles were precipitated in, the tempered martensitic matrix, thereby leading to the additional hardness improvement. Therefore, the hardness of the surface-alloyed layer was further enhanced by tempering, while the residual stress in the layer could be removed and the fracture toughness could be increased.