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Vacuum Hot Pressing 조건이 $SiC_w$/2124AI 금속복합재료의 기계적 성질 및 미세구조에 미치는 영향
홍순형 한국분말야금학회 1994 한국분말재료학회지 (KPMI) Vol.1 No.2
The variation of the microstructures and the mechanical properties with varying vacuum hot pressing temperature and pressure was investigated in PyM processed 20 vol%) SiCw/ 2124Al composites. As increasing the vacuum hot pressing temperature, the aspect ratio of whiskers and density of composites increased due to the softening of 2124Al matrix with the increased amount of liquid phase. The tensile strength of composite increased with increasing vacuum hot pressing temperature up to $570^{\circ}C$ and became saturated above $570^{\circ}C$, To attain the high densification of composites above 99%, the vacuum hot pressing pressure was needed to be above 70 MPa. However, the higher vacuum hot pressing pressure above 70 MPa was not effective to increase the tensile strength due to the reduced aspect ratio of SiC whiskers from damage of whiskers during vacuum hot pressing. A phenomenological equation to predict the tensile strength of $SiC_w$/2124AI composite was proposed as a function including two microstructural parameters, i.e. density of composites and aspect ratio of whiskers. The tensile strength of $SiC_w$/2124AI were found more sensitive to the porosity than other P/M materials due to the higher stress concentration and reduced load transfer efficiency by the pores locating at whisker/matrix interfaces.
Nb 함유 HSLA 강의 저주기 피로실험에서 분위기의 영향 및 소성변형에너지에 관한 연구
홍순형,박종욱,이원종 대한금속재료학회(대한금속학회) 1989 대한금속·재료학회지 Vol.27 No.5
The influence of plastic strain amplitude and gaseous environment on the low cycle fatigue properties has been studied in a Nb-bearing HSLA steel. The cyclic response under plastic-strain controlled loading is determined. Neither the cyclic stress-strain curve (CSSC) shows a plateau nor persistent slip bunds (PSB's) have been observed in the bulk. The cyclic plastic strain energy (ΔW) and the accumulated plastic strain energy (W) have been calculated as a function of plastic strain amplitude (Δ_(εΡ)/2) in the form of Κ(Δ_(εp)/2)^N. The computed values of ΔW and W are in good agreement with the experimental data. The vacuum environment enhances fatigue crack initiation life, fatigue life and W. The environmental effect becomes more severe as the plastic strain amplitude decreases. Tensile properties, cyclic stress response and ΔW are not affected by the gaseous environment.
Fe-10Cr-10Ni-2 W 마르에이징강에서 reverted 오스테나이트의 형태와 결정학적 특징
홍순형,남수우,석진이 대한금속재료학회(대한금속학회) 1992 대한금속·재료학회지 Vol.30 No.3
The morphology and crystallographic feature of austenite formed from martensite during aging have been investigated in a Fe-10Cr-10Ni-2W maraging steel. The microstructure of solution-treated sample is fully martensite before aging. Four types morphology, such as lath-like, allotriomorph, Widmansta¨tten and wedge-shaped austenite. appeared in this maraging steel during aging. The reverted austenite is formed having both a Kurdjumov-Sachs(K-S) orientation relationship and a Nishiyama(N) orientation relationship with martensitic matrix. Furthermore, a wedge-shaped austenite is found to have a twin relationship between adjacent austenites. The twinned austenite is observed to have a very sharpy twin boundary, and longitudinal direction of the twin boundary is dependent upon both the beam direction and the orientation relationships between austenite and martensite.
지식과 학생의 관계에 대한 탐색: 세계와의 인식론적 관계를 넘어 실존적 관계로
홍순형,곽덕주 한국교육철학학회 2023 교육철학연구 Vol.45 No.4
This study began with the problem that although Korean school education is knowledge education, knowledge is leading students to wander rather than influencing important choices or directions in their lives. Korean knowledge education has been based on constructivism to overcome objectivism, but constructivism, like objectivism, has the limitation of keeping students in an epistemological relationship with the world. This is because interpretive-centered signification, a philosophical principle of constructivism, emphasizes knowledge construction solely on the part of the student, leaving students in a “knowing” relationship with the world. Therefore, this study aimed to explore what it means for students’ relationships with knowledge to go beyond the objectification-based nature of an epistemological relationship to adopt an existential relationship based on self-relationship. In an existential relationship, students and their knowledge are related through “becoming,” not “knowing,” demonstrating how students can, through knowledge, become authentic and subjective individuals in the world. This research shows that both the passive or instrumental relationship of knowledge to learners and the active and constructive relationship of so-called competency-based knowledge fail to significantly impact students' lives. Hence, the study attempted to explore another relationship to knowledge that can significantly impact students' orientation. The findings may contribute to the much-discussed discourse on student subjectivity.