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Influence of Addition of Ge on the Microstructure and Corrosion Properties of Magnesium
Kim, Byeongho,Park, Kyungchul,Kimura, Hisamichi,Park, Yongho,Park, Ikmin The Japan Institute of Metals 2012 Materials transactions Vol.53 No.1
<P>The corrosion properties of Mg–<I>x</I>Ge (<I>x</I> = 0, 0.5, 1.0, 1.5 and 2.0 mass%) alloys were investigated. Potentiodynamic polarization and electrochemical impedance spectroscopy tests were carried out in a 3.5% NaCl solution at pH 7.2 to measure the corrosion properties of Mg–<I>x</I>Ge (<I>x</I> = 0, 0.5, 1.0, 1.5 and 2.0 mass%) alloys. Microstructural analysis showed that a Mg<SUB>2</SUB>Ge phase formed mainly in the interdendritic areas. The volume fraction of the Mg<SUB>2</SUB>Ge phase was increased with increasing Ge content. The corrosion resistance of the Mg–<I>x</I>Ge alloys was improved by Ge addition. In particular, the Mg–1.5 mass%Ge alloy showed the superior corrosion resistance of the alloys examined.</P>
용탕가압침투법에 의한 알루미늄 보레이트 강화 Mg-3Al-2Ag-1Zn 금속복합재료의 물성
강호준,배건희,박용하,한상호,박용호,조경목,박익민,Kang Hojune,Bae Gunhee,Park Yongha,Han Sangho,Park Yongho,Cho Kyungmox,Park Ikmin 한국재료학회 2005 한국재료학회지 Vol.15 No.12
In this study, aluminum borate whisker reinforced Mg-3Al-2Ag-1Zn matrix composites were fabricated by the squeeze infiltration technique. The purpose is to develop materials for elevated temperature applications. Microstructure observation revealed successful fabrication of the metal matrix composites, namely no cast defects such as porosity and matrix/reinforcement interface delamination etc. High temperature hardness and creep rupture properties were improved significantly with addition of Ag to the Al borate whisker reinforced Mg alloy composite. $Mg_3Ag$ phase formed during aging heat treatment could improve creep properties of the Mg matrix composites.
Lee, Insup,Park, Ikmin Elsevier 2007 Materials science & engineering. properties, micro Vol.449 No.-
<P><B>Abstract</B></P><P>Plasma radical nitriding was performed to harden the surface of SKD 61 steel for 1–10h at temperature range of 450–550°C. The microstructures and material properties of the radical nitrided layer were characterized in order to investigate the effects of various radical nitriding processing parameters. No compound layer was formed during this process except the experiment carried out at 500°C for 10h. A diffusion depth increased with increasing treatment temperature and time (up to about 150μm). The surface hardness of radical nitrided layer was two times higher than that of the untreated surface. The main phases produced in the diffusion zone were identified to be ϵ-Fe<SUB>2-3</SUB>(N,C) and γ′-Fe<SUB>4</SUB>(N,C). The residual stress of the diffusion layer also increased with increasing treatment temperature and time due to the increase of precipitates. In addition, plasma radical nitriding produces better surface roughness, compared with conventional ion nitriding.</P>
Influence of Pd addition on the creep behavior of AZ61 magnesium alloy
Kim, Byeongho,Kang, Byoungsoo,Park, Yongho,Park, Ikmin Elsevier 2011 Materials science & engineering. properties, micro Vol.528 No.18
<P><B>Graphical abstract</B></P><P>Schematic of crack initiation and propagation during creep.<ce:figure id='fig0005'></ce:figure></P><P><B>Highlights</B></P><P>► The Mg alloys have been successfully fabricated. ► Addition of Pd to AZ61 alloy leads the formation of lamella shape stable Al<SUB>4</SUB>Pd intermetallics. ► The creep resistance of the addition of Pd to AZ61 alloys is largely higher than that of the AZ61 alloy.</P> <P><B>Abstract</B></P><P>The effect of Pd addition (0, 2, and 4wt%) on the microstructure and creep properties of permanent mold AZ61 (Mg–6Al–1Zn) alloy has been studied. The results indicate that Pd addition introduces a lamella-shaped Al<SUB>4</SUB>Pd phase at the grain boundary, in addition to the Mg<SUB>17</SUB>Al<SUB>12</SUB> (β) phase. The addition of Pd also suppresses the precipitation of the Mg<SUB>17</SUB>Al<SUB>12</SUB> phase and residual Al at grain boundaries during solidification. These effects lead to an improvement in the creep behavior of AZ61. Moreover, extended steady-state creep and reductions in both the minimum creep rate and total creep strain are also observed in the case of 4wt% Pd addition.</P>
박판주조법으로 제조된 Zr계 벌크 비정질 합금의 미세파괴기구
이정구,이동근,이성학,김낙준,조경목,박익민 대한금속재료학회 2004 대한금속·재료학회지 Vol.42 No.2
The mechanical property improvement of a strip-cast Zr-base bulk amorphous alloy was explained by clarifying fracture mechanisms. Effects of crystalline phase particles formed in the amorphous matrix during strip casting on strength, ductility, and fracture toughness were explored in detail by directly observing microfracture processes using an in situ loading stage installed inside a scanning electron microscope (SEM) chamber. The compressive and fracture toughness test results indicated that ductility, strength, and fracture toughness of the atrip-cast amorphous alloy were higher than those of the as-cast monolithic amorphous alloy, although the strip-cast alloy contained a considerable amount (4.5 vol. %) of hard, brittle crystalline particles. This improvement of mechanical properties in the strip-cast alloy could be plausibly explained by mechanisms of (1) blocking of crack propagation, (2) formation of multiple shear bands, and (3) crack deflection by crystalline particles. Such property improvement presents new applicability of the strip-cast amorphous alloy containing crystalline particles to structures and components requiring excellent fracture toughness.
Effects of crystalline particles on mechanical properties of strip-cast Zr-base bulk amorphous alloy
Lee, Jung G.,Lee, Dong-Geun,Lee, Sunghak,Cho, Kyung-mox,Park, Ikmin,Kim, Nack J. Elsevier 2005 Materials science & engineering. properties, micro Vol.390 No.1
<P><B>Abstract</B></P><P>Effects of crystalline phase particles formed in a strip-cast Zr-base bulk amorphous alloy on strength, ductility, and fracture toughness were investigated by directly observing microfracture processes using an in situ loading stage installed inside a scanning electron microscope chamber. The compressive and fracture toughness test results indicated that strength, ductility, and fracture toughness of the strip-cast amorphous alloy were higher than those of the as-cast monolithic amorphous alloy, although the strip-cast alloy contained a considerable amount (4.5vol.%) of hard, brittle crystalline particles. According to the in situ microfracture observation, crystalline particles were easily cracked under low stress levels, acted as blocking sites of shear band or crack propagation, and provided initiation sites of multiple shear bands. Thus, the improvement of mechanical properties in the strip-cast alloy could be explained by mechanisms of (1) blocking of crack propagation, (2) formation of multiple shear bands, and (3) crack deflection by crystalline particles.</P>