Do-Hyang Kim

Enhancement of the glass forming ability of Cu−Zr−Al alloys by Ag addition

The thermal stability and glass forming ability of Cu50-xZr43Al7Agx (x=0, 1, 3, 5, and 7) bulk metallic glass alloys have been investigated. The glass forming ability in the Cu−Zr−Al−Ag alloys increased proportionally to the Ag content and show good correlations with thermal parameters such as ΔTx(=Tx-Tg), Trg(=Tg/T1) and γ(=Tx/(Tg+T1)). For the Cu43Zr43Al7Ag7 alloy, fully amorphous rods of 8 mm diameter were successfully fabricated by copper mold casting. Mechanical tests on this composition revealed also remarkable properties with compressive strength around 2000 MPa and large ductility.

High‐Power Density Piezoelectric Energy Harvesting Using Radially Strained Ultrathin Trigonal Tellurium Nanowire Assembly

A high-yield solution-processed ultrathin (<10 nm) trigonal tellurium (t-Te) nanowire (NW) is introduced as a new class of piezoelectric nanomaterial with a six-fold higher piezoelectric constant compared to conventional ZnO NWs for a high-volume power-density nanogenerator (NG). While determining the energy-harvesting principle in a NG consisting of t-Te NW, it is theoretically and experimentally found that t-Te NW is piezoelectrically activated only by creating strain in its radial direction, along which it has an asymmetric crystal structure. Based upon this mechanism, a NG with a monolayer consisting of well-aligned t-Te NWs and a power density of 9 mW/cm(3) is fabricated.

Icosahedral quasicrystalline and hexagonal approximant phases in the Al±Mn±Be alloy system

Abstract We report the formation of a primitive icosahedral quasicrystal with increased stability in Al-Mn-Be alloys close to the compound Al15Mn3Be2 by melt spinning and injection casting. The crystal structure of this compound was unknown. We show that in as-cast as well as heat treated condition the intermetallic phase HI has a hexagonal structure with lattice parameters a = 1.2295 nm and c = 2.4634nm. The space group is P63/mmc. In the injection-cast samples, the quasicrystal coexists with another closely related hexagonal phase H2 with a = 1.2295nm and c = 1.2317nm with a possible space group of P63/mmc. This phase exhibits specific orientation relationships with the icosahedral quasicrystal given by [0001]hex//2f QC and [0110]hex//5f QC, where 2f QC and 5f QC represent twofold and fivefold axes respectively. Electron diffraction patterns from both phases exhibit a close resemblance to the quasicrystalline phase. It is shown that the H1 phase is closely related to μ-Al4Mn with the same c parameter while the a parameter is reduced by τ. Following Kreiner and Franzen, it is postulated that both structures (H1 and H2) can be understood by a simple hexagonal packing of 113 clusters.

Structural evolution during heat treatment of mechanically alloyed Al–Cu–Fe–(Si) alloys

Abstract Structural evolution during mechanical alloying and subsequent heat treatment of Al65Cu20Fe15 and Al65Cu20Fe10Si5 was studied by X-ray diffractometry (XRD), transmission electron microscopy (TEM) and differential scanning calorimetry (DSC). The Al65Cu20Fe15 and Al65Cu20Fe10Si5 powders milled for 10xa0h showed a layered structure consisting of Al-, Cu- and Fe-rich layers. DSC traces obtained from the powder during heating, up to 600°C, showed two exothermic peaks with peak temperatures of 330 and 440°C in Al65Cu20Fe15 and 330 and 500°C in Al65Cu20Fe10Si5 powders. The lower exothermic peaks correspond to the formation of Al2Cu and Al7Cu2Fe phases from the layered structure. The second high temperature exotherms correspond to the formation of Al(Fe,Cu) and 1/1 cubic approximant in the Al65Cu20Fe15 powder and to the formation of Al13Fe4 and 1/1 cubic approximant in the Al65Cu20Fe10Si5 powder. The Al65Cu20Fe15 and Al65Cu20Fe10Si5 powders annealed for 5xa0h at 750°C showed microstructure consisting of Al(Cu,Fe) and Al13Fe4 phases, and Al13Fe4, icosahedral and new approximant phases, respectively. The partial substitution of Fe by Si increased the stability of the 1/1 cubic approximant and icosahedral phases.

Translationally controlled tumour protein is associated with podocyte hypertrophy in a mouse model of type 1 diabetes

Aims/hypothesisTranslationally controlled tumour protein (TCTP) is thought to be involved in cell growth by regulating mTOR complex 1 (mTORC1) signalling. As diabetes characteristically induces podocyte hypertrophy and mTORC1 has been implicated in this process, TCTP may have a role in the pathogenesis of diabetes-induced podocyte hypertrophy.MethodsWe investigated the effects and molecular mechanisms of TCTP in diabetic mice and in high glucose-stimulated cultured podocytes. To characterise the role of TCTP, we conducted lentivirus-mediated gene silencing of TCTP both in vivo and in vitro.ResultsGlomerular production of TCTP was significantly higher in streptozotocin induced-diabetic DBA/2J mice than in control animals. Double-immunofluorescence staining for TCTP and synaptopodin revealed that podocyte was the principal cell responsible for this increase. TCTP knockdown attenuated the activation of mTORC1 downstream effectors and the overproduction of cyclin-dependent kinase inhibitors (CKIs) in diabetic glomeruli, along with a reduction in proteinuria and a decrease in the sizes of podocytes as well as glomeruli. In addition, knockdown of TCTP in db/db mice prevented the development of diabetic nephropathy, as indicated by the amelioration of proteinuria, mesangial expansion, podocytopenia and glomerulosclerosis. In accordance with the in vivo data, TCTP inhibition abrogated high glucose-induced hypertrophy in cultured podocytes, which was accompanied by the downregulation of mTORC1 effectors and CKIs.Conclusions/interpretationThese findings suggest that TCTP might play an important role in the process of podocyte hypertrophy under diabetic conditions via the regulation of mTORC1 activity and the induction of cell-cycle arrest.

Sliding friction and wear behavior of Al-Ni-Co-Si quasicrystalline coatings deposited by the high-velocity oxy-fuel spraying technique

The sliding friction and wear performance of Al–Ni–Co–Si quasicrystalline coatingsdeposited by the high-velocity oxy-fuel technique were investigated under dry slidingconditions. This study indicated that changes in the imposed sliding test conditionsmodified the friction and wear behavior of quasicrystalline coatings. Qualitativeanalysis of the contact interface and wear debris were performed with the aim ofunderstanding the role of the third body on the friction and wear processes.The dependence of the coefficient of friction on the sliding velocity and counterpartmaterial was explained by the stick-slip behavior. It was also shown that testconditions favorable for the formation of thick intermediate layers and the densificationof the coating subsurface led to low wear rates. Large cylindrical particles, formed byagglomeration of small wear debris, were suggested as a beneficial factor for thereduction of the coefficient of friction.I. INTRODUCTIONFollowing the discovery of ordered crystals withquasi-periodicity by Shechtmanet al.

Twinning and texture evolution in binary Mg-Ca and Mg-Zn alloys

Texture evolution and formability in binary Mg-Ca and Mg-Zn alloys have been investigated in the present study. Static recrystallization during annealing treatment of rolled sheets leads to increase of basal pole intensity in Mg-3Zn alloy, but decrease in Mg-xCa alloys (x=0.05, 0.1 and 0.5). With increasing Ca content in Mg-xCa alloys, the basal texture becomes weaker, indicating that Ca is one of the effective elements in weakening the basal texture in Mg alloys. The effect of Ca on weakening the basal texture mainly comes from the presence of Ca atoms in the α-Mg solid solution matrix rather than from the Mg2Ca particles formed during solidification. More frequent occurrence of compression (or double) twins results in weakening of the basal texture possibly due to lower stacking fault energy in Mg-Ca alloy than in Mg-Zn alloy. The room temperature formability of Mg-Ca alloy is highly superior to that of the Mg-Zn alloy.

Synthesis of bulk metallic glass in the Ti-rich part of the Ti-Cu-Ni-Sn-Be-Zr alloy system

Abstract The glass forming ability and crystallization behaviour of melt spun Ti 50−x Cu 25 Ni 15 Sn 3 Be 7 Zr x ( x = 0, 3 and 5) amorphous alloys were investigated using differential scanning calorimetry (DSC), X-ray diffractometry and transmission electron microscopy. With increasing Z r contents, x from 0 to 5, ? T x (= T x − T g ) and T rg (= T g T l ) , where T g = glass transition temperature , T x = crystallization temperature and T l = liquidus temperature , gradually increase from 45 K to 56 K and from 0.57 to 0.60, respectively. The Ti 50 Cu 25 Ni 15 Sn 3 Be 7 alloy shows three exothermic events in the DSC curve; initially the alloy crystallizes by forming a few nanometer scale crystalline phase, followed by decomposition into a mixture of Ti(Ni,Cu), TiCu, Ti 3 Sn, and TiBe 12 phases at high temperature. Furthermore, the alloys containing Zr exhibit the formation of nanocrystalline phases of ∼10 nm size even after the second exothermic event due to their increased atomic packing density. For the Ti 45 Cu 25 Ni 15 Sn 3 Be 7 Zr 5 alloy, fully amorphous rods up to 5 mm in diameter were successfully fabricated by injection casting.

Recent Research and Development Activities on Mg Alloys at CAAM

A brief review of recent research and development activities on light weight Mg alloys at the Center for Advanced Aerospace Materials (CAAM) is reported. Current research projects include various fields such as: (i) development of high strength/ductility Mg alloys; (ii) improvement in corrosion resistant of Mg alloys; (iii) semisolid state processing of Mg alloys and (iv) development of ultralight Mg alloys. For commercial utilization of Mg alloy parts, several problems, such as melting/casting, corrosion and recycling, have to be tackled. This review also contains a brief summary of the development project of Mg alloy parts for commercial application, mainly for automobile parts.

Precipitation behavior of Mg17Al12 in monolithic and Al2O3 short fiber reinforced Mg-Al-Zn alloys

The precipitation behavior of Mg17Al12 in monolithic and Al2O3 short fiber reinforced Mg-Al-Zn alloys was investigated by optical and transmission electron microscopies and hardness measurements. The maximum hardness was obtained when the long and short axes of the platelet type continuous Mg17Al12 precipitates were about 0.3 μm and 0.04 μm, respectively. The area fraction of the discontinuous Mg17Al12 precipitate nodule reached about 0.23. The coarsening behavior of the discontinuous Mg17Al12 precipitate nodule was found to obey the relationship suggested by the Johnson-Mehl-Avrami model. The slope of the Johnson-Mehl-Avrami plot for the Al2O3 short fiber reinforced Mg-Al-Zn alloy was four times larger than that for the monolithic alloy due to the increased number of nucleation sites, i.e. nucleation at the interface between the reinforcing material and the α-Mg matrix as well as at the α-Mg grain boundaries.