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1。 J. Appl. Phys. 105, 07A322 (2009) Temperature stability of field induced anisotropy in soft ferromagnetic Fe,Co-based amorphous and nanocomposite ribbons P. R. Ohodnicki,1,2 D. E. Laughlin,1,2 M. E. McHenry,1 V. Keylin,1,2 and J. Huth2 1Department of Materials Science and Engineering, Carnegie Mellon University, Pittsburgh, Pennsylvania 15213, USA 2Magnetics, Division of Spang and Company, Pittsburgh, Pennsylvania 15238, USA The temperature stability of field induced uniaxial anisotropy (KU) was investigated by thermomagnetic treatments of (Co1−xFex)89Zr7B4 amorphous ribbons after field annealing below and above the crystallization temperature. We conclude: (1) Field annealing treatments are necessary to properly investigate the temperature stability of KU, (2) KU of field crystallized alloys exhibit improved temperature stability relative to alloys remaining amorphous after field annealing, and (3) larger KU is obtained for field crystallization treatments as compared to zero-field crystallization followed by field reannealing. Field crystallization may be required for elevated temperature applications when field induced anisotropy is critical for performance. ©2009 American Institute of Physics 2。 Journal of Alloys and Compounds - Article in Press, Accepted Manuscript Effects of the partial substitutional alloying elements on the crystallization behavior of Mg65Cu25Gd10 metallic glass: Ag versus Ni J. Yina, G.Y. Yuana, b, P.F. Wanga, J. Zhanga, Z.H. Chua and W.J. Dinga, b aNational Engineering Research Center of Light Alloys Net Forming, Shanghai Jiaotong University,800 Dongchuan Road Shanghai,200240,China bState Key Laboratory of Metallic Matrix Composites, Shanghai Jiaotong University,800 Dongchuan Road Shanghai,200240,China Received 17 November 2008; revised 27 February 2009; accepted 2 March 2009. Available online 14 March 2009. Abstract The crystallization behaviors of Mg65Cu25Gd10, Mg65Cu20Ag5Gd10 and Mg65Cu20Ni5Gd10 metallic glasses were compared with respect to the continuous heating and the isothermal annealing. The results showed that both the partial substitution Ag and Ni for Cu in the Mg65Cu25Gd10 glass can increase the activation energy for the first crystallization and however decrease the thermal stability and the crystal growth rate during the isothermal annealing. The difference in the influence on the crystallization behaviors between Ag addition and Ni addition was analyzed in details. The examination of the crystallization product after the isothermal annealing revealed that Ag addition can effectively suppress the formation of the Mg2Cu crystalline phase of Mg65Cu25Gd10 glass while Ni addition can promote the Mg2Cu formation, which is well consistent with the larger glass-forming ability(GFA) of the Mg65Cu20Ag5Gd10 alloy than that of the Mg65Cu20Ni5Gd10 alloy. In addition, the possible relation between the crystallization features with the GFA was discussed. Keywords: Magnesium; Metallic glasses; Crystallization 3。 Journal of Alloys and Compounds - Article in Press, Corrected Proof Air oxidation of a Zr58Cu22Al12Fe8 bulk metallic glass at 350–550 °C W. Kaia, Y.R. Chena, T.H. Hoa, H.H. Hsieha, D.C. Qiaob, F. Jiangb, G. Fanb and P.K. Liawb aInstitute of Materials Engineering, National Taiwan Ocean University, Keelung 20224, Taiwan, ROC bDepartment of Materials Science and Engineering, University of Tennessee, 434 Dougherty Hall, Knoxville, TN 37996, USA Available online 14 March 2009. Abstract The oxidation behavior of the Zr58Cu22Al12Fe8 bulk metallic glasses (-BMG) was studied over the temperature range of 350–550 °C in dry air. The oxidation kinetics of the ZC4-BMG generally follow a multi-stage parabolic-rate law, and the steady-state parabolic-rate constants (kp values) increased with increasing the temperature when it is below the glass transition temperature (Tg = 413.3 °C). Conversely, the kp values were nearly identical from 400 to 550 °C. The scales formed on ZC4-BMG were composed mostly of tetragonal-ZrO2 (t-ZrO2) and minor amounts of Al2O3 and monoclinic-ZrO2 (m-ZrO2). The amounts of both Al2O3 and m-ZrO2 increased with increasing the temperature. In addition, the amorphous substrate remained unchanged after the oxidation for 36 h at T ≤ 375 °C. However, it transformed into different crystalline phases at higher temperatures, which are strongly dependent on the temperature and duration of time. Keywords: Bulk metallic glasses; Oxidation; X-ray diffraction; Thermal analysis; Microscopy 4。 Intermetallics - Article in Press, Corrected Proof Electron-irradiation-induced nano-crystallization in quasicrystal-forming Zr-based metallic glass Takeshi Nagasea, b, Takashi Hosokawab, 1, Kazuya Takizawab and Yukichi Umakoshic aResearch Center for Ultra-High Voltage Electron Microscopy, Osaka University, 7-1 Mihoga-oka, Ibaraki, Osaka 567-0047, Japan bDivision of Materials and Manufacturing Science, Graduate School of Engineering, Osaka University, 2-1 Yamada-oka, Suita, Osaka 565-0871, Japan cNational Institute for Materials Science, 1-2-1 Sengen, Tsukuba, Ibaraki 305-00471, Japan Received 14 October 2008; revised 19 January 2009; accepted 12 February 2009. Available online 14 March 2009. Abstract Phase selection in electron-irradiation-induced crystallization and crystal-to-amorphous-to-crystal (C–A–C) transition at 298 K in quasicrystal-forming Zr–Pt metallic glass alloys were investigated. Two types of f.c.c. nano-crystalline precipitates were formed in amorphous Zr80Pt20 and Zr66.7Pt33.3 alloys under electron irradiation; such unique nano-crystalline structures were not observed during thermal annealing. It was inferred that unique phase selection in electron-irradiation-induced crystallization and thermal crystallization can be explained by the large negative chemical mixing enthalpy (ΔHchem) in Zr–Pd and Zr–Pt alloys. Keywords: B. Metallic glasses; B. Irradiation effects; B. Phase transformation; C. Nanocrystals 5。 PNAS Solution to the problem of the poor cyclic fatigue resistance of bulk metallic glasses Maximilien E. Launeya, Douglas C. Hofmannb, William L. Johnsonb,1 and Robert O. Ritchiea,c,1 aMaterials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720; bKeck Laboratory of Engineering Materials, California Institute of Technology, Pasadena, CA 91125; cDepartment of Materials Science and Engineering, University of California, Berkeley, CA 94720 1To whom correspondence may be addressed. E-mail: wlj@caltech.edu or roritchie@lbl.gov Abstract The recent development of metallic glass-matrix composites represents a particular milestone in engineering materials for structural applications owing to their remarkable combination of strength and toughness. However, metallic glasses are highly susceptible to cyclic fatigue damage, and previous attempts to solve this problem have been largely disappointing. Here, we propose and demonstrate a microstructural design strategy to overcome this limitation by matching the microstructural length scales (of the second phase) to mechanical crack-length scales. Specifically, semisolid processing is used to optimize the volume fraction, morphology, and size of second-phase dendrites to confine any initial deformation (shear banding) to the glassy regions separating dendrite arms having length scales of ≈2 μm, i.e., to less than the critical crack size for failure. Confinement of the damage to such interdendritic regions results in enhancement of fatigue lifetimes and increases the fatigue limit by an order of magnitude, making these “designed” composites as resistant to fatigue damage as high-strength steels and aluminum alloys. These design strategies can be universally applied to any other metallic glass systems. 6。 J. Appl. Phys. 105, 07A326 (2009) Cluster spin-glass state and Kondo behavior in Sm-based bulk metallic glasses C. L. Lu,1 S. Dong,1 K. F. Wang,1 J.-M. Liu,1 Q. Wang,2 and C. Dong2 1Nanjing National Laboratory of Microstructures, Nanjing University, Nanjing 210093, China and International Center for Materials Physics, Chinese Academy of Sciences, Shenyang 110016, China 2State Key Laboratory of Materials Modification, Dalian University of Technology, Dalian 116024, China We investigate the magnetization and electrical transport properties of Sm-based ternary magnetic bulk metallic glasses at low temperatures. A cluster spin-glass phase is evidenced below Tf~25 K, which is probably ascribed to competition among the multifold magnetic interactions and intrinsic structural inhomogeneity, and further demonstrated by the magnetic hysteresis under field-cooling conditions. It is shown that the short-range magnetic clusters play as scattering centers for conductive electrons and result in a Kondo-like transport behavior in highly spin disordered Sm50Al25Co25 at low temperature. ©2009 American Institute of Physics |
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