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1 Journal of Alloys and Compounds - Article in Press, Accepted Manuscript Effect of heat treatment on the microstructure and mechanical properties of Fe-based amorphous coatings Bin-you Fua, b, Ding-yong Hea and Li-dong Zhaob aCollege of Materials Science and Engineering, Beijing University of Technology, Beijing 100124,China bSurface Engineering Institute, RWTH Aachen University, Juelicher Str. 334a, Germany Received 26 June 2008; revised 22 February 2009; accepted 24 February 2009. Available online 9 March 2009. Abstract Amorphous coatings were fabricated by arc spraying and the effect of the post heat treatment on the microstructure and the mechanical properties of arc sprayed coatings were studied. Post heat treatment was conducted in the atmospheric environment within the temperature ranged from 500 °C to 800 °C. The microstructure characteristics were analyzed by means of optical microscopy (OM), X-ray diffraction (XRD), electron probe micro-analyzer (EPMA), scanning electron microscopy (SEM), differential thermal analysis (DTA) and transmission electron microscopy (TEM). It was found that with the increase of anneal temperature, the microstructure of the sprayed coatings had several changes as follows: the reduction of porosity, the decomposition and the crystallization of amorphous phase, the formation of precipitates. The microhardness of the sprayed coatings increased after the heat treatment and it can reached to 1275 HV300g at the post treated at 600 °C. All the coatings exhibited an excellent abrasive wear resistance, approximately 6 times higher than that of the arc-sprayed 3Cr13 coating. Keywords: Amorphous; Heat treatment; Microstructure; Mechanical properties 2 Materials Letters - Article in Press, Accepted Manuscript Extrusion properties of a Zr-based bulk metallic glass G.S. Yua, J.G. Lina and W. Lia aFaculty of Material and Photoelectronic Physics, Key Laboratory of Low Dimensional Materials & Application Technology (Ministry of Education), Xiangtan University, Hunan, Xiangtan 411105, China Received 5 February 2009; accepted 25 February 2009. Available online 9 March 2009. Abstract The extrusion behavior of Zr41.2Ti13.8Cu12.5Ni10Be22.5 metallic glasses in the supercooled liquid region was investigated. Good extrusion formability was observed under low strain rates at the temperatures higher than 395 °C. The metallic glasses were fully extruded without crystallization and failure within the range of T = 395-415 °C under strain rates from 5×10- 3s- 1 to 5×10- 2s- 1, and the deformation behavior of the metallic glasses during the extrusion was found to be in a Newtonian viscous flow mode by a strain rate sensitivity of 1.0. Keywords: bulk metallic glass; extrusion; Newtonian viscous flow 3 Materials Science and Engineering: A - Article in Press, Accepted Manuscript (1) Internal friction of metallic glass measured as function of strain amplitude at various temperatures Y. Hikia, R. Tamurab and S. Takeuchib aFaculty of Science, Tokyo Institute of Technology, Emeritus, 39-3-303 Motoyoyogi, Shibuya-ku, Tokyo 151-0062, Japan bDepartment of Materials Science and Technology, Tokyo University of Science, Noda, Chiba 278-8510, Japan Received 18 May 2008; accepted 2 September 2008. Available online 9 March 2009. Abstract The internal friction Q-1of a Zr-Ti-Cu-Ni-Be metallic glass was measured using the Dynamical Mechanical Analyzer. The dependence of Q-1 on the strain amplitude of vibration A was investigated in the range of A = 10-5 10-4 at the frequency of f = 1 Hz of the bending mode vibration at various temperatures in the range of T = 300 800 K. Q-1 was almost amplitude independent, and was much enhanced near the glass transition temperature Tg ( 620 K). Fluctuations were seen in Q-1-vs-A, which were very severe near Tg. The enhancement and the severe fluctuations of Q-1 near Tg were diminished after the glass was heated above the crystallization temperature Tx ( 713 K). These results were discussed on the basis of static-hysteresis type mechanical loss due to vibration of movable elements near quasi-equilibrium states in glasses. Keywords: Internal friction; Amplitude dependence; Metallic glass; Glass transition (2) Structural inhomogeneity of metallic glass observed by ultrasonic and inelastic x-ray scattering measurements T. Ichitsuboa and E. Matsubaraa aDepartment of Materials Science and Engineering, Kyoto University, Kyoto 606-8501, Japan Received 16 June 2008; accepted 24 September 2008. Available online 9 March 2009. Abstract The structural stability of metallic glasses is frequently deteriorated under ultrasonic perturbation at relatively low temperatures, e.g., near the glass transition temperature Tg, even forthermally stable Pd- and Zr-based metallic glasses. By a mechanical spectroscopy analysis, it is suggested that such an instability, i.e., crystallization, is caused by atomic motions associated with the (slow) β relaxation, that are resonant with the ultrasonic-strain field. Furthermore, such atomic motions below Tg are considered to occur at weakly-bonded regions in a nanoscale inhomogeneous microstructure of glass, which was intuitively inferred from a partially crystallized microstructure obtained by annealing a Pd-based metallic glass just below Tg under ultrasonic perturbation. On this basis, we proposed a structural model of metallic glasses that consists of strongly-bonded regions surrounded by weakly-bonded regions. To reveal the validity of the model, we have also employed the inelastic x-ray scattering technique to measure the sound velocity of nanometer wavelength of longitudinal acoustic phonons. We have found in a completely frozen Pd-based metallic glass that the velocity of nanometer wavelength exceeds ultrasound velocity of millimeter wavelength, which suggests that elastically harder nanoscale regions exist in the glass matrix. Keywords: Bulk metallic glasses; Ultrasonic; Inelastic x-ray scattering; Structural inhomogeneity; Elastic-constant fluctuation; Phonon; positive dispersion [ Last edited by hslining on 2009-9-10 at 16:36 ] |
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