LUẬN VĂN A THESIS SUBMITTED TO THE GRADUATE SCHOOL OF NATURAL AND APPLIED SCIENCES OF MIDDLE EAST TECHNICAL UNIVERSITY

SOLIDIFICATION AND CRYSTALLIZATION BEHAVIOUR OF BULK GLASS FORMING ALLOYS A THESIS SUBMITTED TO THE GRADUATE SCHOOL OF NATURAL AND APPLIED SCIENCES OF MIDDLE EAST TECHNICAL UNIVERSITY BY SULTAN AYBAR IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE IN METALLURGICAL AND MATERIALS ENGINEERING SEPTEMBER 2007 Approval of the thesis: SOLIDIFICATION AND CRYSTALLIZATION BEHAVIOUR OF BULK GLASS FORMING ALLOYS submitted by Sultan AYBAR in partial fulfillment of the requirements for the degree of Master of Science in Metallurgical and Materials Engineering Department, Middle East Technical University by, Prof. Dr. Canan Özgen Dean, Graduate School of Natural and Applied Sciences Prof. Dr. Tayfur Öztürk Head of Department, Metallurgical and Materials Engineering Prof. Dr. M. Vedat Akdeniz Supervisor, Metallurgical and Materials Eng. Dept., METU Prof. Dr. Amdulla O. Mekhrabov Co-supervisor, Metallurgical and Materials Eng. Dept., METU Examining Committee Members: Prof. Dr. Tayfur Öztürk Metallurgical and Materials Eng. Dept., METU Prof. Dr. M. Vedat Akdeniz Metallurgical and Materials Eng. Dept., METU Prof. Dr. Amdulla O. Mekhrabov Metallurgical and Materials Eng. Dept., METU Prof. Dr. İshak Karakaya Metallurgical and Materials Eng. Dept., METU Asst. Prof.Dr. Kâzım TUR Materials Eng. Dept., Atılım University Date: PLAGIARISM I hereby declare that all information in this document has been obtained and presented in accordance with academic rules and ethical conduct. I also declare that, as required by these rules and conduct, I have fully cited and referenced all material and results that are not original to this work. Name, Last name: Sultan Aybar Signature : iii ABSTRACT SOLIDIFICATION AND CRYSTALLIZATION BEHAVIOUR OF BULK GLASS FORMING ALLOYS Aybar, Sultan M.S., Department of Metallurgical and Materials Engineering Supervisor: Prof. Dr. M. Vedat Akdeniz Co-Supervisor: Prof. Dr. Amdulla O. Mekhrabov September 2007, 121 pages The aim of the study was to investigate the crystallization kinetics and solidification behaviour of Fe60Co8Mo5Zr10W2B15 bulk glass forming alloy. The solidification behaviour in near-equilibrium and non-equilibrium cooling conditions was studied. The eutectic and peritectic reactions were found to exist in the solidification sequence of the alloy. The bulk metallic glass formation was achieved by using two methods: quenching from the liquid state and quenching from the semi-state. Scanning electron microscopy, x-ray diffraction and thermal analysis techniques were utilized in the characterization of the samples produced throughout the study. The choice of the starting material and the alloy preparation method was found to be effective in the amorphous phase formation. The critical cooling rate was calculated as 5.35 K/s by using the so-called Barandiaran and Colmenero method which was found to be comparable to the best glass former known to date. iv The isothermal crystallization kinetics of the alloy was studied at temperatures chosen in the supercooled liquid region and above the first crystallization temperature. The activation energies for glass transition and crystallization events were determined by using different analytical methods such as Kissinger and Ozawa methods. The magnetic properties of the alloy in the annealed, amorphous and as-cast states were characterized by using a vibrating sample magnetometer. The alloy was found to have soft magnetic properties in all states, however the annealed specimen was found to have less magnetic energy loss as compared to the others. Keywords: Bulk Glass Forming Alloy, Thermal Analysis, Supercooled Liquid Region, Activation Energy, Critical Cooling Rate. v ... - tailieumienphi.vn