Study On Continuous Casting Technology And High Magnetic Field Treatment Of Glassy Alloys

Glassy alloy has short range order atomic structure, which is different from crystalline alloy. Metallic glasses have lots of special properties, such as high strength, high hardness, high corrosion resistance, good magnetic properties, superplastic forming, micromolding and so on. The research on preparation and modification of metallic glasses are very important for the widely development and applications. Continuous manufacturing techniques of glassy alloys, which have high efficiency and low cost, are strongly demanded for industrial application.A Part of the dissertation is about spark plasma sintering of bulk metallic glasses and modification of amorphous alloys by high magnetic field. The key part of the dissertation are about continuous casting of bulk metallic glass, which contain the theoretical analysis of continuous casting technology for metallic glasses, the design, establishment and debugging by high pure aluminum of vacuum multi-mold continuous casting system, and developing of the metallic glasses continuous casting technology. The microstucture and thermal, magnetic and mechanical properties are investigated by MEF-4A Metallographic Microscope, XRD-6000 diffractometer, DSC822/TGA/SDTA851 thermal analyzer, JDM-13 vibrating sample magnetometer, EPMA-1600 Electron Probe microanalyser, TG220S-Twin JEM-100CxⅡTransmission Electron Microscope, SHIMADZU EHF and MTS NEW-810 Materias Test System. The results of the study are showed bellow:High pure graphite is adopted to make the crucible for continuous casting of bulk metallic glass. The glassy alloy can be melt by electric resistance heating for its relatively low melting temperature and the mould design can be easy for the low solidification shrinkage of glassy alloy.The multi-mold two chamber vacuum pressure continuous casting machine is established. The vacuum chamber is divided into two parts by a panel for the pressure control. The multi-mold is composed of heated graphite mold and water cooling copper mold, which is fixed on that panel. Two different kinds of multi-mold are designed, which could endure high temperature, provide lubrication and large cooling speed.High pure aluminum is used to debug the vacuum multi-mold continuous casting system and aluminum rods are also produced. Contamination from impurities and Hydrogen can be effectively controlled by the vacuum pressure multi-mold continuous casting system. The effect of drawing speed on microstructure and properties of high pure aluminum rods are also discussed.A Zr48Cu36Ag8Al8 glassy alloy rod with a diameter of 10mm and length of 400mm is produced by the two multi-mold continuous casting method. The suitable parameters for multi-mold continuous casting are 950～1000℃,40L/min,0.02～0.05Mpa,2mm/s,5s and 2s for casting temperature, cooling water, Ar pressure, drawing speed, withdraw period and pausing period, respectively. Annular trace is found on the surface of the glassy alloy rods with intermittent drawing speed mode and the distance between two nearest traces changes with the drawing speeds. The glassy alloy rod produced by the multi-mold continuous casting method nearly has the same mechanical properties as the sample fabricated by copper mold casting technology.Fe67Co9.5Nd3Dy0.5B20 bulk metallic glasses produced by spark plasma sintering technique are isotropicaly soft magnetic property. The precipitation of Nd1.1Fe4B4 phase enhanced the coercivity of sintered samples. The good hard magnetic properties for the exchange-coupling effect are obtained when the sample are anneald at 650℃for 15min. The magnetic properties of Fe67Co9.5Nd3Dy0.5B20 glassy alloys are deterioration when the samples are heated in high magnetic field. The crystalline grain size of the Fe56.25Pt18.75B25 amorphous alloy are largely reduced when the sample annealed at temperature above 783K in high magnetic field.