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A Study on the Crystallization of Zr-based Bulk Amorphous Under the Effect of Laser Point Heat Source and Its Establishment of Crystallization Curve

Author: HuangZuo
Tutor: HuangAnGuo
School: Huazhong University of Science and Technology
Course: Materials Processing Engineering
Keywords: amorphous laser spot heat source numerical fitting crystallization curve
CLC: TG139.8
Type: Master's thesis
Year: 2011
Downloads: 24
Quote: 1
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Abstract


Amorphous alloy has excellent mechanical, physical, chemical and electromagnetical properties, and now they are used in aerospace, sports goods, communication products （Cell Phone）, energy and electrical equipment. But due to restriction of its amorphous forming ability, now the largest size of pole-shaped bulk amorphous reaches only 72mm, which limits the use of bulk amorphous alloy in project fields. So it is a better way to adopt appropriate welding method to obtain larger-sized amorphous alloy. Bulk amorphous alloy is thermodynamically in metastable state, thus tends to transform into more stable crystalline at a comparatively low heating rate. Obviously traditional welding method can not provide high enough rate of heating and cooling, so it is necessary to apply rapid heating and cooling methods such as laser and electron beam. Even if we adopt laser welding method, melted zone of welded joint tends to keep amorphous, while heat affected zone is likely to become crystallization. So how to avoid crystallization of heat affected zone becomes a hot research topic.To ensure no crystallization of heat affected zone, i.e. thermal cycle curves of all regions of heat affected zones will not intersect with crystallization curve of bulk amorphous alloy, it is quite necessary to obtain crystallization curve of bulk amorphous alloy. The research of thermal characteristics of amorphous materials mainly analyzes with DSC method. But the highest heating rate of DSC is only 500K/min, while the necessary critical heating rate for most amorphous alloys to keep amorphous when heated is above 500K/min, so it is not enough to establish crystallization curve with only DSC method. This subject plans to establish crystallization curve at low heating rate by DSC method, applies numerical simulation method to establish crystallization curve at high heating rate, conducts fitting of crystallization curves at low and high heating rate via origin 8.0, thus establishes complete crystallization curve of Zr53.7Ni9.4Cu28.5Al8.4 bulk amorphous alloy.To use ANSYS to obtain thermal cycle curve of crystallization critical point of Zr53.7Ni9.4Cu28.5Al8.4 bulk amorphous alloy at high heating rate when there is no laser static heat source, static heat source experiments are conducted on Zr53.7Ni9.4Cu28.5Al8.4 bulk amorphous alloy on the condition of different pulse laser action time, and crystallized amorphous samples are obtained at different technological parameters. Analysis indicates that under the effect of laser static heat source, the phase composition of crystallization region is mainly ZrXCuY, and evolution model of bulk amorphous solder joint at different action time of pulse laser static point heat source are worked out and raised.To further study the crystallization of Zr53.7Ni9.4Cu28.5Al8.4 bulk amorphous alloy in YAG pulse laser spot welding, YAG pulse laser is applied to conduct one spot welding every 0.4mm on Zr53.7Ni9.4Cu28.5Al8.4 bulk amorphous, and organization structure and composition change of different crystallization regions of Zr53.7Ni9.4Cu28.5Al8.4 bulk amorphous alloy are studied via light microscope, SEM and energy spectrum analysis. The result indicates crystallization region mainly consists of remelting area, twice heat affected zone and once heat affected zone, and forms remelting crystallization area, twice heat affected zone- crystallization zone and crystallization belt of once heat affected zone. Crystallization phase of crystallization belt of once heat affected zone is FCC ZrNi2, tetragonal Zr2Cu and hexagonal Zr2Al; Crystallization phase of remelting crystallization area is FCC Zr2Ni; Crystallization phase of twice heat affected zone is hexagonal Zr2Al and Zr4Al3. Crystallization of remelting area attributes to amorphous forming ability of base metal, and chemical composition affects its crystallization greatly. Crystallization of twice heat affected zone and once heat affected zone attributes to thermal stability of heat affected zone, and structure relaxation affects greatly.

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CLC: > Industrial Technology > Metallurgy and Metal Craft > Metallurgy and Heat Treatment > The alloy learn with a variety of properties of alloys > Other special nature of the alloy > Amorphous alloy
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