臺灣大學: 材料科學與工程學研究所薛承輝姚?文Yiu, Pak-ManPak-ManYiu2013-03-222018-06-282013-03-222018-06-282012http://ntur.lib.ntu.edu.tw//handle/246246/251624金屬玻璃可藉由熔融狀態合金經過急速冷卻而獲得。由於非晶結構特徵，賦與金屬玻璃優於結晶合金的高強度、抗腐蝕等特性，近年來一直是諸多學者的研究主題。然而金屬玻璃的塑性較低，使高強度結構工程上的應用一直受到限制，故有關金屬玻璃的塑性變形機制及改善方法的研究至今仍屬重要。金屬玻璃以剪切帶(Shear band)之特殊機制進行塑性變形，集中而不均勻地生成的的剪切帶成為金屬玻璃的弱點，並導致其脆性破壞。 本研究選用具有良好玻璃成形性與延展性的鋯－銅－鋁系統金屬玻璃，系統性地研究施加電脈衝對金屬玻璃塑性之影響。結果顯示所得電脈衝只在特定的情況下可改善金屬玻璃之塑性：電阻加熱一般為負面影響，必須非常低，否則電脈衝產生的熱量將加速應力釋放與脆化。在不同的電脈衝頻率之下，受試金屬玻璃展現不同的機械性能；實驗中更發現調整此頻率可以準確地控制焦耳加熱之溫度，並藉此決定應力釋放之多寡。利用此現象電脈衝將可應用於金屬玻璃熱塑性加工(Thermal plastic forming)，與常規加熱相比，電脈衝技術更為快速準確。The properties of bulk metallic glasses (BMGs), which are fabricated from rapid quenching of molten metal alloy, have been researched for decades. Being structurally amorphous, BMGs process high strength and high corrosion resistance over crystalline alloys. However due to its poor plasticity, BMGs’ engineering application is limited especially for structural purpose. Researchers have been seeking for the mechanism of plastic deformation in BMGs and thus ways to improve. BMGs undertake plastic deformation in a characteristic way: initiating shear bands. It has been commonly agreed that formation of shear bands of metallic glasses is a result of shearing motion between shear transformation zones (STZs), which could be described as core-shell structure of atoms. Despite the intrinsic plasticity is given by STZs, localized and inhomogeneous shear banding always causes weakness and brittle failure in BMGs. On the other hand, due to good glass forming ability and fairly good ductility, Zr-Cu-Al has been extensively studied among existing metallic glass systems. Various ways such as controlling solidification condition and composite were used to improve the plasticity of Zr-based metallic glass. Among many of them, recent research discovers that electrical pulses are effective in improving the intrinsic plasticity of metallic glasses. In this thesis, the effect of applying electropulsing on the plasticity of metallic glasses was investigated systematically. It is concluded that electropulsing does not always improve plasticity of metallic glasses but only when thermal effect brought by Joule heating is small, else it only serve as an accelerated relaxation and embrittlement process. By using different pulsing frequencies, treated metallic glasses showed varying mechanical property. Therefore, the treatment temperature and amount of relaxation can be precisely controlled in this way. Making use of EPT will be a much rapid and accurate technique compared to conventional heating. These phenomena could potentially developed into a new, rapid thermoplastic forming technique.2763862 bytesapplication/pdfen-US奈米壓痕金屬玻璃熱塑性成形電脈衝加工nanoindentationmetalic glasstermoplastic formingelectropulsingthesishttp://ntur.lib.ntu.edu.tw/bitstream/246246/251624/1/ntu-101-R99527067-1.pdf