| Because of the ir uniq ue plastic deformation ability and excellent glass-formingability, Zr-Cu based amorphous alloys have widespread applicatio n prospect in thefie ld of engineering materia ls. In this paper, Zr54Cu38Al8amorphous alloy was chosento be the research object. It was processed by annea ling technology and ceramic rolling.The effects of annealing and ceramic rolling on mechanica l properties, therma lstability, microstructure and crystallization behavior of Zr54Cu38Al8amorphous alloywere studied respective ly.The supercooled liquid region ΔTxand glass transition temperature TgofZr54Cu38Al8amorphous a lloy, which was prepared by copper mo ld suction castingtechno logy, are61K and706K, respective ly. The activation energy of glass trans itionand crystallizatio n are Eg=380kJ/mo l, Ex=269kJ/mol, respective ly. It indicates thatthe amorphous alloy has high therma l stability. The samp le can keep its amorphousstructure after12h annealed at423K. Under low temperature condition, the hardness ofthe specime n remains stable after a slight increase with the extensio n of heatpreservation time. The hardness increases linearly after high-temperature annealing. Inparticular, when the samp le annealed0.5h at793K, its hardness was improved to677(Hv). After annealed at temperatures below Tg, the structure of the samp les remainamorphous, while the ir strength and ductility are significantly improved compared tothe as-cast samp le. Especia lly, the fracture strain of the samp le annea led6h at423Kincreases to37%. The strength of the samp le annealed12h at423K increases to1821MPa, which improves by20.6%compared to as-cast sa mple.With the increase of heat preservation time and annealing temperature, the glasstransition temperature and crystallization temperature of the samp les shift to lowertemperature, thus reduc ing the therma l stability of the amorphous samp le. Afterannealed at temperatures higher than Tg, Zr54Cu38Al8amorphous allo y starts toprecipitate crystalline phase. Primary phase are ma inly CuZr2, Cu10Zr7and CuZr. Withthe increase of annealing te mperature, Cu10Zr7decreased, while CuZr2graduallyincreased, and then precip itate Al2Zr and AlCu2Zr. The amorphous sample is fullycrystallized after annealed0.5h at793K.As-cast Zr54Cu38Al8amorphous alloy exhibits a large plastic deformatio n withoutfracture through ceramic rolling at room temperature and high strain rate (0.5~1s-1).The ma ximum reduction is45%. Work-hardening behavior occurs in the rolling process. Compressive strength and ductility of the samp les are significantly improvedafter ceramic rolling. Especially, when the alloy ro lled to a diameter reductio n of15%,the compressive strength was improved from1510MPa of as-cast samp le to1737MPa.When the reduction was10%, the fracture strain was improved from7.9%of as-castsamp le to24.8%. On the other hand, shear bands morphology in cross section ofas-rolled samp les changes from s imp le and uniform to comp licated and confusing withthe increase of deformation.The thermal stability of Zr54Cu38Al8amorphous alloy was reduced after ceramicrolling. The glass transition temperature Tgand crystallization temperature Txofas-rolled samp les shift to lower temperature. Crystallization entha lpy of as-rolledsamp les decreased with the increase of deformation. On the other hand, the relaxationenthalp y of amorphous specimen increases first and then decreases with increasingdeformation. The changes in mechanica l properties, crystallization behavior andstructural re laxatio n of as-rolled samp les are closely related to the changes of the irown free-volume content. |
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