| Summary: | 碩士 === 義守大學 === 材料科學與工程學系 === 104 === Bulk metallic glasses (BMGs) have attracted attention due to their high strength and outstanding thermal properties. However, the low workability at room temperature of BMGs limited their applications. Therefore, reseachers developed different methods to solve the problem of poor room temperature ductility. For example, the methods of the adding of minor element, themal treatments, rolling and friction are used to improve the mechanical properties of BMGs by the formation of phase transformation and microstructure variation. According to the literature results showed that the method of rolling process is a possible way to increase the room temperature plasticity.
Zr65Cu17.5Ni10Al7.5 bulk metallic glass is the base alloy in this study, which has high GFA (Trg = 0.594) and the fracture stress is about 1200 MPa. The results show that the brittle Zr65Cu17.5Ni10Al7.5 BMGs was plastically deformation at room temperature by the introducing of rolling process before compression test. The compressive fracture strength and strain increased form 1156 MPa and 5.8% (the base alloy) to 1914 MPa and 32.81% (cold-rolled specimen with average true strain 10.03%). The great enhancement of plastic strain can be attributed to the formation of pre-introduced shear bands (called pre-shear band and secondary shear bands) after the pre-rolling process. Dense dispersion of pre-introduced shear bands impeded the propagation of primary shear bands during the compression test and the improved of plasticity of alloys with increasing rolling average true strain (up to average true strain 10.03%).
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