| Summary: | 碩士 === 國立成功大學 === 機械工程學系專班 === 100 === This study uses a split-Hopkinson bar to investigate the plastic deformation behavior of Haynes 188 super alloy at the strain rates of 1000 s-1, 3000 s-1 and 5000 s-1 and the temperatures of 25℃, 400℃and 800℃, respectively. Based on the experimental results and microscopic observations, the correlations between mechanical properties and microstructure are established. The experimental results indicate that the effects of temperature and strain rate on mechanical properties of Haynes 188 super alloy are significant. At constant temperature, the flow stress, work hardening rate and strain rate sensitivity increase with increasing strain rate, but the activation volume decreases. For a constant strain rate, the flow stress, work hardening rate and strain rate sensitivity decrease with increasing temperature, but the activation volume increases. Besides, the Zerilli-Armstrong constitutive equation can be used to describe the plastic deformation of Haynes 188 super alloy precisely. Scanning electron microscopy (SEM) fractographic observations show that the fracture features are characterized by ductile shear fracture and that knobbly structure form with respect to the direction of maximum shear stress. Transmission electron microscopy (TEM) observations show that the dislocation density increases with increasing strain rate, but decreases with increasing temperature. The relationship between the dislocation density and flow stress can be described by the Bailey-Hirsch type relation. The strengthening effect can be attributed by the napid multiplication of dislocations.
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