Low temperature deformation characteristics of yttrium single crystals Public Deposited

http://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/rr1721589

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  • First order prism slip in yttrium single crystals containing a total interstitial impurity content of about 200 wt ppm is almost entirely stage II deformation with a work hardening rate θ/μ of 2·10⁻ ³ . The athermal temperature is about 300°K. Below this temperature an interstitial mechanism is rate controlling for dislocations moving on the first order prism planes. The obstacle energy is 0.31 eV and is substantially independent of temperature. The oxygen impurity does not influence the thermal component of the flow stress, although the athermal component increases with oxygen content. Above 300°K an intersection mechanism controls dislocation movement. Second order pyramidal slip is also almost entirely stage II deformation, but the work hardening rate is 10·10 ⁻³ . The critical resolved shear stress for second order pyramidal slip is about two times higher than for first order prism slip. The athermal temperature is approximately 300°K. Fleischer's criteria supporting an interstitial mechanism as rate controlling for dislocations moving on the second order pyramidal planes are satisfied in the entire temperature range that was investigated, i.e. 77°K to 297°K. The obstacle energy is 0.54 eV at the athermal temperature. However, the Dorn-Rajnak model supporting a Peierls mechanism is satisfied below 165°K, thus this mechanism could be rate controlling below 165°K. Second order pyramidal slip is active when the tensile axis is less than 37 degrees from the C-axis at 300°K. First order prism slip is active at all other orientations. Basal slip could not be activated at any orientation.
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