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Assessment of alloy 709 accelerated creep properties for use in sodium cooled fast reactors
Carter, Alan
Carter, Alan
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2020
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Abstract
The high temperature mechanical properties and microstructural development of Alloy 709 were investigated from temperatures ranging from 550 to 650 °C. Constant load creep, stress dip, and stress relaxation tests were carried out to determine the minimum creep rate exponent and activation volume, as well as the activation energy of creep and stress relaxation. Constant load creep tests were interrupted close to the point of minimum creep rate. These interrupted specimens were used to investigate microstructural development during creep conditions using scanning and transmission electron microscopy. The properties measured during mechanical testing and microstructural development observed during microscopy investigation were studied in an effort to identify controlling deformation mechanism. Two physical models are applied to Alloy 709 in an effort to determine the feasibility of the identified controlling deformation mechanism during creep. The mechanical properties and microstructural development of two aged conditions were investigated in an effort to identify the role of precipitate size, spacing, and type on the creep processes taking place in Alloy 709. The minimum creep rate exponent and activation volume, as well as the activation energy of creep and stress relaxation were determined for the differing age conditions. Constant load creep tests of aged specimens were interrupted close to the moment of minimum creep rate. Microstructural development due to aging as well as due to creep conditions, from interrupted specimens, were investigated with scanning and transmission electron microscopy. The variation between the measured high temperature properties of Alloy 709 were related to the physical differences observed during microscopy.
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