Microstructure and tensile behavior of powder metallurgy FeCrAl accident tolerant fuel cladding

Defect-free seamless FeCrAl cladding tubes with 0.3 mm wall thickness have been successfully developed via full-scale powder metallurgy (PM) manufacturing routes, providing a cost neutral replacement of Zircaloy-2 tubes with enhanced accident tolerant fuel. Microstructure and tensile properties at room temperature and 315 °C were evaluated in the tubing of two yttrium-free FeCrAl alloy compositions PM-C26M and Ferritic Alloy – Sandvik Material Technology (FA-SMT) that differ in Cr, Al, Mo and minor addition of refractory elements. The powder metallurgy FeCrAl tubes reveal finer grain size than the smallest achievable grain size by cast/wrought tube fabrication process, low retained strain, and tensile properties superior to Zircaloy-2 cladding tubes. <101> fiber texture along the tube axial direction was observed. In-situ neutron diffraction during tensile loading shows qualitatively similar trend of intergranular load transfer during elastoplastic deformation in PM-C26M and FA-SMT, while FA-SMT indicates higher dislocation density and PM-C26M reveals more intensive <101> texture evolution along loading direction. Precipitates in FA-SMT are inferred to share load from the matrix, while such load sharing is not evident in PM-C26M. Compared to texture free ferritic steel data in the literature, the <101> fiber texture in the FeCrAl tubes seems to have little effect on the grain-level tensile deformation behavior including elastic anisotropy and plastic anisotropy.