Unexpected {[formula omitted]} pyramidal stacking faults in Zr(Fe, Cr)2 secondary phase particle induced by the C15→C14 Laves phase transformation in Zircaloy-4

Abstract

The formation mechanism of (011¯1)C14 pyramidal stacking faults (SFs) with a 8.6° deflection to the SFs on (111¯)C15 planes of Zr(Fe, Cr)2 secondary phase particle (SPP) in Zircaloy-4 under cyclic deformation were investigated by using transmission electron microscopy. Results showed that local C14 domain structures can be induced into the C15 SPP when the SFs formed on (111¯)C15 close-packed planes by the emission of 16[112]C15 Shockley partial dislocations under cyclic stress effects. Moreover, when the shear stresses along [112¯]C15 direction were large enough to initiate the 16[112¯]C15 partials on every other (111)C15 planes, the C15→C14 Laves phase transformation would be accomplished, resulting in a significant reconstruction of atomic configurations of the SFs on original (111¯)C15 planes. Thus, the formation of (011¯1)C14 pyramidal SFs during C15→C14 phase transformation in SPP were presented.