Neutron irradiation-induced microstructure damage in ultra-high temperature ceramic TiC

Titanium carbide (TiC) is an ultra-high temperature ceramic with potential as a structural material candidate for advanced reactor concepts. However, the irradiation tolerance of TiC is not well understood. Here, we reveal the key irradiation damage microstructure degradation processes in TiC using mixed spectrum neutron irradiations at dose of similar to 2 displacements per atom (dpa) at temperatures of similar to 220, 620, and 1115 degrees C, combined with state-of-art microstructure characterization using transmission electron microscopy (TEM) and high-resolution TEM (HRTEM). The helium injection (similar to 65 atomic parts per million) produced by neutron transmutation also occurred in the sample. TiC was observed to form irradiation induced interstitial-type dislocation loops and He-stabilized cavities. At 220 and 620 degrees C, the analysis of the electron diffraction patterns, rel-rod imaging and HRTEM revealed that the dislocation loops were faulted Frank loops with Burgers vector b(Frank) = 1/3 < 111 > lying on {111} planes. A detailed Burgers vector identification performed by the g.b technique revealed that the dislocation loops forming at 1115 degrees C were unfaulted, edge-type, with Burgers vectors b= a < 100 > and a/2 < 110 > with corresponding {100} and (110) habit planes. Using continuum mechanics, we estimated the critical radius at which a faulted dislocation loop transitions to a perfect loop to be 9nm. Further, no amorphization occurred in TiC under-investigated irradiation conditions while macroscopic swelling under point defect swelling regime was observed. He-stabilized cavities were detected at 1115 degrees C, but not at lower temperature irradiation. These observations indicate the onset of long-range vacancy migration in TiC occurs between 620 and 1115 degrees C. (C) 2019 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.