Abstract
Ultra-high temperature transition-metal ceramics are potential candidates for fusion reactor structural and plasma-facing components. We reveal the irradiation damage microstructural phenomena in Boron-11 enriched titanium diboride (TiB2) using mixed-spectrum neutron irradiations, combined with state-of-art characterization using transmission electron microscopy (TEM) and high resolution TEM. Irradiations were performed using High Flux Isotope Reactor at ~220 and 620 °C up to 2.4x1025 n.m-2 (E>0.1 MeV). The calculated dose including contribution from residual Boron-10 (10B) transmutation recoils, was ~4.2 displacements per atom. TiB2 is susceptible to irradiation damage in terms of dislocation loop formation, cavities and anisotropic swelling induced micro-cracking. At both 220 and 620 °C, TEM revealed dislocation loops on basal and prism planes, with nearly two orders of magnitude higher number density of prism-plane loops. HRTEM, electron diffraction and relrod imaging revealed additional defects on {101 ̅0} planes, identified as faulted prism-plane dislocation loops. High defect cluster density on prism planes will induce a-lattice parameter swelling of TiB2, as reported in literature. This anisotropic lattice parameter swelling induced grain boundary micro-cracking, the extent of which decreased with increasing irradiation temperature. The dominance of irradiation defect clusters on prism planes is different than typical hexagonal ceramics where dislocation loops predominantly form on basal planes, causing c-lattice parameter swelling. Helium generation and temperature rise from the transmutation of residual 10B resulted in matrix and grain boundary cavities for the irradiation at 620 °C. The study additionally signifies isotopic enrichment as a viable approach to produce transition-metal diborides for potential nuclear structural applications.
