The measurement of other properties of irradiated ZrC is limited and often contradictory. Some evi­dence for an increase in mechanical strength with irradiation is available. Andrievskii eta/.164 irradiated sintered ZrC098 at 423 and 1373 Kwith a fast neutron fluence of 1.5 x 1020 cm—2, and found more substantial strengthening at low-temperature irradiation than at high temperature (bend strength increased by 28% vs. 4%, microhardness by 12% vs. 7.3%, and Young’s modulus by 1.2% vs. no increase). Yang eta/.175 irra­diated hot-pressed commercial ZrC0.99 at 1073 K with 2.6 MeV protons to a fluence of 1 x 1019 or

2.3x 1019cm—2 (0.7 or 1.5 dpa), and found Vickers hardness increased after irradiation, with a slightly more pronounced increase at higher fluence (12% increase at 0.7 dpa vs. 14% increase at 1.5 dpa). Inden­tation toughness also increased 79% after 1.5 dpa, but scatter was large. Absent from the literature are stud­ies of irradiation-induced creep of ZrC.

Electrical and thermal conductivity, sensitive to defect concentration, have also been studied. In general, electrical resistivity was found to increase with irradia­tion and thermal conductivity to degrade. Koval’chenko and Rogovoi165 irradiated ZrC098 at 323 Kwith a ther­mal neutron fluence of 1 x 1019—1.5 x 1020cm—2, and resistivity increased by 17-167%, increasing with flu­ence, versus an unirradiated 60 pQ cm. The authors attribute the increase to point defect formation, but low initial lattice parameter suggests high O and N impurity content in any case. Following the same irradiation by Andrievskii eta/.164 described in the pre­ceding paragraph, resistivity was found to increase, with the effect less pronounced for higher irradiation tem­peratures: a 481% increase was measured at 423 K, and a 51% increase at 1373 K, versus an unirradiated 43 pQ cm. In unirradiated ZrC*, resistivity increases as the C/Zr ratio decreases, and Andrievskii eta/.166 found that the increase in resistivity following irradiation at 413 K in a fast neutron fluence of 1 x 1019cm—2 was more pronounced for compositions closer to stoichiom­etry. A 6% increase in resistivity was measured for ZrC07 versus a 213% increase for ZrC0 94.

Thermal conductivity was studied by David eta/.178 following irradiation at 298 K with 28.5 MeV Kr ions to a fluence of 1 x 1016 or 6 x 1016cm—2. The authors distinguished between thermal conductivity degrada­tion due to inelastic and elastic collisions, with inelastic damage in ZrC calculated to occur in the first 3.3 pm into the surface and elastic damage initiating at a depth where dpa increases to 20% of the maximum damage, continuing for 1.4 pm below the inelastic damage. A modulated thermoreflectance microscopy technique was employed to characterize subsurface thermal con­ductivity degradation. Elastic collisions were deemed considerably more damaging than inelastic, reducing thermal conductivity from 20 W m—1 K—1 before irra­diation to less than 1 W m—1 K—1. In the inelastic dam­age region, thermal conductivity of 10 W m—1 K—1 was measured after 1 x 1016 cm—2 fluence and 5 W m—1 K—1 after 6 x 1016cm—2 fluence.