DIRECT OBSERVATION OF SOLUTE SEGREGATION TO VOIDS IN A FAST-NEUTRON IRRADIATED MO-1.0 AT PERCENT TI-ALLOY

The atom-probe field-ion microscope (FIM) has been employed to study segregation effects, to voids, in a Mo/1.0 at% Ti alloy specimen; this specimen had been irradiated with fast neutrons at ~700° C, to a fluence of ~1 × 1022n/cm2 (E > 1 MeV), in the row 7 midplane position of EBR-II. It had been shown previously, by several other research groups, that this alloy exhibits an enhanced swelling relative to pure Mo under fast-neutron irradiation. The results of the present work, on this alloy, indicated that: (1) titanium does not segregate significantly to voids; (2) the concentration of titanium in solid solution and the spatial distribution of titanium was not affected significantly by the irradiation at 700°C; (3) carbon was not detected in solid solution in either the irradiated or unirradiated specimens; (4) the preceding two results indicated that largescale resolution of TiC or Mo2C precipitates had not occurred as a result of the irradiation; and (5) segregation of carbon to a void was detected. The small amount of carbon segregation which had been detected may have been sufficient to enhance the nucleation rate and/or change the sink properties of a void and thus affect the void growth-rate. © 1979.