HETEROGENEOUS PRECIPITATION AT INTERNAL AND EXTERNAL SURFACES DURING IRRADIATION OF NI-12.7 AT PERCENT-SI

Morphological developments during 400-700°C nickel-ion irradiation of Ni-12.7 at.% Si γ/γ′ alloys were analyzed by transmission electron microscopy (TEM) and i.r.-emittance measurements. The irradiation caused thin γ′ films to form on stacking faults and γ′ tori to coat the dislocation loops surrounding these faults. Similar films, containing columnar domains of γ′ separated by anti-phase boundaries (APBs). formed at grain boundaries. Films of γ′ containing APBs also formed on the irradiated surface. The growth of these surface films changes the i.r. emittance from that of the Ni-12.7 at.% Si solid solution toward that of γ′-Ni3Si. The initial rate of this change is related to the initial film growth rate and used to determine this growth rate as a function of irradiation temperature. The film growth rate at 10-3 displacements per atom per second (dpa s-1) was small below 400°C and above 700°C, but appreciable at intermediate temperatures. The maximum growth rate (~30 Å min-1) occurred near 550°C. Film growth rate measured at 600°C was directly proportional to dose rate for dose rates from 10-4 to 10-2 dpa s-1. It is suggested that defect-solute coupling causes the film formation and growth. The temperature dependence of the film growth rate is compared with that of swelling in pure nickel and is discussed in relation to the temperature dependence of defect fluxes arriving at sinks for these defects. © 1979.