The real-time polarization resistance of Alloy 718 during high energy proto
n irradiation (rneasureJ with electrochemical impedance spectroscopy) decre
ased from 1.7 x 10(3) ohm m(2) in the absence of irradiation to 8.2 ohm m(2
) at a proton beam current of 0.4 mA. Because the proton beam spot size was
smaller than the sample (that is, proton flux decreased radially from the
beam center), two methods for determing corrosion rate from polarization re
sistance were employed. The first method assumed that the distribution of c
orrosion was uniform across the entire probe surface. With this assumption,
the corrosion rate was found to vary from 0.041 mu m/yr at an average prot
on current of 0.001 mA-3.1 mu m/yr at an average proton current of 0.40 mA.
The second method used proton flux as a criterion for determining the area
of highest damage. At a peak proton flux of 1.77 x 10(18) p/m(2)s, calcula
ted at an average proton current of 0.40 mA, the corrosion rate was 60.9 mu
m/yr. These results are discussed within the context of water radiolysis a
nd direct 718/proton interactions. (C) 2000 Published by Elsevier Science B
.V. All rights reserved.