The corrosion of Alloy 718 during 800 MeV proton irradiation

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.