A MECHANISM FOR STRESS-CORROSION EMBRITTLEMENT. Summary Report for August 1, 1959-July 31, 1960

The stress level for crack formation as a function of grain size was investigated for a number of alloys. Stresscorrosion embrittlement of Al--4 wt.% Cu in NaCl--H/sub 2/O/sub 2/ solution at room temperature and Armco iron in boiling Ca(NO/sub 3/)/sub 2/-- NH/sub 4/NO/sub 3/ solution was investigated. The stress for crack formation as a function of grain diameter for these alloys was found to be rectified in accordance with the Petch equation. From the slopes of data, surince energies of 160 and 32 ergs/cm/sup 2/ were calculated, respectively, for the aluminum--copper alloy and the Armco iron. These values of surface energy represent appreciable reduction from surface energy in a nonstress corroding medium and therefore support the hypothesis that stress corrosion is a brittle fracture phenomenon. (See also ARF-2152-10.) (auth)