Exoelectron emission from torsional fatigue damage in hardened steels

Exoelectron emission associated with surface fatigue damage in two types of steel was measured by means of an ultraviolet laser scanning system. The localized emission from damage areas in quenched and tempered 1541 steel increased systematically with continued fatigue cycling. Plots of emissionvs cycles were in good agreement with earlier results for 1018 steel. Much of this emission resulted from the accumulation of plastic deformation during the crack initiation stage. In the case of relatively brittle 1144 steel, the dominant source of exoelectrons was a fatigue crack with little associated plasticity. However, shot peening of the 1144 steels completely changed the character of the surface layers. While the core material still cracked in a rather brittle manner, the shot peened layer accumulated a broad distribution of plastic deformation as revealed by the systematic development of exoelectron emission. These results indicate that the accumulation of surface fatigue deformation during the crack initiation stage is a systematic and perhaps universal process when viewed on the appropriate microscale.