EFFECT OF ELECTRON BOMBARDMENT HEATING ON SURFACES OF TUNGSTEN,

Heating to very high temperatures by electron bombardment often roughens or damages metal surfaces. This damage to grain boundaries and grain surfaces is examined in electropolished sheet and foil specimens of tungsten. The effects of heating by stationary and oscillating 10-kv beams are compared with the effects produced by thermal radiation. At moderate temperatures, stationary beams induce grain boundary grooving as does thermal radiation, while oscillating beams produce ripples in the surface. At high temperatures, stationary beams and thermal radiation produce pits, while oscillating beams produce cracks, and tilted and dislodged grains. The more severe effects produced by oscillating beams are shown to be associated with thermal cycling. Author