PLASMA-INDUCED SURFACE DEGRADATION IN 304-STAINLESS-STEEL USED FOR TRIAM-1M LIMITER

Surface degradation in a 304 stainless steel limiter of TRIAM-1M by lo ng-pulse discharge during long period operation has been examined by m eans of X-ray diffraction, scanning electron microscopy and dynamical microindentation tests. Particular exfoliation and hardening of the su rface of the electron drift side were observed. These result from the formation of alpha' martensite induced by hydrogen in the plasma. The stability of the martensitic phase has been studied by annealing exper iments on the cathodically hydrogen charged 316 stainless steel by X-r ay diffraction. Both epsilon and alpha' martensites were formed by 22 h cathodic charging. The former reverts to gamma-phase and/or converts to alpha' martensite below 723 K and the latter reverts to gamma-phas e below 923 K, repectively.