DYNAMICAL PROCESS OF BUBBLES AND PRECIPITATION IN GRAIN BOUNDARIES IN PLASMA FACED MATERIALS

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In order to develop the plasma faced materials, damage and voids(or bubbles)swelling evolution process in plasma faced materials, such as austenitic model alloy, ferritic model alloy, SiC, Al_2O_3, Fe, Ni and Al, have been studied by in-situ electron microscopy with ion accelerator. It was found in Ni, Fe and Al irradiated with helium or hydrogen ions that the nucleation of interstitial type dislocation loops was enhanced by trapping of the self-interstitial atoms at helium. (or hydrogen) ・ vacancy complexes. The coarsening of the bubbles took place in all materials examined through their coalescence during their Brownian motion. The diffusivity of the bubble and its size and temperature dependence was measured according to the random walk theory. Helium bubble precipitation and rapid motion along grain boundaries was found out. To examine the precipitation of the alloy elements, STEM-EELS analysis was carried out. It was clarified that Cr was depleted and Ni was enriched on the bubble surface in Fe-16Cr-17Ni austenitic alloy. However, Cr was enriched on the bubble surface in ferritic Fe-9Cr alloy. Effects of the segregated alloy elements on the bubble mobility was suggested. Helium bubbles in SiC and Al_2O_3 matrixs were stable up to 1100K, but they precipitabed and easily coarsened along grain boundaries.