Damage and surface modification of TiC coated Mo divertor of JT-60

Damage to a TiC coated Mo divertor plate used in JT-60 for about two years was re-examined from a material viewpoint to obtain data concerning utilization of high-Z plasma facing components in future fusion reactors. Serious damage was observed on the edge of several divertor plates located next to a toroidal gap. Due to very high heat fluxes a apart of the edge was melted and a large crack of about 12 cm wide and 2.5 cm deep was caused near the melted edge along a lamination of the Mo plate. Recrystallization by the heat loading embrittled the subsurface region and resulted in cracking and melting at a lower heat loading. The present work suggests that the maximum temperature of the powder metallurgical Mo should be maintained below the recrystallization temperature to prevent material degradation and plasma radiation losses.