Microstructure and mechanical properties of F82H weld metal irradiated in SINQ target-3

The present work is concerned with the microstructure and mechanical behavior of F82H weld metal before and after irradiation to about 11 dpa with simultaneous helium concentrations up to 1000 appm. Optical and TEM observations and micro-hardness test were performed to identify the irradiation effect. Before irradiation, the microstructure of the weld metals is tempered martensite. Precipitates are predominately M23C6 carbides located along martensitic lath boundaries and primary austenite grain boundaries, but some M23C6 carbides rich areas are found. The weld metal has higher dislocation density and also higher hardness than the base metal. Radiation produced a significant change in the microstructure of the weld metal, similar to the F82H base metal irradiated under the same condition. The mean size and the density of defect clusters are comparable to previous results, and the density of helium bubbles is a little higher in the weld metal. The micro-hardness test after irradiation shows significant hardening that does not saturate at higher dose. (C) 2004 Elsevier B.V. All rights reserved.