III - Influence de la microstructure sur le glissement intergranulaire des Alliages 600 et 690

Influence of microstructure on grain boundary sliding (GBS) of 600 and 690 alloys

Abstract

Alloy 600 has been extensively used in nuclear industry for steam generator tubing in pressurized water reactor because of its good corrosion resistance and mechanical properties. However, there have been instances of Intergranular Stress Corrosion Cracking (IGSCC) originating from both the primary and secondary sides on the tubes walls in operating conditions.

The susceptibility of Alloy 600 to IGSCC in primary water depends on material composition and microstructure. Mechanisms controlling cracking have not been identified yet. Nevertheless, several studies envisage the participation of GBS to the phenomenon.

The present work aims at evaluating the influence of interfaces straining mechanisms - GBS - on IGSCC behavior of Alloy 600 and 690. Fiducial grids (step 7 μm, bars width 0. 5 μm) have been engraved on the specimens surface and creep tests have been performed at 500°C with a stress level of 400 MPa. GBS is measured thanks to Scanning Electron Microscopy. Deformation mechanism have been characterized by Transmission Electron Microscopy through post mortem or in situ dynamic experiments.