Experimental and modeling approach of irradiation defects recovery in zirconium alloys: impact of an applied stress

Joë Ribis (1) , Fabien Onimus (1) , Jean-Luc Béchade (1) , Sylvie Doriot (1) , Chantal Cappelaere (2) , Clément Lemaignan (3) , Alain Barbu (4) , Olivier Rabouille (2)

1 SRMA - Service des Recherches Métallurgiques Appliquées
2 SEMI - Service d'Etudes des Matériaux Irradiés
3 DEC - Département d'Etudes des Combustibles
4 SRMP - Service de recherches de métallurgie physique

During neutron irradiation, both interstitial and vacancy loops are formed in high concentration in zirconium alloys. Due to this high density of loops, the material is considerably hardened, but the recovery of the radiation damage during a heat treatment leads to a progressive softening of the irradiated material. The recovery of the radiation induced hardening has been investigated using microhardness tests. Transmission electron microscopy ͑TEM͒ observations performed on irradiated foils have also shown that the loop density falls while the loop size increases during the thermal annealing. Furthermore, the TEM analysis has revealed that only vacancy loops are present in the material after long term annealing, the interstitial loops having entirely disappeared. A numerical cluster dynamic modeling has also been used in order to reproduce the material recovery for various annealing conditions. The microstructural evolution during mechanical testing with various loading conditions has also been studied. It has been shown that during a creep test with low applied stress ͑130 MPa͒ and high temperature ͑450°C͒, the microstructure evolution can essentially be explained by the thermal recovery of the loops leading to glide of dislocations as found for an non-irradiated material. At intermediate temperature ͑400°C͒, it is shown that for low stress level ͑130 MPa͒ the microstructure evolution can also be explained by the thermal recovery of loops, whereas for higher stress ͑250 MPa͒, sweeping of loops by gliding dislocations can also occur. In addition, for an applied stress of 130 MPa and a temperature of 400°C, dislocation density is higher in the irradiated material than in the non-irradiated material deformed in the same conditions. It is also shown that secondary slip systems are more activated in the irradiated material than in the non-irradiated material. From this detailed analysis, the mechanical behavior during creep is interpreted in terms of microscopic deformation mechanisms.

Mots clés: TEM; microhardness; creep; zirconium alloys; dislocation loops; annealing

Domaines: Matériaux

Joë Ribis, Fabien Onimus, Jean-Luc Béchade, Sylvie Doriot, Chantal Cappelaere, et al.. Experimental and modeling approach of irradiation defects recovery in zirconium alloys: impact of an applied stress. Journal of ASTM International (JAI), 2008, 5 (3), pp.JAI101118. ⟨10.1520/JAI101118⟩. ⟨cea-04087843⟩