MECHANISM FOR IRRADIATION INDUCED CREEP IN NANO-CRYSTALLINE DILUTE ALLOYS

One of the main factors limiting the lifetime of materials is deformation due to creep. This failure mechanism is especially important when the material is exposed to radiation and creep is enhanced [1]. While the mechanism controlling creep varies, Irradiation induced creep is controlled by interactions of dislocations with point defects, that are at super- saturation due to the irradiation. A prominent approach for reducing irradiation induce creep in structural materials is the integration of precipitates within the microstructure of the material. The matrix-precipitate interface traps point defects, and thus prevents point defect-dislocation interaction. Along these lines, it was suggested to employ nanocrystalline alloys as radiation resistant material, where small grain size prevents dislocation reactions and the high availability of interfaces serve to trap point defects.

However, it was shown that grain boundary related relaxation due to point defect interactions at the nanocrystalline alloys grain boundary does lead to significant creep rates [2, 3]. We use molecular dynamics simulation to follow nano-crystalline Cu-V and Cu-Nb response to the insertion of point defects into material`s grain boundaries. The variation in observed dynamics and its correlation with simulated creep rates serve to identify the creep controlling mechanism. We show that although significant a-thermal relaxation is evident all through the grain boundary, displacements due to stair-rod dislocations are unique in that they show strong correlation with observed variation in creep rates. These structures are shown to concentrate at triple line and quad junctions.

1. Was, “Fundamentals of Radiation Materials Science: Metals and Alloys”, Springer, Berlin, 2007
2. Y. Ashkenazy; R. S. Averback, Nano letters, 4084-4088, 2012
3. K.Tai; R. S. Averback; P. Bellon; Y. Ashkenazy, Scr. Mater., 65, 163, 2011.