Microstructure criterion for the preferential locations of helium bubble precipitation in a polycrystal

Abstract

Helium bubble distribution at grain boundaries and inside grains affects materials' susceptibility to helium embrittlement. In this paper, we propose a microstructure criterion to quantitatively analyze the helium bubble preference for precipitation locations. The results show that the grain-boundary energy and the helium-to-vacancy ratio are the key factors in determining bubble formation mainly at the grain boundaries or in the grain interiors. Experimental observation based on the electron backscatter diffraction technique confirmed that helium bubbles are more likely to precipitate in the grain interiors of Inconel X750 alloy than pure nickel due to grain-boundary segregation-induced decrease in grain-boundary energy. The precipitation of intergranular bubbles can be reduced by lowering grain-boundary energy and reducing the helium-to-vacancy ratio at grain boundaries. This work provides a general framework for explaining the intrinsic relation between the formation of inter- and intra-granular helium bubbles and promising strategies for designing highly helium-enduring materials.