The Origin of Corrosion Resistance Change Induced by Sn and Nb Alloying in Zr Alloys

Abstract

As nuclear fuel cladding, Zr alloys have need for a good corrosion resistance. For decades, through adjusting content of Sn and Nb, several generations of Zr alloys with excellent corrosion resistance are developed. However, the mechanism of Sn and Nb influencing the corrosion resistance is still not clear. Here, our computational simulations indicate, the segregations of Sn or Nb at grain boundary (GB) can occur, and results in variation of GB cohesion, which influences the difficulty of the formation of micro-cracks in oxide film and then changes protectiveness of oxide film which determines the corrosion resistance. Using the first-principles method, we find that Sn segregation can reduce GB cohesion, and results in a potency of reduction of oxide film protectiveness; however, Nb segregation can enhance GB cohesion, and results in a potency of enhancement of oxide film protectiveness; the results are well consistent with the previous experimental observations that reducing Sn and adding Nb can promote corrosion resistance of Zr alloys. These findings provide a basis for understanding the roles of alloying elements in Zr alloys, which is very useful to future design of new Zr alloys with more excellent corrosion resistance.