First-principles investigations on helium behaviors in oxide-dispersion- strengthened nickel alloys with Hf additions

Oxide-dispersion- strengthened nickel alloys with Hf additions are expected to present high temperature mechanical properties and durable helium resistance based on first-principles density functional theory (DFT) calculations. Energetic and charge density evaluations of the helium behaviors were performed in Ni matrix, Y2Hf2O7 oxide and the oxide/matrix interface. With the presence of coherent Y2Hf2O7 in Ni matrix, chances of helium bubbles in Ni can be greatly diminished. The helium atoms shall occupy the interfacial site initially, then diffuse into in the octahedral sites of Y2Hf2O7, and these oxide-captured He atoms prefer to separate individually. Much higher diffusion barrier of He in Y2Hf2O7 than in nickel is related to the strong hybridization between interstitial He-1s and nearest-neighboring O-2p orbitals.