Role of grain boundary character on oxygen and hydrogen segregation-induced embrittlement in polycrystalline Ni
Density functional theory (DFT) calculations are carried out to investigate the role of grain boundaries on the energetics related to the oxygen and hydrogen segregation-induced embrittlement in polycrystalline Ni systems. Four model grain boundary (GB) systems for nickel are chosen to investigate this effect. These model GBs are the Σ5 (012) GB, the Σ5 (013) GB, the Σ11 (113) GB, and the Σ3 (111) coherent twin boundary (CTB). The chosen GBs enable the investigation of the role of the CTB in the embrittlement and decohesion mechanisms in comparison with the other GBs. The embrittling mechanism considered here is based on the investigation of the energetics related to (a) the segregation of atoms of embrittling species (oxygen, hydrogen) at the GB; (b) the formation of vacancies due to the segregation of embrittling species at the GB; and (c) the energetics related to decohesion at the GB as a function of concentration/accumulation of the embrittling species at the GB. DFT calculations suggest that the segregation of the embrittling species and the embrittling effect are closely related to the local atomic structure of the GB and the associated excess free volume. In particular, it is found that the Σ3 (111) CTB is less prone to segregation of oxygen and hydrogen based on the binding energetics of the embrittling species. However, among all the GBs considered, the Σ3 (111) CTB is found to be most susceptible to GB decohesion and crack formation in the presence of small amounts of segregated oxygen atoms. This dual behavior of the Σ3 (111) CTB is also confirmed for the case of hydrogen as the embrittling species using DFT simulations. Thus, the segregation-resistant Σ3 (111) CTB is observed to be the most susceptible to crack formation in the presence of small amounts of segregated embrittling atoms. The energetics of segregation of the embrittling species and the effect of segregation on the vacancy formation energies and GB decohesion are discussed.
KeywordsGrain Boundary Density Functional Theory Calculation Interstitial Site Vacancy Formation Substitutional Site
This material is based upon work supported by the National Science Foundation (NSF) CMMI Grant-1454547.
- 3.Carpenter W, Kang BS-J, Chang MK (1997) SAGBO Mechanism on high temperature cracking behavior of Ni-base superalloys, Proceeding of the. Superalloys 718, 625, 706, and Various Derivatives, Pittsburgh, p 679Google Scholar
- 4.Smith DF, Smith JS, Russell KC, Smith DF (eds) (1990) Physical metallurgy of controlled expansion invar-type alloys. TMS, Warrendale, p 253Google Scholar
- 5.Browning PF, Henry MF, Rajan K, Loria EA (eds) (1997) Superalloys 718, 625, 706 and various derivatives. TMS, Warrendale, p 665Google Scholar
- 12.Krupp U, Wagenhuber P, Kane WM et al (2005) Environmentally assisted brittle fracture of nickel-base superalloys at high temperatures, 11th international conference on fracture. ICF11, 01Google Scholar
- 20.Kart HH, Cagin T (2008) The effects of boron impurity atoms on nickel Σ5 (012) grain boundary by first principles calculations. J Achiev Mater Manuf Eng 30:177–181Google Scholar
- 22.Yamaguchi M, Shiga M, Kaburaki H (2005) Grain boundary decohesion by impurity segregation in a nickel-sulfur System. Science 21:307–397Google Scholar
- 30.Yamaguchi M, Shiga M, Kaburaki H (2004) Energetics of segregation and embrittling potency for non-transition elements in the Ni Σ5 (012) symmetrical tilt grain boundary: a first-principles study. J Phys 16:3933–3955Google Scholar