Grain boundary embrittlement due to phosphorus in tungsten: An atomistic approach

Tungsten (W) and its alloys exhibit impressive properties for use in structural components of nuclear fusion reactors. However, impurity induced embrittlement of W grain boundaries (GBs) is a major concern for reactor applications, and necessitates the investigation of the impact of the impurities on the fracture behaviour of the GBs. This work comprises four papers (I-IV) that deal with atomistic modelling of the impact of phosphorus (P) impurities, which is one of the prime embrittlers in W, on the GB cohesion.

The atomistic modelling is performed based on linear elastic fracture mechanics theory. Since interatomic potentials constitute one of the key ingredients for atomistic modelling, a potential that can describe the fracture of W GBs and the embritteling effect of P impurities is recognized in Papers I and II. In Paper II, the impact of P impurities on the GB strength is evaluated. Papers III and IV are concerned with developing atomistic modelling strategies to address the challenges posed by impurities and extract the fracture toughness and scale-independent interfacial excess potential of cracks in GBs.

The results show that the peak stress required for brittle failure of GBs under uniaxial tensile loading is generally reduced in the presence of P impurities. This suggests that the GBs are weakened by the impurities and that the potential in Paper II can capture P induced GB embrittlement. Likewise, the developed modelling strategies successfully evaluate the fracture toughness and scale-independent interfacial excess potential for pristine and P inhabited GB cracks. A decreasing trend is observed in these fracture quantities with increasing P impurity content, which corroborates the embritteling effect of P impurities on GB fracture.

In summary, the present work provides efficient approaches to investigate the influence of P impurities on the fracture behaviour in tungsten GBs, which are general to a degree that they can be applied to other types of impurities too. Additionally, the herein generated interfacial excess potential data can be used for continuum scale studies of higher-timescale fracture phenomena in P inhabited GBs.