Mechanical Properties of Plasma-Exposed Tungsten*

Based on molecular-dynamics simulations using properly parametrized interatomic potentials and recently developed machine learning potentials, we examine systematically the effects of plasma exposure related defects on the mechanical properties of plasma-facing component (PFC) tungsten. Our simulations reveal that empty voids are centers of dilatation resulting in the development of tensile stress in the tungsten matrix, whereas He-filled voids (nanobubbles) introduce compressive stress in PFC tungsten. We find that the elastic moduli of PFC tungsten, namely, the bulk, Young, and shear moduli, soften substantially as a function of He content in the tungsten matrix, in addition to the softening caused in the matrix with increasing temperature. Moreover, we establish exponential scaling relations for the elastic moduli of PFC tungsten as a function of its porosity and He content. We also find that He bubble growth significantly affects both the bulk modulus and the Poisson ratio of PFC tungsten, while its effect on the Young and shear moduli of the plasma-exposed material is weak. Beyond the elastic regime, our simulations reveal that the presence of voids reduces the ultimate tensile strength (UTS) of tungsten, which is a monotonically decreasing function of porosity. Introducing He into the voids to form He nanobubbles causes further systematic decrease of the tungsten UTS with increasing He content. The significant impact of He bubble formation and growth on the fracture mechanics and structural response of PFC tungsten also is characterized in detail.