Crack nucleation mechanisms and nucleation conditions were still poorly understood. Experimental evidence suggested that crack nucleation mainly occurred when growing twins, slip or persistent slip bands collide with grain boundaries. These processes were therefore investigated by atomistic simulation. As a first step, simulations were made here of crack nucleation at the Σ = 9 (2¯21) grain boundary in tungsten resulting from an interaction with dislocations. Symmetrical twin boundaries and most other high-angle grain boundaries were relatively stable and acted as barriers to dislocation motion. When a dislocation was absorbed by such grain boundaries, a stress concentration developed at the absorbing site and a crack was nucleated there. Crack nucleation was investigated under different loading conditions. The results showed that crack nucleation was aided significantly by additional dislocation activity. The relevant mechanisms were significantly more complex than that captured by simple pile-up models.Crack Nucleation at the Σ9(2¯21) Symmetrical Tilt Grain Boundary in Tungsten. Y.Cheng, M.Mrovec, P.Gumbsch: Materials Science and Engineering A, 2008, 483-484, 329-32

Figure 3

Diffusivity of W on the (320) Surface of W