Segregation-induced hole drilling at grain boundaries

Grain boundaries in metals provide preferential sites for impurity atoms to segregate, forming an area of the metal with different chemical and physical properties compared to the bulk. This also means that the electron beam damage characteristics of the grain boundary might be different from that of the bulk. Segregation can be expected to make grain boundaries particularly vulnerable to electron-beaminduced hole drilling and beam damage, if the segregation produces a near two-dimensional compound with increased ionicity. Here we report preferential hole drilling at grain boundaries in an Fe-0–4 wt%P alloy. Such a phenomenon confirms evidence from energy-loss spectroscopy that charge transfer occurs between P and Fe at the grain boundary. It also explains why it is easier to detect phosphorus using EDX compared to PEELS, and suggests that the electron beam damage may be a major limiting factor in grain-boundary studies.