In the present paper we propose a connectivity between these two sets of phenomena and as such an interrelationship between two levels of scale. At best, however, we view this as a work in progress because of the complexity of the phenomena and its interpretation. We will emphasize where progress has been made and point out alternative pathways by which hydrogen “embrittlement” might be understood. The research includes a brief review of the indentation size effect on Fe3%Si and W single crystals and its connectivity to a volume to surface area concept. We then briefly review the modified Rice-Thompson model for the brittle to ductile transition applied to Fe3%Si single crystals in the absence and presence of hydrogen. This is all brought together with a length scale that can be measured independently for thin films of Cu/Ti/SiO2/Si. Applications to film deadhesion with and without hydrogen utilize the Rice-Thompson approach. THEORETICAL CONNECTIONS At the smallest scale discussed here, we have found that extremely large enhancements of hardness exist at depths of penetration in the 10–100 nm range [1,2]. Whereas the hardness, H, might be expected to be about three times the bulk yield stress, σys, values of (5–20) σys were found for indentation into {100} planes of Fe-3wt%Si and W single crystals. Results [1] and interpretation [2] are given elsewhere, examples being given in Figure 1. 0 5 10 15 20 25 30 35 40 4 8 12 16 20 (δR)1/3 (nm2/3) ys 0 5 10 15 20 25 0 20 40 60 80 100 (δR)1/3 (nm2/3) ys 85 nm 360 nm 1800 nm 5000 nm Fe 3% Si W <100> FE-3% SI <100> W H / H/σys H / H/σys a) b) Figure 1. Fit of the proposed model [2] for two 〈100〉 oriented single crystals. Single tips of 205 nm and 70 nm radii were used in (a) and multiple spherical tips with radii noted were used in (b). The solid curves in Figures 1(a) and 1(b) represent Eqn. (1) as given by 2 1/3 3 ( / ) = R H V S ys δ σ (1) where V/S is the indent volume to surface ratio, δ is the penetration depth and R is the tip radius of the 90° diamond cones used. For the Fe-3wt%Si this was a 70 nm tip radius while for the W a
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