Issue 35

S. Lesz et alii, Frattura ed Integrità Strutturale, 35 (2016) 206-212; DOI: 10.3221/IGF-ESIS.35.24 208 of rods and are 25, 21 and 17 kJ/m 2 for the samples with diameters of  =2, 3 and 4 mm, respectively. With the increase of rod’s diameter the Young’s modulus and stress decrease, suggesting a soft trend. These changes are probably connected with changes of structure relaxation. In sample in form of rod with 4 mm, where cooling rate of rods during casting is lower, the structure is more relaxed. This indicates that cooling rate plays a significant role in the plasticity of metallic glasses. The compressive fracture surfaces are shown in Figs. 3-5. Fracture morphology of rods has been different on the cross section. Two characteristic features of the compressive fracture morphologies of metallic glasses (MGs) were observed. Diameters of rod samples,  [mm] Young’s modulus, E [GPa] Compressive stress, σ c [MPa] Elastic strain, ε [%] Elastic strain energy, U [kJ/m 2 ] 2 191 1794 0.94 25 3 135 1117 0.83 21 4 105 790 0.75 17 Table 1 : Compressive mechanical properties of samples of the Fe 36 Co 36 B 19 Si 5 Nb 4 BMGs rods used in compression test at room temperature. Figure 1 : X-ray diffraction pattern of the Fe 36 Co 36 B 19 Si 5 Nb 4 BMGs rods with diameters of  =2, 3 and 4 mm. One is the smooth region, as shown in Figs. 3a,c,d, 4a,b,c,d,e, 5a,b. Another typical feature of the compressive fracture morphology of MGs is the vein pattern, as shown in Figs. 3a,b,c,d, 4a,c,d,e,f, 5c,d. The presence of these fracture morphologies indicates that the Fe-based BMG of this study classifies itself as a brittle amorphous material. Figs. 3a-d show the SEM images of the fracture morphology of Fe 36 Co 36 B 19 Si 5 Nb 4 alloy rod with diameter of  = 2 mm after compressive fracture. Fig. 3a shows a main view of the 2 mm diameter BMG sample. The fracture surface of this sample consists of a smooth and vein pattern regions. Fig. 3b shows image of fracture outside surface, there are vein patterns and many cracks. The veins on the compressive fracture surface have an obvious direction probably compatible with direction of plastic strain. Fig. 3c shows an image of fracture of near the core of rod with smooth and vein pattern regions. Extensive cracks perpendicular to the fracture surface (in Fig. 3b) and rare small cracks within the veinlike pattern fracture (in Fig. 3c,d) can be observed. The well-developed fracture surface is observed for rods with a diameter of  = 2 mm. The fracture surface of rods with the diameter of  = 3 mm do not exhibit veinlike pattern in a region of rod core. The fracture surface is small-developed, nearly smooth. Only the edge of the rod the fine vein pattern morphology is observed. It is very interesting that angles between deep cracks formed and surface of the decohesion are from 68  to nearly 90  in relation to crack propagation direction.