Issue 35

S. Lesz et alii, Frattura ed Integrità Strutturale, 35 (2016) 206-212; DOI: 10.3221/IGF-ESIS.35.24 210 Figure 4 : SEM images of the fracture morphology of Fe 36 Co 36 B 19 Si 5 Nb 4 alloy rod with diameter of  =3 mm after compressive fracture; a – main view: smooth and vein pattern regions, b – image of fracture near the core of rod, smooth patterns, c, d – image of fracture near the core of rod, smooth and vein pattern regions, crack is indicated by arrow (d), e, f – image of fracture outside surface, vein and smooth patterns, f – image showing veins, as indicated by the rectangle in (e) at higher magnification. The fracture surface of Fe 36 Co 36 B 19 Si 5 Nb 4 rod with diameter of  = 4 mm after compressive fracture consists of flat region with fine veins pass to the brittle crack region with extended surface, as shown in Fig. 5a. Fig. 5b shows the image of fracture near the core of rod. There are smooth and vein patterns. The fracture surface of rods with  = 4 mm does not exhibit another cracks extended to the material core besides the main fracture with the well-developed surface. Fig. 5c shows the image of fracture outside surface with vein patterns regions. Magnified veins from the area as pointed in Fig. 5c was shown in Fig. 5d. The veins on the compressive fracture surface have an obvious direction as result of initial displace of sample along shear bands. This direction follows the direction of the displacement of a material. As shown in Fig. 5d, the angles between the primary crack propagation direction and a region of secondary cracks is 60  . Presumably it is the effect of the change of the crack propagation direction. It influences the microstructure in areas showing the change of the direction of fine veins. The formation of veins on the compressive fracture surface is closely related to the shear fracture mechanism [9]. It seems that the fracture surface is independent on a strength level [10].