Issue 35

W. Ozgowicz et alii, Frattura ed Integrità Strutturale, 35 (2016) 434-440; DOI: 10.3221/IGF-ESIS.35.49 438 is approx. 95HV05. In the central part of the specimen, there are partially recrystallised grains varying in their size with deformed twins and voids. Figure 7 : Fine recrystallized grains at the boundaries of large α grains in structure of CNCS alloy after tension at 550°C Figure 8 : Cracks at the boundaries of α phase grains in structure of CNCS alloy after tension at 550°C The fractographic investigations have allowed the nature of fractures of the CuNi2Si alloy in an as-forged state, after heat treatment and after deformation in the hot tensile test in the temperature range of 200÷ 800°C to be determined. The results of fracture observations and EDX microanalysis of identified precipitations occurring in the CNCS alloy are shown in microphotographs (Fig. 9÷11). The occurrence of a typical ductile fracture with numerous pits and craters with precipitations at their bottoms has been found in an as-forged state. The concentration of copper (93.21%), nickel (3.55%) and chromium (1.0%) has been revealed in their chemical composition. After supersaturation from 940°C, the nature of the CuNi2Si alloy fracture is similar to that in an as-forged state. The existence of precipitations in fracture of the supersaturated alloy indicates their primary nature. After the tensile test at 200°C, there is a transcrystalline ductile fracture in the tested alloy, with numerous characteristic pits and craters in which the presence of fine precipitations (Fig. 9) with small concentration of copper, nickel, chromium, silicon and manganese as well as sulphur contamination has been found. The ductile nature of the fracture mainly confirms high plasticity of the tested alloy (Fig. 2). Figure 9 : a) Ductile transcrystalline fracture with precipitations in craters, b) microanalysis of chemical composition of precipitation in CuNi2Si alloy after tension at 200°C a) b)