Issue 35

W. Ozgowicz et alii, Frattura ed Integrità Strutturale, 35 (2016) 434-440; DOI: 10.3221/IGF-ESIS.35.49 437 Figure 3 : Grains of α phase in CNCS alloy after supersaturation from 940°C. Figure 4 : Elongated grains of α phase after tension at 200ºC The structure of the tested alloy after hot forging is characterised by fine grains of α solution, elongated towards plastic deformation, with average diameter of approx. 30μm. After supersaturation from 940°C, the grains of α solution with twins of 10÷30 µm were revealed in structure of the CuNi2Si alloy (Fig.3). In structure of the tested alloy stretched at 200°C, the elongated grains of α phase with numerous sliding bands have been revealed (Fig.4). Micro-hardness of the area with sliding bands has been found to be approx. 115 HV05, while hardness measured within the area of the twin is approx. 100 HV05 (Fig.4). After tension at 400°C, the areas of grains, varying in their size, with micro-cracks at their boundaries occur in structure of CNCS alloy (Fig. 5). In addition to large grains of approx. 200μm and micro-hardness of approx. 90 HV05, there are also recrystallised grains (HV05=85) with average diameter of approx. 10μm (Fig.6). After tension at 550°C, micro-hardness of non-recrystallised grains increases up to 151HV05 and of crystallised ones to120HV05 (Fig.7). Micro-cracks and diverse grain size in the tested alloy after tension at 550°C have been found to result in a sudden decrease in plasticity during plastic deformation. These effects are the result of slide at the grain boundaries and intergranular precipitation during hot deformation. Figure 5 : Micro-cracks at the boundaries of α grains in CNCS alloy after deformation at 400ºC Figure 6 : Grains of α phase varying in their size in structure of CNCS alloy after deformation at 400ºC In the specimen rupture zone there are areas of grains with average diameter of approx. 10μm and micro-hardness of approx. 120HV05 as well as micro-cracks along the grain boundaries (Fig. 7), while in the central zone there are large non- recrystallised grains of α phase of approx. 250μm with annealing twins and micro-cracks at the end face of the twins (Fig. 8). After tension at 800°C, fine recrystallised grains of α phase with mean diameter of approx. 10μm as well as cracks and micropores were revealed in structure of the tested alloy within the specimen rupture zone. Micro-hardness of these areas