Issue 35

W. Ozgowicz et alii, Frattura ed Integrità Strutturale, 35 (2016) 11-20; DOI: 10.3221/IGF-ESIS.35.02 11 Focussed on Crack Paths Relation between the plastic instability and fracture of tensile tested Cu-Sn alloys investigated with the application of acoustic emission technique W. Ozgowicz, B.Grzegorczyk Silesian University of Technology, Poland A. Pawełek, W. Wajda, W.Skuza. A.Piątkowski Institute of Metallurgy and Materials Science of Polish Academy of Sciences, Poland Z. Ranachowski Institute of Fundamental Technological Research of the Polish Academy of Sciences, Poland A BSTRACT . The work concerns the application of the acoustic emission (AE) method in testing the mechanical properties of continuously cast industrial tin bronze CuSn6P, which reveals tendencies to instable plastic flow connected particularly with the Portevin-Le Chatelier (PLC) effect. The relations between the jerky flow connected with the PLC effect, AE intensity and the evolution of a fracture of the investigated alloy subjected to the tensile test at a strain rate (   ) of about 1.2·10 -3 s -1 in the range of temperatures (20÷400  C) has been analyzed. It has been found that the highest intensity of the oscillation of stresses, corresponding to the instability of plastic deformation PLC occurred at 200  C, whereas the maximum of the AE activity is at about 200÷250  C. The brittle intergranular fracture starts in the range of equicohersive temperature (T E ) of about 200  C. Plastic deformation of the investigated alloy in the range of the temperature of minimum plasticity, amounting to about 400  C, results in intercrystalline fractures on the entire surface of the stretched samples. K EYWORDS . Copper alloy; Portevin-Le Chatelier phenomenon; Tensile test; Acoustic emission; SEM; Intercrystalline fracture. I NTRODUCTION lastic deformation of copper alloys, particularly those with a small energy of the stacking fault (SFE), for instance tin bronzes and brasses at elevated temperature (about 0.4 to 0.6 T t ) and a strain rate (   ) amounting to about 10 -5 s -1 ÷ ok. 10 -2 s -1 is a complex process, occurring most often in a heterogeneous way, due to the simultaneous effect of several mechanisms of deformation. The knowledge of these mechanisms and structural processes encountered in the given P