Issue 35

W. Ozgowicz et alii, Frattura ed Integrità Strutturale, 35 (2016) 11-20; DOI: 10.3221/IGF-ESIS.35.02 20 4. The activity AE of the recorded signals increases with the rise of the temperature of deformation, reaching its maximum at the temperature of stretching of about 250  C. 5. In the given conditions of plastic deformation no explicit correlation was found between the frequency of oscillations of stresses on the curves  -ε indicating the PLC effect with the frequency of AE events. 6. The intercrystalline brittleness of the investigated tin bronze initiates in the temperature range (T E ), independently of the state of the alloy at its delivery, by the nucleation of microfissures, mainly of the type of wedges at the grain boundaries, privileged with respect to the direction of stretching stresses, mostly at the contact points of three grains, in which concentration of stresses attains it maximum. 7. The deformation of the investigated alloy in the temperature range of minimum plasticity (TMP), being 400  C, leads to the typical effect of intercrystalline brittle cracking of the entire surface of analyzed fractures of the stretched samples. A CKNOWLEDGMENTS he studies were financially supported by Polish National Science Centre, project in competition OPUS 4, grant No 2012/07/B/ST8/03055. R EFERENCES [1] Misra, R.D.K., Prasad, S., On the dynamic embrittlement of copper-chromium alloys by sulphur. J. Mater. Sci., 35 (2000) 3321-3325. [2] Briant, L., Banerji, K., Embrittlement of Engineering Alloys, 25 Aead Press. N.Y. (1983). [3] Ozgowicz, W., Physico-chemical, structural and mechanical factors of intergranular brittleness of  -bronzes at elevated temperature. Publ. Silesian Techn. Univ. Gliwice Mechanics Z.145, (2004) (in Polish). [4] Franklin, S. V., Mertens, F., Marder, M., Portevin–Le Chatelier effect, Phys. Rev. E, 62 (2000) 8195-8206. DOI: 10.1103/PhysRevE.62.8195. [5] Brindley, B.J., Worthington, P.J., Reply to “on the grain-size dependence of the activation energy associated with serrated yielding, Scrip. Metall., 4 (1970) 295–297. DOI: 10.1016/0036-9748(70)90124-9 ca. [6] Ozgowicz, W., Grzegorczyk, B., Pawełek, A., Piątkowski, A., Ranachowski, Z., The influence of the strain rate on the PLC effect and acoustic emission in single crystals of the CuZn30 alloy compressed at elevated temperature, Materiali in tehnologije, 49 (2015) 2 197–202. doi:10.17222/mit.2013.195. [7] Grzegorczyk, B., Effect of PLC in monocrystalline Cu-Zn alloy plastically deformed et elevated temperature, PhD thesis, Silesian Univ. of Technology, Gliwice, (2010) (in Polish). [8] Pawełek, A., Kuśnierz, J., Jasieński, Z., Ranachowski, Z., Bogucka, Acoustic emission and the Portevin - Le Chatelier effect in tensile tested Al alloy before and after processing By accumulative Roll-Bonding (ARB)technique, Archiv. of Metall. and Mater., 54 (2009) 83-88. [9] Majkut, L., Acoustical diagnostics of cracks in beam like structures, Archives of Acoustics, (2006) 17-28. [10] Ranachowski, Z., Methods of measurement and analysis of acoustic emission signal, Institute of Fundamental Technological Research Polish Academy of Sciences, Warsaw, (1997) (in Polish). T