High-tin bronzes are used for church bells and concert bells (carillons). Therefore, beside their decorative value, they should also offer other functional properties, including their permanence and good quality of sound. The latter is highly influenced by the structure of bell material, i.e. mostly by the presence of internal porosity which interferes with vibration of the bell waist and rim, and therefore should be eliminated. The presented investigations concerning the influence of tin content ranging from 20 to 24 wt% on mechanical properties of high-tin bronzes allowed to prove the increase in hardness of these alloys with simultaneous decrease in the tensile and the impact strengths (Rm and KV, respectively) for the increased tin content. Fractures of examined specimens, their porosity and microstructures were also assessed to explain the observed regularities. A reason of the change in the values of mechanical properties was revealed to be the change in the shape of α-phase crystals from dendritic to acicular one, and generation of grain structure related to the increased Sn content in the alloy.
In this article the structural and mechanical properties of grain refinement of Cu-Sn alloys with tin content of 10%, 15% and 20% using the KOBO method have been presented. The direct extrusion by KOBO (name from the combination of the first two letters of the names of its inventors – A. Korbel and W. Bochniak) method employs, during the course of the whole process, a phenomenon of permanent change of strain travel, realized by a periodical, two-sided, plastic metal torsion. Moreover the aim of this work was to study corrosion resistance. The microstructure investigations were performed using an optical microscope Olimpus GX71, a scanning electron microscope (SEM) and a scanning transmission electron microscope (STEM). The mechanical properties were determined with INSTRON 4505/5500 machine. Corrosion tests were performed using «Autolab» set – potentiostat/galvanostat from EcoChemie B.V. with GPES software ver. 4.9. The obtained results showed possibility of KOBO deformation of Cu-Sn casting alloys. KOBO processing contributed to the refinement of grains and improved mechanical properties of the alloys. The addition of tin significantly improved the hardness. Meanwhile, with the increase of tin content the tensile strength and yield strength of alloys decrease gradually. Ductility is controlled by eutectoid composition and especially δ phase, because they initiate nucleation of void at the particle/matrix interface. No significant differences in the corrosion resistance between cast and KOBO processed materials were found.
The most important feature of bells is their sound. Its clarity and beauty depend, first of all, on the bell’s geometry - particularly the shape of its profile, but also on the quality of alloy used to its cast. Hence, if the melting and pouring parameters could influence the alloy’s properties, what influence they would have on the frequencies of bell’s tone. In the article authors present their own approaches to find answers on that and more questions.