From pinches of electrons to new phases: Martensite morphology modification and hypereutectoid microstructure in Cu-9Al-2Mn-xSn (0.5 ≤ x ≤ 6) alloys

Alloying is a common strategy used for the improvement of Cu-Al alloys and understand its effect on phase equilibria is fundamental to predict the material performance. Samples of arc-melted and heat-treated alloys were subjected to differential scanning calorimetry, X-ray diffraction, Vickers microhardness measurements, and microscopy techniques. Results showed that Sn additions increase the volumetric fraction of β 1 ʹ ordered martensite in microstructure, but also result in the presence of harmful pro-eutectoid γ 1 phase. In this sense, they are more effective than Al and Mn additions for the same purpose, which was attributed to an increase in the average electronic content per atom, since Sn has more electrons in its valence shell. Therefore, valence of alloying elements must be kept in mind during alloy design, since some “pinches of electrons” are enough to disturb phase equilibria. • Effects of Sn additions to the Cu-9Al-2Mn alloy were evaluated after quenching • They caused martensite morphology modification and γ 1 phase formation • Valence of the quaternary addition plays a key role in Cu-Al-Mn alloys design