Crystallographic characterization of Cu-In alloys in the 30-37 at.% In region

Abstract

The Cu-In-Sn system is one of the Pb-free options to replace conventional Pb-Sn alloys in electronic industry. However, controversies still exist regarding some regions of the equilibrium phase diagram of the Cu-In-Sn ternary and also of the Cu-In and Cu-Sn binary systems. One of the most controversial fields of the Cu-In binary phase diagram lies between ~33 and 38 at.% In and temperatures ranging from 100 up to 500 °C. In this work, binary Cu-In alloys, with 30-37 at.% In nominal compositions and annealed at two different temperatures (i.e. 300°C and 500°C) for a long period (i.e. 7 months) were characterized by scanning electron microscopy (SEM), wavelength dispersive spectroscopy (WDS) and X-ray diffraction (XRD). Three phases exist over the 33-38 at.% In composition range, namely the phase A at high temperatures and the B and C phases at low temperatures. These three phases can be described as superstructures of the hexagonal phase h (Cu2In) and differ, although slightly, from those previously reported in the literature. In addition, it has been demonstrated that even conventional XRD allows to unequivocally distinguishing between these phases despite their similar crystal structure.