Neutron diffraction study of stability and phase transitions in Cu-Sn-In alloys alternative Pb-free solders

Abstract

In this work, we present an experimental study of structure and phase stability of ternary Cu-Sn-In alloys around 55 at. Cu in the temperature range 100°C T 550°C. We have followed the real-time sequence of phase transformations in succesive heating and cooling ramps, using state-of-the-art neutron powder thermodiffractometry, complemented with calorimetric studies of the phase transitions. Our results give experimental support to the current assessment of the ternary phase diagram in this composition and temperature range, confirming the sequence of transitions η → (η L) → ( L) with transformation temperatures of 210°C and 445°C, respectively. The use of neutrons allowed to overcome common difficulties in phase identification with powder XRD due to absorption and preferred orientation issues. Even the transitions to liquid phases could be successfully identified and monitored in situ, turning the neutron thermodiffraction technique into a valuable tool for phase diagram studies of emerging lead-free solder candidates.