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

In this work we present an experimental study of structure and phase stability in ternary Cu-Sn-In alloys around 55 at.% Cu in the temperature range 100^{\circ}C < T < 550^{\circ}C. We have followed in real-time the sequence of phase transformations in succesive heating and cooling ramps, using state-of-the-art neutron powder thermodiffractometry. These experiments were complemented with calorimetric studies of the same alloys. Our results give experimental support to the current assessment of the ternary phase diagram in this composition and temperature range, yielding the sequence of transitions η-> η+ L -> ε+ L with transformation temperatures of 210^{\circ}C and 445^{\circ}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 this technique into a valuable tool for phase diagram studies of emerging lead-free solder candidates.