  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
\eta -> \eta + L -> \epsilon + 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.
