Near room-temperature formation of Cu3Sn: In-situ synchrotron X-ray diffraction characterization and thermodynamic assessments of its nucleation

Abstract

The fabrication of Cu3Sn at near room temperatures and atmospheric pressure remains out of reach. We propose a novel concept to address this challenge by exploiting both the classical nano-island model for dealloying and the nanocurvature effect on nucleation, in conjunction with bespoke precursor alloy design. In-situ synchrotron X-ray diffraction (XRD) confirmed significant formation of Cu3Sn at both 70°C and 55°C in 180 min via a dealloying-realloying process in the designed precursor alloy Al67Cu18Sn15, compared with much slower formation at 125°C by conventional approaches. Furthermore, Cu3Sn formed just 10 min after Cu6Sn5 emerged at 70°C, being two orders of magnitude faster than in Cu/Cu6Sn5 diffusion couples at 125°C. The energy barrier to the formation of a lenticular Cu3Sn nucleus on Cu6Sn5 nanocaps was assessed systematically using the CALPHAD approach through the initial driving force (DF) concept and DF-plateau method. The predictions were benchmarked against diffusion couple studies, which fully supported the experimental results. In addition, the in-situ synchrotron XRD data on phase evolution was analysed in detail using the well-established Johnson-Mehl-Avrami-Kolmogorov (JMAK) model, which provided further fundamental support to our conceptual design. The concept and methodology demonstrated are expected to be applicable to the fabrication of other challenging materials.