A new investigation of the system Ni–Sn

The system Ni–Sn, being one of the key systems for lead-free soldering, has been the subject of intensive investigations in the 1930s and 1940s. The most recent phase diagram assessment as well as various calculations of this system almost exclusively rely on these data. As the assessment seemed to be based on a rather arbitrary selection of experimental data, a new experimental investigation of this system was considered necessary. In this work a new version of the Ni–Sn system was established following a comprehensive survey of existing literature and the investigation of 27 samples. XRD (including high temperature XRD), DTA, EPMA and metallographic examination were performed on these samples annealed at various temperatures. Especially in the region of Ni3Sn considerable differences to existing phase diagram information were recognized. The crystal structure of the Ni3Sn HT-phase was found to be cubic (BiF3-type) by HT-XRD, and the phase transition was determined to be at higher temperature than reported previously. Furthermore a suggestion for the phase transformation in Ni3Sn2 was included. This region of the system was found to be far more complex than hitherto reported, because of the existence of two further incommensurate Ni3Sn2 low-temperature modifications first discovered by Leineweber et al.