Grain nucleation and growth behavior of (Cu, Ni)6Sn5 in Sn–10Cu–1Ni alloy under pulse current: An in situ observation

Abstract In situ synchrotron X-ray radiography is used to study the effect of pulse current on the nucleation and growth of (Cu, Ni)6Sn5 intermetallic compounds (IMCs) during the solidification of Sn–10Cu–1Ni (wt.%) alloy. The synchrotron tomography analysis reveals that the (Cu, Ni)6Sn5 exhibits a six-fold snowflake-like 3D morphology. As the density of pulse current increases from 0 to 200 A/cm2, (Cu, Ni)6Sn5 gradually exhibits a direction-dependent morphology and the “self-poisoning” phenomenon caused by gravity segregation is weakened. The competitive growth between the neighboring grains is directly observed. In addition, the Boltzmann function is used as a model for fitting the grain density versus temperature at four different current densities where R2 ≥ 0.995 confirms a good correlation of the model with experimental data. The initial nucleation temperature increases with the increasing current density “j” from 0 to 50 A/cm2, while decreases from 50 A/cm2 to 200 A/cm2. Besides, the maximum nucleation rate Imax monotonically increases with the increasing current density; while the final grain density with j = 200 A/cm2 is less than that with j = 50 A/cm2 because of the short nucleation duration. The results of this study provide an opportunity to achieve the active control of (Cu, Ni)6Sn5 morphology by imposing pulse current.