nfang Li

Formation of amorphous structure in Sn3.5Ag droplet by in situ fast scanning calorimetry controllable quenching

Attributing to sensitive fast scanning calorimetry, combined with focused ion beam and high resolution transmission electron microscopy, we observed the solidification structure of single Sn3.5Ag droplet quenched at controllable rate. Amorphous layers in nanometer adjacent to some Ag3Sn crystals were directly detected. Based on solid state amorphization, a nano diffusion couple between primary formed β-Sn matrix and Ag3Sn intermetallic was put forward. Quenched at 15 000 K/s, the concentration gradient in this diffusion area was up to 109 m−1, which could seriously suppress the growth and further homogeneous nucleation of Ag3Sn, leading to the formation of amorphous structure.

Rapid solidification behavior of nano-sized Sn droplets embedded in the Al matrix by nanocalorimetry

Al-10Sn (wt.%) melt-spun ribbons with nano-sized Sn droplets (20–400 nm in diameter) embedded in the Al matrix and bulk Sn distributed at Al grain boundaries were prepared. Differential fast scanning calorimetry (DFSC) based on nanocalorimetry and thin film technique was successfully applied to investigate the rapid solidification behavior of the embedded nano-sized Sn droplets at cooling rates ranging from 103 to 104 K s−1. Two broad exothermic peaks were observed in the DFSC curves. They were ascribed to the solidification of nano-sized Sn droplets with various catalytic activity factors f(θ). The cooling rate dependence of undercooling of nano-sized Sn droplets has been studied experimentally. The two series of undercooling which correspond to the two exothermic peaks increase slightly with the increases of cooling rate. Furthermore, a theoretical description of the experimental DFSC curves based on classical heterogeneous nucleation theory is developed. It is performed advancing a previously developed approach by assuming a smooth dependence of the droplet mass fraction on contact angle, m(θ), with a double Gaussian distribution during the nucleation process. This modified theoretical model is believed to be relevant also for other related rapid solidification processes.