Interfacial reactions between Sn-Bi alloys of different compositions and Ni substrates at 423 K for different durations were investigated. Only one interfacial phase, Ni 3 Sn 4 , was detected despite the existence of several other intermetallic compounds (IMCs) in Ni-Sn and Ni-Bi binary systems. This observation (only Ni 3 Sn 4 was formed at the interface) was explained as a combination of the driving force for formation of the IMC and diffusion of Ni. The change of Ni 3 Sn 4 layer thickness as a function of annealing time, which obeys a parabolic rule, was further confirmed. The thickness of Ni 3 Sn 4 was also found to decrease with increasing Bi content in the Sn-Bi alloy.

The composition-distance profiles in face-centered cubic (fcc) Ni-Sn alloys at 1173, 1223, 1273, and 1323 K were measured by means of electronic probe microanalysis (EPMA) using Ni/Ni-7.3at.%Sn diffusion couples. Based on the available thermodynamic information and various experimental diffusion coefficients, the atomic mobilities of Ni and Sn in fcc Ni-Sn alloys were assessed as a function of temperature and composition in terms of the CALPHAD method using the DICTRA Ò software package. Optimized mobility parameters are presented. Comparisons between the calculated and measured diffusion coefficients show that most of the experimental information can be reproduced reasonably. The obtained mobility parameters can also predict satisfactorily the composition-distance profiles of the Ni/Ni-7.3at.%Sn diffusion couples determined in the present work.

Based on the thermodynamic parameters and experimental diffusion data in the literature, the atomic mobilities of bcc Ti-Sn alloys are assessed by the CALPHAD method using DICTRA software package, and boundary mobility parameters of hcp Ti-Sn alloys were also given in the work. Compared with the calculated and measured diffusion coefficients of bcc Ti-Sn, most of the experimental data are reproduced well. The composition-distance profiles of Ti/Ti-4.9 at.% Sn diffusion couple at 1223 K for 14.4 ks were also predicted using the assessed mobility parameters. It is hopeful to provide useful guidance for the design of Ti-based alloys.

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