Bifurcation of the Kirkendall marker plane and the role of Ni and other impurities on the growth of Kirkendall voids in the Cu–Sn system

Abstract

The presence of bifurcation of the Kirkendall marker plane, a very special phenomenon discovered recently, is found in a technologically important Cu-Sn system. It was predicted based on estimated diffusion coefficients; however, could not be detected following the conventional inert marker experiments. As reported in this study, we could detect the locations of these planes based on the microstructural features examined in SEM and TEM. This strengthens the concept of the physico-chemical approach that relates microstructural evolution with the diffusion rates of components and imparts finer understanding of the growth mechanism of phases. The estimated diffusion coefficients at the Kirkendall marker planes indicates that the reason for the growth of the Kirkendall voids is the nonconsumption of excess vacancies which are generated due to unequal diffusion rate of components. Systematic experiments using different purity of Cu in this study indicates the importance of the presence of impurities on the growth of voids, which increases drastically for ≥ 0.1 wt.% impurity. The growth of voids increases drastically for electroplated Cu, commercially pure Cu and Cu(0.5 at.%Ni) indicating the adverse role of both inorganic and organic impurities. Void size and number distribution analysis indicates the nucleation of new voids along with the growth of existing voids with the increase in annealing time. The newly found location of the Kirkendall marker plane in the Cu 3 Sn phase indicates that voids grow on both the sides of this plane which was not considered earlier for developing theoretical models.

Development of different methods and their efficiencies for the estimation of diffusion coefficients following the diffusion couple technique

“…It should be noted here that a different value of this ratio was reported in Ref. [16], which was an average of data estimated at different locations in different diffusion couples, compared to the data reported in this study estimated based on the micrograph, as shown in Figure 4a.…”

“…Now we compare the efficiencies and difficulties of estimation of the data utilizing the growth of the product phases, as shown in Figure 4a, in the Cu-Sn system. The Cu/Sn diffusion couple was annealed at 200 °C for 81 hrs (i.e., 2 = 2×81×3600 s) in which two phases Cu3Sn and Cu6Sn5 grows in the interdiffusion zone [16]. The average thicknesses of the phases are estimated as 3.5 m (= ∆ 3 ) for Cu3Sn and 13 m (= ∆ 6 5 ) for Cu6Sn5.…”

Li‐Rich Li[Li1/6Fe1/6Ni1/6Mn1/2]O2 (LFNMO) Cathodes: Atomic Scale Insight on the Mechanisms of Cycling Decay and of the Improvement due to Cobalt Phosphate Surface Modification

“…As will be shown by the next set of figures, this contrast corresponds to porosity in the material, which may be on the surface and/or internal. We argue that these are Kirkendall‐type of voids, associated with asymmetric diffusional flux of elements out of the cathode.…”

The Role of Ultrafine Crystalline Behavior and Trace Impurities in Copper on Intermetallic Void Formation

“…This means that bifurcation of the initial Kirkendall plane will occur and each phase should have its own Kirkendall plane Kε and Kη', which has also been experimentally observed. 21 Kirkendall planes have been shown to be stable or unstable. If a trace marker experiment results in a line of markers this indicates a stable Kirkendall plane, however if markers are distributed throughout a phase it is unstable.…”