Papers by Author: C.G. Lee

Abstract: The Multiple-Marker (M-M) method is useful because it enables the determination of the intrinsic diffusion coefficients not only at the Kirkendall marker position but also at places where the M-M are located. However, the analysis is not applicable to the alloys with variable molar volume. In this work, a new graphical method that is applicable to the alloys with variable molar volume is proposed.

Abstract: In general, only one Kirkendall plane can be seen in a diffusion couple. However, bifurcate or trifurcate Kirkendall planes have been reported in Ti/TiAl3 or Co/CoSi2 multi-phase diffusion couples (M-couple) [1,2]. The authors [3] have previously shown a numerical technique to analyze the movement of multiple markers (M-M) embedded in a M-couple taking the molar volume change effect to the diffusion direction into account. Using this technique, one can visualize the places where vacancies (lattice planes) are annihilated or generated in the couple. Here, we try to demonstrate the bifurcate or trifurcate Kirkendall planes in the M-couple and clarify the limited conditions of bifurcate or trifurcate Kirkendall planes by using this numerical technique.

Abstract: Reaction diffusion in liquid Pb free solder- and solid Pb free solder- pure Cu systems has been investigated in the temperature range between 397 K and 563 K. The Pb free solder of which composition is 95.7 mass% Sn, 2.8 mass% Ag, 1.0 mass% Bi and 0.5 mass% Cu and 99.99 mass% oxygen free Cu has been used. In the liquid Pb free solder-pure Cu system, as soon as the solder melted down, an intermetallic compound phase formed preferentially, and grew with increasing diffusion time. Only the phase exists in the experimental time up to 120 seconds. The layer thickness of the phase obeyed the parabolic law. On the other hand, in the solid Pb free solder-pure Cu system two intermetallic compounds  phase and ’ phase form and grew with increasing diffusion time, although the  phase forms after an incubation time at low temperature. The layer thickness of these intermetallic compounds obeyed the parabolic law. The growth rate of ’ phase is greater than that of the  phase. The growth kinetics of the intermetallic compounds and the diffusion behavior in the ’ phase have been investigated.

Abstract: The movement of multiple markers (M-M) embedded in a multiple phases diffusion couple (M-couple) has been numerically analyzed for binary two phases models taking the molar volume change effect to the diffusion direction into account. From the results obtained by this analysis the places where vacancies are annihilated or generated can be visualized. It has been clarified that a part of M-M is necessarily shown by a linear line due to parabolic movement of the inter-phase interface. Some other interesting results obtained in this study will be reported.

Abstract: Oxidation resistance of TiAl3, one of the candidates of coating materials for high temperature structural materials such as Ti3Al and TiAl, has been studied. Specimens were prepared by forming TiAl3 in Al/Ti/Al reaction diffusion couples at 923 K and then TiAl3 layer was exposed to air by dissolving Al plate in a 1N NaOH solution. The obtained TiAl3/Ti/TiAl3 couples were annealed in air in the temperature range from 1173 K to 1468 K. The oxidation rate was compared with that determined by using bulk TiAl3. The present data show a bend on the Arrhenius plot of parabolic phase growth rate constant, k2, at 1323 K. Above 1323K, the constant coincides well with the extrapolated values of bulk data while the value in the lower temperature range is larger than that of bulk specimens. During the oxidation experiments, intermetallic compounds Ti3Al, TiAl and TiAl2 were formed between Ti and TiAl3. Interdiffusion coefficients in the Ti3Al, TiAl phases determined from these diffusion couples are more than one order of magnitude larger than the interdiffusion coefficients determined by previous investigators from single-phase diffusion couples but coincide with the coefficients determined from multi-phase diffusion couples. This difference between interdiffusion coefficients has been discussed and explained by the effect of boundary diffusion in the diffusion layers formed in the multi-phase diffusion couples.