Papers by Keyword: Interdiffusion Coefficients

Abstract: The enhancement of interdiffusion coefficients in bulk Ti-Mo alloy system by the SPS/FAST process was investigated at 1000°C for 8hrs and at 1200°C for 4hrs. During annealing, the current density of the SPS was maintained at an RMS of 188 A/cm² for the sample annealed at 1000°C and 177 A/cm² for the sample annealed at 1200°C and the average heating rate was 200 K/min. The elemental concentration of Ti and Mo across the interdiffusion region was measured using electron probe microanalyzer (EPMA) and the resulting concentration vs distance profiles applied in evaluating the interdiffusion coefficients using the Den-Broeder and the analytical methods. The interdiffusion coefficients calculated using the two methods were then compared in order to ensure accuracy and reliability. Possible enhancement of the diffusion process in SPS was established by comparing interdiffusion coefficients obtained from SPS annealing to those obtained from the literature for the same alloy and annealing temperature but for which no electric current was flowing through the sample. The results showed that interdiffusion coefficients evaluated using the Den-Broeder method were closely similar to those evaluated using the analytical method. The results also showed that the interdiffusion coefficients measured in the presence of an electric current were significantly higher than those obtained from traditional annealing methods. This enhancement can be attributed to increased vacancy concentration and defect mobility facilitated by the electric current while flowing through the Ti-Mo sample.

Abstract: Bond coats play a vital role in multi-layered thermal barrier coatings (TBCs), commonly made of B2 (Ni, Pt)Al. However, the presence of platinum (Pt) makes the bond coats costly. To reduce the overall cost and enhance the working temperature of TBCs, Pt can be partially or completely replaced by ruthenium (Ru). For the development of Ru-based bond coats, understanding the interdiffusion behavior of (Ni, Ru)Al is essential. In the present work, the interdiffusion behavior in the single B2 phase of the ternary (Ni, Ru)Al system was studied at 1100 °C using the diffusion couple technique. Experimental concentration profiles were obtained using an Electron Probe Micro-Analyzer, which was further fitted and analyzed for interdiffusion fluxes by utilizing the MultiDiflux software. Kirkaldy's approach was employed to determine the interdiffusion coefficients in the ternary B2 (Ni, Ru)Al system.

Abstract: nterdiffusion coefficients in α2-Ti3Al and γ-TiAl of conventional TiAl and TiAl-8Nb alloy were measured at the temperature ranging from 1273K to 1523K. Single-phase diffusion couples were employed, and the concentration profiles of Al after annealing were measured by an electron probe microanalyzer (EPMA), and the interdiffusion coefficients were calculated according to the Boltzmann-Matano method. The results showed that there was no significant concentration dependence of interdiffusion coefficients for all the alloys with various phases, and the values of interdiffusion coefficients covered three orders of magnitude (E-17-E-14) with the increase of temperature according to Arrhenius law. In α2-Ti3Al and γ-TiAl phase of conventional TiAl alloys, the pre-exponential factor and activation enthalpy were D0=3.95×10-5m2s-1,Q=276KJmol-1 ;D0=7.26×10-5m2s-1,Q=275KJmol-1 respectively. The pre-exponential factor and activation enthalpy were D0=4.54×10-6m2s-1, Q=244KJmol-1 in γ-TiAl phase of TiAl-8Nb alloys. However, the temperature dependence of interdiffusion coefficients in α2-Ti3Al of TiAl-8Nb alloys did not follow Arrhenius laws very well. With the addition of Nb, the interdiffusion coefficients increased significantly in α2-Ti3Al, but changed slightly in γ-TiAl at high temperature.

Abstract: A method has been developed for calculating diffusion profiles in ternary systems by using effective interdiffusion coefficients of components and Boltzmanns solution for diffusion equation with variable diffusion coefficient. Using this method the concentration profiles for several diffusion couples in the systems Fe-Co-Ni and Cu-Fe-Ni are calculated as examples and some peculiarities of these calculations are discussed, particularly, how to solve some possible difficulties, which may sometimes arise at calculation procedures. It is shown that having the data on effective interdiffusion coefficients and their concentration dependence for at least two components in a ternary diffusion couple, the concentration profiles for all three components can be calculated with good accuracy.