Ternary Diffusion in a RuAl-NiAl Couple
- PDF / 353,170 Bytes
- 7 Pages / 593.972 x 792 pts Page_size
- 37 Downloads / 199 Views
Basic and Applied Research: Section I
Ternary Diffusion in a RuAl-NiAl Couple K.N. Kulkarni, B. Tryon, T.M. Pollock, and M.A. Dayananda
(Submitted January 19, 2007; in revised form June 22, 2007) A ternary diffusion couple assembled with NiAl and RuAl disks and annealed at 1100 C was examined by scanning electron microscopy and analyzed for concentration profiles by electron microprobe analysis. Complete mutual solid solubility with continuous variations in compositions was observed between the binary B2 aluminides. Ternary interdiffusion coefficients were determined with the aid of a program called MultiDiFlux over two composition ranges, one ~ Al Ru-rich and the other Ni-rich, within the diffusion zone. The interdiffusion coefficient, D RuRu ~ Al decreases by an varies little with variation in composition, but the interdiffusion coefficient, D NiNi ~ Al is larger than D ~ Al in order of magnitude from the Ni-rich region to the Ru-rich region. D NiNi RuRu Al Al ~ ~ the Ni-rich region by an order of magnitude. The cross coefficients, D and D , are both NiRu RuNi ~ Al in the Ni-rich region; ~ Al is comparable in magnitude to the main coefficient D positive. D NiRu NiNi hence, Ni interdiffusion flux is enhanced down a Ru concentration gradient but decreased against it. Similarly, Ni interdiffusion is reduced down Al gradients. Characteristic depth parameters calculated for Ni and Ru are larger on the NiAl side than on the RuAl side. Approximate calculations of cumulative intrinsic diffusion fluxes past a Kirkendall plane suggest that the atomic mobility of Ni is larger than that of Ru.
Keywords
modeling, nickel aluminide, ruthenium aluminide, ternary diffusion
1. Introduction Ru additions to Ni-base superalloys and thermal barrier coating (TBC) systems have recently been investigated to increase the high-temperature capabilities of these systems.[1-7] Specifically for TBCs the system life may be prolonged if the creep resistance of NiAl-based bond coats is improved.[8,9] Thus, creep-resistant Ru-containing bond coats for thermal barrier coating systems are of interest, particularly since the creep strength of bulk RuAl has been shown to be substantially higher than that of bulk NiAl.[6] The ternary Ru-Al-Ni system forms the basis of this study. Since NiAl and RuAl both have B2 crystal structures, phase equilibria and the possibility of a miscibility gap in the ternary system have been of interest.[10-17] Based on a recent experimental study of the Ru-Al-Ni ternary system at the temperatures of 1000 and 1100 C,[17] the two B2 phases form a continuous solid solution. A Ru-Al-Ni isotherm at 1100 C is shown in Fig. 1. The lattice parameters for the binary RuAl and NiAl phases are reported[18] to be 0.299 and 0.289 nm, respectively. Since the lattice mismatch between NiAl and RuAl is quite small, K.N. Kulkarni and M.A. Dayananda, School of Materials Engineering, Purdue University, West Lafayette, IN, USA; B. Tryon and T.M. Pollock, Department of Materials Science and Engineering, University of Michigan, Ann Arbor, M
Data Loading...
