Ternary Diffusion in a RuAl-NiAl Couple

Abstract

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 Ru-rich and the other Ni-rich, within the diffusion zone. The interdiffusion coefficient, " D Al RuRu varies little with variation in composition, but the interdiffusion coefficient, " D Al NiNi decreases by an order of magnitude from the Ni-rich region to the Ru-rich region. " D Al NiNi is larger than " D Al RuRu in the Ni-rich region by an order of magnitude. The cross coefficients, " D Al NiRu and " D Al RuNi , are both positive. " D Al NiRu is comparable in magnitude to the main coefficient " D AlNiNi in the Ni-rich region; 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.

Creep Deformation Mechanisms in Ru-Ni-Al Ternary B2 Alloys

“…The interdiffusion coefficientD in the range of 5 · 10 -15 to 10 -14 m 2 /s, [16,41] the PoissonÕs ratio v in the range of 0.286 to 0.307, [42,43] and the shear modulus G in between 72 and 82 GPa [42,43] were realistically selected based on the values of NiAl and RuAl. Ten values were evenly selected in the specified range of each variable, and the creep rates were calculated by listing all the possible combinations of these values of the uncertain variables in Eq.…”

“…The diffusion coefficient D s of Ru was estimated to be within 4 to 8 · 10 -18 m 2 /s in Ru-rich AlNi x Ru 1-x alloys. [16] An average jog height h in the range of 30 to 40 nm was estimated based on the jog heights observed in a c-TiAl alloy. [49,50] The average jog spacing k within the range of 200 to 400 nm was considered along with the range of the dislocation density q s at different applied stresses observed by TEM analyses.…”

“…A recent investigation on a ternary diffusion couple assembled with NiAl and RuAl disks revealed that the interdiffusion coefficient for Ni decreases by an order of magnitude from the Ni-rich region to the Ru-rich region and is an order of magnitude larger than the interdiffusion coefficient for Ru in the Ni-rich region. [16] It was further suggested that the atomic mobility of Ni is larger than that of Ru. [16] Therefore, the Ru/Ni ratio of the Ru-NiAl ternary alloys in the NiAl-RuAl B2 phase region plays a key role in determining the rate-controlling creep mechanisms.…”

“…[16] It was further suggested that the atomic mobility of Ni is larger than that of Ru. [16] Therefore, the Ru/Ni ratio of the Ru-NiAl ternary alloys in the NiAl-RuAl B2 phase region plays a key role in determining the rate-controlling creep mechanisms. A higher Ru/Ni ratio results in slower diffusion and a larger resistance to climb and jog dragging during creep, thus giving higher creep resistance.…”

“…Alloys ANR1, ANR4, and ANR5 show a nominally single-phase structure, although dark regions slightly rich in Ni and lean in Ru were observed in ANR4 and ANR5 alloys. The low diffusivity of Ru in the B2 matrix [16] and relatively long diffusion paths make complete homogenization difficult. The ANR2 alloy has a complex structure containing a fine lamellar structure preferentially located around the grain boundaries, which was identified as the Ni 3 Al phase by both XRD and electron diffraction analyses (Figure 4(a)).…”