Diffusion Quadruple vs Triple: Determining Interdiffusivities for fcc Co–Ni–Ta Alloys

Abstract

Although single-phase diffusion triples have been adopted successfully to deduce interdiffusivities in a much wider composition range than using diffusion couples, recent studies show that diffusion quadruples can further raise efficiency covering an even broader range of compositions than triples. In the present work, two diffusion quadruples of the fcc Co–Ni–Ta alloy system were assembled at 1473 K, allowing for a direct comparison with the former triple scheme. The composition-dependent interdiffusivities were then deduced, and mutually validated by comparing with the results calculated from the triple scheme and the traditional methods (i.e., the Sauer–Freise method and Whittle–Green method). To ensure the universality of the quadruple scheme, one diffusion quadruple was fabricated under universal preparation conditions without strict requirements of the original interfaces. By updating our two-dimensional (2D) numerical inverse scheme, the present quadruple scheme can well handle general cases with both ideal and universal original interfaces. However, since the absolute deviation is not significant and the results obtained by the quadruple scheme are fine-tuning of those from the triple scheme, both the triple and quadruple schemes are acceptable for engineering applications.