Diffusion in high-entropy alloys

An introductory sentence about "sluggish diffusion" in high-entropy alloys is nowadays almost a mandatory statement for any related publication and a common wisdom, although no direct tracer data existed until very recently. In this report we will overview the results of radiotracer experiments on atomic diffusion in the CoCrFeNi and CoCrFeMnNi high-entropy alloys [1, 2]. The measurements are performed in single phase (FCC solid solution) equiatomic compositions and for all constituent elements in an extended temperature interval from 800°C to 1150°C. Two basic contributions are systematically observed for the coarse-grained (grain size above 300 mm) polycrystalline alloys, which are tentatively attributed to the bulk and grain boundary diffusion paths. In order to prove these findings, critical measurements are performed on single crystals and bi-crystals of the equiatomic CoCrFeMnNi alloy grown by the Bridgeman method from the melt. It is found that atomic diffusion in high-entropy alloys is not sluggish at all.

Financial support of the Deutsche Forschungsgemeinschaft DFG, grant DI 1419/13-1, and of RSF Grant No. 16-19-10193 is acknowledged.

[1] Vaidya M., Trubel S., Murty B.S., Wilde G., Divinski S.V., Ni tracer diffusion in CoCrFeNi and CoCrFeMnNi high entropy alloys, JALCOM 688 (2016) 994-1001.

[2] M. Vaidya, K.G. Pradeep, B.S. Murty, G. Wilde, S.V. Divinski, Grain boundary diffusion of Ni in CoCrFeNi and CoCrFeMnNi high entropy alloys, in preparation.