Creep and Magnetism of the CoCrFeNiMn High Entropy Alloy

An equiatomic quinary alloy, CoCrFeMnNi, which crystallizes as a single FCC phase and exhibits apparent thermodynamic stability in a wide temperature range [1], has been investigated as a model for high configurational entropy system. Understanding creep in such compositionally complex alloys is important because controversies still exist concerning their classification into Class I and Class II creep behaviours [2]. Tensile and compression creep tests were performed at temperatures between 873 and 1073 K in a range of applied stresses. Microstructures were investigated using advanced SEM and TEM techniques. Results suggest that the Cantor alloy obeys a phenomenological Norton law with the stress exponent n=3 and thus exhibits a Class I creep behaviour in a wide range of external conditions. These macroscopic characteristics and the associated microstructural evolution are discussed in a light of current creep models.

In the second part, we present first ever experimental data on magnetic transitions in the investigated quinary system. A cooling below about 90 K freezes magnetic moments carried by individual atoms in a spin-glass state. A second magnetic transition of a ferromagnetic type is detected at 40 K. A field-assisted cooling into the temperature regime below 40 K results in a systematic vertical shift of hysteresis curves. This interesting new phenomenon is attributed to stable configurations that local magnetic moments form in the first co-ordination group of Mn atoms.

References

1. F. Otto et al., Acta Mater. 61, pp. 5743 - 5755 (2013).

2. O. D. Sherry and P. M. Burke, Prog. Mat. Sci. 13, 323 - 390 (1968).

Acknowledgement. This research was supported by CSF under the contract no. 14-22834S and by the U.S. Department of Energy, Basic Energy Sciences, Materials Sciences and Engineering Division (alloy preparation).

 

Institution: 

Institute of Physics of Materials, Academy of Sciences of the Czech Republic

Date: 
Thursday, November 16, 2017 - 15:00
Speaker: 
Prof. Antonín Dlouhý