Ordering-mediated local nano-clustering results in unusually large Hall-Petch strengthening coefficients in high entropy alloys

Abstract

This paper reports a dramatic increase in the grain boundary strengthening or Hall-Petch coefficient, K, by systematically investigating the effect of Al addition on tensile yield strength in CoFeNi and CoCrFeNi high entropy alloys (HEAs) or complex concentrated alloys (CCAs). Additionally, detailed atom probe tomography (APT) revealed a high number density of Ni-Al rich nano-clusters in the Al_0.3CoFeNi and Al_0.3CoCrFeNi HEAs/CCAs, which can be rationalized based on the strong chemical ordering tendency between these elements. Consequently, the huge increase in K value can be attributed to the additional stress required for overcoming coherency strain fields arising from these nano-clusters.

GRAPHICAL ABSTRACT

IMPACT STATEMENT

This paper reports that the Hall-Petch co-efficient (K) dramatically increase when Al is added to CoFeNi/CoCrFeNi alloys. Such a trend is attributed to the ordering mediated nano-clustering in Al containing HEA/CCAs.

KEYWORDS:

• Hall-Petch strengthening
• high entropy alloys
• complex concentrated alloys
• clustering
• ordering

Acknowledgements

The work was supported by cooperative agreement between the US Army Research Laboratory and the University of North Texas (grant number W911NF-16-2-0189), and the US Air Force Office of Scientific Research (grant number FA9550-17-1-0395). The authors acknowledge the Materials Research Facility (MRF) at the University of North Texas for use of microscopy facilities.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Data availability

The data that support the findings of this study are available from the corresponding author upon reasonable request.

Additional information

Funding

The work was supported by cooperative agreement between the US Army Research Laboratory and the University of North Texas [grant number W911NF-16-2-0189], and the US Air Force Office of Scientific Research [grant number FA9550-17-1-0395]. The authors acknowledge the Materials Research Facility (MRF) at the University of North Texas for use of microscopy facilities.