Abstract
Discoveries of new multi-principal element alloys (MPEAs) with outstanding performance have been challenging due to the large complexity of the compositional space. Many existing highly alloyed steels already incorporate MPEA concepts and detailed research is readily available, which can be utilized for a more efficient design approach. Inspired by this consideration, Ni- and Co-additions to the Al14.6C4.9Fe53.6Mn26.9 (at%) high‑manganese steel were assessed to introduce B2-precipitates in addition to the κ-carbides to increase strength. Thermodynamic screening in the Al-C-Co-Fe-Mn-Ni system was performed with a custom calphad database and combined with experimental screening to identify novel MPEAs with enhanced mechanical properties. The selected MPEAs were produced by thermo-mechanical processing and the mechanisms active during annealing and deformation were investigated experimentally. The modification with Co did not result in the formation of B2-precipitates and improved mechanical properties. The Ni-added MPEA, Al14.7C4.7Fe49.9Mn26.4Ni4.2, revealed significant precipitation and dispersion hardening by nanoscale κ- and B2-phases combined with excellent strain hardening capacity due to slip band refinement-induced plasticity (SRIP). A combination of 1 to 1.2 GPa yield strength (21.3 % increase) with a total elongation of 20 to 10 % was achieved. The chosen methodology was efficient in the design of a novel MPEA with an improved strength-ductility synergy.
Highlights
Gained much attention in research during the past two decades [1,2]
These alloys often form non-ordered simple crystal structures, such as face-centered cubic or body-centered cubic [3,4]. The latter is usually explained by high configurational entropy promoting the formation of simple crystal structures at high temperatures, and sluggish diffusion preventing the transformation into more complex phases at low temperatures [5]
As the alloy concept relies on multiple principal elements, multi-principal element alloys (MPEAs) allow for high degrees of freedom in their chemical and microstructural design
Summary
Gained much attention in research during the past two decades [1,2]. Instead of relying on one base element, MPEAs are loosely defined as alloys consisting of multiple elements, each with a fraction between 5 and 35 at% [3]. As the alloy concept relies on multiple principal elements, MPEAs allow for high degrees of freedom in their chemical and microstructural design To explore this wide alloy space, several approaches have been employed to screen MPEAs. To explore this wide alloy space, several approaches have been employed to screen MPEAs These were mostly based on CALPHAD-method (CALculation of PHAse Diagrams) [6,7,8] or ab initio [9,10,11,12] calculations combined with conventional [6] or high-throughput [11,13,14] manufacturing methods. The developed CALPHAD database was employed to reveal suitable alloying elements that promote the concurrent formation of κ-carbides and B2-phase in an fcc-based MPEA. Both Ni and Co were identified as suitable candidates that enable the formation of the B2-phase without suppressing κ-carbides. The applicability of the proposed methodology for designing MPEAs based on highly alloyed steel concepts and the underlying materials mechanisms are critically discussed
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