Mechanism-oriented design strategies for the development of new multi-principal element alloys using high-throughput screening methods

• Mechanismen-orientierte Designstrategien für die Entwicklung neuer Mehrkomponentenlegierungen mittels Hochdurchsatzmethoden

Kies, Fabian Martin; Krupp, Ulrich (Thesis advisor); Haase, Christian (Thesis advisor); Glatzel, Uwe (Thesis advisor)

Aachen : RWTH Aachen University (2023)
Dissertation / PhD Thesis

Dissertation, Rheinisch-Westfälische Technische Hochschule Aachen, 2023, Kumulative Dissertation

Abstract

Multi-principal element alloys (MPEAs) are a new alloy class, which started to gain popularity in 2004. The key difference to conventional alloys is a lacking base element, which allows for high degrees of freedom in their design. Property combinations not yet seen in conventional alloys were proposed, and even though research interest increased substantially until now, few MPEAs were found improving over conventional concepts. To make MPEAs viable, multiple metal physical phenomena must be exploited simultaneously, which is done with mechanism-oriented design strategies. Due to the high complexity of the compositional space, however, rigorous and reliable methods are still missing or increasingly difficult. Additionally, theoretical and experimental screening strategies are readily being researched, but are still in their infancy and rarely combined. Therefore, a mechanism-oriented MPEA design strategy was developed combining theoretical and experimental methods, which consider the low maturity of the available theoretical methods and optimizes the experimental methods accordingly. The strategy was developed in three phases: proof of concept on high-Mn steels (HMnSes), transfer to MPEAs and optimization. The focus was set on improving the room temperature strength-ductility trade-off of MPEAs in the AlCCoFeMnNi system. Theoretical screening was carried out by calculation of phase diagrams (CALPHAD) and density functional theory (DFT) approaches, while elemental powder blend additive manufacturing (AM) techniques were applied experimentally. The developed design strategy showed that potentially exceptional MPEAs should be limited in multiple steps to obtain the most optimal alloy of a given system. A screening region is recommended by combining multiple theoretical methods, where mechanism-oriented matrix and precipitate design should take place. A potent shortcut is basing the initial concept on already established alloys, as mechanisms are transferred to the MPEA. Experimental screening should be divided into two steps for increased efficiency. First, surface screening using fast characterization methods are used to further limit potentially exceptional candidates. Detailed screening is left to the most interesting candidates, which ensures low experimental load and enables the derivation of properties by using similarities found in surface screening. The approach was used on two alloys, where the strength-ductility trade-off was effectively improved.

Institutions

• Division of Materials Science and Engineering [520000]
• Chair of Materials Engineering of Metals and Department of Ferrous Metallurgy [522110]