Design of high-strength refractory complex solid-solution alloys

• Published in: npj computational materials Vol. 4; no. 1; pp. 1 - 8
• Main Authors: Singh, Prashant, Sharma, Aayush, Smirnov, A. V., Diallo, Mouhamad S., Ray, Pratik K., Balasubramanian, Ganesh, Johnson, Duane D.
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 28-03-2018; Nature Publishing Group
• Subjects: 639/301/1023/1026; 639/301/1023/303; 639/301/1034/1037; 639/301/1034/1038; 639/301/119/995; Alloys; Approximation; Characterization and Evaluation of Materials; Chemistry and Materials Science; Coherent potential approximation; Computational Intelligence; Computer simulation; Corrosion resistance; Corrosion resistant alloys; Deformation; Dynamic stability; Electronic properties; Electronic structure; Enthalpy; Entropy; High entropy alloys; High strength alloys; Identification methods; MATERIALS SCIENCE; Mathematical and Computational Engineering; Mathematical and Computational Physics; Mathematical Modeling and Industrial Mathematics; Mechanical properties; Modulus of elasticity; Molybdenum; Nickel; Nickel base alloys; Short range order; Superalloys; Theoretical; Titanium; Zirconium
• DOI: 10.1038/s41524-018-0072-0
• EISSN: 2057-3960

Nickel-based superalloys and near-equiatomic high-entropy alloys containing molybdenum are known for higher temperature strength and corrosion resistance. Yet, complex solid-solution alloys offer a huge design space to tune for optimal properties at slightly reduced entropy. For refractory Mo-W-Ta-Ti-Zr, we showcase KKR electronic structure methods via the coherent-potential approximation to identify alloys over five-dimensional design space with improved mechanical properties and necessary global (formation enthalpy) and local (short-range order) stability. Deformation is modeled with classical molecular dynamic simulations, validated from our first-principle data. We predict complex solid-solution alloys of improved stability with greatly enhanced modulus of elasticity (3× at 300 K) over near-equiatomic cases, as validated experimentally, and with higher moduli above 500 K over commercial alloys (2.3× at 2000 K). We also show that optimal complex solid-solution alloys are not described well by classical potentials due to critical electronic effects.
Solid solutions: screening by electronic structure
Combining first-principle calculations with electronic alloy design criteria lead to the identification of desirable complex alloys. A team led by Duane Johnson at Iowa State University, USA, applied density functional theory to explore the design space formed by five refractory elements (molybdenum, tungsten, tantalum, titanium, and zirconium) and identified optimal molybdenum-rich alloy compositions for high temperature strength and corrosion resistance. By predicting structural properties such as the Young’s modulus as well as the short-range atomic order, a lattice constant identified the global stability of each composition and allowed for the fast screening of the design space to select the best compositions. Both molecular dynamics and experimental testing confirmed the predicted mechanical properties. This electronic structure approach can help optimize complex solution alloys for enhanced mechanical properties.