Abstract
We develop a strategy to design and evaluate high-entropy alloys (HEAs) for structural use in the transportation and energy industries. We give HEA goal properties for low (≤150 °C), medium (≤450 °C) and high (≥1,100 °C) use temperatures. A systematic design approach uses palettes of elements chosen to meet target properties of each HEA family and gives methods to build HEAs from these palettes. We show that intermetallic phases are consistent with HEA definitions, and the strategy developed here includes both single-phase, solid solution HEAs and HEAs with intentional addition of a 2nd phase for particulate hardening. A thermodynamic estimate of the effectiveness of configurational entropy to suppress or delay compound formation is given. A 3-stage approach is given to systematically screen and evaluate a vast number of HEAs by integrating high-throughput computations and experiments. CALPHAD methods are used to predict phase equilibria, and high-throughput experiments on materials libraries with controlled composition and microstructure gradients are suggested. Much of this evaluation can be done now, but key components (materials libraries with microstructure gradients and high-throughput tensile testing) are currently missing. Suggestions for future HEA efforts are given.
Highlights
High entropy alloys (HEAs) are a new effort in materials science and engineering
A relatively small number of high-entropy alloys (HEAs) systems currently receive a major portion of attention, and we propose the exploration of an expanded range of HEAs
This analysis gives a general expectation for the probability that compounds may be suppressed in HEAs. These results are consistent with a study of the stability of CoCrFeMnNi with various substitutional elements, where it was concluded that Hmix in non-ideal solutions and of competing compounds must be considered in the phase stability of HEAs [8]
Summary
High entropy alloys (HEAs) are a new effort in materials science and engineering. The first publications appeared not quite 10 years ago [1,2], and HEAs are being considered for a wide range of functional and structural applications [3]. There have been no studies to establish effectiveness of solid solution hardening in creep loading of HEAs. The highest strength conventional metals and alloys used at high temperatures almost always rely on the controlled distribution of a second phase. Given the effectiveness of particle strengthening, we propose expanded HEA efforts to include the intentional addition of second phases As with any new effort, the excitement of new ideas and results generates a dynamic exchange—and a little debate Each of these discussions draws on historical expertise in the exploration, characterization and development of structural metals for high temperature applications
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