Conference Dates

July 17-21, 2016


The field of high entropy alloys (HEAs) is barely 10 years old. It has stimulated new ideas and has inspired the exploration of the vast composition space. Here we give a critical review of this body of work, with the intent of summarizing key findings, uncovering major trends and providing guidance for future efforts. Based on detailed analysis, the following major results emerge. An intense focus is apparent on alloys based on first row transition metal elements. These efforts have discovered an extended, single-phase solid solution phase field and are exploring the extent and properties of this phase field. As a result of this focus, the vast range of complex composition space remains relatively unexplored and still offers a compelling motivation for future studies. Seven distinct alloy families have been reported, and the design of alloy families by selecting elements to achieve a specific, intended purpose is becoming established. A major hypothesis is that configurational entropy in HEAs may favor solid solution phases with simple crystal structures. Detailed analysis of current experiments and calculations does not support this hypothesis. Increasing the number of alloy constituents increases configurational entropy slowly, but increases much more rapidly the probability of including a pair of atoms with interaction energies that are sufficiently negative to overcome configurational entropy. The hypothesis that diffusion may be unusually slow in HEAs is also not supported by the current data. Data for mechanical properties of HEAs will be reviewed and suggestions for new research directions will be offered.

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