A Building Block Approach to Developing a Low-Cost High Strength High Entropy Alloy
Authors:Cody Crosby, Cody Crosby, Aarthi Sridhar
- Lori Bassman, Professor of Engineering , Harvey Mudd College
- Kevin Laws, Senior Lecturer, University of New South Wales
High entropy alloys are multicomponent metallic systems with four or more elements in roughly equiatomic proportions. While researchers have fabricated such alloys that have multiple phases, a single solid solution would greatly enhance the material properties of these alloys. To date, most researchers have picked elements that are close to one another on the periodic table, in the hope that atoms with similar atomic sizes might form a single-phase solid solution. However, using a method that slowly built up to a multicomponent alloy, the formation of a solid solution was optimized at every stage by adding elements with compatible thermodynamic and structural properties. Starting with a binary system of copper and nickel, manganese was first added in 10 at% increments. Using energy dispersive x-ray spectroscopy, the equiatomic ternary, after heat-treating at 900°C, was found to be the most promising. Aluminum was then added to the ternary in 5 at% increments, in the hope that single phase solid solution could be maintained even though the atomic size of aluminum is much larger. The larger atomic size of aluminum should increase the lattice strain and therefore increase the yield strength by impeding dislocation motion. At 20% aluminum, it was found that after significant heat treatment the near-equiatomic quaternary stabilized at solid solution. While work continues on development of a method to alloy zinc to the quaternary alloy, there is a strong focus on illuminating the fundamental principles that govern the formation of these challenging alloys, as the existing parameters of configurational entropy, enthalpies of mixing, and atomic size differences are merely a starting point. On the practical side, the alloy under development has improved mechanical properties while remaining inexpensive for manufacture.