Committee:

Ian Baker, Ph.D. (Chair)  

Geoffroy Hautier, Ph.D. 

Charles Sullivan, Ph.D. 

Jun Cui, Ph.D.

Abstract:

The growing need for electrical power in machines and vehicles comes with it a growing need for critical materials. The current high-performance permanent magnets (PMs) based on rare-earth (RE) elements Nd and Sm cannot escape the problem of raw material cost, geographic scarcity in the earth’s crust, and lack of circular global supply chains. This poses a problem of industrial ecology: can permanent magnets be made from inexpensive, more abundant materials while still meeting comparable performance criteria to RE-PMs? PMs based on the magnetic τ phase of Mn-Al offer a viable alternative to RE PMs. However, years of innovation have not yet achieved real-world performance on par with the theoretical maximums needed to compete with RE PMs. This proposal sets forth a pathway for understanding how the effects of plastic strain and alloying with a ternary element may improve the intrinsic and microstructural characteristics of a Mn-Al PM, bringing it closer to commercialization. 

The key questions this proposal will address are as follows: a) How does the addition of crystalline defects through plastic strain affect the magnetic properties and phase stability of τ Mn-Al? and b) How does the addition of the ternary element, Ti, affect the magnetic properties and phase stability of τ Mn-Al? 

Mn-Al bulk material will be processed using plastic deformation techniques to increase the density of crystalline defects. The τ phase magnetic properties and phase stability will be analyzed and correlated to the strain-induced microstructure and defects. Mn-Al-Ti alloys will be synthesized at multiple compositions to compare how the relative addition of Ti affects the τ phase in terms of both the intrinsic magnetic properties and the microstructure. By separating the two, the mechanisms by which Ti improves the magnetic performance and τ phase stability can be best understood.