Revealing and tailoring mechanical behaviors of multi-principal element alloys under extreme thermomechanical conditions
Abstract
The objective of the proposed research aims at revealing extraordinary mechanical behaviors enabled by short-range order in multi-principal element alloys (MPEAs), with the goal of improving material strength and toughness via tuning the degree of local ordering under extreme thermomechanical environments. MPEAs, or complex concentrated alloys, including medium-/high-entropy alloys that comprise multiple principal elements in high concentration, are typically considered to be ideal solid solutions. This ideal random mixing in MPEAs, however, may only be possible at high temperatures. As the temperature decreases, the enthalpic contribution to total free energy may become predominant, leading to chemical inhomogeneities such as local chemical order (LCO) and segregation. Interestingly, the nanoscale chemical ordering analogous to coherent nanoprecipitate largely impacts the mechanical behaviors of MPEAs. This suggests that the degree of local ordering, which can be tailored under thermomechanical conditions, provides a new avenue for tuning mechanical behaviors of MPEAs. In this proposed project, we will reveal and demonstrate the role of LCO on strength, hardness, and deformation homogeneity (ductility) in MPEAs under combined thermal and mechanical loading conditions. The specific goals are to address the following scientific yet technically relevant questions: (1) How does the degree of local chemical order influence mechanical strength and deformation behaviors of MPEAs? (2) Can LCO promote extra slip and twinning processes at high stress and high strain rate to accommodate impact loading, improving material resiliency under extreme conditions? (3) What are the kinetic processes resulting in a great range of LCO and mechanical properties? We hypothesize that, by exploiting the access energy from extreme thermomechanical environments, the MPEAs can attain extraordinary mechanical strength and toughness, resulting from local chemical ordering that brings massive hardening mechanisms. This central hypothesis will be tested in CrCoNi alloy (a medium entropy alloy with an extraordinarily high toughness) using a set of computational techniques, including molecular dynamics (MD), Monte Carlo (MC), accelerated MD, climbing image nudged elastic band (NEB) method. These computational tools will reveal mechanistic insight into how the MPEAs with different degrees of local ordering respond in extreme thermomechanical environments, laying the groundwork for exploiting the strong and tough MPEAs in stress-adaptive structures.
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- Jun 25, 2021
- Source ID
- W911NF2110150
Entities
People
- Penghui Cao
Organizations
- Army Contracting Command
- United States Army
- University of California, Irvine