Plastic Deformation Stability and Hardening Behavior of Complex High-entropy Alloys (HEAs) with Innovative Multi-component Nanoparticles

Description

High-entropy alloys (HEAs), as the newly emerging materials, show a promising prospect to overcome the performance limitation of conventional structural materials. As demonstrated in our preliminary results, coherent precipitation of multi-component nanoparticles (MCNPs) based on the face-centered-cubic (FCC) HEAs offers a highly effective strategy to achieve a superb strength-ductility combination. These elaborately designed L12-type MCNPs can not only significantly strengthen the alloys, but also simultaneously ductilize them with an extraordinary plastic stability. This unusual discovery is remarkably different from that of traditional materials. However, some critical issues involving these innovative MCNPs and the associated mechanical behaviors remain to be clarified. In this proposed research, we aim at three scientific aspects for an in-depth understanding of these novel HEAs: (1) the intrinsic structural features of the MCNPs and their impacts on the macro/microscopic deformation mechanisms; (2) the thermal stability of the MCNPs and the mechanical performance of the novel HEAs at elevated temperatures; and (3) the intrinsic mechanical behaviors and environmental brittleness of the bulk L12alloys.Firstly, selected HEAs based on the Fe-Co-Ni-Cr-Al-Ti system will be chosen as the model materials for generating various MCNPs embedded in the FCC matrix. The intrinsic chemistry and lattice misfit of the MCNPs will be carefully determined by atom probe tomography (APT) coupled with transmission electron microscope (TEM) and X-ray diffraction (XRD) methods. Subsequently, the tensile properties will be determined experimentally, and dislocation evolutions in the deformed specimens will be characterized by TEM and neutron diffraction. The critical features of these MCNPs for controlling the deformation instability in precipitation-hardening HEAs will be clearly elucidated.Secondly, we plan to systematically investigate the phase stability of the MCNPs, including the phase transformation and kinetic coarsening behaviors under long-term thermal exposures. Multi-scale tests will also be conducted to critically evaluate their mechanical properties at elevated-temperatures, including the creep and oxidation resistance.Finally, we intend to determine the intrinsic mechanical properties of the bulk multicomponent L12alloys, especially the environmental brittleness. Some selected L12alloys with different compositions will be prepared and tested under various testing atmospheres.The successful implementation of this proposal will lead to a comprehensive understanding of the intrinsic correlation between the innovative MCNPs and deformation mechanisms. Of particular importance, the output results can provide us an effective guidance for the accelerated design of novel precipitation-hardening HEAs with superior mechanical properties for engineering applications.