Grain-Boundary Toughening Mechanisms and Thermal Resistance of Novel Nanoparticles-Strengthened High-Entropy Alloys with Hetero-Lamellar Grain Structures at Intermediate Temperatures

Description

The rapidly growing demand for increased energy efficiency in modern industries like aerospace and power generation necessitates the innovation of advanced alloys with superb thermal-mechanical performances. As the emerging novel metallic materials, the face-centered-cubic (FCC) high-entropy alloys (HEAs) reinforced by high-density coherent L12 (ordered FCC) nanoparticles have attracted intense interest recently, offering significant advantages over many conventional alloys currently in use. Benefiting from the intrinsic ductile nature of the constituent nanophases, together with the coherent interfaces between them, this kind of nanoparticles-strengthened HEAs (NS-HEAs) have been demonstrated with superior strength-ductility combinations from cryogenic to room temperatures. More intriguingly, the excellent coarsening resistance and unique yield strength anomaly behavior (i.e., yield strength increase with increasing temperatures) of the ordered L12 phase render these NS-HEAs highly attractive to elevated-temperatures structural applications with potentially excellent resistance to softening and creep deformation. Unfortunately, most current NS-HEAs in polycrystalline forms usually suffer from serious intergranular brittle fractures at intermediated temperatures, especially at the temperature of 800 °C, which significantly limits their practical use at elevated temperatures. Such a thorny problem has also been frequently encountered in many conventional wrought superalloys. Surprisingly, in our preliminary work, we deliberately developed a novel NS-HEAs with a unique hetero-lamellar grain (HLG) structure, which exhibited exceptionally high resistance to intermediate-temperature embrittlement (ITE). Nevertheless, several fundamental issues remain largely unaddressed and require more in-depth studies in this project. By using multi-scale experimental techniques and theoretical calculations, we aim at systemically investigating the processing-structure-properties relationship of these newly discovered HLG-NS-HEAs at the intermediate temperatures, emphasizing on the intrinsic origins governing the ITE behaviors. The effects of alloy microstructure, testing atmosphere, and strain rate will be quantitatively studied. Moreover, in-depth studies on their thermal resistance including the microstructural stability and creep resistance will also be carried out. The establishment and successful implementation of this project are expected to offer quantitative insights into the intrinsic relationships between the alloy composition, phase structure, grain boundary feature, and associated thermal-mechanical behaviors of such a new class of HLG-NS-HEA. More importantly, the results accomplished here will provide a strong theoretical basis and technical guidance to advance the innovative design of novel high-performance structural materials for elevated-temperature applications. All these research achievements will be crucial to improving engineering reliability and energy efficiency in a broad range of industrial fields, including aerospace, automotive, energy, and other applications.