Executive Summary : | The development of ultra-strong materials that are ductile and cost-effective is highly desired for various structural applications. The increase in material strength reduces the weight of structural components; thereby increasing the fuel efficiency and reducing the environmental hazard without compromising on the safety. High entropy alloys (HEAs) have gained much research attention due to their wide scope of composition stemming from their distinctive alloy design approach. This distinct design approach has been progressing since the discovery of HEAs. In this regard, Fe-based medium entropy alloys (Fe-MEAs) have been gaining a lot of research interest to reduce the cost and utilize the transformation induced plasticity (TRIP) and twinning induced plasticity (TWIP) effects to demonstrate superior tensile properties at room and cryogenic temperatures. In this proposed work, maraging characteristics from steel will be explored in Fe-MEAs. The proposed study aims to develop a new maraging medium entropy alloy that exhibits ultra-high strength (over 2 GPa) with reasonable ductility and good fracture toughness. As a first step, a set of compositions will be designed based on the literature on maraging steels and Fe-MEAs. Thermo-Calc and rapid experimental screening throughput will be utilized to narrow down the compositions. A preliminary microstructural characterization and hardness test will be performed to verify the maraging characteristics. Upon optimizing the composition, a detailed microstructural characterization will be performed after solutionizing, quenching, and age hardening treatments to understand the martensite and precipitate characteristics using a transmission electron microscope (TEM) and electron backscattered diffraction techniques (EBSD). Besides, precipitate evolution and other microstructural evolution, such as austenite reversion with aging treatment, will be investigated. In-situ transmission electron microscopy will be exploited to understand the nucleation, growth, and kinetics of precipitation and austenite reversion. A detailed tensile behavior and fracture toughness with a different fraction of precipitates, precipitate size, and austenite fraction will be investigated, and the obtained properties will be correlated with the microstructure. Post-deformation microstructural characterization will be carried out to understand the strengthening and deformation mechanisms. It is expected that such a novel alloy design concept with superior mechanical properties will find a broader range of potential applications, including automotive future electric vehicles, aerospace, tooling industries, and outer space applications. |