FANG Jieyichen
PhD in Mechanical Engineering
Supervisors: Dr JIAO Zengbao & Prof. FU Mingwang
Research interest: High-temperature alloys
Research work: High-entropy alloys (HEAs) are newly emerging advanced metallic materials with unique microstructure and excellent mechanical properties. In contrast to conventional alloys with one primary element and several minor alloying dopants, HEAs typically contain four or more multiple principal elements. Precipitation-hardened HEAs, especially those strengthened by coherent L12-nanoparticles, have enabled a new space for the development of advanced structural materials with superior mechanical properties at both room and high temperatures. From the application and processing points of view, there is a temperature-rise and down period which will affect the entropy contribution and solid solubility. Therefore, understanding phase stability and transformations at intermediate temperatures is crucial for tailoring microstructures and mechanical properties of L12-strengthened HEAs. In this study, the crystal structure, morphology, chemical composition of nanoscale precipitates and matrix of L12-strengthened HEAs at different temperatures were systematically investigated through scanning electron microscopy, X-ray diffraction, atom probe tomography, and thermodynamic calculations. Our results reveal that L12 precipitates can be formed at all the studied temperatures, but their morphology change as the aging temperatures decreases. In addition, the matrix structure changes from fcc-type to bcc-type upon long-term annealing at relatively low temperatures. The microstructural evolution and phase transformations of these alloys were discussed from the thermodynamic and kinetic points of view. This research not only sheds light on fundamentals of phase stability and transformations at intermediate temperatures but also provides guidance for microstructural control of L12-strengthened high-entropy alloys.
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SHI Xingyi
PhD in Mechanical Engineering
Supervisor: Dr AN Liang
Research interest: Fuel cells
Research work: In the last decade, the rising demand for the utilization of renewable energy has drawn more and more attention to energy conversion and storage systems. Among various energy conversion systems, direct liquid fuel cells (DLFCs) with their high energy density and facile fuel storage have received increasing attention. However, most of DLFCs must use noble metal catalysts for liquid fuel oxidation reactions, but yield limited fuel cell performance, greatly hindering their widespread application. Recently, an electrically rechargeable liquid fuel (e-fuel) system, typically consisting of an e-fuel charger for energy storage and an e-fuel cell for power generation, has attracted worldwide attention.1 Compared to the conventional alcoholic liquid fuels, this liquid e-fuel offers three major advantages including: i) good rechargeability, ii) high electrochemical reactivity even on carbon-based materials; and iii) good cost-effectiveness and durability.
Here, we report a power generation system, direct liquid e-fuel cell,2 consisting of a catalyst-free graphite-felt anode and a conventional oxygen cathode separated by a proton exchange membrane, resulting in a maximum current density of 750 mA cm−2, a peak power density of 293 mW cm−2, and an energy efficiency of 42.3% at room temperature, which is much higher than the performances achieved by conventional direct liquid fuel cells, as shown in Fig. 1. This emerging technology, capable of fast recharging, could be a powerful, efficient, cost-effective, and durable power generation device, showing great potential for commercialization in the future fuel cell electric vehicle industry (Fig. 2).
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