Alloy Design of Novel L12-Type High-Entropy Intermetallic Alloys (Heias) for Advanced Structural Applications

Description

The great demand for improving energy efficiency in power generation and aeroengines has placed the development of advanced intermetallic alloys at the forefront of materials science. The L12-type intermetallic alloys have shown significant superiorities for high-temperature applications owing to their many unique properties, such as high melting temperature, low density, high yield strength and good oxidation resistance at elevated temperatures. It is also known that this intermetallic alloy is the most important strengthening constituent in commercial superalloys for their high-temperature strength and creep resistance. However, previous studies are mainly concentrated on simple Ni3Al materials, which generally contain limited ternary elements. Although such “plain” aluminides can be further incorporated with alloying additions, but these efforts generally cause a significant ductility loss of alloys.By contrast, we recently discovered that the high-entropy intermetallic alloys (HEIAs) based on complex (Ni,Co,Fe)3(Ti,Al,Fe) compositions can simultaneously enhance both strength and ductility of alloys at ambient temperatures. More importantly, in our early work, we surprisingly discovered that such complex HEIAs in their bulk form possess much superior mechanical properties than those of the simple Ni3Al-based alloys for structural applications. However, in spite of these exciting properties, some critical issues of these newly discovered HEIAs still remain unclear and need further in depth investigations, including phase transformation behaviors, thermal stabilities, mechanical properties and underlying mechanisms at elevated temperatures. Therefore, our present proposal is aiming at systemically investigating the phase transformation and deformation micro-mechanisms of the HEIAs and then correlating these understandings with their unique mechanical behaviors, in particular, the yielding strength and creep resistance at elevated temperatures. Based on a combination of theoretical calculations and the state-of-the-art experimental techniques, we intend to elucidate the effects of alloying additions on the microstructural stability, yielding anomaly, oxidation and creep resistance at various temperatures. Furthermore, the moisture- and oxygen-induced brittleness at room and elevated temperatures have been reported as a major concern for the practical application of intermetallic alloys. To this end, impacts of alloying additions and processing conditions on the ductility of HEIAs will be carefully investigated.The successful implementation of this proposal will provide a quantitative insight into the intrinsic correlations between the chemical compositions, microstructures and associated thermo-mechanical properties of these innovative HEIAs. The output results are vital for the accelerated design of new-generation high-temperature structural materials based on HEIAs for advanced engine and turbine disk applications with improved energy efficiency and engineering reliability.