Production of Novel Low Density High Entropy Alloys: Experimental and Theoretical Approaches
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abstract
The debate between growing economies and increased environmental burdens forces countries to make excessive efforts to reduce their energy consumption. Qatar is one of those countries that commits to these efforts. In its strategic 2030 vision, â Qatar has already committed to enforcing international standards for environmental protection when designing and implementing its industrial projectsâ such as oil, gas, petrochemicals, and heavy industries (e.g., Qatar Steel and Qatar Aluminum). The reduction of weight in structural materials, such as aluminum-based and iron-based alloys that are utilized in everyday aspects in the State of Qatar, has a great potential for reducing the consumption of energy and minimizing the burden on the environment. This is exactly where the utilization of light materials with high strength plays a very important role. High entropy alloys (HEAs) are a new class of multi-component alloy systems in which the design of the alloys is based not on adding solutes to a single â baseâ element, but rather on choosing elements that will form solid solutions when mixed at near equi-atomic concentrations. Within a decade, new research on these novel materials showed that some alloys exhibit remarkable properties. In general, HEAs containing passivating elements such as Cr exhibit equivalent or superior corrosion-resistant properties compared to conventional alloys. Furthermore, some HEAs exhibit exceptional combination of properties, such as combined strength-ductility performance, improved fatigue resistance, high fracture toughness, and high thermal stability (see Section 2.2.1.3). The response of some HEAs is even more remarkable when exploiting strengthening effects due to controlled precipitation of coherent secondary phases, and grain refinement. Many of the discovered HEAs are comprised of 3d transition metals, some containing other elements like Al and Zn and more recently a number of refractory metal alloys have been developed. However, the number of studies of low-density high entropy alloys (LDHEAs) has been relatively few. We have recently obtained a single phase LDHEA with the composition Mg10Li20Sc20Ti30Al20, which has a FCC structure by mechanical alloying. The average grain size of this novel LDHEA was ~ 20 nm and the alloy exhibited an extremely high hardness of 5.8 GPa and a nominal density of 2.7 g/cm3..........
