Additive Fabrication of Lightweight High Entropy Alloys: Microstructural Transformations and Mechanical Performance

The increasing demand for metallic materials with superior mechanical properties for applications in extreme conditions, particularly aerospace and defence, has driven the exploration of multi-functional high-performance materials. High-entropy alloys (HEAs) stand out as a distinctive class of advanced materials distinguished by their unique multicomponent composition exhibiting excellent properties, such as high mechanical strength, hardness, corrosion resistance, and oxidation resistance. Unlike conventional alloys that typically comprise one or two primary elements, HEAs integrate five or more alloying elements, resulting in a pronounced high configurational entropy. In most cases, the content of each principal element ranges between 5 at.% and 35 at.%. Recently, laser-directed energy deposition (DED), an additive manufacturing process, has gained increasing interest in manufacturing HEA materials due to the rapid production of complex features, the ability to process advanced materials, and the minimization of material waste. In a laser DED process, metallic powder is accurately delivered and melted by a laser beam in a layer-by-layer fashion at specific locations, enabling the formation of complex and precise 3D structures. Since DED features a layered formation mechanism, controlling the process parameters allows better control over the thermal history of the build material leading to unique microstructures and mechanical properties. This work focuses on revealing the heating and solidification mechanisms during the laser DED fabrication of a new class of lightweight Al-based HEAs. Preliminary results showed that the addition of small percentages of microalloying elements in the HEA leads to significant improvements in the yield strength and ultimate tensile strength of the material, which may be attributed to the reduction in hot cracking susceptibility during the laser DED process. This work further evaluates the printability of the Al-based HEA by characterizing its solidification microstructure, offering valuable insights into the relationship between laser DED process parameters and microstructure in the DED builds.