In a breakthrough, scientists have developed a technique to 3D print high-strength aluminium alloys that are used for aircraft and automobile parts. The method can be applied to additional alloy families such as high-strength steels and nickel-based superalloys difficult to 3D print using existing techniques.
"We're using a 70-year-old nucleation theory to solve a 100-year-old problem with a 21st century machine," said Hunter Martin, PhD student at University of California, Santa Barbara in the US. Additive manufacturing of metals typically begins with alloy powders that are applied in thin layers and heated with a laser or other direct heat source to melt and solidify the layers.
Normally, if high-strength unweldable aluminium alloys such as Al7075 or AL6061 are used, the resulting parts suffer severe hot cracking - a condition that causes the metal part to be pulled apart like a flaky biscuit. The new nanoparticle functionalisation technique solves this problem by decorating high-strength unweldable alloy powders with specially selected nanoparticles. The nanoparticle-functionalised powder is fed into a 3D printer, which layers the powder and laser-fuses each layer to construct a three-dimensional object.
During melting and solidification, the nanoparticles act as nucleation sites for the desired alloy microstructure, preventing hot cracking and allowing for retention of full alloy strength in the manufactured part. Since the melting and solidification in additive manufacturing is analogous to welding, the technique can also be used to make unweldable alloys weldable. This technique is also scalable and employs low-cost materials. Conventional alloy powders and nanoparticles produce printer feedstock with nanoparticles distributed uniformly on the surface of the powder grains.
"Our first goal was figuring out how to eliminate the hot cracking altogether. We sought to control microstructure and the solution should be something that naturally happens with the way this material solidifies," Martin said. The research was published in the journal Nature.
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