Researchers develop 3D-printed shape memory alloy with superior superelasticity: 3D printing leads to fabricating a shape memory alloy with increased superelasticity

Laser powder bed fusion, a 3D printing technology, offers potential in the manufacturing industry, especially when manufacturing nickel-titanium shape memory alloys with complex geometries. Although this manufacturing technique is attractive for applications in the biomedical and aerospace industries, it has rarely demonstrated the superelasticity required for specific applications using nickel-titanium shape memory alloys. Defects generated and changes applied to the material during the 3D printing process prevented the superelasticity from appearing in 3D printed nickel-titanium.

Researchers from Texas A&M University recently demonstrated superior tensile superelasticity by making a shape memory alloy by laser powder bed fusion, which nearly doubles the maximum superelasticity reported in the 3D printing literature.

Nickel-titanium shape memory alloys have different applications due to their ability to return to their original shape upon heating or upon removal of the applied voltage. Therefore, they can be used in biomedical and aerospace industries for stents, implants, surgical devices and aircraft wings. However, developing and manufacturing these materials properly requires extensive research to characterize functional properties and examine the microstructure.

“Shape memory alloys are smart materials that can remember their high-temperature shapes,” said Dr. Lei Xue, a former doctoral student at the Department of Materials Science and Technology and the first author of the publication. “Although they can be used in many ways, the manufacture of shape memory alloys for complex shapes requires fine-tuning to ensure that the material exhibits the desired properties.”

Laser powder bed fusion is an additive manufacturing technique that presents a way to produce nickel-titanium shape memory alloys efficiently and effectively, offering a path to rapid manufacturing or prototyping. This technology, similar to polymer 3D printing, uses a laser to fuse metal or alloy powders layer by layer. The layer-by-layer process is advantageous because it can create parts with complex geometries that would be impossible in traditional manufacturing.

“Using a 3D printer, we spread the alloy powder over a substrate and then use the laser to melt the powder, forming an entire layer,” says Xue. “We repeat this layering, scanning the same or different patterns until the desired structure is formed.”

Unfortunately, most nickel-titanium materials cannot withstand the current laser powder bed fusion process, which often results in printing defects such as porosity, skew or delamination caused by large thermal gradient and brittleness from oxidation. In addition, the laser may change the composition of the material due to evaporation during printing.

To combat this problem, the researchers used an optimization framework that they created in a previous study, which can determine optimal process parameters to achieve defect-free structure and specific material properties.

With this framework, as well as the change in composition and refined process parameters, the researchers manufactured nickel-titanium parts that consistently exhibited a tensile strength at room temperature of 6% in the printed state (without heat treatment after manufacture). This level of superelasticity is almost twice as high as previously seen in the 3D printing literature.

The ability to produce shape memory alloys through 3D printing with increased superelasticity means that the materials are more capable of handling applied deformation. Using 3D printing to develop these superior materials will reduce the cost and time of the manufacturing process.

In the future, the researchers hope that their discoveries will lead to increased use of printed nickel-titanium shape memory alloys in biomedical and space applications.

“This study can serve as a guide on how to print nickel-titanium shape memory alloys with desired mechanical and functional properties,” says Xue. “If we can tailor the crystallographic structure and the microstructure, there are many more applications in which these shape memory alloys can be used.”

This research was funded by the US Army Research Laboratory, the National Priorities Research Program Grant, the Qatar National Research Fund, and the US National Science Foundation Grant.

Other contributors to the publication include materials science and the head of the engineering department, Dr. Ibrahim Karaman; materials science and engineering professors Kadri Can Atli and Dr. Raymundo Arroyave; former materials science and engineering student Dr. Abhinav Srivastava and current student Nathan Hite; Wm Michael Barnes ’64 Department of Industrial Systems and Engineering Professor Dr. Alaa Elwany; industrial systems and engineering student Chen Zhang; and U.S. Army Research Laboratory researchers Dr. Asher C. Leff, Dr. Adam A. Wilson and Dr. Darin J. Sharar.

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Material provided by Texas A&M University. Original written by Michelle Revels. Note! The content can be edited for style and length.

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