Laser powder bed fusion, a 3D-printing technique, offers potential in the manufacturing industry, particularly when fabricating nickel-titanium shape memory alloys with complex geometries. This manufacturing method is appealing for aerospace and biomedical applications, but it has not yet demonstrated the superelasticity needed for specific applications of nickel-titanium form memory alloys. The 3D-printed nickel titanium was not able to display the superelasticity due to defects and other changes made during 3D printing.
Researchers from Texas A&M University recently showcased superior tensile superelasticity by fabricating a shape memory alloy through laser powder bed fusion, nearly doubling the maximum superelasticity reported in literature for 3D printing.
This study was published in vol. 229 of the Acta Materialia journal.
Nickel-titanium shape memory alloys have various applications due to their ability to return to their original shape upon heating or upon removal of the applied stress. They can be used in aerospace and biomedical fields to make stents, implants and surgical devices, as well as aircraft wings. These materials require extensive research to determine their functional properties and analyze the microstructure.
“Shape memories alloys are smart materials that can recall their high-temperature forms,” stated Dr. LeiXue, who was a former student in the Department of Materials Science and Engineering and is the first author of this publication. Although they can be used in many ways, it is difficult to fabricate shape memory alloys into complex forms. This is because the material must be tuned to achieve the desired properties. “
Laser bed fusion is an additive manufacturing method that allows you to quickly and efficiently produce nickel-titanium form memory alloys. Similar to polymer 3D printing this technique uses a laser to fuse metals or alloy powders layer after layer. This layer-by-layer method is advantageous because it allows for parts with complicated geometries to be created that are not possible in traditional manufacturing.
” Using a 3D Printer, we spread the alloy powder on a substrate, then use the laser melt the powder to form one layer.” said Xue. “We continue this layering until we get the desired structure. We scan different patterns or the same pattern. “
Unfortunately, most nickel-titanium materials cannot withstand the current laser powder bed fusion process, often resulting in printing defects such as porosity, warping or delamination caused by large thermal gradient and brittleness from oxidation. The laser can also alter the material’s composition due to evaporation.
To combat this problem, the researchers used an optimization frame they had created in a previous study. This framework can help determine the optimal process parameters to achieve defect-free structures and specific material properties.
Using this framework and changing in composition and refinement of process parameters, researchers were able to fabricate nickel-titanium parts with a consistent room temperature tensile strength of 6%. This was in the as-printed condition, without heat treatment. This superelasticity is almost twice that of 3D printing literature.
3D printing can produce shape memory alloys with higher superelasticity. This makes them more capable of handling applied distortion. 3D printing is a great way to reduce manufacturing time and cost.