New Laser Powder Bed Fusion Shape Memory Alloy Developed Abroad

2023-12-22

Laser powder bed fusion (LPBF) technology is an additive manufacturing technology that provides an effective and efficient method for the rapid manufacturing or forming of nickel titanium shape memory alloys. This technology is similar to polymer 3D printing, which uses lasers to melt metal or alloy powders layer by layer. By repeating this layering operation, scan the same or different patterns until the desired structure is formed.

In recent years, laser powder bed fusion has become a promising 3D printing technology in the manufacturing industry, and its applications in biomedical and aerospace fields are very attractive. Today, Wikimedia · Laser will share with you two new developments in the field of laser powder bed fusion technology:

Super elastic shape memory alloy manufactured by laser powder bed fusion technology

Laser powder bed fusion technology always shows great potential in manufacturing nickel titanium shape memory alloys with complex geometric shapes. However, it rarely exhibits the superelasticity required for specific applications using nickel titanium shape memory alloys. The defects generated during the 3D printing process and the changes applied to the material make it difficult for 3D printed nickel titanium to have superelasticity.

Recently, researchers from Texas A&M University (TAMU) manufactured a shape memory alloy using laser powder bed fusion technology. Amazingly, this alloy exhibits "excellent tensile superelasticity", almost twice the maximum superelasticity reported in existing literature for 3D printing.

Due to its ability to restore its original shape after heating or removing applied stress, nickel titanium shape memory alloys are suitable for various applications, such as scaffolds, implants, surgical equipment, and aircraft wings in biomedical and aerospace fields.

Dr. Lei Xue, the first author of the paper, pointed out that "Shape memory alloys are intelligent materials that can remember high-temperature shapes. Although these alloys can be used in various ways, manufacturing them into complex shapes requires fine-tuning to ensure that the material exhibits the required properties."

Most nickel titanium materials cannot withstand the current laser powder bed fusion process, which often leads to printing defects such as porosity, warping or delamination caused by large thermal gradients, and brittleness caused by oxidation. In addition, lasers can alter the composition of materials as evaporation occurs during the printing process.

To overcome this issue, researchers used the optimization framework they created in previous studies, which can determine the optimal process parameters to achieve defect free structures. The nickel titanium parts manufactured by researchers maintained 6% tensile superelasticity at room temperature without post manufacturing heat treatment. This level of superelasticity is almost twice that of 3D printed alloys recorded in previous literature.

The ability to produce shape memory alloys through 3D printing technology and the enhanced superelasticity mean that this material is more capable of handling applied deformations. Using 3D printing to develop these high-quality materials will reduce the cost and time of the manufacturing process.

In the future, researchers hope that their findings will lead to more use of nickel titanium shape memory alloys in biomedical and aerospace applications. Dr. Lei Xue added, "If we can adjust the crystal structure and microstructure, the applications of these shape memory alloys will be much more extensive."

This study was funded by grants from the US Army Research Laboratory, the National Priority Research Program, the Qatar National Research Foundation, and the National Science Foundation. The results were published in this month's Acta Materia.

Laser ultrasonic detection of defects generated in LPBF metal 3D printing

The recent progress in the field of laser powder bed fusion is not limited to this. Recently, researchers at Lawrence Livermore National Laboratory (LLNL) proposed a diagnostic method using surface acoustic waves (SAW), which is generated by laser-based ultrasound and can reveal small surface and subsurface defects in laser powder bed fusion metal 3D printing.

The research team claims that their developed system can effectively and accurately evaluate the trajectory of liquefied metal powder during the laser powder bed fusion 3D printing process. Real time detection, faster acquisition and processing of data can be achieved by scattering acoustic energy from melt lines, voids, and surface features. The research team validated this discovery using optical microscopy and X-ray computed tomography (CT).

According to researchers, SAW is highly suitable for characterizing melt lines in laser powder bed fusion 3D printing due to their surface and near surface sensitivity. To test this potential, the LLNL team conducted experiments by directly entering a vacuum chamber with a fiber laser and generating a laser melting line, and producing titanium alloy samples using power lasers of 100 watts, 150 watts, and 350 watts for analysis. Afterwards, they developed a method for generating and detecting surface acoustic waves, using pulsed laser to generate ultrasonic waves and measuring displacement using a photorefractive laser interferometer.

This work is funded by the Laboratory Guided Research and Development (LDRD) project, and the related papers have recently been published in Scientific Reports.

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