Carnegie Mellon University Research May Lead to Enhanced Design to Reduce Porosity in 3D Printed Titanium, Leading to Stronger Parts
UPDATE: We have been informed by a source on behalf of Carnegie Mellon University’s College of Engineering and the Next Manufacturing Center that the information originally presented in this article cast the research findings incorrectly and inappropriately. The original source seen on the CMU research, which was released by OpenPR, contained significant inaccuracies and incorrectly attributed research and key quotes to another party. Though this inaccuracy was uncovered and accurate information seen in an article from the Argonne Laboratory prior to publishing, the context that the research found titanium to be “fatally flawed” was mistakenly left within this article, and since this phrase was neither used nor suggested by any of the researchers involved in the study, has been subsequently removed.
The implications behind these findings are actually much more positive than I, the author of this article, had previously been led to believe. In part of a public statement released by Carnegie Mellon’s College of Engineering on the inaccuracy of our article (and similar pieces run in other publications), it was explained that the research findings on porosity aren’t detrimental to metal 3D printing, but will lead to stronger and more reliable metal 3D printed parts in the future. Rather than a flaw in titanium, the research actually supports potential improvements, which was not originally displayed in the editorial tone or context of the following article.
The Carnegie Mellon’s College of Engineering states, “The study in question was published in January in The Journal of The Minerals, Metals & Materials Society by Rollett, co-director of the NextManufacturing Center, one of the world’s leading research centers for additive manufacturing (also known as 3-D printing). The study focuses on improving the internal structure of metals for additive manufacturing.”
“The NextManufacturing Center is one of a very small number of university groups using advanced characterization techniques in the metals 3-D printing space. Visualizing porosity in 3-D with such high precision is a breakthrough capability in additive research. A strong understanding of the fundamental science of additive manufacturing materials is necessary to use them in aerospace and other demanding applications. Findings from this particular study have given the NextManufacturing Center the knowledge required to design the porosity out of these materials, which will translate to stronger, more reliable end parts. These findings are significant to advancing metals additive manufacturing so results can quickly be transferred from research into industry.”
Of all the materials that have been formatted for 3D printing—particularly in the medical and aerospace industries—titanium has become the eye of the prize. Whether it’s used to produce a 3D printed vertebral implant, a beak replacement for an injured macaw, or even for building fire-fighting drones, there’s no denying the presence that titanium materials have in the increasingly expansive metal 3D printing market. It seemed that there was nowhere to go but up for this valuable metal alloy, but a recent study from the Pittsburgh, Pennsylvania-based Carnegie Mellon University suggests that the current state of 3D printed titanium may be flawed.
After conducting deep x-rays on 3D printed titanium, researchers have discovered porosity within the material, which stems back to the powder-based production technique. Using the most popular form of titanium, Ti-gAI-4V (6% aluminum and 4% vanadium), the team from Carnegie Mellon turned to the Illinois-based US Department of Energy’s (DOE’s) Argonne National Laboratory to help analyze the material with intense synchrotron x-rays and an advanced rapid imaging tool known as microtomography. Their findings showed that when titanium powders are used with a Selective Laser Melting (SLM) 3D printer or an Electron Beam Melting (EBM) technique, gas is trapped in the resulting liquid layer, which creates porous bubbles within the 3D printed metal.
These minute spaces can range from a couple to a few hundred microns, and are also randomly distributed, causing a potential fault line in objects that are produced with titanium powder material. This news is especially alarming because of the immense value 3D printed titanium now has in the medical and aerospace industries. Not only has titanium allowed for patient-specific implants and customized aerospace parts, it has also reduced cost and waste while doing so. This critical research may be potentially alarming for the aerospace industry, which requires components that usually endure massive amounts of stress. It’s less of an issue for medical applications, considering that any form of titanium is seen as a stronger material than the bone that it is replacing.
Though processes like SLM have proven beneficial in many ways, this research may lead to some changes in the way titanium—along with other metal-based materials—is 3D printed. The research team found that the power, speed, and spacing of the printer’s laser beam could all impact the porosity within the titanium 3D print. The CMU researchers observed the porosity within several samples of Ti-6Al-4V, all of which were printed with differing parameters using an EBM process. Although these adjusted parameters helped the research team to reduce porosity in the 3D printed titanium, they were unable to eliminate it completely.
According to the CMU research, it’s nearly impossible to completely eliminate porosity from titanium, but they also believe that there is a sweet spot somewhere between unmelted powder and too much powder that could optimize the way that 3D printed titanium is produced. The research team will now turn to researching titanium in its powder stage, which Rollett believes could be the stage in which porosity begins. The research findings were published in the Journal of Minerals, Metals, and Materials Society, entitled “Evaluating the Effect of Processing Parameters on Porosity in Electron Beam Melted Ti-6Al-4V via Synchrotron X-ray Microtomography“, which was co-authored by Rollett, Ross Cunningham, Sneha P. Narra, Tugce Ozturkt, and Jack Beuth.
“Relative to printing speed and spacing, if you decrease the power level and the melt pool becomes too small, you may leave behind unmelted powder, which is a source of porosity,” said Anthony Rollett, Professor of Materials Science and Engineering at CMU. “However, if you increase the power level too much, you risk creating deep holes, called keyholes, with the electron beam that also leave behind voids.”
This study is certainly alarming for the 3D printing community as a whole, as metal 3D printing has been slowly integrated into a much broader range of applications. But the news should be most worrisome to those within aerospace industry, which has been looking to increase their use of 3D printed titanium for mission critical components. Though aerospace companies like Boeing and Airbus may need to take a step back and reexamine their implementation of 3D printed titanium parts, the increasingly well-researched industry should be able to persevere and overcome. Discuss further in the Titanium 3D Printing Issues forum over at 3DPB.com.
[Source: Argonne National Laboratory]
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