Singapore: Researchers Test Potential of High Entropy Alloys in EBM Metal 3D Printing https://ift.tt/2U8FM85 Metal 3D printing is becoming invaluable for many manufacturers today worldwide, and the research regarding processes and materials continues as researchers from both Singapore Institute of Manufacturing Technology and Nanyang Technological University explore metal powders being used in electron beam melting (EBM) technology today in ‘Additively manufactured CoCrFeNiMn high-entropy alloy via pre-alloyed powder.’ Most studies regarding serious manufacturing practices and their interest in 3D printing with metal center around the best ways to produce strong, complex geometries. Here, the authors review whether CoCrFeNiMn high entropy alloy (HEA) parts produced through EBM—very similar to the popular selective laser sintering (SLS) process—is a realistic improvement over conventional casting techniques. CoCrFeNiMn is known as an equiatomic alloy powder made through vacuum induction via atomization with argon gas. As a single face-centered-cubic (FCC) crystal structure, CoCrFeNiMn has been the focus of a wide variety of research throughout the years due to:
The scientists point out that while HEAS like CoCrFeNiMn perform well in cryogenic temperatures, melting, casting, and mechanical alloying are the ‘dominant preparation methods,’ often leading to issues with both voids and porosity. Powder bed fusion additive manufacturing (PBFAM) offers potential for fabricated HEAs due to the following features:
EBM relies on high energy preheating up to 1100 °C, offers reduced stress on reactive parts, and has been known to be successful in production of HEA parts previously. Along with evaluating CoCrFeNiMn in terms of its microstructure and mechanical properties, researchers were able to produce it through gas atomization for this study, producing further analysis in powder flow, particle size, density, defect, printability, and more. For better ease in 3D printing, the atomized powder was separated into four different categories: ≤25 μm, 25–45 μm, 45–105 μm and 105–300 μm. Respectively, this allows for spark plasma sintering/injection molding, selective laser melting (SLM), EBM, and laser-aided AM. Flowability is one of the important features in PBFAM, and can be determined in different ways, but for this study was evaluated through the Hall flowmeter funnel and pronounced excellent. Particle size was evaluated, with good printability proven, and parts were inspected for defects based on Archimedes principle and OM observation. Further, microhardness was evaluated as follows:
Chemical composition analysis revealed ‘spherical morphology’ and only a few irregular particles, with all particles overall created as solidifying droplets collided in the ‘turbulent flow’ of atomization.
The scientists agree that while previous processes may have led to obstacles in using HEA powder, gas optimization makes such materials a definite consideration for mass production, stating that the powders offered all the following:
The researchers do point out, however, that there could be safety issues due to the ‘high density of satellites,’ although it does not seem to affect the EBM printing process. Porosity is a concern however, and the researchers tentatively suggest the hot isostatic press process for elimination of such issues in additive manufacturing, but it is costly and can be limiting for most applications.
Ultimately, the team concluded that all important features of the process studied here deem it suitable for PBFAM technology and new materials, further stating:
As 3D printing with metal in a variety of different methods begins to infiltrate industries focused on intense manufacturing processes, the study of the materials and powders that accompany this technology continues to grow, as exemplified in the automobile industry, aerospace, military and ammunitions endeavors—and far more. Find out more about the PBFAM process and the use of new materials in 3D printing here. What do you think of this news? Let us know your thoughts! Join the discussion of this and other 3D printing topics at 3DPrintBoard.com. [Source / Images: ‘ Additively manufactured CoCrFeNiMn high-entropy alloy via pre-alloyed powder’]
Printing via 3DPrint.com | The Voice of 3D Printing / Additive Manufacturing https://3dprint.com February 26, 2019 at 01:27PM
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